JPH1127550A - Color image-processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct background elimination processing, in response to an image of an original by obtaining a difference between the maximum value and the minimum value of RGB data for each pixel and comparing the difference value with a minimum value of a pixel the difference of which is smaller than a setting value, so as to determine a background density. SOLUTION: A difference detection circuit 502 subtracts the minimum value from the maximum value in density of RGB data for each pixel in order to determine a difference. A MIN detection circuit 503 detects a minimum value of the density of the RGB data for each pixel. A background detection circuit 504 provides a system control means with an output of a minimum value of a pixel the difference of which is detected by the difference detection circuit 502 is smaller than a setting value as a background density RD- DATA. The system control means compares the RD- DATA with a preset density value to determine stepwise a background elimination value. Thus, the background elimination processing in response to the background density of an image of an original is conducted, and the background elimination is applied properly to an original having dirty spots or rear side strike through.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus used in a digital color copying machine or the like, and more particularly to a color image processing apparatus for performing a background removal process on a document image.

[0002]

2. Description of the Related Art Conventionally, when an image of an old document having a discolored paper color is formed by a color image forming apparatus which is not equipped with a background processing function, the background of the old document is faithfully faithfully converted to a light yellow image. It is formed. However, in many cases, it is not necessary to faithfully reproduce the background color of an old document. Rather, the background is colored, which makes it difficult to read an imaged old document.

In order to solve the above-mentioned problem, the "copying apparatus" disclosed in Japanese Patent Application Laid-Open No. Hei 1-213073 of the prior art 1 performs background removal processing using a histogram, and performs processing based on the density distribution of three primary color signals of a document image. It is characterized in that a clear image is formed by detecting an image having a high frequency as a background density and changing a portion lighter than the background density to a predetermined density.

[0004]

However, the copying apparatus according to the prior art 1 detects a high frequency image as a background density based on the density distribution of the three primary color signals of the original image.
The color is removed, but the background is not removed when the one with the highest frequency is 0. Therefore, for example, an original with a sparsely white background or an original with a show-through is indistinguishable from the original density, but is conspicuous. It was not possible to cope with the case where it was desired to remove the background to an unacceptable degree.

The present invention has been made in view of the background of the background removal processing of a color image processing apparatus as described above, and performs background removal under optimum conditions corresponding to a document image to form a high quality image. It is an object of the present invention to provide a color image processing apparatus for performing the above.

[0006]

In order to achieve the above object, a color image processing apparatus according to the present invention comprises an image reading means for optically scanning a document image and converting it into image data;
A color separation unit that separates the read image data into RGB data of three primary colors, an image forming unit that forms an image using the image data, and a background density RD based on the density distribution of the RGB data A background density detecting means for detecting DATA; a control means for controlling each means; and a background density RD detected by the background density detecting means. It is preferable to determine the background removal amount based on DATA.

The background density detecting means detects difference between the maximum value and the minimum value of the density of the RGB data for each pixel using the RGB data, and detects the minimum value of the image data for each pixel. And a minimum value detecting unit that compares the minimum value of the pixel whose difference value detected by the difference detecting unit is smaller than a preset value, and determines the minimum value having the smallest density in the background density RD. It may be sent to the control means as DATA.

[0008] The control means sets the density setting values TH1 and TH2 set in advance to determine the background removal amount, with the background density RD detected by the background density detection means. DATA
It is preferable to set the background removal amount by comparing with.

[0009] The control means includes a background density RD. DATA
Should be controlled so that the background removal operation is not performed when is larger than TH1.

[0010] Further, the control means includes a background density RD. DATA
Is less than or equal to TH1 and greater than TH2,
Background density RD It is preferable to control the background removal processing using DATA as a reference for the background removal amount.

[0011] The control means includes a background density RD. DATA
Is less than or equal to TH2, control may be performed so that the background removal processing is performed using OFFSET as a reference for the background removal amount.

[0012] The apparatus further comprises operation input means capable of inputting by an operator, and when the operator sets to cancel the background removal mode from the operation input means, regardless of the background density detected by the background density detection means. It is good not to perform the background removal operation.

