JP6127808B2 - Correction apparatus, image reading apparatus, image forming apparatus, and program - Google Patents

Description

  The present invention relates to a correction apparatus, an image reading apparatus, an image forming apparatus, and a program.

  Patent Document 1 generates light in which light from different light emitters is synthesized, reads a light source that irradiates the irradiated body with the light, and light that is irradiated from the light source and reflected from the irradiated body, Reading means for generating image information relating to the irradiated object, and the image information in which the irradiated object is a color sample composed of the color of light generated by any one of the light emitters that generates the light of the light source. A correction amount setting unit that sets a correction amount to be applied to the image information related to the irradiated object that is acquired from the reading unit and is generated by the reading unit according to the acquired image information; and the correction amount setting unit There is disclosed an image reading apparatus comprising correction means for correcting image information relating to the irradiated object generated by the reading means using the set correction amount.

JP 2011-023833 A

  It is an object of the present invention to provide a correction device, an image reading device, an image forming device, and a program that realize image reading with high color reproducibility.

In order to achieve the above object, the correction device according to claim 1 shows the first image information obtained by reading the reference image indicating the predetermined color, and the predetermined color degree. Conversion means for converting the first color level into second image information in a color space having a second color level indicating a color level different from the first color level; and the first color level in the second image information. value, the first correcting equation the first color for correcting such difference between the target value becomes smaller values of the first color level in the color of the first color level value and said reference image First derivation means for deriving using a difference between a level value and a first threshold value of the first color level; and a value of the second color level in the second image information as a value of the second color level. And a target of the value of the second color level in the color of the reference image Derived using a difference between the second second threshold value correcting equation the value of the first color level which is corrected by said first correction equation the first color level for correcting such difference decreases with Second derivation means for correcting the value of the first color level based on the first correction formula, and based on the second correction formula derived using the corrected value of the first color level. Correction for correcting the image information of the image to be corrected by correcting the value of the second color level and applying the corrected value of the first color level and the corrected value of the second color level Means.

According to a second aspect of the present invention, in the first aspect of the invention, each of the first deriving unit and the second deriving unit includes a color to be corrected and a color to be corrected. using a predetermined first threshold and the second threshold value every one in which determining the corrected region is an area of the image information to be corrected.

Further, an invention according to claim 3, in the invention described in claim 1 or claim 2, wherein the second deriving means, with each different multiple corresponding to the correction target region correction formula the A second correction formula is derived.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the second derivation means includes at least a part of the plurality of correction target areas, and the second correction equation of the preceding stage The second correction formula is sequentially derived one by one using the derivation result.

Further, the invention according to claim 5 is the invention according to claim 3 , wherein the second derivation means is derived by the first derivation means because each of the plurality of correction target areas does not overlap. Later, the second correction formula is derived in parallel with each stage.

On the other hand, in order to achieve the above object, an image reading apparatus according to claim 6 corrects image information obtained by the image reading means and an image reading means for reading the reference image and the image to be corrected. The correction device according to any one of claims 1 to 5 is provided.

In order to achieve the above object, an image forming apparatus according to claim 7 is configured to display an image based on the image reading apparatus according to claim 6 and image information corrected by the correction device of the image reading apparatus. And an image forming unit to be formed.

Furthermore, in order to achieve the above object, the program according to claim 8 , the program stores the first image information obtained by reading a reference image indicating a predetermined color as a predetermined color. Conversion means for converting into second image information of a color space having a first color level indicating the degree of color and a second color level indicating a degree of color different from the first color level, and the second image information in the second image information A first correction formula for correcting the value of the first color level so that the difference between the value of the first color level and the target value of the value of the first color level in the color of the reference image is small. First derivation means for deriving using the difference between the value of the first color level and the first threshold value of the first color level, and the value of the second color level in the second image information as the second In the color level value and the color of the reference image The serial value of the first color level that is corrected by the second correcting said first correcting equation the expression for correcting such difference decreases between the target value of the second color level value and said first color level Second derivation means for deriving using a difference from the threshold value of 2 , and correcting the value of the first color level based on the first correction formula, and using the corrected value of the first color level The second color level value is corrected based on the derived second correction formula, and the corrected first color level value and the corrected second color level value are applied to be corrected. It is intended to function as correction means for correcting the image information of the image.

Claim 1, according to the invention described in claims 6 to 8, as compared with the case of not applying the present invention, it is possible to color reproducibility can be realized a high image reading, an effect that is obtained It is done.

  According to the second aspect of the present invention, it is possible to obtain an effect that the amount of processing is reduced and correction processing can be performed at a higher speed than in the case where the correction target region is not defined.

According to the third aspect of the present invention, it is possible to obtain an effect that the correction target region can be enlarged as compared with the case where the present invention is not applied.

According to the fourth aspect of the present invention, compared with the case where each stage is derived in parallel after the first deriving means derives, the second correction expression is further determined according to the result of the previous color correction processing. It is possible to perform color correction processing and to share resources for each color correction processing.

According to the fifth aspect of the present invention, it is possible to reduce the number of stages of color correction processing as compared to the case where the second correction expression is sequentially derived one by one using the derivation result of the second correction expression of the previous stage. An effect is obtained.

1 is a schematic cross-sectional view illustrating an example of a configuration of an image forming apparatus according to an embodiment. 1 is a schematic cross-sectional view illustrating an example of a configuration of an image reading apparatus according to an embodiment. It is a block diagram which shows an example of a structure of the control part which concerns on embodiment. It is a block diagram which shows an example of a structure of the signal processing part which concerns on embodiment. It is a block diagram which shows an example of a structure of the color correction circuit which concerns on embodiment. It is a figure which shows an example of the calibration chart which concerns on embodiment. It is a figure which shows the color space for demonstrating the color calibration process which concerns on embodiment. It is a flowchart which shows the flow of a process of the correction coefficient calculation process program which concerns on embodiment. It is a flowchart which shows the flow of a process of the color correction process program which concerns on embodiment. It is a figure for demonstrating the color proofreading processing system which concerns on 2nd Embodiment.

