JP2005333499A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing color adjustment at low cost and appropriately, when images read by different original read stations are recorded and outputted in an image forming portion. <P>SOLUTION: When ACC (auto color calibration) is performed, a copying apparatus 1 makes a gray-scale transformation table set in an image processing printer γ converting circuit 713 when a gray scale pattern is read, differ from a gray-scale transformation table set in the circuit 713 when an original is read. Accordingly, the quality of images can be enhanced by reducing the unevenness of read values such that the read value differs at each machine due to the change of time of an optical system of a scanner 300, and a machine difference between a photoelectric conversion element of a CCD or the like and a infrared-ray cut filter or the like, and by density-adjusting an output image when outputting image data that are read at the different scanner 300, in conformity to the characteristic of each scanner 300. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that performs inexpensive and appropriate color adjustment when an image read by a different document reading unit is recorded and output by an image forming unit.

In general, in an image forming apparatus such as a digital color copying apparatus, a document reading unit reads a document using an RGB three-color CCD (Charge Coupled Device), and the image forming unit records it on recording paper based on the read image data of the document. An image is formed. The color copying apparatus is usually set so that good color reproducibility can be obtained for a printed document. However, depending on the setting state, when a document other than a printed document such as photographic paper is copied, Depending on the color, the color reproducibility may be deteriorated or a completely different color (hue) may be reproduced.
This is due to the metamerism of the manuscript, and is due to the difference in manuscript type and color material such as printed manuscript and photographic paper. That is, the spectral reflection characteristic in the visible light wavelength region, the spectral transmission characteristic of the filter used in the CCD, the spectral sensitivity of the CCD, the spectral product of the light intensity of the copying machine, and the spectral of the human eye This is caused by differences in sensitivity (and the color temperature of the proof under observation).
Therefore, in the conventional color copying apparatus, the scanner unit and printer unit in the color copying apparatus are calibrated at the time of factory shipment of the color copying apparatus so that the same color reproducibility as the original can be obtained. Thus, an image processing parameter used for image processing in an IPU (Image Processing Unit) or printer unit is obtained, and printing is performed using the image processing parameter.

  The applicant firstly scans and reads the original image optically, converts the input image signal from the reading means into an output image signal by an image signal conversion table, and outputs the output image signal. Means for writing image information on an image carrier in response to an output image signal; means for transferring an image on the image carrier onto a transfer material to form an image; and means for generating a plurality of gradation patterns In the image forming apparatus, comprising: means for creating and selecting an image signal conversion table based on a reading value generated by this means and formed on the transfer paper by the means for reading the image; The tone pattern read signal is composed of a plurality of signals having different spectral sensitivities, and means for storing correction coefficients for the plurality of signals having different spectral sensitivities is provided. Based on the correction coefficient from the means for storing it has proposed an image forming apparatus that corrects a read signal of the gradation pattern (see Patent Document 1).

  In other words, this prior art creates a gradation correction table that obtains a good gradation by correcting the spectral sensitivity of image reading means that differs for each image forming apparatus, and also performs automatic gradation correction (ACC: Auto Color Calibration). ), The correction coefficient set for each toner is automatically adjusted in the market using a reference chart to achieve good color reproducibility.

  The applicant first reads the reference chart by the reading means, creates correction data for the reading means based on the image data of the read reference chart, and based on the reference data for correcting the output means. Image processing including each process of reading the image output by the output unit by the reading unit corrected by the generated correction data and generating correction data of the output unit based on the read image data A method has been proposed (see Patent Document 2).

  Furthermore, in color copying machines, variations in spectral transmittance of CCD filters are corrected by shading correction so that RGB data is aligned for achromatic colors such as white and gray, but wavelength dependence on spectral characteristics However, there is a case where the RGB values that are output are different for each apparatus.

Such a difference creates a YMCK tone correction table so as to obtain a good color balance, reads a YMCK tone pattern or a transfer sheet on which a color patch is recorded with a scanner, and uses the read value of the printer unit. This affects the generation of a gradation correction table (γ correction table) for correcting gradation characteristics (in the case of ACC), which causes a deviation from an ideal state. In addition, when the spectral transmission characteristic changes due to the change of the CCD of the scanner or when the spectral reflection characteristic of the YMCK toner to be used changes, the RGB ratio of the read value of the YMCK toner changes. If the RGB ratio of the read value of the scanner with respect to the YMCK toner is changed in this way and then corrected with the RGB ratio before the change, the deviation from the appropriate value is increased.
Therefore, the applicant of the present invention has an image reading unit that optically scans and reads a document image, an image processing unit that converts an input image signal from the image reading unit, and outputs the image signal as an image signal. Image writing means for writing information on an image carrier, image forming means for forming an image on a transfer material having the image carrier, image signal generating means for generating a plurality of gradation patterns, and the image processing An image signal conversion table for converting the input image signal into an output image signal, and an image signal conversion based on the signals read by the image reading means for the plurality of gradation patterns recorded on the transfer material. A means for creating and selecting a table and a detecting means for detecting development characteristics are provided. Based on the result detected by the detecting means, a writing signal for a gradation pattern formed on the transfer material is provided. It proposes an image forming apparatus to change the level (see Patent Document 2).
In other words, this conventional technique changes the writing value of the gradation pattern used to create the YMCK gradation correction table according to the development characteristics, and reduces the YMCK gradation correction with a small number of gradation patterns. You are trying to run the table with good accuracy.

Japanese Patent Laid-Open No. 10-191061 Japanese Patent Laid-Open No. 11-69157

  However, each of the above prior arts aims to make the output density constant. However, the scanner for reading is fixed to a specific one, and when outputting image data read by different scanners. Thus, the density of the output image cannot be adjusted in accordance with the characteristics of the respective scanners, and improvement is required.

  Accordingly, the invention according to claim 1 is based on a predetermined image signal conversion table based on a read image signal output from an image reading unit that optically scans a document, reads a color image of the document, and outputs a read image signal. The image signal conversion table of the first image signal converting means for gradation conversion is read by the image reading means by using the image reading means as a reference chart consisting of a plurality of achromatic color patches and a plurality of different chromatic color patches. The image signal is generated based on the reference data stored in advance in the storage means corresponding to the patch of the image, and the image signal after the tone conversion of the first image signal conversion means is color-converted by the color conversion means. The image signal conversion table of the second image signal converting means for generating the output image signal by converting the gradation based on the image signal conversion table of When creating / selecting the gradation pattern formed on the transfer material by the image forming means based on the image signal of the plurality of gradation patterns to be created / selected based on the image signal, the gradation pattern is read. Sometimes, the image signal conversion table set in the first image signal conversion unit and the image signal conversion table set in the first image signal conversion unit at the time of reading a document are made different so that the optical system of the image reading unit can be changed. Output image when outputting the image data read by image reading means such as different scanners, reducing the variation that the reading values differ from machine to machine due to machine changes such as time-dependent changes, photoelectric conversion elements such as CCD and infrared cut filter An object of the present invention is to provide an image forming apparatus that improves the image quality by adjusting the density according to the characteristics of the respective image reading means.

  According to the second aspect of the present invention, an image signal conversion table set in the first image signal conversion unit at the time of reading a document image is generated from the achromatic color patch in the reference chart and the reference data of the achromatic color patch in the storage unit, An image signal conversion table to be set in the first image signal conversion unit at the time of gradation pattern reading is generated from the achromatic color patch and the chromatic color patch of the reference chart, so that the read image signal based on the mechanical difference of the image reading unit such as a scanner It is an object of the present invention to provide an image forming apparatus capable of preventing the variation of image quality and improving the adjustment accuracy of automatic gradation correction (ACC) and further improving the image quality.

  According to a third aspect of the present invention, an image signal conversion table set in the first image signal conversion unit at the time of gradation pattern reading is selected from among image signals obtained by reading a plurality of different color patches of the reference chart with the image reading unit. Image reading means corresponding to a complementary color signal of a YMC recording material (toner or the like) among RGB image signals obtained by reading different color patches of the reference chart by using a common one-component image signal It is an object of the present invention to provide an image forming apparatus that improves the adjustment accuracy of the image signal conversion table by using the read image signal and improves the image quality even when linked output is performed. .

  According to a fourth aspect of the present invention, an image signal conversion table set in the first image signal conversion means at the time of gradation pattern reading is used, and among image signals obtained by reading a plurality of patches of different colors in the reference chart by the image reading means. A characteristic of the spectral reflectance of the printing ink of the reference chart is calculated by calculating a predetermined coefficient that differs depending on the read patch for the common one-component image signal and generating the coefficient according to the image signal obtained by the calculation. The image signal conversion table for automatic gradation correction (ACC) is created by correcting the difference between the spectral reflectance characteristics of the recording material of the image forming means that records and outputs the gradation pattern, and further increases the image. An object of the present invention is to provide an image forming apparatus that improves quality.

  An image forming apparatus according to a first aspect of the present invention includes an image reading unit that optically scans a document to read a color image of the document and outputs a read image signal, and a read image signal output from the image reading unit. First image signal conversion means for performing gradation conversion based on a predetermined image signal conversion table, color conversion means for color-converting the image signal after the gradation conversion, and the color-converted image signal as a predetermined image signal Second image signal conversion means for generating an output image signal by performing gradation conversion based on the conversion table; and forming a color recording agent image on the image carrier in accordance with the output image signal; Image forming means for transferring a recording agent image onto a transfer material to form an image, gradation pattern generating means for generating image signals of a plurality of gradation patterns, and image signals generated by the gradation pattern generating means Based on said image Creating and selecting the image signal conversion table to be set in the second image signal converting unit based on an image signal when the image reading unit reads the gradation pattern formed on the transfer material by the generating unit; A reference chart consisting of a plurality of achromatic patches of different gradation levels and a plurality of different chromatic patches is read by the image reading means, and the reference data stored in advance in the storage means corresponding to the patches of the reference chart An image forming apparatus that creates the image signal conversion table to be set in the first image signal conversion unit based on the image signal conversion table to be set in the first image signal conversion unit and the original when reading the gradation pattern The above object is achieved by differentiating the image signal conversion table set in the first image signal converting means when reading the image. It is.

  In this case, for example, as described in claim 2, the image forming apparatus sets the image signal conversion table to be set in the first image signal conversion unit at the time of reading the document image as the empty image in the reference chart. The image signal conversion table generated from the chromatic patch and the reference data of the achromatic color patch of the storage means and set in the first image signal conversion means at the time of reading the gradation pattern is the achromatic color patch of the reference chart. It may be generated from the chromatic color patch.

  Further, for example, as described in claim 3, the image forming apparatus sets the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern to a plurality of different colors of the reference chart. May be generated using a common one-component image signal among the image signals obtained by reading the patch by the image reading means.

  Further, for example, as described in claim 4, the image forming apparatus sets the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern to a plurality of different colors of the reference chart. A predetermined coefficient that differs depending on the read patch is calculated for a common one-component image signal among the image signals obtained by reading the patch by the image reading means, and according to the image signal obtained by the calculation It may be generated.

  According to the image forming apparatus of the first aspect of the present invention, the read image signal output from the image reading unit that optically scans the original, reads the color image of the original, and outputs the read image signal is used as the predetermined image signal. The image signal conversion table of the first image signal conversion means for gradation conversion based on the conversion table is read by the image reading means with a reference chart consisting of a plurality of achromatic patches of different gradation levels and a plurality of different chromatic patches. The image signal is generated based on the reference data stored in advance in the storage means corresponding to the patch of the reference chart, and the color signal is converted by the color conversion means after the gradation conversion of the first image signal conversion means. The image signal conversion table of the second image signal conversion means for generating the output image signal by converting the gradation of the image signal based on a predetermined image signal conversion table is represented by a gradation pattern. When creating / selecting the gradation pattern formed on the transfer material by the image forming means based on the image signal of the plurality of gradation patterns generated by the forming means based on the image signal when the image reading means is read, Since the image signal conversion table set in the first image signal conversion unit at the time of reading the tone pattern is different from the image signal conversion table set in the first image signal conversion unit at the time of reading the document, the image reading unit It is possible to reduce variations in reading values from machine to machine due to machine changes such as optical system changes over time, photoelectric conversion elements such as CCDs and infrared cut filters, and image data read by image reading means such as different scanners. The image quality can be improved by adjusting the density of the output image at the time of output in accordance with the characteristics of the respective image reading means.

  According to the image forming apparatus of the second aspect of the present invention, the image signal conversion table set in the first image signal conversion unit when reading the document image is obtained by using the achromatic color patch in the reference chart and the achromatic color patch in the storage unit. Since the image signal conversion table generated from the reference data and set in the first image signal conversion means at the time of gradation pattern reading is generated from the achromatic color patch and the chromatic color patch of the reference chart, there is a mechanical difference between the image reading means such as a scanner. As a result, it is possible to prevent variations in the read image signal based on the image quality, improve the accuracy of automatic gradation correction (ACC) adjustment, and further improve the image quality.