A density setting value T for determining the background removal amount
H1 and TH2 are preferably changed from the operation input means so as to be optimally set according to the operation mode set by the operator.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a color image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 8 show an embodiment of the color image processing apparatus according to the present invention.

FIG. 1 is a diagram showing a schematic configuration of a mechanism when a color image processing apparatus of the present invention is applied to a digital copying machine. In the digital copying machine of the present embodiment shown in FIG. 1, 100 is a laser printer, 200 is an automatic document feeder, 300 is an operation board, 400 is an image scanner, and 500 is an external sensor.

An image scanner 400 mechanically moves a moving body on which an illumination lamp 402 disposed below a contact glass 401 is mounted at a constant speed in the left-right direction (sub-scanning direction) of FIG. This is an image reading unit that reads. The light emitted from the illumination lamp 402 is reflected on the surface of the document placed on the contact glass 401 according to the density of the document image. This reflected light, that is, the light image of the document, passes through a number of mirrors and lenses and enters the dichroic prism 410.

The dichroic prism 410 splits the incident light into three colors of R, G and B according to the wavelength. The three split lights are respectively incident on different one-dimensional charge-coupled device (CCD) image sensors 410. In this way, the three one-dimensional image sensors 410 provided in the image scanner 400 allow the main scanning direction 1
The R, G, B color components of the line can be read simultaneously. The two-dimensional image of the document is sequentially read by the sub-scanning of the moving body.

The external sensor 500 includes the image scanner 4
As in the case of 00, it is built in a handy type scanner composed of a CCD that can simultaneously detect the R, G, B color components of the original image. ADF200 is an image scanner 4
, And can hold a large number of originals placed on the original platen 210.

When a document feeding operation is performed, the rotating call roller 212 contacts the uppermost document upper surface, and the contacted document is fed out. 213 is a separation roller for avoiding double feeding. The original fed out to a predetermined position is driven by a pull-out roller 217 and a conveyor belt 216 to drive the contact glass 401 of the image scanner 400.
When it is further transported above and advances to the predetermined reading position,
That is, it stops when the leading edge of the document reaches the left end position of the contact glass 401.

When the reading of the original is completed, the conveyor belt 2
16 is driven again, the original on the contact glass 401 is discharged, and the next original is sent to the reading position.

An optical sensor for detecting whether a document is loaded or not, a document presence / absence sensor 211 is provided in front of the calling roller 212, and a leading end of the document and a document output sensor are provided between the separation roller 213 and the pull-out roller 217. An optical sensor for detecting the size and a document leading edge sensor 214 are provided.

The original leading edge sensor 214 is composed of a plurality of sensors arranged at different positions in the main scanning direction (a direction perpendicular to the paper surface). The original size, that is, the original width can be detected.

Further, a pulse generator for outputting a pulse corresponding to the rotation amount is provided to a sheet feeding motor (not shown),
The control device of the ADF 200 detects the size of the document in the sub-scanning direction, that is, the length of the document, by measuring the time required for the document to pass through the document leading edge sensor 214. In addition,
The call roller 212 and the separation roller 213 are driven by a paper feed motor, and the pull-out roller 217 and the transport belt 216 are driven by a transport motor. The registration sensor 215 composed of an optical sensor is
7 is arranged downstream.

Next, the schematic structure and operation of the laser printer 100 will be described. Image reproduction is performed on the photosensitive drum 1. Around the photosensitive drum 1, a series of electrophotographic process units, that is, a charger 5, a writing unit 3, a developing unit 4, a transfer drum 2, a cleaning unit 6, and the like are provided.

The writing unit 3 is provided with a laser diode (not shown), and the laser light emitted from the laser diode emits a rotating polyhedron 3b, a lens 3c, a mirror 3d,
Then, the light is irradiated onto the surface of the photosensitive drum 1 through the lens 3e. The rotating polygon mirror 3b is driven to rotate at a constant high speed by the polygon motor 3a.