[First Embodiment]
Hereinafter, an example of an embodiment for carrying out the present invention will be described in detail with reference to the drawings.
In the following description, the present invention will be described by exemplifying an embodiment in which the present invention is applied to an image forming apparatus having an image reading apparatus including the correction device according to the present invention.

First, the configuration of the image forming apparatus 10 according to the present embodiment will be described with reference to FIG.
An image forming apparatus 10 according to the present embodiment shown in FIG. 1 is a multi-function apparatus having a copy function, a print function, a facsimile function, etc., and includes an image reading apparatus 12 and an image forming apparatus section 14. It is configured.

  The image forming apparatus unit 14 according to the present embodiment includes an image forming unit 20 that forms an image based on image data of each color of yellow (Y), magenta (M), cyan (C), and black (K), A controller 40 that controls the overall operation of the image forming apparatus 10 and an external device such as a personal computer (PC) via a network such as a LAN (Local Area Network), a WAN (Wide Area Network), and the Internet. And a communication unit 44 that transmits and receives image data and the like. Further, the image forming apparatus unit 14 performs predetermined image processing on the facsimile (FAX) unit 46 that transmits and receives image data through a public line, and image data transferred from the image reading device 12, the control unit 40, and the like. And a U / I (user interface) unit 48 that receives instructions from the user and presents information related to image reading and image formation to the user.

The image forming unit 20 is a functional unit that forms an image by, for example, an electrophotographic method, and is arranged in parallel for each color of yellow (Y), magenta (M), cyan (C), and black (K). Are provided with four image forming units 21Y, 21M, 21C, and 21K (hereinafter, collectively referred to as “image forming unit 21”).
Each image forming unit 21 includes, for example, a photosensitive drum 22 that forms an electrostatic latent image and holds a toner image, a charger 23 that charges the surface of the photosensitive drum 22 with a predetermined potential, and a charger 23. To the print head 24 that exposes the charged photosensitive drum 22 based on the image data, the developing unit 25 that develops the electrostatic latent image formed on the photosensitive drum 22, and the toner image intermediate transfer body 27 described later. And a cleaner 26 that cleans the surface of the photosensitive drum 22 after the transfer.

  The image forming unit 20 also includes an intermediate transfer body 27 on which the toner images of the respective colors formed by the developing device 25 are transferred onto the photosensitive drums 22 of the image forming units 21 and the toner images of the respective colors formed by the image forming units 21. Are sequentially transferred (primary transfer) to the intermediate transfer member 27, and the toner image transferred and superimposed on the intermediate transfer member 27 is collectively transferred (secondary transfer) to the recording medium (recording paper P). A secondary transfer roll 29 and a fixing device 30 for fixing the secondary transferred image on the recording paper P are provided.

  The respective color toner images formed by the respective image forming units 21 are sequentially electrostatically transferred onto the intermediate transfer body 27 by the primary transfer roll 28 to form a composite toner image in which the respective color toners are superimposed. The synthetic toner image on the intermediate transfer member 27 is conveyed to the area where the secondary transfer roll 29 is disposed as the intermediate transfer member 27 moves in the direction of arrow A in FIG. 1 is collectively electrostatically transferred onto the recording paper P supplied in the direction of arrow B. Thereafter, the synthetic toner image electrostatically transferred onto the recording paper P is fixed on the recording paper P by being subjected to a fixing process by the fixing device 30.

  Next, the image reading apparatus 12 according to the present embodiment will be described with reference to FIG. FIG. 2 shows a schematic configuration of the image reading device 12. As shown in FIG. 2, the image reading apparatus 12 includes an automatic document feeder 50 and an image reading processing unit 52 that reads an image formed on the surface of the document.

  The automatic document feeder 50 according to the present embodiment includes a document table 60 on which a document is placed, a document conveyance path 61 that conveys the document, and a discharge table 62 that discharges the document after the image is read. It consists of

  The document conveyance path 61 is formed in a U-shape, and around the document conveyance path 61, there are a sheet delivery roll 63, a delivery roll 64, a pre-positioning roll 65, a positioning roll 66, a platen roll 67, an out-roll 68, A discharge roll 69 is provided. The paper feed roll 63 descends when the original is fed and picks up the original placed on the original table 60. The sending roll 64 supplies the document at the top of the documents sent from the paper sending roll 63 to the inside. The pre-positioning roll 65 temporarily stops the document sent from the sending roll 64 and corrects the skew feeding. The alignment roll 66 temporarily stops the document sent from the pre-alignment roll 65 and adjusts the reading timing. The platen roll 67 causes a document passing through the document transport path 61 to face a second platen glass 74 described later. The out roll 68 and the discharge roll 69 discharge the read document to the discharge table 62.

  The image reading device 12 has a function of flowing and reading the surface of a document sent from the document table 60 by the automatic document feeder 50 and a function of reading the surface of a document placed on a first platen glass 70 described later. I have.

  The image reading processing unit 52 includes a CCD (Charge Coupled Device) image sensor 88, a signal processing unit 90, a scanner control unit 92, and the like in a housing 75.

  On the surface of the housing 75 facing the automatic document feeder 50, a first platen glass 70 on which a document to be read is placed, a white reference plate 72, and a document for reading the document being conveyed by the automatic document feeder 50. A second platen glass 74 serving as an opening for irradiating light is provided.

