JP2965906B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for automatically adjusting the contrast between a background portion and an image portion in a document image.

[0002]

2. Description of the Related Art An image forming apparatus such as a digital copying machine having an automatic density adjusting function has already been commercialized and put into practical use. In a digital copying machine, light is irradiated to a document image, light reflected from the document image is received, and the received reflected light is photoelectrically converted by a CCD element to obtain digital image data. Based on the image data thus obtained, a density histogram indicating a pixel distribution for each density of the image data is created, and automatic density adjustment is performed by using the density histogram and correcting the density range of the image data. Automatic density adjustment using such a density histogram is disclosed in Japanese Patent Publication No. 64-6588 and Japanese Patent Publication No.
30143 publication.

When an automatic density adjusting function of a digital copying machine is used, for example, when an original having a high background density, such as a newspaper, which is unsatisfactory in an analog copying machine, is copied, the background portion can be removed and copied. It becomes possible. Further, in this case, it is possible to increase the density of the character portion.

[0004]

The use of the automatic density adjustment function as described above makes it possible to remove the background density of the original image. On the other hand, if it is desired to intentionally leave the background of the document, it is necessary to cancel the automatic density adjustment function and adjust the density by manual density adjustment. In addition, if the entire density is increased by manual density adjustment to leave the background, there may be a case where adverse effects such as characters being broken are caused. In particular, if copying is repeated many times from a copy of an original in which fine characters are written on a background having a halftone density, for example, a color background (copy-to-copy), characters may be lost or uneven density may occur. And more problems have occurred.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of clearly reproducing images such as characters and photographs while leaving a base in an original image. To provide.

[0006]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above-mentioned problems .
Reads an original image containing an image section and a background section
Image reading means for removing the background portion from the original image.
To reduce the density range of the image area.
Image data of the original image read by the image reading means
Density range correction means for correcting, the reference of the background portion
Comparing means for comparing a reference density value with a predetermined threshold value,
As a result of the comparison by the comparing means, the reference density value is
If it is larger than the predetermined threshold, the density range correction means
For the image data from which the background has been removed,
Background addition processing means for adding a background corresponding to the density value;
Image data to which a background has been added by the background addition processing means
Image forming method for forming an image based on an image on an image forming medium
And a step. An image forming apparatus according to the present invention includes an image forming unit
Image of a document containing the original and the background part
An image reading unit, and an original read by the image reading unit.
Discriminates the type of original image based on the image data of the original image
Image type discriminating means; and
Remove and expand the density range of the image area before
Image data of the original image read by the image reading means.
Density range correction means for correcting data, and a reference for the background portion
And a threshold value set for each type of document image.
The document indicated by the determination result of the image type determination means among the values
Comparing means for comparing the image type with a threshold value;
As a result of the comparison by the column, the reference density value becomes a comparison target.
If the density range is larger than the threshold value,
For the image data from which the background part has been removed, the reference density
Background adding means for adding a background according to the value;
Based on the image data to which the background has been added by the scene addition processing means.
Image forming means for forming the image formed on the image forming medium
It has. According to the image forming apparatus of the present invention, the image section and the
Image reading that scans the original image including the background portion
Taking means, removing the background portion from the document image,
The image reader is designed to increase the density range of the image area.
Correct the image data of the original image read by the step
Density range correction means and the density range correction means
A predetermined background is added to the image data from which the background has been removed.
And background adding processing means for pressurizing, the background adding processing unit
Image based on the image data with the background added
Image forming means for forming on a forming medium.

[0007] The image forming apparatus of the present invention includes an image portion thereof
Image reading for reading a document image including a background portion in the background
Means for removing the background portion from the original image,
The image reading means so as to expand a density range of an image portion;
To correct the image data of the original image read by
Degree range correction means, comparison means for comparing a reference density value serving as a reference of the background portion with a predetermined threshold value, and the comparison means
As a result of the comparison, the reference density value is lower than the predetermined threshold value.
When the background part is larger than
Add a predetermined background to the removed image data
Background addition processing means, and the background addition processing means
The image based on the image data with the
Image forming means for forming on the body .

[0008] An image forming apparatus according to the present invention comprises an image section and an image section.
Image reading for reading a document image including a background portion in the background
Means and an original image read by the image reading means
Image that determines the type of original image based on the image data
Type determining means for removing the background portion from the original image
The image area so as to expand the density range of the image area.
The image data of the original image read by the image reading means
A density range correcting means for correcting the image type determination unit type discrimination document image by, and in response to said reference density value as a reference of the background portion, an image background portion by the density range correction means is removed Background adding means for adding a predetermined background to the data; and image forming means for forming an image on the image forming medium based on the image data to which the background has been added by the background adding processing means. .

[0009] The image forming apparatus of the present invention includes an image portion thereof
Image reading for reading a document image including a background portion in the background
Means, and an image of the original image read by the reading means.
Based on the image data, the density of the pixels constituting the original image
Detecting means for detecting a degree distribution, and detecting by the detecting means
Based on the result, the pixels constituting the image portion of the original image
The image data is supplemented so that the density distribution range of
Density range correcting means for correcting, and the density range correcting means
Corresponds to the background part for the image data corrected by
Background addition processing means for adding image data having a density;
The image to which the data has been added by the background addition processing means.
Form an image on an image forming medium based on image data
Image forming means.

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

As a result of taking the above measures, the following effects occur.

According to the image forming apparatus of the present invention, the background portion
Image data in which the density range of the image area has been expanded and
A predetermined background is added to the
An image based on the obtained image data is formed. This
The contrast between the image area and the background area is enhanced,
To clearly reproduce the image part while leaving the background part
Can be.

According to the image forming apparatus of the present invention, the background portion
Image data in which the density range of the image area has been expanded and
Against the threshold set according to the type of the original image.
The background corresponding to the original background part is added, and the original background part
The image based on the image data with the background added according to
Is done. As a result, the optimum
Under the conditions, the contrast between the image part and the background part is enhanced,
As a result, the image part is clearly reproduced while leaving the original background part
can do.

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram showing the internal structure of a digital copying machine as an embodiment of the image forming apparatus of the present invention.

As shown in FIG. 2, the digital copying machine includes an apparatus main body 10, in which a scanner section 4 functioning as image reading means and a printer section 6 functioning as image forming means described later. Is provided.

On the upper surface of the apparatus main body 10, an original placing table 12 made of transparent glass on which an object to be read, that is, the original D is placed, is provided. An automatic document feeder 7 (hereinafter, referred to as an ADF) for automatically feeding a document onto the document table 12 is provided on the upper surface of the apparatus body 10.
The ADF 7 is provided so as to be openable and closable with respect to the document table 12, and transfers the document D placed on the document table 1 to the document table 1.
It also functions as a document holder that is brought into close contact with 2.