An image control device (not shown) controls the light emission timing of a laser diode driven by a binary signal (recording / non-recording) in pixel units corresponding to the density of an image to be recorded, by sequentially scanning each pixel position. The driving signal of the laser diode is controlled so as to synchronize with the rotating / deflecting operation of the rotating polygon mirror 3b. That is, the on / off control of the laser diode is performed so that a laser beam corresponding to the density (recording / non-recording) of the pixel is irradiated at each scanning position of the image on the surface of the photosensitive drum 1.

The surface of the photosensitive drum 1 is uniformly charged to a high potential in advance by corona discharge by the charger 5. When this surface is irradiated with the laser light emitted from the writing unit 3, the charging potential changes according to the intensity of the light. That is, a potential distribution is formed on the photosensitive drum 1 in accordance with the presence or absence of the laser light emitted from the laser diode included in the writing unit 3.

By the above operation, a potential distribution corresponding to the density of the original image, that is, an electrostatic latent image is formed on the photosensitive drum 1. This electrostatic latent image is visualized by a developing unit 4 disposed downstream of the writing unit 3.

In this embodiment, the developing unit 4 is provided with four sets of developing units 4M, 4C, 4Y and 4BK, each of which has a different color M (magenta) and C (M). Cyan, Y (yellow) and BK (black) toners.

Since the laser printer 100 is configured so that any one of the four developing units is selectively energized, the electrostatic latent image is formed of any one of the colors M, C, Y or Bk. Visualized with toner.

On the other hand, the transfer paper stored in the paper feed cassette 11 is fed out by the paper feed roller 12, fed to the surface of the transfer drum 2 at a timing by the registration roller 13, and adsorbed on the surface. It moves with the rotation of the transfer drum 2. Then, at a position close to the surface of the photosensitive drum 1, the toner image formed on the photosensitive drum 1 is transferred to the surface of the transfer paper by charging by the transfer charger 7.

In the case of the single-color copy mode, the transfer of the toner image is completed, and the transfer sheet separated from the transfer drum 2 is fixed and discharged to the discharge tray 10.

In the case of the full color mode, B
It is necessary to form images of four colors of K, M, C and Y on a single sheet of transfer paper. In this case, first, the photosensitive drum 1
A BK color toner image is formed thereon, and the BK color toner image is transferred onto a transfer sheet. Then, the next M color toner image is formed on the photosensitive drum 1 without separating the transfer sheet from the transfer drum 2. The toner image is transferred to the transfer paper again.

Further, for the C and Y colors, a toner image is formed on the photosensitive drum 1 and transferred to a transfer paper. That is, one color image is formed on the transfer paper by repeating the process of forming and transferring the toner image. When the transfer of all the toner images is completed, the transfer paper is separated from the transfer drum 2 by charging by the separation charger 8, and after being subjected to the fixing process of the toner image by the fixing device 9, is discharged to the discharge tray 10.

FIG. 2 is a circuit block diagram showing a schematic configuration of an electrical unit when the color image processing apparatus of the present invention is applied to a digital copying machine. The operation control of the entire copying machine is controlled by a system controller 50 composed of a microcomputer.
Is controlled by The synchronization control circuit 60 generates a clock pulse as a reference for control timing, and inputs and outputs various synchronization signals for synchronizing signals between the control units.

In this embodiment, the main scanning synchronization signal based on the scanning timing is synchronized with the start of scanning of the laser beam by the rotation of the rotary polygon mirror 3b of the laser printer 100. R read by the image scanner 400,
The G and B image signals are A / D converted and output as 8-bit color image information. This image information is output to the laser printer 100 after undergoing various processes in the image processing unit.

The image processing unit has a scanner gamma correction 7
1. RGB smoothing filter 72, color correction 73, under color removal (UCR) / UCA 74, selector 75, edge enhancement filter 76, printer gamma 77, gradation processing 78, image area separation 79, ACS 80, and background detection 81 It has a circuit.