  According to the image forming apparatus of the third aspect, the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern is read by the image reading unit by reading a plurality of patches of different colors of the reference chart. Since it is generated using a common one-component image signal among the obtained image signals, it is used as a complementary color signal of YMC recording material (toner etc.) among RGB image signals obtained by reading patches of different colors on the reference chart. By generating the image signal conversion table using the read image signal of the corresponding image reading unit, the adjustment accuracy of the image signal conversion table can be improved, and the image quality can be improved even in the case of linked output. .

  According to the image forming apparatus of the fourth aspect, the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern is read by the image reading unit by reading a plurality of patches of different colors of the reference chart. A predetermined coefficient that differs depending on the read patch is calculated for a common one-component image signal among the obtained image signals, and is generated according to the image signal obtained by the calculation. Creates an image signal conversion table for automatic gradation correction (ACC) by correcting the difference between the spectral reflectance characteristics and the spectral reflectance characteristics of the recording material of the image forming means that records and outputs the gradation pattern. Image quality can be further improved.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The scope of the present invention limits this invention especially in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

  1 to 39 are views showing a first embodiment of the image forming apparatus according to the present invention. FIG. 1 shows an electrophotographic copying apparatus 1 to which the first embodiment of the image forming apparatus according to the present invention is applied. It is a principal part schematic structure front view.

  In FIG. 1, the copying apparatus 1 includes a printer unit 100, a paper feed unit 200, a scanner unit 300, and the like inside a main body housing 2, and a contact glass 3 is disposed on the upper surface of the main body housing 2. ing. The copying apparatus 1 is provided with an ADF (Auto Document Feeder) 400 at the top thereof. The ADF 400 separates a plurality of documents G set on the document table 401 one by one, and feeds rollers and documents. The belt 402 is transported to a document reading position by the scanner unit 300 on the contact glass 3, and the scanned document G is discharged onto a paper output tray (not shown) by the document transport belt 402.

  The paper feeding unit 200 includes a paper feeding tray 201, a reversing unit 202, a conveyance roller (not shown), and the like, and separates a plurality of transfer sheets (transfer materials) P in the paper feeding tray 201 one by one. To the unit 100. The reversing unit 202 reverses the front and back surfaces of the transfer paper P on which the image has been formed by the printer unit 100 and sends it again to the printer unit 100 to form an image on the back surface. In addition, a paper feed tray 203 on which the transfer paper P is manually set is provided on one side surface of the main body housing 101. The paper feed unit 200 also transfers the transfer paper P on the paper feed tray 203. It is conveyed to the printer unit 100.

  A paper discharge tray 204 is disposed on the side surface of the main body casing 101 opposite to the paper feed tray 203, and the transfer paper P on which image formation has been completed by the printer unit 100 is placed on the paper discharge tray 204. It is discharged sequentially.

  The printer unit 100 is provided at a substantially central portion inside the main body housing 2, and an annular intermediate transfer belt 101 is disposed in a substantially diagonal direction in the vertical direction over a predetermined length at the central portion of the printer unit 100. The intermediate transfer belt 101 is stretched between a driving roller 102 and a transfer roller 103 and is driven to rotate clockwise as indicated by an arrow in FIG. 1, and black (K) and yellow (Y) along the intermediate transfer belt 101. In addition, organic photoconductor (OPC) drums 104K to 104C of φ30 [mm] as a total of four image carriers of three colors of magenta (M) and cyan (C) are disposed. Around the photosensitive drums 104K to 104C, the chargers 105K to 105C for charging the surfaces of the photosensitive drums 104K to 104C and the surfaces of the uniformly charged photosensitive drums 104K to 104C are irradiated with laser light. A laser optical system 106 for forming an electrostatic latent image, a black developing unit 107K for supplying each color toner to the electrostatic latent image and developing the toner image for each color, and Y (yellow), M (magenta), C (Cyan) three color developing units 107Y, 107M, and 107C, bias rollers 108K to 108C for applying a transfer voltage to the intermediate transfer belt 101, and the surfaces of the photosensitive drums 104K to 104C after being transferred, although not labeled. A cleaning device for removing residual toner, and electric power remaining on the surfaces of the photosensitive drums 104K to 104C after transfer. Discharger or the like are sequentially arranged to eliminate.

  The printer unit 100 uniformly charges the photosensitive drums 104K to 104C rotated in the counterclockwise direction by the charging chargers 105K to 105C, and applies the color of each color to the uniformly charged photosensitive drums 104K to 104C. A laser beam modulated with data is irradiated from the laser optical system 106 to form an electrostatic latent image, and each of the photosensitive drums 104K to 104C on which the electrostatic latent image is formed is developed by each color developing unit 107K to 107C. Toner is supplied to form a toner image. The printer unit 100 applies a transfer voltage to the intermediate transfer belt 101 by the bias rollers 108K to 108C, and sequentially superimposes and transfers the toner images of the respective colors on the photosensitive drums 104K to 104C to the intermediate transfer belt 101. Transfer a full color toner image.

  In the printer unit 100, a pressure roller 109 is disposed at a position facing the transfer roller 103 with the intermediate transfer belt 101 interposed therebetween, and a transfer from the paper supply unit 200 is performed between the pressure roller 109 and the transfer roller 103. The paper P is conveyed. A conveyance roller 110 and a registration roller 111 are disposed on the conveyance path of the transfer paper P to the pressure roller 109 and the transfer roller 103. The conveyance roller 110 transfers the transfer paper P from the paper feeding unit 200 to the registration roller. Then, the registration roller 111 conveys the transferred transfer paper P between the pressure roller 109 and the transfer roller 103 by adjusting the timing with the toner image on the intermediate transfer belt 101.

The transfer roller 103 applies a transfer voltage to the intermediate transfer belt 101 to transfer the toner image on the intermediate transfer belt 101 onto the transfer paper P conveyed between the pressure roller 109.
In the printer unit 100, a conveyance belt 112 and a fixing unit 113 are disposed on the downstream side in the conveyance direction of the transfer paper P on which the transfer of the toner image is completed. The toner image is transferred and separated from the intermediate transfer belt 101. The transfer paper P is transported to the fixing unit 113 by the transport belt 112. The fixing unit 113 includes a fixing roller 114 that is heated to a fixing temperature and a pressure roller 115 that is in pressure contact with the fixing roller 114, and the transfer roller 114 and the pressure roller 115 that are driven to rotate the transfer paper P that has been conveyed. Then, the toner image on the transfer paper P is fixed to the transfer paper P and discharged onto a paper discharge tray 204 provided on the side surface of the main body housing 2.
As shown in FIG. 2 in an enlarged manner, the scanner unit 300 reflects the light from the halogen lamp 302 provided with the lamp shade 301 and the original G or the halogen lamp 302 to the original G or a white reference plate (not shown). A first traveling body 305 equipped with a first mirror 303 and a second mirror 304 that reflects light reflected from the original G and the white reference plate, a third mirror 306 that sequentially reflects light reflected by the second mirror 304, and a second mirror 306. The first traveling body includes a second traveling body 308 having four mirrors 307, two switchable infrared cut filters 309 and 310, a lens 311 and a CCD (Charge Coupled Device) 312 as a photoelectric conversion element. While moving the 305 and the second traveling body 308 in the sub-scanning direction (direction indicated by the arrow a in FIG. 2) at a predetermined moving speed, the first G is applied to the document G on the contact glass 3. Reading light is emitted from the halogen lamp 302 on the traveling body 305, and reflected light from the document G is reflected by the second mirror 304 to the third mirror 306 on the second traveling body 308. The scanner unit 300 reflects the reflected light from the second mirror 304 with the third mirror 306 in the direction of the fourth mirror 307, and reflects the reflected light with the fourth mirror in the direction of the infrared cut filters 309 and 310. Infrared light is cut by the infrared cut filter 309 or the infrared cut filter 310 located on the road and is incident on the lens 311. The scanner unit 300 condenses incident light on the CCD 312, and the CCD 312 photoelectrically converts the incident light to read an image of the original G and output it as an analog image signal.
As shown in FIG. 3, the copying apparatus 1 is provided with an operation unit 500 on the upper surface of the main body housing 2. The operation unit 500 includes a start key 501, a clear / stop key 502, a numeric keypad 503, an interrupt. A key 504, a memory call key 505, a preheat / mode clear key 506, a color adjustment / registration key 507, a program key 508, an option key 509, an area processing key 510, a liquid crystal screen 511, and the like are provided.
The control system of the copying apparatus 1 is configured as shown in FIG. 4, and a CPU (Central Processing Unit) of a system controller 600 that controls each part of the copying apparatus 1 and executes processing as the copying apparatus 1. 601; ROM (Read Only Memory) 602 for storing various programs and data; RAM (Random Access Memory) 603 used as a work memory for the CPU 601; Interface I / O 604 for connecting the CPU 601 and various circuit units; and various sensor controls Unit 605, power supply / bias control unit 606, drive control unit 607, operation control unit 608, communication control unit 609, storage device control unit 610, storage device 611, IPU 612, laser optical system drive unit 613, toner replenishment circuit 614, etc. I have.
The various sensor control unit 605 includes a toner density sensor 615 installed in each of the YMCK developing units 107K to 107C, an optical sensor 616a to 616c installed in each of the YMCK image forming units 107K to 107C, a potential sensor 617, and an environment. Sensors 618 and the like are connected, and sensor signals from these sensors 615 to 618 are output to the CPU 601 via the interface I / O 604. The optical sensor 616a is disposed to face each of the photosensitive drums 104K to 104C, and detects the amount of toner adhered on the photosensitive drums 104K to 104C. The optical sensor 616b is disposed in the vicinity of each of the photosensitive drums 104K to 104C so as to face the intermediate transfer belt 101, and detects the toner adhesion amount on the intermediate transfer belt 101. The optical sensor 616 c is disposed to face the conveyance belt 112 and detects the amount of toner attached on the conveyance belt 112. In practice, detection may be performed at any one of the optical sensors 616a to 616c.

  The optical sensor 616a is arranged outside the image area in the axial direction of the photosensitive drums 104K to 104C and in the vicinity of the image area, and includes a light emitting element such as a light emitting diode and a light receiving element such as a photosensor. The toner adhesion amount in the toner image of the detection pattern latent image formed on the photosensitive drums 104K to 104C and the toner adhesion amount on the background portion are detected for each color, and the so-called residual after the neutralization of the photosensitive drums 104K to 104C. The potential is detected and detection signals are output to various sensor control units 605. Based on the detection signal from the optical sensor 616a, the various sensor control units 605 obtain a ratio between the toner adhesion amount in the detection pattern toner image and the toner adhesion amount in the background portion, and compare the ratio value with a reference value. A change in the image density is detected, and the control value of the toner density sensor 615 for each color of YMCK is corrected. In practice, the optical sensor 616a is not necessarily provided in each of the photosensitive drums 104K to 104C, and may be detected by any one of the photosensitive drums 104K to 104C.

  The toner concentration sensor 615 is disposed in each of the developing units 107K to 107C, detects the toner concentration based on a change in magnetic permeability of the developer present in the developing units 107K to 107C, and controls the detection signal with various sensors. Output to the unit 605. When the various sensor control units 605 compare the detected toner density value with the reference value based on the detection sensor from the toner density sensor 615 and determine that the toner density falls below a certain value and the toner is in an insufficient condition, A toner supply signal having a magnitude corresponding to the shortage is output to the toner supply circuit 614. The toner supply circuit 614 supplies toner to the corresponding developing units 104K to 104C based on the toner supply signal.