The ADF 7 includes a document tray 8 on which a document D is set, an empty sensor 9 for detecting the presence or absence of a document, a pickup roller 14 for taking out documents one by one from the document tray 8, and a paper feed roller for transporting the taken out document. 1
5. A pair of aligning rollers 16 for aligning the leading edge of the document,
A transport belt 18 is provided so as to cover almost the entire document table 12. The plurality of originals set upward on the original tray 8 are taken out in order from the bottom page, that is, the last page, are aligned by the aligning roller pair 16, and are placed on the original by the transport belt 18. The sheet is transported to a predetermined position on the table 12.

In the ADF 7, a reversing roller 20, a non-reversing sensor 21, a flapper 22, and a paper discharging roller 23 are disposed at an end opposite to the aligning roller pair 16 with the transport belt 18 interposed therebetween. The document D whose image information has been read by the scanner unit 4 described below is sent out from the document table 12 by the conveyance belt 18 and
0, flapper 21, and discharge roller 22
The document is discharged onto the document discharge unit 24 on the upper surface of F7. When reading the back side of the original D, the original D transported by the transport belt 18 is switched by switching the flapper 22.
After being reversed by the reversing roller 20, the sheet is again sent to a predetermined position on the document table 12 by the transport belt 18.

The scanner unit 4 provided in the apparatus main body 10
Has an exposure lamp 25 as a light source for illuminating the document D placed on the document table 12, and a first mirror 26 for deflecting the reflected light from the document D in a predetermined direction. The first mirror 25 and the first mirror 26 are attached to a first carriage 27 disposed below the document table 12.

The first carriage 27 is mounted on the original table 12.
And is reciprocally moved below the document table 12 by a drive motor via a toothed belt or the like (not shown).

A second carriage 28 which can move in parallel with the original placing table 12 is provided below the original placing table 12. On the second carriage 28, second and third mirrors 30, 31 for sequentially deflecting the reflected light from the document D deflected by the first mirror 26 are attached at right angles to each other. The second carriage 28 is connected to the first carriage 27 by a toothed belt or the like that drives the first carriage 27.
, And is moved in parallel with the first carriage along the document table 12 at a half speed.

An image forming lens 32 for converging the light reflected from the third mirror 31 on the second carriage 28 and a light receiving the light condensed by the image forming lens are provided below the document table 12. And a CCD sensor 34 for performing photoelectric conversion. The imaging lens 32 is movably disposed via a drive mechanism in a plane including the optical axis of the light deflected by the third mirror 31, and moves the reflected light at a desired magnification by moving itself. Form an image. And the CCD sensor 34
The incident reflected light is photoelectrically converted, and an electric signal corresponding to the read original D is output.

On the other hand, the printer unit 6 includes a laser exposure unit 40
It has. The laser exposure unit 40 rotates a semiconductor laser 41 as a light source, a polygon mirror 36 as a scanning member that continuously deflects the laser light emitted from the semiconductor laser 41, and rotates the polygon mirror 36 at a predetermined rotation speed described later. A polygon motor 37 is also used as a driving scanning motor.
And an optical system 42 for deflecting the laser light from the polygon mirror and guiding it to a photosensitive drum 44 described later. The laser exposure unit 40 having such a configuration is fixed and supported by a support frame (not shown) of the apparatus main body 10.

The semiconductor laser 41 is controlled on and off in accordance with image information of the document D read by the scanner unit 4 or facsimile transmission / reception document information. The laser light is transmitted via the polygon mirror 36 and the optical system 42. The electrostatic latent image is formed on the peripheral surface of the photosensitive drum 44 by scanning the peripheral surface of the photosensitive drum 44 toward the photosensitive drum 44.

The printer section 6 has a rotatable photosensitive drum 44 serving as an image carrier disposed substantially at the center of the apparatus main body 10. And a desired electrostatic latent image is formed. Around the photoreceptor drum 44, a charging charger 45 for charging the peripheral surface of the drum to a predetermined charge, and a toner as a developer to supply an electrostatic latent image formed on the peripheral surface of the photoreceptor drum 44 with a desired toner is provided. A developing device 46 for developing at an image density, and a peeling charger 47 for separating a transfer material fed from a paper cassette described later, that is, a copy sheet P from the photosensitive drum 44, A transfer charger 48 for transferring the toner image formed on the photosensitive drum 44 to the paper P, a peeling claw 49 for peeling the copy paper P from the peripheral surface of the photosensitive drum 44, a cleaning unit 50 for cleaning the toner remaining on the peripheral surface of the photosensitive drum 44, A static eliminator 51 for neutralizing the peripheral surface of the photosensitive drum 44 is arranged in order.

An upper cassette 52, a middle cassette 53, and a lower cassette 54, which can be pulled out from the apparatus main body, are disposed in a lower part in the apparatus main body 10 in a stacked state.
Copy papers of different sizes are loaded in each cassette. A large-capacity feeder 5 is located beside these cassettes.
The large-capacity feeder 55 accommodates about 3000 copy sheets P of a frequently used size, for example, A4 size copy sheets P. Above the large-capacity feeder 55, a paper feed cassette 57 also serving as a manual feed tray 56 is detachably mounted.

In the apparatus main body 10, a transport path 5 extending from each cassette and the large capacity feeder 55 through a transfer portion located between the photosensitive drum 44 and the transfer charger 48 is provided.
The fixing device 60 is provided at the end of the transport path 58. A discharge port 61 is formed on a side wall of the apparatus main body 10 facing the fixing device 60, and a discharge tray 62 is formed on the discharge port.
Is installed.

In the vicinity of the upper cassette 52, the middle cassette 53, the lower cassette 54, the paper cassette 57 and the large capacity feeder 55, there are provided pickup rollers 63 for taking out the sheets P one by one from the cassette or the large capacity feeder. Have been. The transport path 58 is provided with a number of paper feed roller pairs 64 for transporting the copy sheet P taken out by the pickup roller 63 through the transport path 58.

A pair of registration rollers 65 is provided upstream of the photosensitive drum 44 in the transport path 58. The registration roller pair 65 corrects the inclination of the copy paper P taken out, aligns the leading end of the toner image on the photosensitive drum 44 with the leading end of the copy paper P, and adjusts the moving speed of the peripheral surface of the photosensitive drum 44 to The copy paper P is fed to the transfer unit at the same speed. A pre-alignment sensor 66 for detecting the arrival of the copy sheet P is provided in front of the registration roller pair 65, that is, on the side of the feed roller 64.

The copy paper P taken out one by one from each cassette or the large-capacity feeder 55 by the pickup roller 63 is sent to the registration roller pair 65 by the paper supply roller pair 64. Then, the copy paper P is sent to the transfer section after the leading end is aligned by the registration roller pair 65.

In the transfer section, the developer image formed on the photosensitive drum 44, that is, the toner image, is transferred onto the sheet P by the transfer charger 48. The copy paper P on which the toner image has been transferred is separated from the peripheral surface of the photosensitive drum 44 by the action of the separation charger 47 and the separation claw 49,
The sheet is conveyed to the fixing device 60 via a conveyance belt 67 that forms a part of the conveyance path 52. Then, after the developer image is fused and fixed to the copy paper P by the fixing device 60, the copy paper P
Is discharged onto the paper discharge tray 62 through the discharge port 61 by the paper feed roller pair 68 and the paper discharge roller pair 69.