The scanner gamma correction 71 converts the reflectance linear RGB data read by the image scanner 400 into linear density RGB data.

The RGB smoothing filter 72 performs a smoothing process for suppressing moire caused by a halftone dot document. The color correction circuit 73 converts the image information of each color of R, G, and B into image information of each color of Y, M, and C, which are complementary colors thereof.

In the UCR / UCA circuit 74, the input Y,
A black component included in the color of the image signal obtained by synthesizing all the image information of the M and C colors is extracted and output as a BK signal. The black component is removed from the image signals of the remaining colors, and the YMC component is removed. Is added.

The selector 75 is connected to the system controller 50
, One of the input Y, M, C, and BK color signals is selected and output to the next block.

The edge emphasizing filter circuit 76 emphasizes the edge information of the character portion or the picture portion, and the printer gamma 77 sets a curve corresponding to the printer characteristics and makes the density linear including gradation processing. .

The gradation processing circuit 78 is a circuit for binarizing the inputted 8-bit density information or converting it into multi-valued data.
Generally, dither processing is often performed, and an image signal subjected to dither processing is output to the laser printer 100.

The output of the scanner gamma 71 is sent to an image area separation circuit 79, an ACS circuit 80, and a background detection circuit 81.

The image area separating circuit 79 has a circuit for determining whether an input image is a character part or a picture part, and a circuit for determining whether the image is chromatic or achromatic.
The result is sent to each processing block in units of one pixel. In each processing block, processing is switched according to the result of the image area separation circuit 79.

The ACS circuit 80 determines whether the original set on the scanner 200 is a black-and-white original or a color original, and sends the result to the system controller 50 at the end of the Bk scan. If the original is a color original, the remaining three scans are performed, and if the original is a black and white original, the operation is terminated by Bk scan.

The background detection circuit 81 is a central block of the present invention, and detects the background density of the document surface at the time of Bk scanning or pre-scanning, and the system controller 50.
To determine the amount of background removal during subsequent development.

FIG. 3 is a block diagram showing in detail the configuration of a block for performing background removal processing in the image processing section shown in FIG. In the present embodiment, the background removal processing is performed by the scanner gamma 71, the color correction 73, and the printer gamma 77.
Done by one block. The parameters used in the image processing blocks 71 to 81 are all set by the CPU of the system controller 50.

Next, a method of removing the background applied to this embodiment will be described with reference to FIG. In FIG. 4, in the background removal method of the present embodiment, when a curve when background removal is not performed is a solid line, an arbitrary density setting value A (not shown)
A two-stage background removal method in which the image is completely removed when the value is 1 or less, and is gradually removed between a density setting value A2 (not shown) and a density setting value A1 which is set to a value slightly larger than the density setting value A1. Is adopted. This curve is used as it is in the scanner gamma 71 and the printer gamma 77 as a gamma table.

Although the above-described two-stage background removal method is a suitable method to be applied to the present invention, it is not limited to this method, and other various methods can be applied. It is.

Next, the background detecting section 81 which is a feature of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram showing the configuration of the background detection unit 81 in detail. The background detection unit 81 smoothes the RGB data corrected by the scanner gamma correction 71 using a smoothing filter to remove noise and the like, and the density of the RGB data sent for each pixel. , A MIN detection circuit 503 for detecting the minimum value of the density of RGB data sent for each pixel, and a pixel detection circuit for detecting each pixel detected by the difference detection circuit. And a background detection circuit 504 for detecting a background density based on a difference value for each pixel and a minimum value for each pixel detected by the MIN detection circuit.

In the background detecting section 81 having the above configuration, the background detecting circuit 504 compares the difference value detected by the difference detecting circuit 502 with a preset value set in the background detecting circuit 504. Then, the minimum value of the pixel having a smaller difference value than the set value is input from the MIN circuit 503 as a background candidate.

The background detection circuit 504 compares the background candidates of the entire image obtained by the above operation and determines the value of the smallest density among the background candidates as the background density RD. It is sent to the system controller 50 as DATA.