The potential sensor 617 detects the surface potential of each of the photosensitive drums 104 </ b> K to 104 </ b> C, which are image carriers, and outputs detection signals to various sensor control units 605.
The power source / bias control unit 606 controls the supply of power to the developing units 107K to 107C and the power circuit 619. The power circuit 619 supplies a predetermined charging discharge voltage to the charging chargers 105K to 105C, and the developing units 107K to 107K. A developing bias having a predetermined voltage is supplied to 107C, and a predetermined transfer voltage is supplied to the bias rollers 108K to 108C and the charging chargers 105K to 105C.
The drive control unit 607 supplies toner to the laser optical system drive unit 613 that adjusts the laser output of the laser optical system 106, the intermediate transfer belt drive unit 620 that controls the rotational drive of the intermediate transfer belt 101, and the developing units 107K to 107C. The driving of the toner replenishing circuit 614 for performing the above is controlled. The operation control unit 608 performs the acquisition of the operation content in the operation unit 500, the lighting control of lamps and the like, the display control of the liquid crystal screen 511, and the like under the control of the CPU 601.
A network such as the Internet or an intranet is connected to the communication control unit 609, and communication is performed via the network. The storage device 611 is configured by a hard disk or the like, and stores various types of information, particularly image data, under the control of the storage device control unit 610.
Next, the IPU 612 will be described with reference to FIG. As shown in FIG. 5, the IPU 612 includes a shading correction circuit 701, an area processing unit 702, a scanner γ conversion unit 703, an image memory 704, an image separation unit 705, an I / F (interface) 706, an MTF (Modulation Transfer Function) filter. 707, hue determination circuit 708, color conversion UCR (Under Color Removal) processing circuit 709, pattern generation unit (gradation pattern generation means) 710, scaling circuit 711, image processing circuit 712, image processing printer γ A conversion circuit (first image signal conversion unit) 713, a gradation processing circuit (color conversion unit) 714, a CPU 715, a ROM 716, a RAM 717, and the like are provided.
The printer unit 100 includes an I / F selector 721, a pattern generation unit (tone pattern generation unit) 722, an image forming printer γ correction circuit (second image signal conversion unit) 723, and image formation of the printer unit 100. The printer engine 724 and the like that actually perform the above are provided.
The CPU 715 is connected to the ROM 716 and the RAM 717 via a bus 718, and is connected to the system controller 600 through a serial I / F, and commands from the operation unit 500 and the like are transmitted through the system controller 600. The CPU 715 sets various parameters in necessary units of the IPU 612 based on the image quality mode, density information, region information, and the like transmitted from the operation unit 500 or the like.
The scanner unit 300 color-separates the original G on the contact glass 3 into R, G, and B, for example, reads it with 10 bits, and outputs the read image signal of the original G to the shading correction circuit 701 of the IPU 612.
The shading correction circuit 701 corrects unevenness in the main scanning direction of the image signal input from the scanner unit 300 and outputs the image signal to the scanner γ conversion unit 703 as an 8-bit signal, for example.
The area processing unit 702 generates an area signal for distinguishing which area in the original G the image data currently being processed belongs to, and parameters used in subsequent image processing are switched by this area signal. . For each designated area, the area processing unit 702 includes a color correction coefficient, a spatial filter, an optimum color correction coefficient for each original G, such as characters, silver halide photographs (photographic paper), printed originals, inkjets, highlighters, maps, thermal transfer originals, Image processing parameters such as a gradation conversion table are set for each image area.
The scanner γ conversion unit 703 converts the read signal from the scanner unit 300 from reflectance data to lightness data, and stores it in the image memory 704. The image memory 704 stores the image signal after the scanner γ conversion, and outputs it to the MTF filter 707 via the image separation unit 705 and the I / F 706. The image separation unit 705 determines the character part and the photographic part of the image of the document G and the chromatic / achromatic color, and outputs the determination result to the MTF filter 707.
The MTF filter 707 responds to the edge degree of the image signal in addition to the process of changing the frequency characteristics of the image signal such as edge enhancement and smoothing according to the user's preference such as a sharp image or a soft image. Edge enhancement processing (adaptive edge enhancement processing). For example, the MTF filter 707 performs so-called adaptive edge enhancement on each of the R, G, and B signals, which performs edge enhancement on a character edge and does not perform edge enhancement on a halftone image.
Specifically, for example, the MTF filter 707 includes a smoothing filter 730, an edge amount detection filter 731, a Laplacian filter 732, a smoothing filter 733, a table conversion 734, an accumulator 735, and an adder 736, as shown in FIG. Etc., and the smoothing filter 730 smoothes the image signal converted from the reflectance linearity to the lightness linearity by the scanner γ conversion unit 703 by using the coefficient shown below, and the Laplacian filter 732 is obtained as the image signal A. And output to the adder 736.

  Next, the 3 × 3 Laplacian filter 732 extracts a differential component of the image data by using a filter as shown in FIG. 7 and outputs it as an image signal B to the integrator 735.

Of the 10-bit image signal that is not subjected to γ conversion by the scanner γ conversion unit 703, for example, the upper 8-bit component is input to the edge amount detection filter 731. The edge amount detection filter 731 is shown in FIG. Using the sub-scanning direction edge detection filter shown in FIG. 8B, the main scanning direction edge detection filter shown in FIG. 8B and the oblique direction detection filter shown in FIG. 8C and FIG. Among the detected edge amounts, the maximum value is output to the smoothing filter 733 as the edge degree.
The smoothing filter 733 smoothes the edge degree detected by the edge amount detection filter 731 using, for example, the following coefficient as necessary, and the sensitivity difference between the even pixels and the odd pixels of the scanner unit 300 is smoothed. The influence is reduced and the result is output to the table conversion circuit 734.

  The table conversion circuit 734 converts the obtained edge degree into a table and outputs it as an image signal C to the integrator 735. In this case, the table conversion circuit 734 designates the density of lines and dots (including contrast and density) and the smoothness of the halftone dot portion according to the table values. The edge degree becomes the largest with black lines or dots on a white background, and becomes smaller as the boundary between pixels becomes smoother as in finely printed halftone dots, silver halide photographs, thermal transfer originals, and the like.

The accumulator 735 takes the product of the edge degree (image signal C) converted by the table conversion circuit 734 and the output value (image signal B) of the Laplacian filter 732 and outputs the product to the adder 736 as an image signal D. An adder 736 adds the smoothed image signal (image signal A) to the image signal D, and outputs the resultant signal as an image signal E to the hue determination circuit 708 and the color conversion UCR processing circuit 709, which are subsequent image processing circuits. .
The color conversion UCR processing circuit 709 corrects the difference between the color separation characteristics of the input system and the spectral characteristics of the color material of the output system, and calculates the amount of the color material YMC necessary for faithful color reproduction; And a UCR processing unit for replacing a portion where three colors of YMC overlap with K (black). The color conversion UCR processing circuit 709 performs the color correction process by performing a matrix operation such as the following equation (1).

Here, s (R), s (G), and s (B) indicate R, G, and B signals of the scanner unit 300 after the scanner γ conversion processing, and hue is White, Black, Yellow, Red, and Magenta. , Blue, Cyan, Green, etc. are shown. This division of hue is an example and may be divided more finely. The matrix coefficient aij (hue) is determined for each hue according to the spectral characteristics of the input system and the output system (color material).
Here, the primary masking equation is taken as an example, but if a second-order term such as s (B) × s (B), s (B) × s (G) or a higher-order term is used, Color correction can be performed with higher accuracy. Further, the Neugebauer equation may be used instead of the masking equation, and Y, M, and C are obtained from the values of s (B), s (G), and s (R) by any method. be able to.

  Also, the color conversion UCR processing circuit 709 performs hue determination as follows, for example. In other words, the relationship between the reading value of the scanner unit 300 and the colorimetric value is expressed by the following equation (2) using a predetermined coefficient bij (i, j = 1, 2, 3).

From the definition of the colorimetric value, L ^* = 116 ((Y / Yn) ∧ (1/3)) − 16
However, when Y / Yn> 0.008856,
Or L ^* = 903.3 (Y / Yn)
However, when Y / Yn <= 0.00856,
a ^* = 500 (f (X / Xn) -f (Y / Yn))
b ^* = 200 (f (Y / Yn) -f (Z / Zn))
Here, when t> 0.0080856, f (t) = t∧ (1/3)
Or when t <= 0.008856, f (t) = 70787 ^* t + 16/116
Yn, Xn, and Zn are constants.

And C ^* = (a ^* ∧2 + b ^* ∧2) ∧0.5
hab = arctan (b ^* / a)
Therefore, it is possible to determine which hue (see FIG. 9) corresponds to a pixel on the document G read from the RGB signal of the scanner unit 300.
In FIG. 9, the center of the upper concentric circle is an achromatic axis with a ^* = b ^* = 0 in the L ^* a ^* b ^* color system. The distance from the center of the circle in the radial direction is indicated by saturation C ^* , and the angle from a straight line of a ^* > 0 and b ^* = 0 to a point is expressed by a hue angle h ^* . Each hue of Yellow, Red, Magenta, Blue, Cyan, and Green has a saturation with saturation C ^* ≧ C0 ^* with respect to a reference value C0 ^* with saturation, and the hue angle is, for example, Yellow: H1 ^* ≦ h ^* <H6 ^* , Red: H2 ^* ≦ h ^* <H1 ^* , Magenta: H3 ^* ≦ h ^* <0 and 0 ≦ h ^* <H2 ^* , Blue: H4 ^* ≦ h ^* < H3 ^* , Cyan: H5 ^* ≦ h ^* <H4 ^* , Green: H6 ^* ≦ h ^* <H5 ^*, etc.

The vertical axis in the lower part of FIG. 9 represents L ^* (lightness), the saturation C ^* is defined as C ^* ≦ C0 ^* , and White: L = 100, Black: L = 0, and the like.

  Further, simply, the hue is determined from the ratio s (B): s (G): s (R) of each signal of s (B), s (G), and s (R) and the absolute value. You can also.

  On the other hand, the color conversion UCR processing circuit 709 performs color correction processing by calculating using the following equation (3).

Y ′ = Y−α · min (Y, M, C)
M ′ = M−α · min (Y, M, C)
C ′ = C−α · min (Y, M, C)
Bk = α · min (Y, M, C) (3)
In the above equation, α is a coefficient that determines the amount of UCR, and when α = 1, 100% UCR processing is performed. α may be a constant value. For example, when α is close to 1 in the high density portion and close to 0 in the highlight portion (low image density portion), the image in the highlight portion can be smoothed.

The color correction coefficient is changed to 12 hues obtained by further dividing the 6 hues of RGBYMC into 2 parts and further to every 14 hues of black and white.
The hue determination circuit 708 determines to which hue the image data read by the scanner unit 300 belongs, and outputs the determination result to the color conversion UCR processing circuit 709.
The color conversion UCR processing circuit 709 selects the color correction coefficient for each hue based on the determination result of the hue determination circuit 708 and performs the color correction process.
A scaling circuit 711 performs vertical / horizontal scaling on the image data for which color correction processing has been completed, and an image processing (creating) circuit 712 performs repeat processing or the like on the image data for which scaling processing has been completed. The data is output to the processing printer γ conversion circuit 713.
The image processing printer γ conversion circuit 713 corrects the image signal according to the image quality mode such as characters and photographs, and can simultaneously perform background skipping. The image processing printer γ conversion circuit 713 has a plurality of (for example, 10) gradation conversion tables (image signal conversion tables) that can be switched in accordance with the area signal generated by the image processing circuit 712. Select the optimum gradation conversion table for each original such as text, silver halide photograph (printing paper), printed original, inkjet, highlighter pen, map, thermal transfer original, etc. from multiple image processing parameters and enter the image quality mode The corresponding image signal is corrected and output to the gradation processing circuit 714.
The gradation processing circuit 714 performs dither processing on the image data input from the image processing printer γ conversion circuit 713, and outputs it to the interface selector 722 of the printer unit 100.
The gradation processing circuit 714 can select dither processing of any size from 1 × 1 no dither processing to dither processing consisting of m × n pixels (m and n are positive integers), for example, up to 36 pixels Up to dither processing using the pixels. The dither size using all 36 pixels is, for example, a total of 36 pixels of 6 pixels in the main scanning direction × 6 pixels in the sub scanning direction, or a total of 36 pixels of 18 pixels in the main scanning direction × 2 pixels in the sub scanning direction. There is.
FIG. 10A shows an example in which a total of 36 pixels of 6 pixels in the main scanning direction × 6 pixels in the sub-scanning direction are used for the dither processing, and FIG. The example of the index table which recorded the correspondence with the number of the gradation table applied to the pixel is shown. 11A to 11C show examples of a gradation processing table (dither table) of 2 main scanning pixels × 2 sub scanning pixels.
The gradation processing circuit 714 stores the index table and the gradation processing table in a temporary memory called an internal register, and the setting value for each is controlled by the CPU 715.
In the gradation processing tables of FIGS. 11A to 11C, the horizontal axis indicates the image signal input to the pixel, and the vertical axis indicates the output value from the pixel. FIG. 11A shows three gradation processing tables T1, T2, and T3. FIG. 11B shows a gradation processing table for T1 to T5. The gradation processing tables for T1 and T2 are the same as those in FIG. 11A, but the gradation processing for T4 and T5 is performed. The table is different. FIG. 11C illustrates a gradation processing table for T6, T7, and T3. The gradation processing table for T3 is common to FIG.
In FIG. 10, when a value is set so that the pixel number is shifted by one pixel in the main scanning direction, the index table is as shown in FIG. Although not shown in the drawing, it can be set to shift in the sub-scanning direction. By setting the shift amount in the main scanning direction and the shift amount in the sub-scanning direction, each color of YMCK can be set. Gradation processing with different screen angles can be set for each.
An index table corresponding to dithering of 2 pixels in the main scanning direction × 2 pixels in the sub-scanning direction is shown in FIG.
In this case, since the output of the gradation processing circuit 714 lowers the pixel frequency to ½, the image data bus has a 16-bit width so that data for two pixels can be simultaneously transferred to the printer unit 100. (2 pieces of 8-bit image data).
In FIG. 5 again, as described above, the printer unit 100 is connected to the IPU 612 by the I / F selector 721, and the I / F selector 721 reads the image data read by the scanner unit 300 from an external image. It has a switching function for outputting it for processing by a processing device or the like, or for outputting image data from an external host computer 740 or image processing device by the printer unit 100. Note that image data from the external host computer 740 is input to the I / F selector 721 via the printer controller 741.