Under the conveyance path 58, the copy sheet P having passed through the fixing device 60 is reversed, and the registration roller pair 65 is again turned.
An automatic double-sided device 70 for sending to the printer is provided. The automatic double-sided device 70 includes a temporary stacking unit 71 for temporarily stacking the copy sheets P, and a reversing path 7 that diverges from the transport path 58 and reverses the copy sheet P that has passed through the fixing unit 60 and guides the copy sheet P to the temporary stacking unit 71.
2, a pickup roller 73 for taking out the copy papers P accumulated in the temporary accumulation section one by one, and a paper feed roller 75 for feeding the taken out paper to a pair of registration rollers 65 through a transport path 74. Further, at a branch portion between the transport path 58 and the reversing path 72, a distribution gate 76 for selectively distributing the copy sheet P to the discharge port 61 or the reversing path 72 is provided.

When performing double-sided copying, the copy paper P that has passed through the fixing device 60 is guided to a reversing path 72 by a sorting gate 76, and is temporarily accumulated in a temporary accumulating unit 71 in a reversed state. The sheet is sent to a pair of registration rollers 65 through a conveyance path 74 by a roller 73 and a pair of sheet feeding rollers 75. Then, after the copy paper P is aligned by the registration roller pair 65, the copy paper P is sent to the transfer unit again, and the toner image is transferred to the back surface of the copy paper P. Thereafter, the copy sheet P is discharged onto the discharge tray 62 via the transport path 58, the fixing device 60, and the discharge roller 69.

The digital copying machine further includes an operation panel 80 and a main control unit 90 shown in FIG.

The operation panel 80 includes a print key 81 for instructing the start of copying, and conditions for image output in the digital copying machine, such as the number of copies or the number of prints and the magnification.
Alternatively, for example, a plurality of push button switches, a color CRT, or an input unit 82 provided with a transparent touch sensor panel 82a on a liquid crystal screen, or an operation panel, for inputting the designation of partial copying and the coordinates of the area. A panel CPU 83 for controlling the printer 80 includes a numeric keypad 84 used for setting the number of copies and the copy magnification. The input unit 82 is arranged in accordance with an operation procedure relating to the digital copying machine or conditions to be input, and has a plurality of input keys on which, for example, pictorial symbols, numbers, characters, character strings, and the like are displayed.

FIG. 1 is a block diagram schematically showing the electrical connection of the digital copying machine in FIG. 2 and the flow of signals for control.

According to FIG. 1, the digital copier includes a main CPU 91 in the main control unit 90, a scanner CPU 100 in the scanner unit 4, and a printer CPU in the printer unit 6.
It comprises 110 CPUs.

The main CPU 91 is connected to the printer CPU 11
The main CPU 91 issues an operation instruction to the printer CP.
U110 returns a status status. The printer CPU 110 and the scanner CPU 100 perform serial communication, and the printer CPU 110 issues an operation instruction.
The scanner CPU 100 returns a status status. The operation panel 80 is connected to the main CPU 91.

The main control unit 90 includes a main CPU 91, an RO
M92, RAM 93, NVM 94, shared RAM 95, image processing unit 96, page memory control unit 97, page memory 98, and image synthesizing unit 99.

The main CPU 91 controls the entire main control section 90. The ROM 92 stores a control program. The RAM 93 temporarily stores data. NVM (Nonvolatile RAM) 94
Is a non-volatile memory that is backed up by a battery (not shown), and retains data on the NVM 94 when the power is turned off. The shared RAM 95
It is used for performing bidirectional communication between the main CPU 91 and the printer CPU 110.

The image processing section 96 is provided with a circuit for creating a density histogram formed by the number of pixels for each density range of the image data based on the image data, and correcting the image data based on the density histogram. ing. The image processing section 96 has a compression / expansion circuit 96a for compressing or expanding image data. The page memory control unit 97 stores and reads out image data in the page memory 98. Page memory 98
Has an area in which image data for a plurality of pages can be stored, and is formed so that data obtained by compressing image data from the scanner unit 4 can be stored for each page. The image synthesizing unit 99 synthesizes two pieces of image data.

The scanner section 4 includes a scanner CPU 100 for controlling the entire scanner section 4, a ROM 101 for storing a control program and the like, and a RAM 10 for data storage.
2. CCD driver 10 for driving CCD sensor 34
3. A scan motor driver 104 for controlling the rotation of a motor for moving the exposure lamp 25 and mirrors 26, 27, 28, etc., an A / D conversion circuit for converting an analog signal from the CCD sensor 34 into a digital signal, and the CCD sensor 3.
4 due to variations in temperature or changes in ambient temperature
The shading correction circuit 105 corrects the fluctuation of the threshold level with respect to the output signal from the CD sensor 34, and the image correction unit 105 includes a line memory for temporarily storing the shading-corrected digital signal from the shading correction circuit.

The printer section 6 includes a printer CPU 110 for controlling the entire printer section 6, a ROM 111 for storing control programs and the like, and a RAM 11 for data storage.
2. Laser driver 113 for turning on / off light emission by semiconductor laser 41, polygon motor driver 11 for controlling rotation of polygon motor 37 of laser unit 40
4. A paper transport unit 115 for controlling the transport of the paper P by the transport path 58, a charging charger 45, a developing unit 46, and a developing process unit 116 for performing charging, development and transfer using the transfer charger 48, and a fixing unit 60 are controlled. The image forming apparatus includes a fixing control unit 117 and an option unit 118.

The image processing section 96 and the page memory 9
8. The image synthesizing unit 99, the image correcting unit 105, and the laser driver 113 are connected by an image data bus 120.

FIG. 3 is a block diagram showing a schematic configuration of the image processing section 96 including the histogram creating circuit.

The histogram creating circuit 130 creates the above-mentioned density histogram based on the image data from the scanner section 4. The density histogram created by the histogram creating circuit 130 is supplied to the correction reference value calculation unit 131 and is also supplied to the main CPU 91. The correction reference value calculation unit 131 calculates a correction reference value (described later) based on the histogram created by the histogram creation circuit 130. Range correction circuit 132
Corrects the density range (described later) using the correction reference value from the correction reference value calculation unit 131, and performs automatic density adjustment in real time. The timing signal generator 133 is based on the clock signal from the clock generator 134, and
Various kinds of timing signals necessary for each block in 6 are generated. The image quality improvement circuit 135 includes a low-pass filter, a high-frequency emphasis circuit, and the like, and further improves the image quality of the image whose range has been corrected by the range correction circuit 132. The enlargement / reduction circuit 136 enlarges / reduces the image as required, and the gradation processing circuit 137 processes the gradation of the image using a dither method or an error diffusion method. The image signal processed in this way is sent to the printer unit 6 to form an image, or is stored in the page memory 98.

FIGS. 4 and 5 show the outline of the density histogram to be created. For example, in the case of reading one image of A4, assuming that reading is performed at 400 dpi, the total number of pixels G is as follows.