The system controller 50 includes a density detector
Background density RD sent from 81 Ground by DATA
Determine the removal amount. The system controller 50 has
The set values TH1 and TH2 for determining the removal amount are recorded in advance.
Remembered. TH1 needs to remove the background with this device.
Density is set to no
Set to degree. TH1 and TH2 are the dynamics of this device.
It can be changed to the optimal value according to the operation mode
And

The system controller 50 controls the background density RD sent from the density detecting section 81. DATA is TH above
When it is larger than 1, control is performed so that the apparatus does not perform the background removal operation. The background density RD DATA is TH
RD when it is less than 1 and greater than TH2 D
ATA is selected as a reference value for background removal, and control is performed so as to perform background removal processing. Further, the background density RD DATA is TH
When the value is equal to or less than 2, OFFSET is selected as a reference amount for background removal, and control is performed so that background removal processing is performed.

Further, the color image processing apparatus of the present invention has an operation section 300 having a background removal ON / OFF key 307 for switching ON / OFF of the background removal mode. FIG. 8 is a diagram illustrating an example of the operation unit 300. The background removal ON / OFF key 307 is turned off at the operation unit 300
In this case, even if the background detection unit 81 detects the background density, the background removal operation is not performed. When the background removal ON / OFF key 307 is set to ON, the background removal processing is performed according to the removal reference amount determined by the system controller 50.

FIGS. 6 and 7 show the state of the background removal processing.
This will be described with reference to FIG. First, the background removal ON / OFF key is set to O
If it is FF, the background removal processing is not performed and an image is formed using the density indicated by the straight line in FIG. In addition, skin removal O
The N / OFF key is ON and the background density RD sent from the background detection unit 81 When DATA is not “0” as shown in FIG. 6A but a value between TH1 and TH2, RD indicated by a dashed line in FIG. DAT
A background removal process is performed using A as a reference amount for background removal. Further, the background density RD sent from the background detection unit 81 DAT
When A is “0” as shown in FIG. 6B, background removal processing is performed using OFFSET indicated by the dashed line in FIG. 7b as a background removal reference amount.

According to the above-described embodiment, by changing the amount of background removal stepwise according to the read background density value, a mottled original or a show-through original that could not be processed until now is processed. The background can be automatically removed.

In the past, only switching between newspaper originals and other originals was possible.
By providing the FF key, it is possible to switch between a newspaper original, a show-through original, and other originals.

Further, in order to obtain the amount of background removal, a simple apparatus is used instead of providing a new apparatus, so that the circuit configuration can be kept as it is, and there is no need to increase the cost. It is.

[0061]

As is apparent from the above description, in the color image processing apparatus of the present invention, the background density detecting means obtains the difference between the maximum value and the minimum value of the RGB data and the minimum value for each pixel, and calculates the difference value. Is compared with the minimum value of a pixel smaller than a preset value set in the background density detecting means, and the background density RD D
Determine the ATA.

The control means uses the preset values TH1 and TH2 for determining the preset background removal amount, and the background density RD sent from the background density detection means. DATA is classified to determine the background removal amount, and the operation of the background removal process is switched.

The background density RD detected by the background density detecting means
When DATA is equal to or higher than the density setting value TH1 that does not require the background removal processing set in advance by the control means, the background removal processing is not performed, so that processing according to the state of the document image can be performed.

The background density RD detected by the background density detecting means DATA is smaller than the above-mentioned TH1, and the set value TH of the concentration set in the control means, which is to be cut off, is set.
When it is 2 or more, the background density RD Since the background removal processing is performed using DATA as the reference amount for background removal, the background removal processing can be performed according to the situation of the document image.

The background density RD detected by the background density detecting means When DATA is equal to or less than the above TH2, OF
Since the background removal processing is performed using FSET as a reference amount of background removal, the background removal processing can be performed according to the situation of the document image.

Further, by changing the amount of background removal stepwise according to the read background density value, a mottled original which could not be processed until now,
Alternatively, the background removal of the show-through document can be automatically performed.