  In addition, the image reading processing unit 52 is stationary at the reading position M of the second platen glass 74 or a full rate carriage 76 that reads an image while scanning (scanning) the entire first platen glass 70. A half-rate carriage 78 for guiding the light obtained from the above to the CCD image sensor 88 is provided in the housing 75.

  The full-rate carriage 76 includes an illumination unit 80 having a light source for irradiating light on the document, a diffuse reflection member 83 that reflects the light emitted from the illumination unit 80 while diffusing the light toward the document surface, and a reflection obtained from the document surface. A first mirror 82 that reflects light toward the half-rate carriage 78 is provided.

  The half-rate carriage 78 includes a second mirror 85 and a third mirror 84 that guide the light obtained from the full-rate carriage 76 to the CCD image sensor 88.

As an example, lighting unit 80 according to the present embodiment is configured by arranging a plurality of white light emitting diodes (LEDs) as light sources.
As an example, the white LED according to the present embodiment is configured by disposing a transparent resin containing a yellow fluorescent material around a blue LED chip. The yellow fluorescent material around the blue LED chip is excited by the blue light emitted from the blue LED chip to generate yellow fluorescence. Add the yellow and the blue from the complementary blue LED chip (synthesize)
Generate white light.

The CCD image sensor 88 according to the present embodiment photoelectrically converts the optical image formed by the imaging lens 86 that optically reduces the optical image obtained from the half-rate carriage 78 to red (R) and green. It has a function of generating each color signal (image signal) of (G) and blue (B).
As an example, the CCD image sensor 88 has a configuration in which one-dimensional line sensors for R, G, and B colors are arranged in a set of three rows.

  The scanner control unit 92 has a function of controlling the operation of the image reading device 12, and the signal processing unit 90 processes the image signals (R, G, B) of each color from the CCD image sensor 88. A function of generating image data. The scanner control unit 92 and the signal processing unit 90 are connected to the control unit 40 and the image processing unit 42 of the image forming apparatus unit 14 through signal lines, respectively, and transmit / receive control signals and image data to / from each other.

Next, a procedure for reading an image in the image reading apparatus 12 according to the present embodiment will be described.
When the image reading device 12 reads a document placed on the first platen glass 70, based on a user operation instruction from the U / I unit 48 of the image forming device unit 14, the control unit of the image forming device unit 14. 40 instructs the scanner control unit 92 to read a document placed on the first platen glass 70.

  Upon receiving an instruction to read a document placed on the first platen glass 70 from the control unit 40 of the image forming apparatus unit 14, the scanner control unit 92 moves the full rate carriage 76 and the half rate carriage 78 in the scanning direction (the direction of arrow C in FIG. 2). ). Further, the illumination unit 80 of the full rate carriage 76 emits light and irradiates the document surface. By the irradiation, the reflected light from the document is guided to the imaging lens 86 through the first mirror 82, the second mirror 85, and the third mirror 84. The light guided to the imaging lens 86 is imaged on the light receiving surface of the CCD image sensor 88. The CCD image sensor 88 reads one line for each of R, G, and B colors substantially simultaneously. Then, reading in the line direction is performed by scanning over the entire document size, thereby reading the document for one page.

  The image signals (R, G, B) obtained by the CCD image sensor 88 in this way are transferred to the signal processing unit 90 and subjected to various signal processing.

  On the other hand, when the image reading device 12 reads a document placed on the document table 60, the control unit of the image forming device unit 14 is based on a user operation instruction from the U / I unit 48 of the image forming device unit 14. 40 instructs the scanner control unit 92 to read a document placed on the document table 60.

Upon receiving an instruction to read a document placed on the document table 60 from the control unit 40, the scanner control unit 92 moves the document placed on the document table 60 to the reading position M of the second platen glass 74 along the document conveyance path 61. Transport. At this time, the full-rate carriage 76 and the half-rate carriage 78 are positioned in a state where they are stopped at the solid line positions shown in FIG. Then, the illumination unit 80 of the full rate carriage 76 emits light and irradiates the document surface. As a result, the reflected light of the document that is brought into close contact with the second platen glass 74 by the platen roll 67 is converted into the first mirror 82,
The light is guided to the imaging lens 86 through the second mirror 85 and the third mirror 84. The light guided to the imaging lens 86 is imaged on the light receiving surface of the CCD image sensor 88. The CCD image sensor 88 reads one line for each of R, G, and B colors substantially simultaneously. Then, the entire original is passed through the reading position M of the second platen glass 74 to read the original for one page.

  Image signals (R, G, B) obtained by the CCD image sensor 88 are transferred to the signal processing unit 90 and subjected to various signal processing.

  Next, the configuration of the control unit 40 according to the present embodiment will be described with reference to FIG. FIG. 3 is a block diagram illustrating an example of the configuration of the control unit 40. The control unit 40 according to the present embodiment includes a CPU 93, a RAM 94, a ROM 95, an NVM (Non Volatile Memory) 97, and an I / F (interface) unit 98. The CPU 93, the RAM 94, the ROM 95, the NVM 97, and the I / F unit 98 are connected so that information and the like can be exchanged with each other via a bus 99 such as a control bus or a data bus.

  The CPU 93 fetches the program 96 stored in the ROM 95 or the like into the RAM 94, executes the fetched program, and controls the overall operation of the image forming apparatus 10. The RAM 94 secures a work area when the CPU 93 executes the program 96. The ROM 95 stores various setting values used for processing in the CPU 93, a correction coefficient calculation process whose details will be described later, a program 96 for color correction processing, and the like. In the present embodiment, when the program 96 is executed by the CPU 93, correction coefficient calculation processing and color correction processing are performed. The NVM 97 is a flash memory or the like backed up by a battery that retains data even when power supply is interrupted. The I / F unit 98 controls input / output of signals to / from components such as the signal processing unit 90 and the scanner control unit 92 of the image reading apparatus 12 connected to the control unit 40.