G = 210 × 297 × (400 / 25.4) ² Each pixel having the number G of pixels has a density, and here, the density is expressed by 8 bits. The horizontal axis in FIG. 4 indicates the density, that is, the pixel value, and the vertical axis indicates the frequency (number of pixels) indicating how many pixels of which density existed with respect to the density.

As shown in FIG. 4, in this embodiment, the density is divided into 16, and the density of 256 levels is simplified to 16 levels. That is, the lower 4 bits of the 8-bit pixel value are ignored. By employing 16 divisions in this way, the hardware is greatly simplified. Further, the amount of information necessary as a histogram even in 16 divisions is sufficiently ensured in the automatic density adjustment function. FIG. 5 shows a method of equally dividing the image into 16 parts. The division number 0 is in the range of pixel values 0 to F, the division number 1 is in the range of pixel values 10 to 1F, and so on.
The pixel value range is set up to.

Before describing the histogram creation circuit 130 in detail, the range correction of the correction reference value calculation unit 131 and the range correction circuit 132 will be described. Range correction is a function used for cutting the background as a background portion in the automatic exposure function of an analog copying machine. Generally, when an original is read digitally and a density histogram is created, the result is as shown in FIG. In the case of a manuscript such as a newspaper, the background density is considerable, so that one peak is formed in the background density portion as shown by M in FIG. 6 and one peak is also formed in the character density portion such as N. Here, in the analog copying machine, the brightness of the exposure lamp is controlled to eliminate the background density portion, but in the digital copying machine, the same effect is obtained by the following signal processing.

To explain with a simple example, the densities DW and DB corresponding to the peak points of the M peak and the N peak shown in FIG. 6 are obtained, and the following calculation is performed to obtain the density histogram as shown in FIG. Is converted to a simple distribution. Here, the density DW
And DB are called correction reference values, and the histogram creation circuit 1
The correction reference value calculation unit 131 calculates the correction reference value calculation unit 131 based on the histogram of each scan line created by the reference numeral 30.

DN = (DI−DW) × FFH / (DB−DW) where DI is the input pixel density, DN is the corrected pixel density, and FFH is the maximum pixel density. That is, the range (density range) between M and N in FIG. 6 is expanded to the range of 0 to FFh.

Next, an outline of a histogram creation method will be described.
The following formula is a basic calculation formula for creating a histogram, and the histogram is created for each main scanning line. A reference value for range correction is obtained each time the histogram creation processing for one line is completed, and the range correction processing is performed based on the reference value. Further, the total number of data constituting the histogram is always a constant value.

A ′ = A−αA + αB where A ′: corrected frequency (number of pixels) corresponding to each density of the current line A: frequency corresponding to each density calculated up to the previous line B: current line Is a value multiplied by the frequency value accumulated in each line, and indicates the contribution rate to the histogram. This α
Is set in accordance with the number of lines, as shown in FIG. 8, and has 14 values (one power of 2), that is, 1,1 / 1 /
2, 1/4, 1/8, 1/16, 1/32, ..., 1 /
2048, 1/4096, 1/8192 (= 1/213)
Is selected from

Next, the histogram creation circuit 130 will be described. First, the histogram creation circuit 130 calculates A ′ = (A ′) + αB for each input pixel during one line reading, and secondly, during the period from one line reading to the next line reading, that is, the pixel density is input. If not, (A ′) = A−αA is calculated for each density frequency in the histogram. Thus, the histogram creation circuit 130
Is the corrected frequency value A ′ = A−αA for the current line
+ ΑB is generated. From the histogram thus created, a reference value for range correction is calculated by the correction reference value calculation unit 131.

Two modes, mode 0 and mode 1, are provided for histogram generation, and one mode is selected as necessary.

Mode 0: Weighting coefficient variation addition mode depending on the number of sub-scanning lines Mode 1: Constant weighting coefficient addition mode for input pixels Mode 0 is, as described above, the value of coefficient α according to the number of main scanning line counts And create a histogram. In mode 1, a histogram is created with constant coefficients regardless of the count value of the main scanning line.

FIG. 9 is a block diagram showing a detailed configuration of the histogram creation circuit 130. One terminal of the switch 141 has a pixel density signal IDAT4 from the scanner unit 4.
To IDAT7 are input, and signals CDT00 to CDT03 of output data from the counter 142 are input to the other terminal. The switch 141 is also connected to the timing signal generator 1.
33, one of the input signals is selected according to the selection signal from the selector 33, and the selected signals SLDT0 to SLDT3 are selected by the selector 1
45 and the clock generator 143. Here, the pixel density signals IDAT4 to IDAT7 are the upper 4 bits of the pixel density, and IDAT0 to IDAT3 are ignored for the reason described above. The timing signal CTL0 from the timing signal generator 133 is at a high level between each line, that is, when the pixel density signal is not read,
1 selects and outputs the signal from the counter 142.

When calculating (A ′) = A−αA, the counter 142 sets the clock generator 143 and the selector 145
The required value (count value) is supplied to. Counter 142
Generates a 4-bit count value for generating the 16 outputs of the clock generator 143 in order when the above-mentioned pixel density signal is not read. Counter 1
Reference numeral 42 denotes a timing signal generator 1 to which the counter clock signal CT1CK is input from the timing signal generator 133.
The counter is cleared by the counter clear signal CT1CL from the counter 33. The counter clear signal CT1CL becomes low level when the pixel density signal is read, and the counter 1
Clear 42.

The clock generation unit 143 selects the selection input signal SL
In accordance with DT0 to DT3, one of 16 outputs FCK0 to FCK is selected and output at the cycle of the input clock signal MCK. FIG. 10 shows the relationship between the input and output signals of the clock generator 143.

The histogram registers (flip-flops) 144 _{1 to} 144 _F store the corrected frequency (WDAT) for each pixel density in the input clock signals FCK 0 to FCK.
It latches and outputs at the rising edge of. Input signal WDAT
Is A′-αA or (A ′) + αB described above. The corrected frequency signals H0 to HF from the histogram registers 144 _{1 to} 144 _F are also output to the correction reference value calculation unit 131.

[0076] The selector 145, the concentration of the 16 steps from the histogram registers 144 ₁ ~144 _F H0~HF
Is input, the frequency (the number of pixels) corresponding to
H0 according to input signals SLDT0 to SLDT3 from
1 out of 16 data (each having a bus width of 26 bits)
Data is selected and a signal HSDT is output.

The sub-scanning line number counter 153 receives the line synchronization signal HDEN from the timing signal generator 133 and outputs the count value signals FDAT00 to FDAT12 to the clock generator 152 as shown in the timing chart of FIG. In response to a clear signal CRST from the main CPU 91, the document is cleared each time one page of the document is scanned.

The clock generator 152 outputs the output signals FDAT0 to FDAT1 from the sub-scanning line number counter 153.
2, and the pixel synchronization clock signal GC from the scanner unit 4.
K is input and the signal HCK is output to the counter 151 and the added value generation unit 150. The clock generator 152 determines that the value of the signal FDAT is 1, 3, 7, F, 1F, 3F, 7F,
In any one of 1FF, 3FF, 7FF, FFF, and 1FFF, one clock of the input pixel synchronization clock signal is output. The clock generation unit 152 is configured by an AND circuit, and when all the line number signals FDAT are “1”,
DAT = 1, 3 (11), 7 (111), F (111
In 1), ..., one clock is output.