An image forming printer γ (process control γ) γ correction circuit 723 converts an image signal from the I / F selector 721 using a gradation conversion table (image signal conversion table), and performs laser modulation of the printer engine 724. Output to the circuit.
In the copying apparatus 1, as described above, the image signal from the host computer 740 is input to the I / F selector 721 through the printer controller 741, the gradation is converted by the image forming printer γ correction circuit 723, and the printer engine 724. By performing image formation in this way, it can be used as a printer.
In the copying apparatus 1, the CPU 715 uses the RAM 717 as a work memory based on a program in the ROM 716 and controls each part of the IPU 612, thereby executing the image processing. The CPU 715 performs system image processing through a serial I / F. When a command such as an image quality mode, density information, and area information is transmitted from the operation unit 500 or the like through the system controller 600 and connected to the controller 600, the IPU 612 is sent to the IPU 612 based on the image quality mode, density information, area information, and the like. Various parameters are set and image processing is performed.
The pattern generation unit 710 of the IPU 612 and the pattern generation unit 722 of the printer unit 100 generate gradation patterns used by the IPU 612 and the printer unit 100, respectively.
In addition, as described above, the area processing unit 702 generates an area signal for distinguishing which area in the document G the image data currently being processed belongs to, and based on this area signal, the subsequent image is generated. Although parameters used in the processing are switched, the concept of area processing of the area processing unit 702 can be illustrated as shown in FIG. That is, in FIG. 14, an area corresponding to image data obtained by reading a document G having a plurality of areas such as a character area (area 0), a photographic paper area (area 1), and an inkjet area (area 2) with the scanner unit 300 is displayed. The processing unit 702 compares the designated area information (region information) on the document G with the reading position information at the time of image reading, and generates an area signal. As shown in FIG. 14 for the image processing printer γ conversion circuit 713 and the gradation processing circuit 714, the IPU 612 is based on the area signal from the area processing unit 702, the scanner γ conversion unit 703, the MTF filter 707, and the color conversion. Parameters used in the UCR processing circuit 709, the image processing circuit 712, the image processing printer γ conversion circuit 713, and the gradation processing circuit 714 are changed.
For example, the image processing printer γ conversion circuit 713 decodes the area signal from the area processing unit 702 with a decoder, and a selector (character (table 1), inkjet (table 2), photographic paper (table 3), and printing (print ( Select from a plurality of gradation conversion tables such as Table 4). In the document G of FIG. 14, an example in which a character region 0, a photographic paper region 1, and an inkjet region 2 exist is illustrated. The image processing printer γ conversion circuit 713 performs the processing for the character region 0. Thus, the gradation conversion table 1 for characters, the gradation conversion table 3 for photographic paper for the photographic paper region 1, and the gradation conversion table 2 for inkjet for the region 2 of the inkjet. select.
The gradation processing circuit 714 performs processing that does not use dither by the selector 2 based on a signal obtained by decoding the area signal again by the decoder with respect to the image signal subjected to gradation conversion by the image processing printer γ conversion circuit 713. Of the gradation processing such as dithering and error diffusion processing, the gradation processing to be used is switched. Note that the gradation processing circuit 714 performs error diffusion processing on the inkjet document G and the inkjet region of the document G.
The gradation processing circuit 714 selects whether the image signal after gradation processing is the line 1 or the line 2 based on the reading position information by the decoder. The selection is switched every time one pixel differs in the sub-scanning direction. The gradation processing circuit 714 temporarily stores the data of the line 1 in a FIFO (First In First Out) memory located downstream of the selector, and outputs the data of the line 1 and the line 2 to thereby change the pixel frequency. The signal is reduced to 1/2 and output to the I / F selector 721.

  The copying apparatus 1 includes a laser modulation circuit 120 as shown in FIG. 15 in the laser optical system 106 of the printer unit 100, and includes a look-up table (LUT) 121 and a pulse width modulation circuit (PWM) 122. And a power modulation circuit (PM) 123 and the like. The writing frequency in the laser modulation circuit 120 is 18.6 [MHz], and the scanning time of one pixel is 53.8 [nsec].

The look-up table (LUT) 121 receives 8-bit image data, and the look-up table (LUT) γ-converts the input image data and outputs it to the pulse width modulation circuit (PWM) 122. The pulse width modulation circuit (PWM) 122 converts an 8-bit image signal input from the look-up table (LUT) 121 into an 8-value pulse width and converts it into a power modulation circuit (PM). ) 123, and the power modulation circuit (PM) 123 performs 32-level power modulation with the lower 5 bits. A laser diode (LD) 124 and a photodetector (PD) 125 are connected to the power modulation circuit (PM) 123, and the power modulation circuit (PM) 123 is based on a signal obtained by modulating the laser diode (LD) 124. While emitting light, the emission intensity of the laser diode (LD) 124 is monitored based on a monitor signal from the photodetector (PD) 125, and correction is performed for each dot. The maximum value of the intensity of the laser beam emitted from the laser diode (LD) 124 can be varied to 8 bits (256 levels) independently of the image signal.
Further, the beam diameter in the main scanning direction with respect to the size of one pixel of the laser beam emitted from the laser diode (LD) 124 (the width when the intensity of the stationary beam is attenuated to 1 / e ² with respect to the maximum value) Defined) is 600 DPI, one pixel 42.3 [μm], the main scanning direction 50 [μm] and the sub-scanning direction 60 [μm] are used.
The laser modulation circuit 120 is prepared corresponding to each of the image data of line 1 and line 2 described with reference to FIG. 14, and the image data of line 1 and line 2 is synchronized, and the photosensitive drum 104K to 104C are scanned in parallel in the main scanning direction.
Next, as shown in FIG. 16, the scanner unit 300 has a circuit block configuration. The CCD 312, the amplifier circuit 321, the S / H (sample hold) circuit 322, the A / D conversion circuit 323, and the black correction circuit 324 are arranged. A CCD driver 325, a pulse generator 326, a clock generator 327, and the like.
The scanner unit 300 irradiates the original G with the halogen lamp 302 shown in FIG. 2, separates the reflected light from the original G by the RGB filter of the CCD 312, reads the image of the original G with the CCD 312, and analogizes from the CCD 312. Are output to the amplifier circuit 321. The CCD driver 325 supplies a pulse signal for driving the CCD 312, and a pulse source necessary for driving the CCD driver 325 is generated by a pulse generator 326. The pulse generator 326 generates a pulse signal using the clock signal oscillated by the clock generator 327 made of a crystal oscillator or the like as a reference signal, and is necessary for the S / H circuit 322 to sample and hold the image signal from the CCD 312. A timing signal is supplied to the S / H circuit 322.
The amplifier circuit 321 amplifies the analog image signal from the CCD 312 to a predetermined level and outputs it to the S / H circuit 322. The S / H circuit 322 samples and holds the image signal from the amplifier circuit 321 to perform A / The data is output to the D conversion circuit 323. The A / D conversion circuit 323 digitizes the analog image signal sampled and held by the S / H circuit 322, for example, into an 8-bit signal, and outputs it to the black correction circuit 324. The black correction circuit 324 For image data digitally converted by the conversion circuit 323, variation in black level (electric signal when the amount of light is small) between chips of the CCD 312 and between pixels is reduced, and streaks and unevenness occur in the black portion of the image. Is output to the shading correction circuit 701 of the IPU 612.
As described above, the shading correction circuit 701 corrects the white level (electrical signal when the amount of light is large) and moves the scanner unit 300 to the position of the uniform white reference plate as shown in FIG. Based on the white data at the time of irradiation, correction is performed by correcting variations in sensitivity of the irradiation system, optical system, and CCD 312.
The image signal from the shading correction circuit 701 is processed by the image processing unit from the area processing unit 702 to the gradation processing circuit 714 of the IPU 612 and is recorded and output by the printer unit 100. The circuits 715 are controlled by the CPU 715 based on programs and data in the ROM 716 and the RAM 717.
The amplification amount of the amplifying circuit 321 is determined so that the output value of the A / D conversion circuit 323 becomes a desired value with respect to a specific document density. A value of 0.05 (reflectance: 0.891) is obtained as 240 values with 8-bit signal values, and at the time of shading correction, the gain is lowered to increase the sensitivity of shading correction. The reason for this is that with an amplification factor during normal copying, if there is a large amount of reflected light, an 8-bit signal that exceeds 255 values will saturate to 255 values, resulting in errors in shading correction. This is because it occurs. That is, FIG. 18 is a schematic diagram in which the read signal of the image amplified by the amplifier circuit 321 is sampled and held by the S / H circuit 322. The horizontal axis represents the amplified analog image signal through the S / H circuit 322. The passing time and the vertical axis represent the magnitude of the amplified analog signal. The analog signal is sampled and held at a predetermined sample and hold time shown in FIG. 18, and the signal is sent to the A / D conversion circuit 323. FIG. 18 is an image signal obtained by reading a white level. The amplified image signal is, for example, 240 values as a value after A / D conversion at the time of copying, and 180 values at the time of white correction. An example of a signal is shown.

Next, the operation of this embodiment will be described. In using the copying function, the copying apparatus 1 of this embodiment executes scanner calibration described below at least once in advance.
Scanner calibration is performed using, for example, a reference chart HC as shown in FIG. In this reference chart HC, the color patch portion is originally drawn in color, but in FIG. 19, it is displayed in black and white indicating the difference in color with different hatching as a patent drawing. In FIG. 19, the reference chart HC has a plurality of gray patches with achromatic colors and different image densities arranged at the center, and a plurality of color patches with different hues arranged on the left and right. Each color of RGBYMC is arranged, and specifically, the hue angle h ^* is 0 ≦ h ^* <360 ° [degree] with respect to lightness L ^* , saturation C ^* , and hue h ^* . Hereinafter, as an example, the hue angle interval Δh ^* = 60 [deg] of each color patch is set to Yellow (h ^* = 0 [deg]), Red (h ^* = 60 [ deg]), Magenta (h ^* = 120 [deg]), Blue (h ^* = 180 [deg]), Cyan (h ^* = 240 [deg]), Green (h ^* = 300 [deg]), etc. . In addition, a numerical value is an example and does not necessarily need to be exactly the same. For example, Yellow (h ^* = 5 [deg]), Red (h ^* = 55 [deg]), and the like.
The above example is a case where color patches for six colors of YMCRGB are arranged, but the hue h ^* is divided more finely, for example, Δh ^* = 30 [deg], etc. May be arranged.
The procedure for executing the scanner calibration is shown as a sequence diagram in FIG.
First, when the user or service person selects various setting modes on the liquid crystal screen 511 of the operation unit 500 shown in FIG. 3, the copying apparatus 1 displays various adjustment screens as shown in FIG. 21 on the liquid crystal screen 511. When execution of “scanner calibration” is selected on these various adjustment screens, the scanner calibration mode is entered, and a scanner calibration start screen as shown in FIG. 22 is displayed on the liquid crystal screen 511. In this scanner / calibration mode, the user or serviceman places the reference chart HC on the contact glass 3 as the document table, and the “read start” key on the scanner / calibration start screen on the liquid crystal screen 511 shown in FIG. Is pressed (S1 in FIG. 20).
When the operation unit 500 gives an instruction to start reading the reference chart HC, the copying apparatus 1 instructs the scanner unit 300 to read the reference chart HC from the system controller 600, as indicated by S2 in FIG. As shown by S3 in FIG. 20, the scanner unit 300 executes reading of the reference chart HC to obtain RGB signal read values for each patch of the reference chart HC, and as shown by S4 in FIG. The reading value of the reference chart HC is transmitted to the IPU 612.
On the other hand, as shown by S5 in FIG. 20, the reading reference value (reference data) of the reference chart HC is read from the nonvolatile RAM (storage means) in the system controller 600, and the system controller is read as shown by S6 in FIG. 600 to IPU 612. Then, when reading the reference chart HC, the copying apparatus 1 displays on the liquid crystal screen 511 a screen indicating that reading is in progress as shown in FIG.
When the IPU 612 receives the reading value and the reading reference value of the reference chart HC, the IPU 612 calculates the image processing parameter as shown in S7 in FIG. 20, and sets the calculation result parameter as the system controller as shown in S8 in FIG. 600.
The system controller 600 stores the received parameters in the nonvolatile RAM, as indicated by S9 in FIG.
Next, a method for creating the scanner γ conversion table from the read values of the achromatic color patches in the reference chart HC (see FIG. 19) in S7 of the sequence diagram of FIG. 20 will be described based on the quaternary chart shown in FIG.