  Next, a signal processing unit 90 having a function of processing each color image signal (R, G, B) generated by the CCD image sensor 88 will be described with reference to FIG. FIG. 4 is a block diagram illustrating an example of the configuration of the signal processing unit 90 according to the present embodiment.

  As shown in FIG. 4, the signal processing unit 90 according to the present embodiment includes a sample and hold circuit 100, a black level adjustment circuit 102, an amplification circuit 104, an A / D (analog / digital) conversion circuit 106, and shading. And a correction circuit 108.

  The sample hold circuit 100 has a function of sampling (sampling) the analog image signals (R, G, B) of each color transferred from the CCD image sensor 88 and performing a sampling hold for holding (holding) a predetermined period. It is what you have. The black level adjustment circuit 102 corresponds to the black color of a read original (hereinafter also referred to as “read original”) for the analog image signals (R, G, B) sampled and held by the sample hold circuit 100. And the black level of the output of the image reading device 12 have a function of adjusting so that they match (including substantially the same). The amplifier circuit 104 has a function of amplifying the analog image signal (R, G, B) after being adjusted by the black level adjustment circuit 102. The A / D conversion circuit 106 has a function of A / D converting the analog image signal (R, G, B) amplified by the amplification circuit 104 and converting it into image data (R, G, B) which is digital data. It is what you have. The shading correction circuit 108 corrects unevenness of read output due to the characteristics of the illumination unit 80 and the CCD image sensor 88 for the image data (R, G, B) converted by the A / D conversion circuit 106. The function of performing the shading correction processing for adjusting the white level of the read document and the white level of the output of the image reading device 12 to match (including substantially the same).

The signal processing unit 90 further includes a delay circuit 110, a color conversion circuit 112, a color correction circuit 114,
And a signal processing control circuit 116.

  The delay circuit 110 calculates a difference in reading time between each image data caused by a positional shift in the sub-scanning direction of the one-dimensional line sensors for R, G, and B constituting the CCD image sensor 88 as an R image. It has a function of correcting based on data.

  The color conversion circuit 112 uses a predetermined color conversion parameter to convert image data (R, G, B) in the RGB color space (device-dependent color space) into L * a * b * colors that are luminance color difference color spaces. It has a function of performing color conversion processing for converting into image data (L *, a *, b *) in a space (device-independent color space). Here, the “color conversion parameter” refers to, for example, converting RGB color space image data (R, G, B) into L * a * b * color space image data (L *, a *, b *). In this case, it is a parameter that defines the correspondence between the image data (R, G, B) and the image data (L *, a *, b *).

  The color correction circuit 114 mainly corrects the color of the image data (L *, a *, b *) output from the color conversion circuit 112 in accordance with the variation in the color of the white LEDs constituting the illumination unit 80. The image data (L *, a *, b *) subjected to the color correction processing by the color correction circuit 114 is transferred to the image processing unit 42 provided in the image forming apparatus unit 14, and the output color is output from the image processing unit 42. Color conversion processing to space image data (C, M, Y, K) is performed. The image processing unit 42 that performs color conversion processing to image data (C, M, Y, K) in the output color space may be provided inside the image reading processing unit 52.

  The signal processing control circuit 116 is controlled by the control unit 40 of the image forming apparatus unit 14, the sample hold circuit 100, the black level adjustment circuit 102, the amplification circuit 104, the A / D conversion circuit 106, the shading correction circuit 108, the color. This has a function of controlling operations of the conversion circuit 112 and the color correction circuit 114.

  Next, the details of the color correction circuit 114 will be described with reference to FIG. FIG. 5 is a block diagram showing an example of the configuration of the color correction circuit according to the present embodiment.

As shown in FIG. 5, the color correction circuit 114 according to the present embodiment includes a correction coefficient calculation unit 114A, a correction coefficient storage unit 114B, a correction target region setting unit 114C, and a correction unit 114D.
The correction coefficient calculation unit 114A calculates a correction coefficient K in the arithmetic expression used in the color calibration process according to the present embodiment. The correction coefficient storage unit 114B stores the correction coefficient K calculated by the correction coefficient calculation unit 114A. For example, the correction target area setting unit 114C sets an area in the L * a * b * color space to be subjected to color correction processing when the image reading processing unit 52 reads an image of a document. The correction unit 114D reads the correction coefficient K corresponding to the correction target region in the L * a * b * color space set by the correction target region setting unit 114C with reference to the correction coefficient storage unit 114B.
The color correction process for the correction target area is executed using the arithmetic expression into which the value of K is substituted.
Details of the color proofing process using the arithmetic expression according to the present embodiment will be described later.

Here, the color calibration process according to the present embodiment will be described in detail.
In the image reading processing unit 52 of the image forming apparatus 10 according to the present embodiment, as described above, as an example of the light source of the illumination unit 80 that illuminates the document surface, the blue LED chip and the blue LED chip are arranged around the blue LED chip. The white LED comprised including the transparent resin containing the made yellow fluorescent substance was used.

  Here, in the white LED, as described above, the fluorescent material around the blue LED chip is excited by the blue light emitted from the blue LED chip to generate yellow fluorescence, thereby adding blue and yellow in a complementary color relationship. Together, it produces white light. For this reason, the color of the light generated by the white LED varies in the yellow direction or the blue direction due to manufacturing variations related to the dispersion state of the fluorescent material, manufacturing variations in the emission wavelength of the blue LED chip, and the image reading processing unit 52. In some cases, the reading accuracy related to the color tone may be deteriorated.

In order to cope with this problem, the image forming apparatus 10 according to the present embodiment reads a calibration chart relating to the color and executes the reading result when the image reading processing unit 52 executes calibration such as shading correction. A color calibration process is performed for each pixel so as to approach the target value. Then, using the result (specifically, the correction formula) obtained by the color calibration processing, the image correction processing when the image reading processing unit 52 reads an image of a document or the like is executed on a pixel basis.
Hereinafter, the color calibration processing according to the present embodiment will be described in detail.