The counter 151 includes a clock generator 152
When the clock signal HCK is input from the controller 14 and the mode 0, the count value signals CDT20 to CDT23 are
7 is output. The counter 151 is also cleared for each page by the clear signal CRST from the main CPU 91. The count values CDT20 to CDT23 are values for selecting α as shown in FIG.

The fixed coefficient value register 155 outputs a fixed coefficient value in the mode 1. The switch 156 is connected to the CPU 9
The mode is switched in response to the mode signal SL1 from mode 1, and is set to the counter 151 side in mode 0 and is set to the register 155 side in mode 1.

The subtraction value generation unit 146 calculates (A ′) = A−α
“ΑA” for calculating A is output. Subtraction value generator 1
46 receives the output signal HSDT from the selector 145 and generates a value obtained by dividing the signal HSDT by a power of 2 (shifts the signal HSDT).

The selector 147 performs an operation (A ') between each line, that is, when no pixel signal is read.
= A-αA, the input signals SSL0 to SSL3
Determined according to. That is, when the values of the input signals SSL0 to SSL3 are “1”, the selector 147 (the signal HS
DT value / 2, when the input value is "2" (signal HSD
T value) / 2 2,..., When the input value is C (signal HS
(DT value) / 2 13 is output.

The subtraction section 149 subtracts (A ′) = A−αA
I do. The subtraction unit 149 receives the density signal HSDT (A in the above equation) from the selector 145, receives the subtraction number signal SDT (αA in the above equation) from the selector 147, and outputs a signal YDAT as a result of the subtraction. .

Addition value generating section (shift register) 150
Generates “αB” when calculating A ′ = (A ′) + αB. The addition value generation unit 150 includes a clock generation unit 152
The clock signal HCK is input from the
Is output to the adding section 148. The addition value generation unit 150 also
It is cleared for each page by a clear signal CRST from the main CPU 91. FIG.
The initial value output is 2000H when the clear signal CRST is input, and the present value becomes 1 each time the clock signal HCK from the clock generator 152 is input thereafter.
/ 2 is output. Since this output is a hexadecimal number, for example, 1/2 of the current value 2000H is 1000H, and 1/2 of the current value 1000H is 800H. FIG. 12 shows a change in each signal corresponding to a change in the signal FDAT.

The adding section 148 calculates the addition A ′ = (A ′) + α
Perform B. The addition unit 148 receives the frequency signal HSDT from the selector 145 and the signal XDAT of the addition data from the addition value generation unit 150, and outputs a signal ZDAT as a result of the addition. FIG. 13 shows an example of addition of the signal ZDAT.

The switch 154 switches between (A ′) = A−αA and A ′ = (A ′) + αB. To one terminal of the switch 154, the addition result signal ZDAT from the addition unit 148 is input, and the subtraction result signal YDAT from the subtraction unit 149 is input to the other terminal.
One input is selected according to TL1, and the selection result signal WD
The AT is output to the histogram registers 144 ₁ to 144 _F.

Next, the creation of a histogram with the configuration shown in FIG. 9 will be described with reference to the timing charts of FIGS. 14, 15 and 16.

FIG. 14 is a timing chart showing a state when A '= (A') + αB is calculated for each input pixel during reading of one line. The signal MCK is a main clock and is synchronized with the pixel signal. The signal VDEN is a page synchronization signal, and the signal HDEN is a line synchronization signal. Pixel density signals IDAT4 to IDAT7 from the scanner unit 4
Are the upper 4 bits of the pixel density and are input to the switch 141. In this case, the sub-scanning valid signal CTL0 is enabled (low level), and the switch 141
DAT4 to IDAT7 are sent to the selector 145 and the clock generator 143.

The selector 145 outputs the pixel signals IDAT4 to IDAT4.
DAT7, ie, the output (frequency) of the histogram registers 1441 to 144F is selected according to the value of the selection input signal,
The selected frequency signal HSDT is output. Signal HSDT
Is added by a coefficient (XDAT) weighted according to the number of lines in the adder 148. Since the switch 154 is set to the adder 148 side in this case by the input signal CTL1, the addition result signal ZDAT returns to the histogram registers 144 ₁ to 144 _F.

Next, the clock generator 143 outputs the pixel signal I
The clock signal FCK0-
Outputs FCKF. Each histogram register 144 ₁
To 144 _F at the rise of the clock signal FCK0-FCKF, respectively latches i.e. stores the value of the output signal WDAT switch 154. By performing the above processing for each pixel of one line, a histogram of one line is generated, a reference value for pixel density adjustment is calculated, and the reference value is used for the processing of the next line.

Next, during the period from one line reading to the next line reading, that is, when no pixel density signal is input, the frequency of each density in the histogram is (A ') = A-αA
Is calculated.

FIG. 15 is a timing chart showing the state of the subtraction process. The switch 141 is connected to the selection signal CT.
It is switched to the counter 142 side by L0, and the switch 1
54 is switched to the subtractor 149 side by the selection signal CTL1. The selector 147 determines the coefficient (in mode 0) or the fixed coefficient (in mode 1) determined by the number of sub-scanning counters.
, The respective histogram values are subtracted. After the subtraction operation is completed, the process proceeds to a normal histogram creation operation. By repeating the above-described operation, a histogram in which the total data amount is variable and constant is created each time each main scanning line is read.

As described above, according to the above embodiment, a histogram can be obtained for each main scanning line, and real-time automatic density adjustment using the histogram becomes possible. Further, the frequency is multiplied by a weight coefficient changed according to the number of read lines, and the frequency is accumulated, whereby a histogram with a variable total data amount is created each time each main scanning line is read. When the weighting coefficient is fixed, a histogram corresponding to a sudden change in the density of the document image can be obtained.

Hereinafter, the background storage mode function, which is the point of the present invention, will be described.

The background preservation mode is a mode in which the image portion of the original image can be clearly reproduced and the original image can be copied with the background portion remaining. When such a background storage mode is used, even when the background density of the original image is high, the image portion can be clearly reproduced with the background remaining. Further, in this background preservation mode, it is also possible to add a background different from the background of the original image to copy.

Each process in the background preservation mode is executed by the background preservation mode process execution section shown in FIG. The background preservation mode processing execution unit is mainly composed of the histogram creation circuit 130, the correction reference value calculation unit 131, and the range correction circuit 132 described with reference to FIG. Further, the range correction circuit 132 is provided with an LD (Line Delay) 13.
2a, range correction unit 132b, pattern generation unit 132
c, background storage determination unit 132d, background storage processing unit 132e
It consists of. The processing in each unit in the range correction circuit 132 will be sequentially described in conjunction with the description of the background preservation mode.