  In the quaternary chart of FIG. 24, the first quadrant (I) represents the scanner γ conversion table to be obtained, the horizontal axis represents the input value to the scanner γ conversion table, and the vertical axis represents the output after the scanner γ conversion. ing. The vertical axis of the fourth quadrant (IV) represents the read value of the achromatic color patch, and the graph represents the target value (reference value) for obtaining the scanner γ conversion table from the read value of the achromatic color patch. The horizontal axis of the third quadrant (III) is the reference value of the reading value of the achromatic color patch, and the graph represents the reading result obtained by reading the achromatic gray scale patch by the scanner unit 300. The second quadrant (II) is no conversion (through).

  Based on the characteristics shown in the quaternary chart of FIG. 24, the scanner γ conversion tables of b and b ′ of the first quadrant are created from the results a and a ′ of the read values of the third quadrant.

  The target values of the reading values shown in the fourth quadrant of the quaternary chart of FIG. 24 may be different target values for each of the RGB components of the scanner γ conversion table used at the time of document copying, or the same target value. It may be a value.

  As described above, the scanner γ conversion table is created so as to correct the machine difference of the scanner unit 300.

  Note that, in the scanner γ conversion table used in ACC (automatic gradation correction), which will be described later, unlike the above-described scanner (document reading) scanner γ conversion table, spectral reflection of toner on transfer paper to be read is performed. The scanner γ conversion table for reading the ACC pattern is created using the reading value of the chromatic color patch of the reference chart HC so that the sensitivity is high with respect to the rate characteristic and the influence of the spectral sensitivity variation of the CCD 312 is corrected.

  Then, as described later, a scanner γ conversion table for reading an ACC pattern (see FIG. 32) is created from a chromatic color patch and an achromatic color patch having different colors, and a yellow toner reading scanner γ. A method for creating a correction table (scanner γ conversion table) will be described as an example with reference to FIG.

  The chromatic color patch used for correcting the yellow toner is as shown in FIG. 25, for example, and this chromatic color patch is extracted for correcting the yellow toner. It is an example of the numerical value which read the color patch with the scanner used as a reference | standard. When reading yellow toner, the blue signal is used because the sensitivity of the blue signal is high. Also, different blue signals are output from a plurality of chromatic color patches having different colors. White, 2. Yellow (Yellow), 5. Blue, 6. Cyan, 10. Gray, 11. A correction table for reading yellow toner is created by using a blue signal among black RGB read signals.

Then, in creating a correction table for yellow reading at the time of ACC execution, the reference chart HC is created with printing ink, and thus a deviation from the spectral reflectance of toner occurs. An example of the correction coefficient for Blue is shown.
The correction coefficient can be obtained based on FIG. 26 showing the relationship between the spectral sensitivity of the CCD 312 for the blue signal and the spectral reflectance of yellow toner in terms of the wavelength λ. The horizontal axis of FIG. 26 is the wavelength λ, and the vertical axis is the spectral sensitivity [%] of the CCD 312 shown on the left axis for the graph (a), and on the right side for the graphs (c) and (d). This is the spectral reflectance [%] of the toner indicated on the axis. In FIG. 26, (a) is the spectral sensitivity of the blue signal filter, (c) is the spectral reflectance of yellow toner, and (d) is the spectral reflectance of yellow ink. , (D) show the spectral reflectance of the black (Bk) toner when the adhesion amount is small. For the spectral sensitivity of (a), the product of the spectral energy of the light source (halogen lamp 302) is used for the spectral transmittance of the blue filter of the CCD 312.

  As can be seen from FIG. 26, the output B (CCD 312, color material) of the blue signal is the spectral sensitivity S (CCD, λ) of the CCD 312 and the spectral reflectance ρ (color material) of the color material with respect to the wavelength λ. , Λ, area ratio) is an integral value for wavelength λ with respect to the product S (CCD, λ) × ρ (color material, λ, area ratio). That is, it is given by the following equation (4).

  Blue signals for the spectral sensitivity characteristic a of the CCD 312 when reading yellow toner (hereinafter abbreviated as Y toner) and yellow ink (hereinafter abbreviated as Y ink) are respectively expressed by the following equations (5). ) And (6).

Here, the spectral sensitivity S (a, λ) is a representative value of the scanner unit 300, and the Y toner ρ (Y toner, λ) and the spectral reflectance ρ (Y ink, λ) of the Y ink are spectroscopically measured. Obtained by measuring with a colorimeter. Thus, B (a, Y toner) and B (a, Y ink) can be obtained.

  From the read value B (Y ink) of the blue signal obtained by reading the yellow patch of the printing ink on the reference chart HC, the Y toner is read for the Y toner read value at the time of ACC execution. When predicting the read value B (Y toner) in this case, the following equation (7) is used as the coefficient k (Yellow) to be corrected.

B (Y toner) = k (Yellow) × B (Y ink) (7)
However, k (Yellow) = B (a, Y toner, 100%) / B (a, Y ink, 100%).
In the above description, the yellow toner is described. However, for other color patches, the spectral reflectance and calculation of the yellow toner are calculated in a region where the blue spectral sensitivity of the CCD 312 is not zero. The Y toner area ratio or the toner adhesion amount per unit area [mg / cm ² ]), which has substantially the same color patch reflectivity as the printing ink to be used, is used.
For example, the spectral reflectance characteristics (i) of the blue-green ink shown in FIG. 27, the spectral reflectance (c) of the yellow toner with an area ratio of 50%, and the read value of the blue signal are yellow (Yellow). ) For a patch (Black, Green, etc.) that obtains a reading value lower than the reading value of toner (ink), the coefficient is set to 1 without calculating the correction coefficient. The correction coefficient k obtained in this way can be shown as in FIG.

  Next, a method of creating a conversion table for ACC pattern reading value correction will be described based on a quaternary chart of the ACC pattern reading value correction table shown in FIG.

  The first quadrant (I) in FIG. 28 represents a conversion table for correcting the ACC pattern reading value to be obtained. The horizontal axis represents the CCD pattern reading value and the vertical axis represents the value after conversion. The vertical axis of the fourth quadrant (IV) represents the read values after correction with the correction coefficient k of the chromatic and achromatic patches, and the graph shows the ACC pattern from the read values of the chromatic and achromatic patches. It represents a target value (reference value) for obtaining a conversion table for reading value correction. The horizontal axis of the third quadrant (III) is the reference value of the read values of the chromatic and achromatic patches, and the graph corrects the read values obtained by reading the chromatic and achromatic patches with the correction coefficient k. Value. The second quadrant (II) is no conversion (through).

  Then, according to the characteristics shown in FIG. 28, conversion for correcting the ACC pattern reading value obtained from b and b ′ of the first quadrant (I) from the reading values a and a ′ of the third quadrant (III), respectively. A table (correction table) D [ii] (ii = 0, 1, 2,..., 255) is created.

  The target value of the read value shown in the fourth quadrant (IV) of FIG. 28 is created for each toner of YMCK read by the ACC pattern. In this way, ACC (automatic gradation correction) adjustment accuracy can be improved.

  FIG. 29 shows an example of numerical values obtained by reading a color patch extracted for correcting cyan toner with a reference scanner. When reading cyan toner, the red signal is used because the sensitivity of the red signal is high. Therefore, different red signal values are output from a plurality of chromatic color patches having different colors. White, 2. 2. Yellow (Yellow) Red (or 4. Magenta); Colors between Magenta and Blue 1,6. 6. Color between Magenta and Blue Blue, 8 Cyan, 10. Gray, 11. A correction table for reading cyan toner at the time of executing ACC is created by using the chromatic color of black and the red signal of the achromatic patch.

  In this way, variations in the read image signal based on the mechanical difference of the scanner unit 300 can be prevented, and the adjustment accuracy of automatic gradation correction (ACC) can be improved, thereby further improving the image quality. be able to.

  Further, the gradation conversion table set in the image processing printer γ conversion circuit 713 at the time of gradation pattern reading is a common one of image signals obtained by reading a plurality of different color patches of the reference chart HC with the scanner unit 300. Since it is generated using the component image signal, the read image signal of the scanner unit 300 corresponding to the complementary color signal of YMC toner is used among the RGB image signals obtained by reading the patches of different colors of the reference chart HC. By generating the gradation conversion table, it is possible to improve the adjustment accuracy of the gradation conversion table, and it is possible to improve the image quality even when linked output is performed.

  Further, when creating the scanner γ conversion table for reading Cyan at the time of ACC execution, the reference chart HC is created with printing ink, so that deviation from the spectral reflectance of the toner occurs. Therefore, FIG. 29 shows an example of the correction coefficient for red.

  This corrects the difference between the spectral reflectance characteristic of the printing ink of the reference chart HC and the spectral reflectance characteristic of the toner of the printer unit 100 that records and outputs the gradation pattern, and further automatic gradation correction. A scanner γ conversion table that is an image signal conversion table for (ACC) can be created, and the image quality can be further improved.

  Next, an operation screen for selecting an ACC (automatic gradation correction) function for image density (gradation) will be described.

  When the ACC (automatic gradation correction) menu is called on the liquid crystal screen 511 of the operation unit 500 shown in FIG. 3, the various adjustment screens shown in FIG. 21 are displayed. When [execute] automatic gradation correction for use is selected, an automatic gradation correction start screen shown in FIG. 30 is displayed on the liquid crystal screen 511. In this case, when copy use is selected on the various adjustment screens of FIG. 21, a gradation correction table used when using copy is prepared, and when printer use is selected, the gradation when using the printer is selected. A correction table is prepared based on the reference data.

  In the various adjustment screens in FIG. 21, if the result of image formation using the changed YMCK tone correction table is not desirable, the YMCK tone correction table before processing can be selected. , "Undo" key is displayed.

  In the various adjustment screens shown in FIG. 21, when “Automatic gradation correction setting” is selected, “background correction”, “high density correction”, “RGB ratio correction”, “execution”, The key for selecting “Non-execution” is displayed. In the “Auto gradation correction setting” menu, “Auto gradation correction setting” and “Light intensity unevenness detection setting” can be selected. Note that these selections are not always necessary, and may be always “execution”.

  Then, as described above, the copying apparatus 1 creates a scanner γ conversion table for each RGB read component used at the time of copying from an achromatic color patch. On the other hand, the copying apparatus 1 corrects the read values of the YMCK gradation patterns obtained by reading the adjustment pattern output during execution of ACC (automatic gradation correction) from the chromatic color patches and the achromatic color patches. Therefore, in the former process, three RGB conversion tables are used, and in the latter process, four YMCK conversion tables are used.

  Here, the operation of automatic gradation correction (ACC) of image density (gradation property) will be described based on the flowchart shown in FIG.

  When “execution” of automatic gradation correction for copy use or printer use is selected on the various adjustment screens shown in FIG. 21, the automatic gradation correction start screen shown in FIG. When the “print start” key is pressed at the start of automatic gradation correction, a plurality of density gradation patterns corresponding to each color mode of YMCK, each character, and each picture, as shown in FIG. 32, are displayed. It is formed on transfer paper (transfer material) P (step S101).

  This density gradation pattern is stored and set in advance in the ROM 716 of the IPU 612, and the written values of the pattern are 16 patterns of 00h, 11h, 22h,..., EEh, FFh in hexadecimal notation. . In FIG. 32, patches for five gradations are displayed excluding the background portion, but any value can be selected from the 00h-FFh 8-bit signal. In the density gradation pattern, a toner pattern of a character mode and a photographic mode is formed. In the character mode, a dithering process such as pattern processing is not performed, and a pattern is formed with 256 gradations of one dot. Dither processing is performed.

When the copying apparatus 1 outputs a pattern to the transfer paper (transfer material) P, as shown in FIG. 33, onto the contact glass 3 that is a document table of the transfer paper (transfer material) P on which the density gradation pattern is recorded and output. Is displayed on the liquid crystal screen 511. When the transfer paper on which the density gradation pattern is formed is placed on the contact glass 3 in accordance with the instruction on this screen (step S102), “read start” is selected on the screen of FIG. "Is selected (step S103). If" Cancel "is selected, the process is terminated.
When “reading start” is selected in step S103, the copying apparatus 1 causes the scanner unit 300 to perform main scanning sub-scanning on the transfer paper on which the density gradation pattern is formed, and reads the RGB data of the YMCK density pattern ( Step S104). At this time, the scanner unit 300 reads the data of the pattern portion of the transfer paper on which the density gradation pattern is formed and the data of the background portion of the transfer paper.

  The copying apparatus 1 determines whether the data of the pattern portion of the transfer paper has been read normally (step S105). If the data is not read correctly, the copying apparatus 1 checks whether it is the second time that the data is not read normally (step S105). S106). If it is the first time, the copying apparatus 1 displays the screen of FIG. 33 on the liquid crystal screen 511 again, and when reading is instructed, returns to step S104 and performs the same processing as above (steps S104 and S106). In step S106, if it is the second time that reading is not performed normally, the process is terminated.

  In step S105, when the data of the pattern portion of the transfer paper is normally read, the copying apparatus 1 uses the ACC pattern reading value correction table D [ii] (ii = 0, 1, 2,..., 255) are converted and corrected for each color of YMCK (step S107), and the background correction processing using the background data is performed based on the selection results on the various adjustment screens in FIG. Execution “/“ non-execution ”is determined (step S108).