FIG. 6 shows an example of a calibration chart TC used in the color calibration process according to the present embodiment.
As shown in FIG. 6, the calibration chart TC according to the present embodiment includes cyan (denoted as (C) in the figure, the same applies to the following colors), magenta (M), yellow (Y), red (R ), Green (G), blue (B), and black (K), a pattern indicating the density at a predetermined level (11 levels in the present embodiment) (hereinafter, from the darker to the lighter) (It may be referred to as “density pattern 1” to “density pattern 11”).

FIG. 7 shows RGB color space image data (R, G, B) obtained by reading the calibration chart TC with the CCD image sensor 88, and L * a * b * color space image data (L *, a (*, B *) shows an example of the result of conversion (the part indicated by “reading value” in the figure). In FIG. 7, the horizontal axis is the a * axis, the vertical axis is the b * axis, and a * and b * are values in a predetermined range (in the present embodiment, a range of −100 to 100). (However, in FIG. 7, a part of a * and b * is shown.) The read values in FIG. 7 are cyan (C),
For each color of magenta (M), yellow (Y), red (R), green (G), blue (B), and black (K), read values (a *, b) corresponding to patterns indicating 11 levels of density. *) (Coordinates in the a * -b * plane) is plotted. That is, for example, regarding yellow (Y), the points indicated by □ are plotted from the outside toward the origin as 11 points corresponding to the density patterns 1 to 11 in FIG. Therefore, a total of 77 points for 7 colors are plotted for 11 colors.

  In addition, the portion indicated by “target value” in FIG. 7 (the point indicated by ◆ in FIG. 7) is a viewpoint of color reproducibility in the image reading processing unit 52 when the calibration chart TC is read. Thus, an example of (a *, b *) values of each density pattern of each color to be targeted is shown.

  On the other hand, in the color calibration processing according to the present embodiment, after the calibration chart TC is read by the CCD image sensor 88 of the image reading processing unit 52, the accuracy of the color calibration processing is improved based on the read value. The correction unit 114D performs a color calibration process including a plurality of stages of calibration in which the corresponding areas to be corrected (correction target areas) are different.

In the color calibration processing according to the present embodiment, the calculation represented by the following equation (1) is executed as color calibration processing A which is the first stage color calibration processing.

Output value = (input value−THA) × KA + THA (| input value |> | THA |)
Output value = input value (| input value | ≦ | THA |)
... Formula (1)

Here, the area designation constant THA (hereinafter, when there is no distinction between color calibration processes, may be referred to as “area designation constant TH”) is an area to be corrected by the value of a * or b * (hereinafter, referred to as “area designation constant TH”).
The correction target area by the color calibration process A may be referred to as “correction target area A”. ) And may be stored in advance in the ROM 95 or the like.

Further, the correction coefficient KA (hereinafter referred to as “correction coefficient K” when the color calibration process is not distinguished) is a coefficient calculated every time the color calibration process is executed in calibration or the like. The calculated coefficients are stored in the correction coefficient storage unit 114B and the like. In the equation (1), color calibration processing is performed when the absolute value of the input value exceeds the absolute value of THA,
If the absolute value of the input value is less than or equal to the absolute value of THA, the color calibration process is not performed. However, in this embodiment, in one color calibration process, either positive or negative half of a * or b * is the target of the color calibration process. In other words, in the present embodiment, if THA is positive, an area where a * or b * is positive is subjected to color calibration processing. If THA is negative, an area where a * or b * is negative is color. Subject to calibration processing.

In the color proofing process according to the present embodiment, a color proofing process B which is a second stage color proofing process indicated by the following equation (2) is further performed.

Output value = (input value 1−THB) × KB + input value 2 (| input value 1 |> | THB |)
Output value = input value 2 (| input value 1 | ≦ | THB |)
Equation (2) Here, the region designation constant THB is a constant that defines a region to be corrected by the value of a * or b * (hereinafter sometimes referred to as “correction target region B”). It may be stored in advance in the ROM 95 or the like. However, in the expression (2), the a * or b * selected by the input value 1, the input value 2, and the output value are different. That is, if the input value 1 is a *, the input value 2 and the output value are b *, and if the input value 1 is b *, the input value 2 and the output value are a *. That is, in Equation (2), a threshold is set for a * (b *), and b * (a *) is corrected according to the amount exceeding the threshold. The reason for this is generally that there is a correlation between the variation of a * and the variation of b *, and in the region where the variation of b * (a *) is large, the variation of a * (b *) is also large. Because it can be considered large.

  The correction coefficient KB is a coefficient calculated every time color calibration processing is executed in calibration or the like, and the calculated coefficient is stored in the correction coefficient storage unit 114B or the like. Also in the equation (2), color calibration processing is performed when the absolute value of the input value exceeds the absolute value of THB, and color calibration processing is not performed when the absolute value of the input value is equal to or less than the absolute value of THB. Similar to the above formula (1), the object of the color proofing process of one time is a half of either a * or b *.

Next, the color calibration processing A and the color calibration processing B will be specifically described using numerical examples.
As described above, in the color calibration process according to the present embodiment, the process of bringing the read value in FIG. 7 closer to the target value is performed. In this example, THA and THB are both area designation constants for b *, that is, b * defines the correction target area A and the correction target area B. The specific values of THA and THB may be defined by estimating a region where the deviation of the read value from the target value is expected to be large. In this embodiment, as an example, THA = 30,
It is assumed that THB = 30 (mainly a yellow (Y) region. Hereinafter, a color included in the correction target region may be referred to as a “correction target color HC”).