The background saving mode is set in the input unit 8 shown in FIG.
This is executed by switching with the background storage mode switching button 82b displayed on the second touch panel 82a. When the mode cannot be switched to the background storage mode by the background storage mode switching button 82b, the standard mode is executed. In the standard mode, an image in which the background of the document image has been removed by the conventional automatic density adjustment is output.

Now, the operation of the image forming apparatus in the background preservation mode will be described.

First, before reading a document image, histogram processing, black run length processing, document size detection, etc., of the document image are performed as pre-scanning processing. Is determined. However, when a memory capable of storing page images is provided as in the image forming apparatus described with reference to FIGS. 1 and 2, a document image is read without performing a prescan operation, and the read document image is read. May be stored in the memory, and the processing performed in the pre-scan described above may be executed based on the stored image data.

The above-described histogram is usually used in the range correction processing for each scanning line of the original. However, the base pattern used in the original type discrimination processing and the pattern generation unit 132c according to the present invention is the same as that of the original. Of the histogram processing result after the scanning line is read.

The above-described black run length process is performed as a correction process for determining the type of the document, and is a process for obtaining the maximum length of the connection (run) of black pixels on the scan line of the document. Holds the maximum value of the data of all lines of the original. However, processing is performed with reference to the black run length of the previous line,
Parts such as ruled lines are canceled. In addition, the maximum value of the black run length may be provided with an overflow process or the like (8-bit width) due to the restriction of the circuit scale, and the bit may be limited.

The document type discriminating process proceeds based on the result of the histogram process, the result of the black run length, the discriminating condition of each document type, and the like. The determination result obtained by the document type determination processing is used to automatically select a value of a background storage effective threshold provided for each document type used by a background storage determination unit 132d described below. That is, the determination result of the document type is necessary for selecting the background preservation effective threshold value according to the document type. The density histogram result is obtained by reading a histogram value obtained by the histogram processing by the prescan processing operation from the histogram register by CPU access. The black run length result is obtained by reading the value obtained by the black run length processing from the black run length register by CPU access.

Here, a method of determining the type of a document will be described with reference to FIGS. It is assumed that the determination of the document type described below is performed by the main CPU 91.

First, a method of determining character likeness will be described with reference to a density histogram of FIG.

The character-likeness is determined by the background peak P11 [
i] and the division number P11 before and after this background peak P11
[i-1] and P11 [i + 1], and the character peak P1
2 [i] and division numbers P before and after this character peak P12
This is performed depending on the ratio of the total sum of 12 [i-1] and P12 [i + 1] to the whole.

To determine the character likeness, a character frequency determination threshold (cth) is provided as a character likeness condition register, and if the sum is equal to or greater than the character frequency determination threshold, it is determined that the original is a character image-like original. Note that the character frequency determination threshold is
It is assumed that the information is stored in the RAM 93 or the like in advance.

That is, the character-likeness is determined as follows.

WA1 = P11 [i-1] + P11 [i]
+ P11 [i + 1] WA1 = P12 [i-1] + P12 [i] + P12 [i
+1] WA = WA1 + WA2 If WA ≧ cth, it is determined that the document is a character-like original. In other cases, it is determined that the original is not a character-like original.

When it is determined that the original is a character-like original, an intermediate density determination threshold (pth) is provided as a processing register for the intermediate density range A. , A character document and a character / photo document are discriminated. The intermediate density range A is
A division number P11 [i that is three divisions larger than the background peak P11
+3] to a division number P12 [i-3] that is three divisions smaller than the character peak P12. When all the histogram values in the intermediate density range A are smaller than the intermediate density determination threshold (all histograms in the intermediate density range A <pt
h), it is determined that the document is a text document. Otherwise, it is determined that the document is a text / photo document.

Further, for a document determined to be a character, fine character determination is performed. For the determination of the small character, a black width determination coefficient and a black run length threshold (bkmax) are provided as a condition register for the small character likelihood, and the histogram value of the small character determination range C divided into three before and after the character peak P12 is used as the small character determination threshold X. (X = character peak P12 × black width discrimination coefficient / 1
6) If it is larger and the black run length is smaller than the black run length threshold value, it is determined that the original is a small character document. Otherwise, it is determined that the original is a standard character original. It is assumed that the black width determination coefficient and the black run length threshold are stored in the RAM 93 or the like in advance.

Next, a method of determining the likeness of a photograph will be described with reference to the density histogram of FIG.

To determine the likeness of the photograph, a white width discrimination coefficient is provided as a condition register, and the histogram value of the photo document discrimination range B divided into three before and after the background peak P21 is used as the photograph document discrimination threshold Z (Z = base peak value P1 × White width discrimination coefficient / 16)
If it is larger, the document is determined to be a photo-like original. In other cases, it is determined that the original is not a photograph. In addition,
It is assumed that the white width determination coefficient is stored in the RAM 93 or the like in advance.

Documents that cannot be completely discriminated by the above-described image discrimination, that is, documents that do not correspond to character images or photo images, are discriminated as character / photo images as shown in FIG.

Here, an example of the type determination of a document image will be described.

For example, it is assumed that the result of the density histogram as shown in FIG. 22 is obtained. First, based on the result of the density histogram, it is determined from the character image likelihood. At this time, assuming that the character frequency determination threshold (cth) is set to 3500 pixels, the character likeness is determined as follows.

WA1 = P11 [i-1] + P11 [i] + P11 [i + 1] = P11 [0] + P11 [1] + P11 [2] = 2133 WA2 = P12 [i-1] + P12 [i] + P12 [i + 1] = P12 [C] + P12 [D] + P12 [E] = 1490 WA = WA1 + WA2 = 3623 In this case, since the condition of WA ≧ cth is satisfied, the document is determined to be a character-like document.

Next, a distinction is made between a character original and a character / photo original. At this time, it is assumed that the intermediate density determination threshold (pth) is set to 220. Intermediate density range A
Is a division number P11 that is three divisions larger than the background peak P11.
It is between [i + 3] and the division number P12 [i-3] that is three divisions smaller than the character peak P12. Therefore, since all the histogram values in the intermediate density range A of the density histogram in FIG. 22 are smaller than the intermediate density determination threshold (pth), this document image is determined to be a text document.

Further, a fine character document is determined. At this time, the black width discrimination coefficient is 4, and the black run length threshold (bkma)
It is assumed that x) is set to 160. The fine character determination range C is divided into three parts before and after the character peak P12. Therefore, the fine character determination range C of the density histogram in FIG.
The division numbers are A to F. Assuming that the black run length read by the predetermined process is 200, the thin character determination threshold value X is as follows.

X = Character peak value P12 × Black width discrimination coefficient / 16 = 928 × 416 = 232 In other words, in this case, all the histogram values of the fine character discrimination range C> X and the black run length <bkmax are satisfied. Since it is not, it is determined that the original is a standard character original. In this way, the document type determination process is performed.

The above-described document type discrimination processing is performed in accordance with FIG.
This will be described together with the flowchart shown in FIG.

First, a prescan operation of the original is performed (ST102), and a histogram process is performed (ST1).
04). The register reading of the histogram value created by this histogram processing and the reading of the black run length are performed (ST106), and thereafter, a substantial document type determination processing is performed.