If “execution” of the background correction process using the background data is selected in step S108, the copying apparatus 1 performs the background data correction process on the read data (step S109), and a high image of the reference data. Whether the density portion correction is “executed” / “not executed” is determined based on the selection results on the various adjustment screens in FIG. 21 (step S110).
If “execution” of the correction of the high image density portion of the reference data is selected in step S110, the copying apparatus 1 performs a correction process of the high image density portion on the reference data (step S111), and YMCK tone correction. A table is created and selected (step S112). If the reference data is not corrected in step S110, the copying apparatus 1 creates and selects the YMCK gradation correction table without correcting the reference data (step S112).
When the YMCK tone correction table is created and selected, the copying apparatus 1 checks whether the above processing has been executed for each color of YMCK (step S113). If the above processing has not been executed for each color of YMCK, the copying apparatus 1 proceeds to step S105. Returning to the above, the above processing is executed for each color of YMCK (steps S105 to S113).
When the above processing is performed for each color of YMCK in step S113, the copying apparatus 1 checks whether the above processing has been completed for each image quality mode for photographs and characters (step S114). Returning, processing is performed in the same manner as described above (steps S105 to S114), and when the processing is completed for each picture quality mode of photograph and text in step S114, the processing is ended.

  Then, as shown in FIG. 34, the copying apparatus 1 displays a screen indicating that automatic gradation correction is being performed on the liquid crystal screen 511 during the above processing, and displays an image in the YMCK gradation correction table after the processing is completed. If the result of the formation is not desirable, a “restore” key is displayed on the various adjustment screens of FIG. 21 so that the YMCK gradation correction table before processing can be selected.

  Next, the background correction process will be described. There are two purposes for the background correction processing, and one is to correct the whiteness of the transfer paper used during ACC. This background correction process is because even if an image is formed on the same machine at the same time, the value read by the scanner unit 300 differs depending on the whiteness of the transfer paper to be used. As a demerit when the correction is not performed, for example, when recycled paper or the like having low whiteness is used for ACC, since the recycled paper generally has a lot of yellow components, a yellow gradation correction table is created. When correction is made so that the yellow component is reduced, but in this state, when copying is performed using art paper or the like with high whiteness, an image with less yellow component is obtained and the desired color reproduction cannot be obtained. Is that there is.

Another reason for the background correction processing is that when the thickness of the transfer paper (paper thickness) used at the time of ACC is thin, the color of a pressure plate or the like that presses the transfer paper is seen through and read by the scanner unit 300. For example, when the ADF 400 is installed instead of the pressure plate, a belt 402 is used for transporting the original G. The transport belt 402 has low whiteness due to the rubber-based material used. However, since there is a slight gray color, the read image signal is also read as an image signal that is apparently high, and is created so as to be thinner when the YMCK tone correction table is created. In this state, when a transfer sheet having a large paper thickness and poor transparency is used for ACC, an image having a low overall density is reproduced, so that a desirable image is not necessarily obtained.
In order to prevent the above-described problems, the read image signal of the pattern portion is corrected from the read image signal of the paper background portion based on the image signal of the paper background portion.

  However, there is an advantage even when the above correction is not performed, and when using a transfer paper with a lot of yellow components, such as recycled paper, the color without yellow correction is not suitable for colors containing yellow components. The reproduction may be improved. In addition, when only the transfer paper having a thin paper thickness is always used, there is an advantage that the gradation correction table is created in a state matched to the thin paper.

Therefore, the copying apparatus 1 can turn on / off the correction of the background portion according to the use status of the copying apparatus 1 and the user's preference by operating the keys of the operation unit 500.
Next, the operation and processing for automatic gradation correction will be described. A read value obtained by reading the pattern in which the write value LD [i] (i = 0, 1,..., 9) of the gradation pattern (see FIG. 32) formed on the transfer paper is read by the scanner unit 300 is obtained. V [t] [i] ≡ (r [t] [i], g [t] [i], b [t] [i]) (t = Y, M, C, or, K, i = 0, 1, ..., 9).

Instead of (r, g, b), brightness, saturation, hue angle (L ^* , c ^* , h ^* ), or brightness, redness, blueness (L ^* , a ^* , b ^* ), etc. May be represented.

  The reference white reading value stored in advance in the ROM 716 or the RAM 717 is set to (r [W], g [W], b [W]).

  Next, a method of generating a gradation conversion table (LUT) performed by the image processing printer γ conversion circuit 713 when ACC is executed will be described.

  In the gradation pattern read value v [t] [i] ≡ (r [t] [i], g [t] [i], b [t] [i]), the image signal of each complementary color of YMC toner. Are b [t] [i], g [t] [i], and r [t] [i], respectively, so that only the complementary color image signals are used. Here, for simplicity of description, a [t] [i] (i = 0, 1, 2,..., 9; t = C, M, Y, or, K) is used. Processing is simple if a gradation conversion table is created. For black toner, sufficient accuracy can be obtained by using any of RGB image signals, but here, a G (green) component is used.

  The reference data includes the reading value v0 [t] [i] ≡ (r0 [t] [i], g0 [t] [i], b0 [t] [i]) of the scanner unit 300 and the corresponding laser writing value. It is given by a set of LD [i] (i = 1, 2,..., M). Similarly, in order to simplify the description using only YMC complementary color image signals, A [t] [n [i]] (0 ≦ n [i] ≦ 255; i = 1, 2,... , M; t = Y, M, C, or, K). m is the number of reference data.

The YMCK gradation conversion table is obtained by comparing the a [LD] with the reference data A [n] stored in the ROM 716.
Here, n is an input value to the YMCK gradation conversion table, and the reference data A [n] is the YMC toner output with the laser writing value LD [i] after the input value n is YMCK gradation converted. The target value of the read image signal obtained by reading the pattern with the scanner unit 300. Here, the reference data includes two types of values: a reference value A [n] that is corrected according to the image density that can be output by the printer, and a reference value A [n] that is not corrected. The copying apparatus 1 determines whether to perform correction based on determination data stored in advance in the ROM 716 or the RAM 717.

  Then, the copying apparatus 1 obtains the laser output value LD [n] corresponding to the input value n to the YMCK gradation conversion table by obtaining the LD corresponding to A [n] from the a [LD].

  By obtaining this laser output value LD [n] with respect to the input values i = 0, 1,..., 255 (in the case of an 8-bit signal), a gradation conversion table can be obtained.

In this case, instead of performing the above processing on all values for the input values n = 00h, 01h,..., FFh (166 base number) for the YMCK gradation conversion table, ni = 0, 11h, 22h,. .. The above processing is performed for the jump value such as FFh, and other points are interpolated with a spline function or the like, or among the YMCKγ correction tables stored in the ROM 716 in advance, the above The closest table that passes through the set of (0, LD [0]), (11h, LD [11h]), (22h, LD [22h]), ..., (FFh, LD [FFh]) Select.
The above process will be described with reference to FIG. In the first quadrant (a) of FIG. 35, the horizontal axis is the input value n to the YMCK gradation conversion table, and the vertical axis is the reading value (after processing) of the scanner unit 300, see above. Data A [i] is represented. The reading values (after processing) of the scanner unit 300 are RGBγ conversion (no conversion is performed here) with respect to the value obtained by reading the gradation pattern with the scanner unit 300, and several reading data in the gradation pattern. It is a value after the averaging process and the addition process, and is processed here as a 12-bit data signal in order to improve calculation accuracy.
In the second quadrant (b) of FIG. 35, the horizontal axis represents the read value (after processing) of the scanner unit 300, similarly to the vertical axis.

  In the third quadrant (c) of FIG. 35, the vertical axis represents the writing value of the laser beam (LD). The data a [LD] which is the laser beam writing value represents the characteristics of the printer unit 100, and the writing value of the laser beam (LD) of the pattern actually formed is 00h (background), 11h. , 22h,..., EEh, FFh are 16 points and show skipped values. Here, the detected points are interpolated and treated as a continuous graph.

  The graph (d) of the fourth quadrant in FIG. 35 is the YMCK gradation conversion table LD [i], and the purpose is to obtain this YMCK gradation conversion table.

  The vertical axis and horizontal axis of the graph (f) are the same as the vertical axis and horizontal axis of the graph (d). When forming a gradation pattern for detection, the YMCK gradation conversion table (g) shown in the graph (f) is used.

  The horizontal axis of the graph (e) is the same as that of the third quadrant (c), and the writing value of the laser beam (LD) at the time of gradation pattern creation and the reading value of the gradation pattern scanner unit 300 (after processing) ) For the sake of convenience for expressing the relationship with ().

In FIG. 35, reference data A [n] is obtained for a certain input value n, and a laser beam (LD) output LD [n] for obtaining A [n] is used as a gradation pattern read value a [LD]. Is obtained along the arrow (l) in the figure.
Next, the calculation procedure of ACC will be described based on the flowchart of FIG. In FIG. 36, in the gradation conversion table creation processing at the time of ACC, first, the copying apparatus 1 receives input values necessary for obtaining a YMCKγ correction table (gradation conversion table), for example, n [i] = 11 (h ) × i (i = 0, 1,..., Imax = 15) is determined (step S201).
That is, the graph of the printer characteristics of the third quadrant is the same as that of the graph when RGBγ conversion is performed, but the characteristics of the RGBγ conversion table of the second quadrant are different. Accordingly, it is necessary to change the reference data of the first quadrant, but the characteristics of the final result YMCK gradation conversion table LD [n] match.

  As described above, this is dealt with by changing the reference data depending on whether or not processing is performed using the RGBγ conversion table. An example of the RGBγ conversion table used in this embodiment is shown.

  Next, the copying apparatus 1 corrects the reference data A [n] according to the image density that can be output by the printer unit 100 (step S202).

  That is, the writing value of the laser beam for obtaining the maximum image density that can be created by the printer unit 100 is FFh (hexadecimal number display), and the read value m [FFh] of the gradation pattern at this time is mmax. Reference data A [i] (i = 0, 1,..., I1) that is not corrected from the low image density side to the intermediate image density side, and reference data A [i] (not corrected on the high image density side) , imax−1) (i1 ≦ i2, i2 ≦ imax−1) and reference data A [i] (i = i1 + 1,..., i2) to be corrected.

  Hereinafter, a specific calculation method will be described on the assumption that the image signal is proportional to the document reflectance without RGB-γ conversion. From the reference data A [i2 + 1] having the lowest image density in the high image density portion and the reference data A [i1] having the lowest image density in the low image density portion among the reference data not subjected to correction, the following equation (8 ) To obtain the difference Δref of the data.

Δref = A [i1] −A [i2 + 1] (8)
Here, Δref> 0 in the case of reflectance linearity or lightness linear that does not perform RGBγ conversion, which is inversion processing.
On the other hand, the difference Δdet is similarly obtained from the read value mmax of the gradation pattern capable of obtaining the maximum image density that can be created by the printer unit 100, by the following equation (9).

Δdet = A [i1] −mmax (9)
Then, reference data A [i] (i = i1 + 1,..., I2) obtained by correcting the high density portion is obtained by the following equation (10).

A [i] = A [i1] + (A [i] −A [i1]) × (Δdet / Δref) (10)
However, i = i1 + 1, i1 + 2,..., I2-1, i2.

Next, the copying apparatus 1 obtains the read image signal m [i] of the scanner unit 300 corresponding to n [i] from the reference data A [n] (step S203).
In order to obtain the read image signal m [i], actually, the reference data A [n [j]] (0 ≦ n [j] ≦ 255, j = 0) corresponding to the skipped n [j]. ,..., Jmax, n [j] ≦ n [k] forj ≦ k) are obtained as follows.
That is, j (0 ≦ j ≦ jmax) that satisfies n [j] ≦ n [i] <n [j + 1] is obtained.

In the case of an 8-bit image signal, the reference data is obtained as n [0] = 0, n [jmax] = 255, n [jmax + 1] = n [jmax] +1, A [jmax + 1] = A [jmax]. Calculation becomes easy.
Further, the reference data interval n [j] is as small as possible, so that the accuracy of the finally obtained γ correction table increases.

Next, the copying apparatus 1 uses the correction table D [ii] (ii = 0, 1, 2,...) Indicating the ACC pattern read value a [LD] with respect to the write value LD as b or b ′ in FIG. .., 255) to correct as follows (step S204).
a1 [LD] = D [a [LD]]
This a1 [LD] is expressed as a [LD] below.

  From j thus obtained, m [i] is obtained by the following equation (11).

m [i] = A [j] + (A [j + 1] -A [i]). (n [i] -n [j])
/ (N [j + 1] -n [j]) (11)
In the above formula (10), interpolation is performed by a linear expression, but interpolation may be performed by a high-order function, a spline function, or the like. In that case, it is given by the following equation (12).