First, Equation (1) when the value of the area designation constant THA is 30 is re-presented as Equation (3) below.

b * output value = (b * input value−30) × KA + 30 (b * input value> 30) b * output value = b * input value (0 <b * input value ≦ 30) Formula (3)

Further, Expression (2) when the region designation constant THB is set to 30 is shown again as Expression (4) below.

a * output value = (b * input value−30) × KB + a * input value (b * input value> 30) a * output value = a * input value (0 <b * input value ≦ 30) ... Formula (4)

  In the example shown in FIG. 7, the read value (3, 81) (the value of (a *, b *), the same applies hereinafter) indicated by the point P0 is taken as an example, and the color calibration process A in equation (3) and the color calibration in equation (4). The calibration result by the process B will be described.

  First, Table 1 shows the result of the color proofing process A. In the present embodiment, the value of the correction coefficient KA obtained by the method described later is KA = 1.3. The read value P0 (3, 81) is the calibration value PA (3, 96) by the color calibration process A. However, the value of a * still deviates from the target value P * (− 6, 96). The target value P * (− 6, 96) is the target value for yellow (Y).

  Therefore, in the present embodiment, a color calibration process B that is a color calibration related to a * is further performed using the equation (4). Table 2 shows the result of the color proofing process B. In the present embodiment, the value of the correction coefficient KB obtained by the method described later is set to KB = −0.1. By the color proofing process B, it can be seen that the calibration value PA (3, 96) becomes the calibration value PB (-4, 96), which is closer to the target value P * (-6, 96).

  As shown in FIG. 7, as a result of the color calibration process A and the color calibration process B, it can be seen that other points in the region of b *> 30 mainly yellow (Y) are also approaching the target value.

  Next, a correction coefficient calculation process for calculating the correction coefficient K executed by the image forming apparatus 10 according to the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a processing flow of the correction coefficient calculation processing program according to the present embodiment.

  In the process shown in FIG. 8, when the user executes calibration or the like of the image reading processing unit 52, the execution of the color calibration process is designated from the U / I unit 48 or the like, and the calibration chart TC is set on the document table 60. In this case, the CPU 93 reads the correction coefficient calculation processing program stored in the ROM 95 or the like and executes the correction coefficient calculation processing program.

In this embodiment, the correction coefficient calculation processing program is stored in the ROM 95 or the like as an example. However, the present invention is not limited to this, and the correction coefficient calculation processing program is stored in a computer-readable storage. A form provided in a state stored in a medium, a form distributed via wired or wireless communication means, and the like may be applied.
In the present embodiment, the correction coefficient calculation process is realized by a software configuration using a computer by executing a program, but the present invention is not limited to this. For example, you may implement | achieve by the hardware structure which employ | adopted ASIC (Application Specific Integrated Circuit), or the combination of a hardware structure and a software structure.

As shown in FIG. 8, first, 1 is assigned to the variable i in step S100, and the calibration chart TC is read in step S102. The variable i is a variable for counting the number of circulations of a correction coefficient calculation processing loop that is repeatedly performed while changing the value of the correction coefficient, which will be described later, by a certain amount. In this embodiment, as described above, the format of the read result in step S102 is
This is the format of image data (R, G, B).

  In the next step S104, an image of the correction target color HC (at least one of cyan (C), magenta (M), yellow (Y), red (R), green (G), and blue (B)). Data (R, G, B) (hereinafter may be referred to as “RGB image data HC”) is read.

In the next step S106, the RGB image data HC is converted into image data (L *, a *, b *) (hereinafter, the converted result may be referred to as “Lab image data HC”).
In the next step S108, the area designation constant TH for the correction target color HC previously stored in the ROM 95 or the like is set as the area designation constant TH in the expression (1) or (2), and the correction coefficient K is set. An initial value of 1.0 is set.

In the next step S110, the a * or b * input value of the point to be calibrated in the Lab image data HC is substituted into the expression (1) or (2) to execute the color proofing process and output. Find the value.
At this time, the point to be calibrated in the Lab image data HC may be a point that is predicted to have the maximum difference from the target value.

In the next step S112, whether or not the difference ε = | output value−target value |, which is the absolute value of the difference between the output value obtained in step S110, is within an allowable range, that is, the following formula (5 ) Is determined.
ε = | Output value−Target value | ≦ Allowable range (5)
In addition, the specific value of the allowable range in Expression (5) corresponds to a color difference that is indistinguishable when visually recognized, for example, in the value of a * or b * at −100 to 100 full scale. A value may be used, and it may be about 3 as an example.

If the determination in step S112 is affirmative, the correction coefficient storage unit 114B stores the value of the correction coefficient K held at that time in the next step S120, and the correction coefficient calculation processing program ends.
On the other hand, if a negative determination is made in step S112, the process proceeds to step S114, and it is determined whether or not the variable i has reached the limit value N of the repeated calculation.

  If a negative determination is made in step S114, in step S116, a certain amount α is added in the direction in which the difference ε converges within the allowable range, and the value of the correction coefficient K at that time is changed to K + α. 1 is incremented by 1 and the process returns to step S110 to execute the color proofing process again.

  On the other hand, if the determination in step S114 is affirmative, the value of K is set to 1.0 in step S118, the process proceeds to step S120, and the value of the correction coefficient K is stored in the correction coefficient storage unit 114B. The calculation processing program is terminated. This process is an error process for preventing the loop from falling into an infinite loop.

  The correction coefficient K stored in the correction coefficient storage unit 114B by the above processing is executed by the correction unit 114D in color correction processing using Formula (1) or Formula (2) in the subsequent image reading process, for example. It is referred when it is done.