First, it is assumed that character-like discrimination processing is performed (ST108). If it is determined that the document is not a character-like document (ST108, NO), photograph document discrimination processing is performed (ST110). . Here, if it is determined that the document is not a photo document (ST110, NO), this document is determined to be a text / photo document, and a background preservation effective threshold Thcp described later is set (ST112). In addition,
The background preservation effective threshold will be described later in detail.

In the photo original discrimination process (ST11
0), if it is determined that the document is a photo original (ST110, Y
ES), the background preservation effective threshold Thp is set (ST1).
14).

In the process of determining the character likeness (ST10
8) If it is determined that the original is a character-like original (ST10)
8, YES), a text document discrimination process is performed (ST11).
6). If it is determined in the text original discrimination process that the intermediate density range is equal to or smaller than the threshold value (ST116, NO), a fine text original discrimination process is performed (ST118). In this fine text document discrimination process, when it is determined that the area around the character peak is equal to or smaller than the threshold (ST118, NO), this document is determined to be a standard character document, and the background saving effective threshold Thc
Is set (ST120).

In the small character original discrimination processing (ST11
8) If it is determined that the area around the character peak is larger than the threshold value (ST118, YES), this document is determined to be a fine character document, and the background saving effective threshold Thcs is set (ST122).

In the character document discriminating process (ST11)
6) If it is determined that the intermediate density range is larger than the threshold value (ST116, YES), this document is determined to be a text / photo document, and the background preservation effective threshold Thcp is set (ST124).

The background preservation effective threshold is used to make the background preservation mode function in consideration of the type of the document, that is, the characteristics of the document. For example, in the case of a photographic original, since a large amount of data in the intermediate density portion of the image data after the automatic density adjustment is desired to be left, a threshold value lower than the background storage level of the text original is set. In the case of a text / photo document and a fine text document, a threshold of a different range level is set for the text document and the photo document. Note that the background preservation effective threshold is stored in the RAM 93.
Shall be stored in

As described above, the image type determination processing is performed, and the background preservation effective threshold value is set according to the image type.

Here, the background storage mode execution section shown in FIG. 17 will be described.

The correction reference value calculation section 131 outputs a white reference value (base reference value) and a black reference value. The white reference value is a value serving as a reference for a base portion, and for example, a base peak value is set as a white reference value. The black reference is a value serving as a reference for an image portion.

In the range correction section 132b, based on the white reference value and the black reference value from the correction reference value calculation section 131,
A range correction process is performed on the image data output from the LD (Line Delay) 132a. Specifically, a range correction process is performed to remove the background as a background portion from the image data and extend the density range of a character image / photo image or the like as the image portion at a predetermined ratio.

The pattern generator 132c generates a base pattern corresponding to the white reference value obtained by the prescan or an arbitrarily set data value. The background storage determination unit 132d compares and determines the white reference value and the background storage effective threshold. In the base storage processing unit 132e, the pattern generation unit 132 according to the determination result of the base storage determination unit 132d
c using the pattern generated in step c as a background.
This is combined with the image data that has been range-corrected in 32b.

Here, the background preservation mode processing will be described with reference to FIG.
This will be described with reference to the flowchart of FIG.

The background preservation effective threshold (Thc, Thc) is stored in advance in the preservation preservation threshold level register for each document type.
s, Thp, Thcp) are set in advance, and the background save mode is executed by switching to the background save mode with the background save mode switching button 82b. Alternatively, a default function may be used to automatically set the background preservation mode when the digital copying machine is started.

When the print key 81 is depressed, a pre-scan is performed, and the original discrimination processing described with reference to FIG. 23 is performed (ST100). By this document discriminating process, the type of the document is specified, and the background preservation effective threshold used by the background preservation determination unit 132d and the white reference value in the pattern generation unit are determined.

At this time, various guides as shown in FIG. 18 are displayed on the touch panel 82, and changes in various settings are received from the touch panel 82. Here, a case will be described in which the touch panel 82 can change the document type, base, and base storage effective threshold.

The document type is changed with reference to the document determination result. In other words, when the result of the document discrimination indicates "Is the document a character document?", If there is no problem with the character document, the user presses the YES key 82c. To set a photo document, the photo document key 82e is pressed. To set a text / photo document, the text / photo document key 82 is pressed. When the result of the document discrimination is not a character document, the character document key 82d is pressed to set the character document. As described above, by setting the type of the document arbitrarily, the user can set the type of the document when the result of the document determination by the document type determining unit is inappropriate. As a result, an appropriate background adding process according to the type of the document can be realized.

The change of the background is performed according to the background change guidance. That is, when "Do you want to change the background" is displayed, and when the background is not changed, the user presses the NO key 82g. When the NO key 82g is pressed, a base pattern formed from the white reference value obtained by the prescan is set. When changing the background, the density key 82h, the registered pattern key 82i, or the new setting key 82j is pressed. When the density key 82h is pressed, a background density change screen is displayed, and a change in the background density is accepted. When the registered pattern key 82i is pressed, a plurality of registered base patterns registered in advance are displayed. The user can arbitrarily select a base pattern from the plurality of registered base patterns. The registered base pattern includes a uniform pattern over the entire surface, a pseudo intermediate color pattern, a lattice pattern, and the like. When the new setting key 82j is pressed, a new setting screen for the base pattern is displayed, and the new setting for the base pattern is accepted. The base pattern newly set by the new setting key 82j is newly added to the registered base pattern.
It should be noted that the registration key 82i is used by the density key 82h.
Registration pattern selected in and the new setting key 82j
It is also possible to change the density of a newly set registered pattern. Since an arbitrary background can be set as described above, the background can be freely changed without being tied to the background of the original document image.

The change of the background saving effective threshold is performed according to the guidance for changing the background storage effective threshold. That is, when "Do you want to change the background storage effective threshold value" is displayed, and when the background storage effective threshold value is not changed, the NO key 82k is pressed. YES to change the background preservation effective threshold
Press the key 82l. When the YES key 821 is pressed, a background saving effective threshold change screen is displayed, and a change in the background saving effective threshold is accepted. Note that the effects associated with the change in the background storage effective threshold will be described later.

When there is no change in the settings displayed on the touch panel 82, when the confirmation key 82m is pressed, all the settings displayed on the touch panel 82 are determined.

As described above, when the settings such as the document type, the background, and the background preservation effective threshold are changed or confirmed by the touch panel 82 (ST202, ST204), the normal copying operation is started (ST206). At this time, a normal real-time range correction process is performed on the document, and the correction reference value calculation unit 131 outputs a white reference value and a black reference value for the image data (ST208).

On the other hand, in the background storage determination section 132d,
The white reference value output from the correction reference value calculation unit 131 and RA
A comparison with the background preservation effective threshold value supplied from M93 is performed (ST210). This background storage determination unit 132d
Is a value reflecting the document type determination result or the document type set by the user. That is, the background preservation effective threshold corresponding to the document type is selected and supplied from the RAM 93 to the background preservation determination unit 132d.