When the copying apparatus 1 obtains m [i], it obtains the writing value LD [i] of the laser beam (LD) for obtaining m [i] in the same procedure (step S205).
When processing image signal data that has not been subjected to RGBγ conversion, a [LD] decreases as the value of the laser beam (LD) increases, as shown below.

For LD [k] <LD [k + 1], a [LD [k]] ≧ a [LD [k + 1]]
Here, the values at the time of pattern formation are 10 values of LD [k] = 00h, 11h, 22h,..., 66h, 88h, AAh, FFh, (k = 0, 1,..., 9). did. This is because the change in the reading value of the scanner unit 300 with respect to the toner adhesion amount is large at an image density with a small amount of toner adhesion. This is because the change in the reading value of the scanner unit 300 with respect to the toner adhesion amount is small, so that the interval is widened for reading.

  In this way, it is possible to suppress toner consumption as compared with the case of increasing the number of patterns such as LD [k] = 00h, 11h, 22h,..., EEh, FFh (16 points in total) and the like. In the image density area, there is little change to the LD writing value, and the read value is likely to be reversed due to potential unevenness on the photosensitive drums 104K to 104C, toner adhesion unevenness, fixing unevenness, potential unevenness and the like. There is a merit that even if the interval between the LD write values is narrowed, it is not always effective in improving the accuracy. For this reason, the pattern is formed with the LD write values as described above.

  Then, LD [i] is set as follows for LD [k] where a [LD [k]] ≧ m [i]> a [LD [k + 1]].

LD [i] = LD [k] + (LD [k + 1] -LD [k]). (M [i] -a [LD [k]])
/ (A [LD [k + 1]]-a [LD [k]])
When 0 ≦ k ≦ kmax (kmax> 0) and a [LD [kmax]]> m [i] (when the image density of the target value obtained from the reference data is high), LD [ i] is predicted by extrapolating with a linear equation as follows.

LD [i] = LD [k] + (LD [kmax] −LD [kmax−1])
(M [i] -a [LD [kmax-1]])
/ (A [LD [kmax]]-a [LD [kmax-1]])
As described above, a set (n [i], LD [i]) (i = 0, 1,..., 15) of the input value n [i] and the output value LD [i] to the YMCKγ correction table is obtained. Can do.
As described above, extrapolation may be performed by a method such as taking a logarithm as well as extrapolating by a linear expression.
Then, based on the obtained (n [i], LD [i]) (i = 0, 1,..., 15), interpolation is performed with a spline function or the like, or it is stored in the ROM 716. A gradation conversion table is obtained by selecting the γ correction table (step S206).

  Then, the copying apparatus 1 detects the development characteristics (characteristics of the toner adhesion amount with respect to the development potential) as shown in FIG. 37 in order to prevent the background stain (“fogging”) and to secure the density.

That is, as shown in FIG. 37, the copying apparatus 1 forms np detection pattern (density gradation pattern) latent images on the photosensitive drums 104K to 104C (step S301), and acquires the detection output of the potential sensor. (Step S302).
That is, as shown in FIG. 38, np (for example, np = 12) detection patterns (density gradation patterns) are formed on the photosensitive drums 104K to 104C, and the photosensitive drums 104K to 104C are exposed by the potential sensor 617 that detects the surface potential. The surface potential VSi (i = 1, 2,..., Np) of the body drums 104K to 104C is read. The laser output used for forming the detection pattern at this time is, for example, an image signal value (in hexadecimal notation) having the following value.
00h, 10h, 20h, 30h, 40h, 50h,
60h, 70h, 90h, B0h, E0h, FFh
Next, the copying apparatus 1 develops the latent images of the detection patterns of the photosensitive drums 104K to 104C with the developing units 107K to 107C to form latent images (step S303), and downstream of the photosensitive drums 104K to 104C in the rotation direction. The detection outputs VPi (i = 1, 2,..., Np) of the toner images on the photosensitive drums 104K to 104C are acquired by the optical sensors 616K to 616C disposed on the side (step S304).
The copying apparatus 1 develops development characteristics based on the surface potential VSi of the photosensitive drums 104K to 104C acquired by the potential sensor 617 and the detection output VPi of the toner image on the photosensitive drums 104K to 104C acquired by the optical sensors 616K to 616C. Is predicted (step S305), and a gradation conversion table is created (step S306).
Therefore, first, the output of the optical sensors 616K to 616C and the image signal correction method are performed as shown in FIG. In the graph (a) of FIG. 39, the vertical axis represents the laser output or image output signal, the horizontal axis represents the output of the optical sensors 616K to 616C, and np density gradation pattern latent images are represented on the photosensitive drum. It is obtained by forming on 104K to 104C, developing, and detecting the reflected light amount of the toner image with the optical sensors 616K to 616C.
In the graph (b) of FIG. 39, the vertical axis represents the laser output, the horizontal axis represents the surface potential of the photosensitive drums 104K to 104C, and the optical attenuation of the photosensitive drums 104K to 104C is the same as the graph (a). It represents a characteristic. Similarly to the graph (a), the graph (b) is obtained by measuring the surface potential with the potential sensor 617 when np density gradation pattern latent images are formed on the photosensitive drums 104K to 104C. It is obtained.
A graph (c) in FIG. 39 represents a gradation conversion table used when the printer unit 100 forms an image. The horizontal axis represents an image input signal (for example, an amount proportional to the density of the original image), The vertical axis represents the image signal (image output signal) after the laser output or the image input signal is converted by the gradation conversion table. Now, the image input signal has a resolution of 8 bits (256 values), and the amount of laser writing light similarly has a resolution of 8 (-10) bits between the minimum value and the maximum value of the laser. ing. The graph (a) in FIG. 39 shows the relationship between the laser output used during detection and the image input signal.
In the graph (d) of FIG. 39, the vertical axis represents the toner adhesion amount on the photosensitive drums 104k to 104C, the horizontal axis represents the output of the optical sensors 616K to 616C, and the output characteristics of the optical sensors 616K to 616C. ing. The output characteristics of the optical sensors 616K to 616C in this graph (d) vary depending on the type of the optical sensors 616K to 616C to be used, the mounting angle, the distance from the photosensitive drums 104K to 104C, etc., but are known in advance. It is constant.
In the graph (e) of FIG. 39, the vertical axis represents the toner adhesion amount, and the horizontal axis represents the surface potential of the photosensitive drums 104K to 104C, and the surface potential of the photosensitive drums 104K to 104C and the photosensitive drum. The relationship between the toner adhesion amount on 104K to 104C, that is, development characteristics is shown. In FIG. 39 (e), h represents the DC component of the developing bias.
A graph (f) in FIG. 39 represents the relationship of the toner adhesion amount on the photosensitive drums 104K to 104C with respect to the image input signal.
From FIG. 39, the output VPi of the optical sensors 616K to 616C is converted to the toner adhesion amount (M / A) i [mg / cm ² ] (i = 1) on the photosensitive drums 104K to 104C using the relationship of the graph (d). 2, ..., np). For example, the reflected light of the toner image formed on the photosensitive drums 104K to 104C is detected by the optical sensors 616K to 616C and sent to the CPU 715 as a detection signal, and the CPU 715 uses VSP and VSG as the toner of the reference pattern portion, respectively. As the optical sensor output and the background output from the adhesion amount, the adhesion amount m ₁ [g / cm ² ] per unit area of the toner adhered to the reference pattern is calculated based on the following equation (13).
m ₁ = −ln (VSP / VSG) / β (13)
Here, β is a constant determined by the optical sensors 616K to 616C and the toner, and in the case of black toner, β = −6.0 × 103 [cm ² / g]. Note that yellow, cyan, and magenta can be similarly converted.
In the above description, the adhesion amount m ₁ [g / cm ² ] per unit area of the toner adhered to the reference pattern is obtained by calculation. However, it is obtained by conversion using a lookup table created in advance. May be.
As described above, the relationship between the surface potential VSi of the photosensitive drums 104K to 104C and the toner adhesion amount (M / A) i on the photosensitive drums 104K to 104C is obtained, and the development of the graph (e) in FIG. Characteristic j is obtained.
However, as shown in the graph (d) of FIG. 39, the output of the optical sensors 616K to 616C is higher than a certain toner adhesion amount (M / A) C (M / A) ≧ (M / A) C. ) Shows a constant value VPmin. On the other hand, as shown in the graph (b), the surface potential of the photoconductive drums 104K to 104C actually decreases with respect to an image signal equal to or larger than the image signal n in the graph (c) of FIG. Despite the change in the amount of adhesion, the amount of toner adhesion (M / A) on the photosensitive drums 104k to 104C is always a constant value (M / A) C. For this reason, in the graph (e), even if the actual development characteristic is the graph c, the development characteristic obtained from the detection result is as shown by j, and between the actual value c and the detected value j. Deviation occurs.
In order to compensate for the deviation between the actual development characteristics and the development characteristics obtained from the detected values, the following correction is performed.
When the detected value VPi of the optical sensors 616K to 616C with respect to the image signal i is equal to or larger than the predetermined value VPc, the toner adhesion amount on the photosensitive drums 104K to 104C or substantially proportional to the detected value VPi (M / A) i Convert to. From these values, a relational expression between the output value VSi of the potential sensor 617 and (M / A) i is obtained as in the following expression (14) using a linear expression, for example.

(M / A) i = a × VSi + b (14)
However, VPi ≧ VPc
Alternatively, a relational expression such as the following expression (15) is obtained with the DC component of the developing bias as Vdc.

(M / A) i = a × (VSi−Vdc) + b (15)
However, VPi ≧ VPc
Here, a and b are coefficients, and are determined from the values of VSi and (M / A) i using a method such as a least square method.
Now, assuming that the toner adhesion amount on the photosensitive drums 104K to 104C where the output values of the optical sensors 616K to 616C are VPc is (M / A) C, (M / A) i ≦ (M / A) C The same amount of adhesion is satisfied, and there may be a large deviation from the linear relationship with the surface potential. To prevent such a case, (M / A) min ≦ (M / A) ≦ (M / A) The coefficients a and b in the above equation (14) are determined for the detection result of the toner adhesion amount on the photosensitive drums 104K to 104C satisfying C.
In the above description, the toner adhesion amount is used. However, the detection output of the optical sensors 616K to 616C corresponding to (M / A) min is VPmax, and the toner adhesion area corresponding to the toner adhesion area satisfying the following expression (16). From the above, the coefficients a and b in the above equation (14) may be determined.
VPc ≦ VP ≦ VPmax (16)
As described above, the gradation conversion table set in the image processing printer γ conversion circuit 713 at the time of gradation pattern reading is the same among the image signals obtained by reading a plurality of different color patches of the reference chart HC with the scanner unit 300. When predetermined coefficients a and b that differ depending on the read patch are calculated for one component image signal to be generated and generated according to the image signal obtained by the calculation, the spectral reflectance of the printing ink of the reference chart HC is calculated. A gradation conversion table for automatic gradation correction (ACC) can be created by correcting the difference between the characteristic and the characteristic of the spectral reflectance of the toner of the printer unit 100 that records and outputs the gradation pattern, The image quality can be further improved.

  40 and 41 are diagrams showing a second embodiment of the image forming apparatus of the present invention. FIG. 40 is a block diagram of a color copying apparatus 1000 to which the second embodiment of the image forming apparatus of the present invention is applied. It is.

In FIG. 40, the color copying apparatus 1000 includes a scanner unit 1001, an IPU unit 1002, a printer unit 1003, an operation unit 1004, a parameter calculation unit 1005, a control unit 1006, a transmission / reception unit 1007, and the like. Connected so that data can be sent and received.
The scanner unit 1001 performs main scanning / sub-scanning on the original G and the calibration pattern, reads the image data of the original G and the calibration pattern, reads the original reflected light by the optical system, and converts it into an electrical signal by the CCD. The A / D converter performs digitization processing, shading correction processing (processing for correcting illuminance distribution unevenness of the light source), scanner γ correction processing (processing for correcting density characteristics of the reading system), and the like.

  The IPU unit 1002 is a unit that performs image processing such as processing editing on image data, and includes shading correction processing (processing for correcting illuminance distribution unevenness of a light source), scanner γ correction processing (processing for correcting density characteristics of a reading system). ), MTF correction processing, smoothing processing, arbitrary scaling in the main scanning direction, density conversion (γ conversion processing: corresponding to density notch), simple multi-value processing, simple binarization processing, error diffusion processing, dither processing, Processing such as dot arrangement phase control processing (right-side dots and left-side dots), isolated point removal processing, image area separation processing (color determination, attribute determination, adaptive processing), density conversion processing, and the like is performed.

  The printer unit 1003 is a unit that writes image data onto transfer paper or the like, and performs edge smoothing processing (jaggy correction processing), dot rearrangement correction processing, image signal pulse control processing, parallel data and serial data format conversion. Processing such as processing is performed.