  In the above embodiment, the configuration in which the correction coefficient calculation processing is realized by a software configuration has been described as an example. However, when the correction coefficient calculation processing is realized by a hardware configuration, each block in the correction circuit 114 shown in FIG. It may be prepared in advance by hardware such as ASIC.

  Next, with reference to FIG. 9, the color correction process executed in the image reading process of a document or the like in the image forming apparatus 10 according to the present embodiment will be described. FIG. 9 is a flowchart showing a processing flow of the color correction processing program according to the present embodiment.

  In the process shown in FIG. 9, the user sets a document on the document table 60 of the image reading device 12 and instructs the start of reading via the U / I unit 48 or the like, so that the CPU 93 stores the color stored in the ROM 95 or the like. This is done by reading the correction processing program and executing the color correction processing program.

Referring to FIG. 9, first, in step S200, an image of an original is read by image reading device 12, and image data (R, G, B) is acquired as original image information.
In the next step S202, the image data (R, G, B) acquired in step S200 is converted into image data (L *, a *, b *) using color conversion parameters.

In the next step S204, a correction target area that is a target for color correction processing is set.
As described above, the correction target area is set by specifying the correction target color HC and the area specifying constant TH. The area designation constant TH may be stored in advance in a storage unit such as the ROM 96 for each correction target color HC, and read from the storage unit when the color correction process is executed.

  Note that the correction target area may be set, for example, by attaching attribute information indicating that each pixel is a color correction target. In this case, in the color correction process at the next stage, the pixel to which the attribute information is attached may be the target of color correction.

In the next step S206, the correction coefficient K corresponding to the correction target area is read from the correction coefficient storage unit 114B.
In the next step S208, color correction processing is executed for each pixel in the correction target region using the above-described equations (1) and (2).

In the next step S210, it is determined whether or not the color correction processing has been completed for all the pixels in the correction target area.
If a negative determination is made in step S210, the process returns to step S208 to execute color correction processing for the next correction target pixel.
On the other hand, if the determination in step S210 is affirmative, the main color correction processing program ends.

  As is apparent from the above description, the image forming apparatus 10 according to the present embodiment realizes image reading with high color reproducibility.

  In the embodiment described above, the point to be calibrated in the Lab image data HC is selected as the point where the difference from the target value is predicted to be the maximum, but is not limited to this. The color correction process may be executed for all points of the Lab image data HC, and the average value of the calculated plurality of correction coefficients K may be used as the target correction coefficient K.

  In the above embodiment, color calibration processing is performed for a region where the absolute value of the input value exceeds the absolute value of the region designation constant TH (a region satisfying | input value |> | THB |, ie, a region far from the origin). However, the present invention is not limited to this. For example, the color calibration process may be performed for the region closer to the origin in accordance with the deviation state between the read value and the target value.

[Second Embodiment]
Hereinafter, with reference to FIG. 7 again, the color calibration process executed by the image forming apparatus 10 according to the present embodiment will be described. In the first embodiment, the color calibration process is executed when the correction target color HC is yellow (Y). In the present embodiment, the correction target color HC is added to yellow (Y). A color calibration process is performed for an area (correction target area C) when cyan (C) and blue (B) are selected.

Referring to FIG. 7, the yellow (Y) region is close to the target value by the color calibration processing A and the color calibration processing B, but the cyan (C) and blue (B) regions are still shifted from the target value. You can see that
Therefore, in the present embodiment, in addition to the color calibration process A, the color calibration process C that is the color calibration process for the cyan (C) and blue (B) regions is further performed using the equation (2).

As an example, the region designation constant THC in the color calibration process C according to the present embodiment is THC = −28. The above formula (2) in which THC = −28 is substituted is shown again as the following formula (6).
a * output value = (b * input value − (− 28)) × KC + a * input value (b * input value <−28)
a * output value = b * input value (0> b * input value ≧ −28) Expression (6)

Based on Expression (6), a color calibration process C for bringing the point in the cyan (C) region indicated by the read value Q0 (−39, −47) in FIG. 7 closer to the target value Q * (−33, −48). Execute. In the correction coefficient calculation process shown in FIG. 8, when the correction coefficient KC in the color calibration process C is calculated with TH = −28, KC = −0.4. Therefore, since the value of a * for b * = − 47 is a * = − 32, a calibration value QC (−32, −47) in which Q0 is calibrated by the color calibration process C is obtained.
Table 3 shows the results of the above color proofing process. Since Q0 (−39, −47) is not a correction target of the color calibration process A shown in Expression (3), the calibration value QA (−39, −47) by the color calibration process A in Table 3 is There is no change from the read value Q0.

From Table 3, the calibration value QC (−32, −47), which is the result of the color calibration process C, approaches the target value Q * (−33, −48) from the read value Q0 (−39, −47). I understand that.
Although a specific description of the color calibration process is omitted, as is apparent from FIG. 7, the read value R0 (corresponding to blue (B)) also becomes the calibration value RC and becomes the target value R * by this color calibration process C. You can see that you are approaching. That is, the color proofing process C is mainly performed on the negative half of b * in addition to the yellow (Y) color correction process existing mainly on the positive half of b * according to the first embodiment. Color calibration processing is further performed for cyan (C) and blue (B).

As described above, in the present embodiment, by performing the color calibration process C in addition to the color calibration process A and the color calibration process B, the read values of the respective colors as a whole further approach the target value.
Moreover, for red (R), magenta (M), and green (G), which originally have a small difference between the read value and the target value, as shown in FIG. 7, color calibration processing A, color calibration processing B, and The value is hardly changed by the color proofing process C. Therefore, as a result of the color calibration process A, the color calibration process B, and the color calibration process C, a color calibration process is performed in which all read values of the calibration chart TC are brought close to the target value as a whole.