In the past, it was only possible to switch between a newspaper manuscript and other manuscripts. However, by setting whether or not to perform the background removal processing using the operation input means, the newspaper manuscript and the show-through manuscript can be changed. Switching to another document is possible.

Further, in order to obtain the background removal amount, a simple apparatus is used instead of providing a new apparatus, so that the circuit configuration can be kept as it is, and there is no need to increase the cost, and it is practical when commercializing. It is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a schematic configuration of a mechanism when a color image processing apparatus of the present invention is applied to a digital color copying machine.

FIG. 2 is a block diagram illustrating a schematic configuration of an electrical unit of the digital color copying machine.

FIG. 3 is a block diagram illustrating a schematic configuration of an electrical unit of the digital color copying machine.

FIG. 4 is a diagram illustrating a background removal curve used as an example of the background removal.

FIG. 5 is a block diagram illustrating a configuration of a background detection unit of the digital color copying machine.

6A is a diagram showing a density distribution of a newspaper manuscript or the like, and FIG.
FIG. 4 is a diagram showing a density distribution of a show-through document or the like.

FIG. 7 is a diagram illustrating a background removal curve applied to the color image processing apparatus of the present invention.

FIG. 8 is a diagram illustrating an example of an operation unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 transfer drum 3 writing unit 4 developing unit 9 fixing device 10 paper output tray 11 paper feed cassette 50 system controller 60 synchronization control circuit 71 scanner gamma 72 smoothing filter 73 color correction 74 UCR / UCA 75 selector 76 edge enhancement filter 77 Printer gamma 78 Gradation processing 79 Image area separation 80 ACS 81 Background detection unit 100 Laser printer 200 Automatic document feeder 300 Operation unit 307 Background removal ON / OFF key 400 Image scanner 500 External sensor

Claims (8)

[Claims] 1. An image reading means for optically scanning a document image to convert it into image data, a color separating means for separating the read image data into RGB data of three primary colors, and an image forming means for forming an image The background density RD based on the density distribution of the RGB data
A background density detecting unit that detects DATA; and a control unit that controls each of the units. The background density RD detected by the background density detecting unit.
A color image processing apparatus for determining a background removal amount based on DATA. 2. The background density detecting means includes: a difference detecting means for detecting a difference between a maximum value and a minimum value of density of RGB data for each pixel using the RGB data; and a minimum value of RGB data for each pixel. Minimum value detection means for detecting a value, the difference value detected by the difference detection means is compared with the minimum value of a pixel smaller than a preset value, the smallest minimum value among them Background density RD DAT
2. The color image processing apparatus according to claim 1, wherein the color image is output to the control unit as A. 3. The background density RD detected by the background density detection means, the density setting values TH1 and TH2 set in advance to determine the background removal amount.
3. The color image processing apparatus according to claim 1, wherein the background removal amount is set by comparing with the data. 4. The control unit according to claim 1, wherein the background density RD D
2. The control device according to claim 1, wherein when ATA is larger than TH1, control is performed so as not to perform the background removal operation.
4. The color image processing apparatus according to any one of claims 1 to 3. 5. The control means according to claim 1, wherein said background density RD D
When ATA is equal to or less than TH1 and greater than TH2, the background density RD The color image processing apparatus according to claim 1, wherein control is performed such that the background removal processing is performed using DATA as a reference of the background removal amount. 6. The control unit according to claim 1, wherein the background density RD D
When ATA is less than TH2, OFFSET
The color image processing apparatus according to any one of claims 1 to 5, wherein the control is performed such that the background removal processing is performed with reference to the background removal amount. 7. An operation input means capable of inputting by an operator, wherein when the setting is made by the operator to release the background removal mode from the operation input means, the background detected by the background density detection means is provided. 7. The color image processing apparatus according to claim 1, wherein the background removal operation is not performed regardless of the density. 8. The density setting values TH1 and TH2 for determining the background removal amount are changed from operation input means so as to be optimally set in accordance with an operation mode set by an operator. A color image processing apparatus according to claim 1.