  The parameter calculation unit 1005 reads the calibration pattern data when the color copying apparatus 1000 plays a role as a child color copying apparatus when connected to the other color copying apparatuses 2000 and 3000 in FIG. (Hereinafter referred to as “calibration data”) is a unit that performs calibration.

  The parameter calculation unit 1005 generally performs processing such as machine difference correction processing, background correction processing, and high-density portion correction on the calibration data, so that the reading characteristics and child colors of the parent color copying apparatus are obtained. Image processing parameters related to printing characteristics of the copying apparatus are calculated. The image processing parameters are stored in the control unit 1006 and are used for processing in the IPU unit 1002 and the printer unit 1003 when printing image data received from the parent color copying apparatus.

  The transmission / reception unit 1007 is a unit that transmits / receives data to / from the external color copying apparatuses 2000 and 3000 via the Internet cable 5000 and the HUB (hub) 5001. For example, when the color copying apparatus 1000 functions as a parent color copying apparatus, a calibration processing start instruction command, calibration data, linked printing start instruction command, document image data, etc. are sent to the child color copying apparatus 2000, Send to 3000.

  The operation unit 1004 is a unit that receives processing conditions of each unit of the color copying apparatus 1000 from the user. For example, a calibration processing start instruction, a calibration pattern reading start instruction, a linked printing start instruction, a document reading start instruction, the number of copies to be printed, and the like are received.

  The control unit 1006 is a unit that controls each unit of the color copying apparatus 1000 based on the processing conditions received by the operation unit 1004. For example, the control unit 1006 controls each unit to print out a calibration pattern. Then, each unit is controlled to calculate image processing parameters corresponding to the reading characteristics.

Further, the color copying apparatuses 1000, 2000, and 3000 are connected to a server 4000 through an internet cable 5000 and a hub 5001 so that data can be transmitted and received.
Each of the color copying apparatuses 1000, 2000, and 3000 transmits the read image data to the server 4000 and stores it in a recording device such as a hard disk or a CD-ROM (not shown) of the server 4000.
When printing the image data stored in the server 4000, the image data stored in the server 4000 is called when output printing is necessary, and transmitted to the nearest color copying apparatuses 1000, 2000, 3000. Print. When a large number of copies is required, the image data is transmitted to a plurality of color copying apparatuses 1000, 2000, 3000, and the plurality of color copying apparatuses 1000, 2000, 3000 are connected to perform print output simultaneously.
When a plurality of color copying apparatuses 1000, 2000, and 3000 are connected and printed at the same time, it is necessary to print out in a state where there is no difference between the color copying apparatuses 1000, 2000, and 3000. Therefore, for example, when the image data read by the color copying apparatus 1000 is stored in the server 4000, the machine difference correction value of the color copying apparatus 1000 is transmitted to the server 4000, and the server 4000 associates the image data with the image data. The correction value is stored. When the image data read by the color copying apparatus 1000 is printed out by another color copying apparatus 2000 or 3000 that has executed automatic gradation correction (ACC) using an ACC pattern (calibration pattern) as described above. When the server 4000 transmits the machine difference correction value of the color copying apparatus 1000 to the color copying apparatus 2000 and the color copying apparatus 3000, the color copying apparatus 2000 and the color copying apparatus 3000 receive the machine difference correction value of the color copying apparatus 1000. The image processing parameters for the color copying apparatus 2000 and the color copying apparatus 3000 are created and changed from the difference between the machine difference correction values of the color copying apparatus 2000 and the color copying apparatus 3000 and the machine difference correction value of the color copying apparatus 1000. To do. Thereafter, when image data is transmitted from the server 4000, the color copying apparatus 2000 and the color copying apparatus 3000 perform image processing on the image data transmitted from the server 4000 by using the image processing parameters, and perform printing. Do.

  Thus, also in the case of concatenated output, the adjustment accuracy of the gradation conversion table can be improved, and the image quality can be improved.

  The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the scope of the invention. Needless to say.

  When an image read by the document reading unit is recorded and output by various image forming units, it can be applied to an image forming apparatus such as a color copying apparatus that performs color adjustment at a low cost and appropriately.

1 is a schematic front view of a main part of an electrophotographic copying apparatus to which a first embodiment of an image forming apparatus of the present invention is applied. FIG. 2 is an enlarged front view of a scanner unit and an ADF portion of the copying apparatus of FIG. 1. FIG. 2 is a top view of the copying apparatus of FIG. 1. FIG. 2 is a front view of a main part schematic configuration showing a control system of the copying apparatus of FIG. 1. FIG. 2 is a circuit block configuration diagram centering on an IPU and a printer unit of the copying apparatus of FIG. 1. FIG. 6 is a detailed circuit block diagram of the MTF in FIG. 5. The figure which shows an example of the Laplacian filter of FIG. The figure which shows the subscanning direction edge detection filter (a), the main scanning direction edge detection filter (b), and the diagonal direction detection filters (c) and (d) as an example of the edge amount detection filter of FIG. The figure which shows a hue. FIG. 6 is a diagram illustrating an example of a pixel number (a) and an index table when a total of 36 pixels of 6 pixels in the main scanning direction × 6 pixels in the sub-scanning direction are used for dither processing in the gradation processing circuit of FIG. 5. FIG. 11 is a diagram showing an example of a gradation processing table of 2 main scanning pixels × 2 sub scanning pixels in the case of the index table of FIG. 10. FIG. 11 is a diagram showing a pixel number and an index table when the pixel number of FIG. 10 is shifted by one pixel in the main scanning direction. The figure which shows an example of the index table corresponding to the dither of 2 pixels of main scanning directions x 2 pixels of subscanning directions. The conceptual diagram of the area process of the area process part of FIG. FIG. 2 is a block diagram of a laser modulation circuit of a printer unit of the copying apparatus of FIG. 1. FIG. 2 is a circuit block configuration diagram of the scanner unit in FIG. 1. FIG. 18 is a conceptual diagram of white correction and black correction by the shading correction circuit of FIG. 17. FIG. 6 is an explanatory diagram of a read signal sample hold process by the S / H circuit of FIG. 5. The top view of an example of the reference | standard chart used by scanner calibration. FIG. 2 is a sequence diagram showing a procedure for executing scanner calibration by the copying apparatus of FIG. 1. The figure which shows the liquid crystal screen which displays various adjustment screens. The figure which shows the liquid crystal screen which displays a scanner calibration start screen. The figure which shows the liquid crystal screen which displays the reading screen of a reference | standard chart in scanner calibration mode. The figure which shows the quaternary chart in scanner calibration. FIG. 6 is a diagram illustrating an example of reading reference values for chromatic and achromatic patches for correcting yellow toner. The figure which shows the relationship between the spectral sensitivity of CCD of a blue signal, and the spectral reflectance of yellow toner by the relationship with a wavelength. The figure which shows the relationship between the spectral reflectance characteristic of a blue-green ink, the spectral reflectance of the yellow toner of 50% of area ratio, and the read value of a blue signal with a wavelength. The figure which shows the quaternary chart of the table for ACC pattern reading value correction | amendment. FIG. 10 is a diagram illustrating an example of reading reference values for chromatic and achromatic patches for cyan toner correction. The figure which shows the liquid crystal screen which displays an automatic gradation correction start screen. 3 is a flowchart showing ACC processing by the copying apparatus of FIG. 1. The figure which shows an example of the gradation pattern output on a transfer paper by ACC process. The figure which shows the liquid crystal screen which displays the screen which prompts the setting of the transfer paper on the contact glass in FIG. 32 where the gradation pattern was output by the ACC process. The figure which shows the liquid crystal screen which displays the screen during reading of the gradation pattern recording transfer paper by ACC process. The figure which shows the quaternary chart for demonstrating the calculation method in ACC process. The flowchart which shows the gradation conversion table creation process at the time of ACC. 7 is a flowchart showing development characteristic detection processing. FIG. 38 is a diagram showing a detection pattern formed on the photosensitive drum by the development characteristic detection process of FIG. 37 and a detection state by the optical sensor. Explanatory drawing of the correction process of the image signal in ACC process. FIG. 3 is a block diagram of a color copying apparatus to which a second embodiment of the image forming apparatus of the present invention is applied. FIG. 42 is a block configuration diagram when the color copying apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copying apparatus 2 Main body case 3 Contact glass 100 Printer part 101 Intermediate transfer belt 102 Drive roller 103 Transfer roller 104K-104C Photosensitive drum 105K-105C Charge charger 106 Laser optical system 107K-107C Developing unit 108K-108C Bias roller 109 Addition Pressure roller 110 Conveying roller 111 Registration roller 112 Conveying belt 113 Fixing unit 114 Fixing roller 115 Pressure roller 120 Laser modulation circuit 121 Look-up table (LUT)
122 Pulse width modulation circuit 123 Power modulation circuit 124 Laser diode (LD)
125 Photodetector (PD)
200 Paper Feed Unit 201 Paper Feed Tray 202 Reversing Unit 203 Paper Feed Tray 204 Paper Discharge Tray 300 Scanner Unit 301 Lamp Shade 302 Halogen Lamp 303 First Mirror 304 Second Mirror 305 First Traveling Body 306 Third Mirror 307 Fourth Mirror 308 Second traveling body 309, 310 Infrared cut filter 311 Lens 312 CCD
321 Amplification circuit 322 S / H (sample hold) circuit 323 A / D conversion circuit 324 Black correction circuit 325 CCD driver 326 Pulse generator 327 Clock generator 400 ADF
401 Document Plate 402 Document Conveying Belt 500 Operation Unit 501 Start Key 502 Clear / Stop Key 503 Ten Key 504 Interrupt Key 505 Memory Call Key 506 Preheat / Mode Clear Key 507 Color Adjustment / Registration Key 508 Program Key 509 Option Key 510 Area Processing Key 511 LCD screen 600 System controller 601 CPU
602 ROM
603 RAM
604 interface I / O
605 Various sensor control units 606 Power supply / bias control unit 607 Drive control unit 608 Operation control unit 609 Communication control unit 610 Storage device control unit 611 Storage device 612 IPU
613 Laser optical system driving unit 614 Toner replenishment circuit 615 Toner density sensors 616a to 616c Optical sensor 617 Potential sensor 618 Environmental sensor 701 Shading correction circuit 702 Area processing unit 703 Scanner γ conversion unit 704 Image memory 705 Image separation unit 706 I / F ( interface)
707 MTF filter 708 Hue determination circuit 709 Color conversion UCR processing circuit 710 Pattern generation unit 711 Scaling circuit 712 Image processing circuit 713 Image processing printer γ conversion circuit 714 Tone processing circuit 715 CPU
716 ROM
717 RAM
718 Bus 721 I / F selector 722 Pattern generation unit 723 Image forming printer γ correction circuit 724 Printer engine 730 Smoothing filter 731 Edge amount detection filter 732 Laplacian filter 733 Smoothing filter 734 Table conversion 735 Accumulator 736 Adder 740 Host Computer 741 Printer controller G Document P Transfer paper

Claims (4)

  An image reading unit that optically scans a document to read a color image of the document and outputs a read image signal, and a gradation conversion of the read image signal output from the image reading unit based on a predetermined image signal conversion table First image signal converting means, color converting means for color-converting the image signal after gradation conversion, and gradation conversion of the color-converted image signal based on a predetermined image signal conversion table to output an image A second image signal converting means for generating a signal, a color recording agent image is formed on the image carrier in accordance with the output image signal, and the recording agent image on the image carrier is transferred onto a transfer material to form an image On the transfer material by the image forming unit based on the image signal generated by the gradation pattern generating unit. Formed above Creating and selecting the image signal conversion table to be set in the second image signal conversion means based on the image signal when the tone pattern is read by the image reading means, and a plurality of achromatic patches having different gradation levels; A reference chart composed of a plurality of different chromatic color patches is read by the image reading means and set in the first image signal converting means based on reference data previously stored in the storage means corresponding to the patches of the reference chart. In the image forming apparatus for creating the image signal conversion table, the image signal conversion table set in the first image signal conversion unit when reading the gradation pattern and the first image signal conversion unit when reading a document. An image forming apparatus, wherein the image signal conversion table to be set is different.   The image forming apparatus uses the image signal conversion table set in the first image signal conversion unit when reading the document image as reference data for the achromatic patch in the reference chart and the achromatic patch in the storage unit. The image signal conversion table generated from the image and set in the first image signal conversion means at the time of reading the gradation pattern is generated from the achromatic color patch and the chromatic color patch of the reference chart. The image forming apparatus according to 1.   The image forming apparatus obtains the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern, and an image obtained by reading a plurality of patches of different colors of the reference chart with the image reading unit. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus generates the image using one common image signal among the signals. The image forming apparatus obtains the image signal conversion table set in the first image signal conversion unit at the time of reading the gradation pattern, and an image obtained by reading a plurality of patches of different colors of the reference chart with the image reading unit. 4. The image according to claim 3, wherein a predetermined coefficient different depending on the read patch is calculated for a common one-component image signal among the signals, and generated according to the image signal obtained by the calculation. Forming equipment.

Images