If the white reference value is larger than the background preservation effective threshold as a result of the comparison judgment by the background preservation judgment section 132d (ST210, YES), the background preservation judgment signal is set to "H" and the range correction section 132b outputs the signal. The image data that has been subjected to the range correction process (ST212) is further subjected to a background preservation process (ST214). That is,
This means that a base pattern generated from the pattern generating unit 132c is added to the image data on which the range correction processing has been performed. This base pattern generation unit 132
c generated from the touch panel 82a
This is the pattern set in.

In the range correction process in ST212, the image data is corrected for automatic density adjustment based on the values of the white reference value and the black reference value output from the correction reference value calculation section 131. That is, by this range correction processing,
The background portion of the image data is removed, and the density of the image portion is increased.

Predetermined image processing such as halftone processing is performed on the image data that has been subjected to the range correction and the background preservation processing (ST218), and a printing operation is performed (ST220).

If the white reference value is equal to or less than the background storage effective threshold as a result of the comparison determination by the background storage determination unit 132d (ST210, NO), the background storage determination signal is set to "L" and the range correction unit 132b performs range correction. Processing (ST
The background saving processing is not performed on the image data subjected to 212). Then, predetermined image processing such as halftone processing is performed on the image data on which only the range correction has been performed (ST218), and a printing operation is performed (S218).
T220).

FIG. 25 shows a state before and after execution of the above-described background preservation mode. In the background preservation mode, range correction is performed. By automatic density adjustment by this range correction function, the range width between the background peak P11 and the character peak P12 is widened, and the character peak P12 is changed to the character peak P1.
Can lift to 2 '. Then, by adding the density of the background peak P1 to the image data that has been subjected to such range correction and outputting the image data, it is possible to clearly reproduce images such as characters and photographs while leaving the background.
Of course, the base pattern added as the base can be arbitrarily changed by the user.

Here, the effect of changing the setting of the background preservation effective threshold will be described. As described in the flowchart of FIG. 24, the background preservation processing is performed only when the white reference value is larger than the background preservation effective threshold. For example, FIG.
In the case where the background peak P11 as shown in (1) is used as the white reference value, the background preservation process is performed only when the background density level is higher than the background preservation effective threshold. That is, in the background storage mode, the background is deleted or left depending on the density of the background.

Therefore, it is possible to adjust the background deletion level by changing the setting of the background preservation effective threshold. For example, if the background preservation effective threshold is set to a relatively large value, the background with low density is removed. Conversely, if the background preservation effective threshold is set to a relatively small value, a background with a low density can be added as a background.

When the white reference value rises and falls near the background preservation effective threshold, the background may be deleted or added, resulting in unevenness in the entire image. In such a case, the background can be completely deleted from the image or the background can be added to the entire image by changing (up or down) the background preservation effective threshold.

[0151]

As described in detail above, according to the present invention,
It is possible to provide an image forming apparatus capable of clearly reproducing images such as characters and photographs while leaving a base in an original image.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a control circuit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of an internal mechanism of the image forming apparatus.

FIG. 3 is a block diagram illustrating a schematic configuration of an image processing unit.

FIG. 4 is a diagram showing a density histogram created based on image data.

FIG. 5 is a diagram for explaining a density histogram.

FIG. 6 is a view for explaining a correction reference value and a range correction.

FIG. 7 is a diagram illustrating a correction reference value and a range correction.

FIG. 8 is a view for explaining the number of sub-scanning lines in mode 0 and a coefficient α corresponding thereto.

FIG. 9 is a block diagram illustrating a schematic configuration of a histogram creation circuit.

FIG. 10 is a diagram for explaining the timing of an output clock signal corresponding to the input pixel density in the clock generation unit.

FIG. 11 is a diagram illustrating an output example of an addition value generation unit.

FIG. 12 is a diagram showing a change in each signal corresponding to a change in a signal FDAT.

FIG. 13 is a diagram illustrating an example of addition of a signal ZDAT.

FIG. 14 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 15 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 16 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 17 is a block diagram illustrating a schematic configuration of a background storage mode execution unit.

FIG. 18 is a diagram illustrating a display example of a touch panel in the input unit.

FIG. 19 is a diagram illustrating an example of a density histogram of a text document.

FIG. 20 is a diagram illustrating an example of a density histogram of a photo document.

FIG. 21 is a diagram illustrating an example of a density histogram of a text / photo document.

FIG. 22 is a diagram showing a result of a density histogram.

FIG. 23 is a flowchart illustrating the flow of a document determination process.

FIG. 24 is a flowchart illustrating the flow of a background preservation mode.

FIG. 25 is a diagram showing a state before and after execution of a background storage mode.

[Explanation of symbols]

Reference Signs List 4 scanner unit (image reading unit) 6 printer unit (image forming unit) 80 operation panel 82 input unit 90 main control unit 91 main CPU (image type determination unit) 96 image processing unit (image type determination) Means, density range correction means, background addition processing means, comparison means) 130: histogram creation circuit (image type determination means, density range correction means) 131: correction reference value calculation unit (density range correction means) 132: range correction circuit ( Density range correction means, background addition processing means, comparison means) 132b ... range correction section (density range correction means) 132c ... pattern generation section (background addition processing means) 132d ... background storage determination section (comparison means) 132e ... background storage processing Section (background addition processing means)

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-230870 (JP, A) JP-A-4-313744 (JP, A) JP-A-3-282891 (JP, A) JP-A-5-230 120417 (JP, A) JP-A-5-252402 (JP, A) JP-A-4-332263 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 1 / 40-1 / 409 H04N 1/46 H04N 1/60 H04N 1/38-1/393

Claims (2)

(57) [Claims] 1. An original including an image part and a background part in the background.
Image reading means for reading a manuscript image;
The background portion is removed, and the density range of the image portion is expanded.
Original image read by the image reading means
Density range correction means for correcting the image data, and a ratio between a reference density value serving as a reference of the background portion and a predetermined threshold value.
Means for comparingAs a result of the comparison by the comparing means, the reference density value is
If it is larger than the predetermined threshold, the density range correction means
For the image data from which the background has been removed,
Background addition processing means for adding a background corresponding to the density value;  Image data to which a background has been added by the background addition processing means.
Forming an image based on data on an image forming medium
And an image forming apparatus. 2. An original comprising an image part and a background part in the background.
Image reading means for reading a draft image;
Original based on the image data of the original image
Image type determining means for determining the type of image; removing the background portion from the document image;
Reading by the image reading means so as to expand the degree range.
Density range for correcting image data of scanned original image
Correction means;A reference density value serving as a reference for the background portion, and a type of original image
Of the thresholds set separately, the judgment of the image
A comparison method for comparing the threshold value of the type of the original image indicated by another result
Steps and As a result of the comparison by the comparing means, the reference density value is compared.
If it is larger than the target threshold, the density range correction
The image data from which the background has been removed by means
Background addition processing means for adding a background corresponding to the reference density value
When,  Image data to which a background has been added by the background addition processing means.
Forming an image based on data on an image forming medium
And an image forming apparatus.