  In this embodiment, in addition to the color calibration process A (correction target color HC is yellow (Y)), two color calibration processes (color correction process B when the correction target color HC is yellow (Y) and the correction target are performed. Although an example in which the color HC performs the color calibration process C) of cyan (C) and blue (B) has been described, the present invention is not limited to this, and red (R) depending on the degree of deviation of the read value from the target value. ), Magenta (M), and green (G) may be subjected to color calibration processing according to the equation (2). In this case, the input value 1, the input value 2, and the output values a * and b * may be reversed from those in the above embodiment.

Here, with reference to FIG. 10 , a color calibration processing method when the color calibration processing B or the color calibration processing C is performed following the color calibration processing A will be described.

10 (a) is described above, the color calibration process A (area designated constant THA = 30, the correction coefficient KA = 1.3, the correction target color HC = Y (yellow), hereinafter the same) color calibration after execution of A column system is shown in which processing B is executed and color calibration processing C is executed after color calibration processing B is executed.

Column system shown in FIG. 10 (a), a plurality of color calibration process, if you want to further color calibration process at a later stage according to the result of the previous color calibration process (when the correction target region is overlapped) and each color This is effective when sharing calibration processing resources (such as a program or an ASIC in which the function of the program is implemented in hardware) is desired.
Incidentally, in FIG. 10 (a), the order of the color calibration process B and the color calibration process C may be reversed.

On the other hand, FIG. 10 (b), after the execution of the color calibration process A, shows a parallel method to perform the color calibration process D which integrates color calibration process B and the color calibration process C.
In color calibration processing D, color calibration processing B is executed when the input value (b * in the above embodiment) is input value> 30, and color calibration processing C is executed when the input value <−28. To do.
Parallel method shown in FIG. 10 (b), a plurality of color calibration processing is employed when the correction target region is different from each other, there is an advantage that fewer stages of the color calibration process is.

Here, in each of the above embodiments, mainly the color of the yellow (Y) -blue (B) region in the image reading processing unit 52 mainly due to the variation in the color of light generated by the white LED. Although a mode for dealing with a decrease in reading accuracy has been described as an example, the present invention is not limited to this.
You may apply to the fluctuation | variation of the color in the area | region of the other color resulting from another cause. In this case, the correction coefficient K may be calculated by defining the region designation constant TH for a * or b * according to the correction target color HC.

In each of the above embodiments, the correction coefficient calculation process is performed by setting the correction target color HC for the image data (R, G, B) read by the CCD image sensor. Not limited to. For example, the correction coefficient calculation processing is performed by setting the correction target color HC for the image data (L *, a *, b *) after the image data (R, G, B) is converted by the color conversion circuit 112. It is good as well. The flow of the correction coefficient calculation processing program in this case is
For example, in FIG. 8, step S104 and step S106 may be interchanged.

  In each of the above embodiments, the calibration chart for seven colors of cyan (C), magenta (M), yellow (Y), red (R), green (G), blue (B), and black (K). However, the present invention is not limited to this. For example, when the image forming apparatus has an image forming unit of a color other than cyan (C), magenta (M), yellow (Y), and black (K), the density for the other color is indicated. You may use the calibration chart which added the pattern.

Further, in each of the above embodiments, the description has been given by taking as an example the mode using the L * a * b * color space that is the luminance color difference color space as the color space for performing the color calibration process and the color correction process, but the present invention is not limited to this. Instead, for example, a YCbCr color space, which is another luminance color difference color space, or the like may be used. further,
Color conversion processing and color correction processing may be performed in the RGB color space without performing color space conversion.

  In each of the above embodiments, the present invention has been described by exemplifying an embodiment in which the present invention is applied to an electrophotographic image forming apparatus. However, the present invention is not limited to this, and may be applied to, for example, an inkjet image forming apparatus. .

  Furthermore, the flow of processing of the correction coefficient calculation processing program and the color correction processing program described in the above embodiment (see FIGS. 8 and 9) is an example, and unnecessary steps are within the scope of the present invention. You may delete, add a new step, and change processing order.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image reading apparatus 14 Image forming apparatus part 20 Image forming part 21 Image forming unit 22 Photosensitive drum 23 Charger 24 Print head 25 Developer 26 Cleaner 27 Intermediate transfer body 28 Primary transfer roll 29 Secondary transfer roll 30 Fixing devices 31A and 31B Paper storage unit 40 Control unit 42 Image processing unit 44 Communication unit 46 FAX unit 48 U / I unit 50 Automatic document feeder 52 Image reading processing unit 60 Document table 61 Document conveyance path 62 Discharge table 63 Sheet delivery roll 64 Delivery roll 65 Pre-positioning roll 66 Positioning roll 67 Platen roll 68 Out roll 69 Discharge roll 70 First platen glass 72 White reference plate 74 Second platen glass 75 Housing 76 Full-rate carriage 78 Half-rate carriage 80 Illumination unit 82 First 1 mirror 83 enlargement Reflecting member 84 third mirror 85 second mirror 86 forming lens 88 CCD image sensor 90 signal processing unit 92 the scanner control unit 93 CPU
94 RAM
95 ROM
96 Program 97 NVM
98 I / F section 99 Bus 100 Sample hold circuit 102 Black level adjustment circuit 104 Amplifying circuit 106 A / D conversion circuit 108 Shading correction circuit 110 Delay circuit 112 Color conversion circuit 114 Color correction circuit 114A Correction coefficient calculation section 114B Correction coefficient storage section 114C Correction target area setting section 114D Correction section 116 Signal processing control circuit HC Correction target color K Correction coefficient M Reading position P Recording paper TC Calibration chart TH Area designation constant

Claims (8)

The first image information obtained by reading the reference image indicating the predetermined color is set to a first color level indicating the predetermined color and a color level different from the first color level. Conversion means for converting into second image information in a color space having a second color level shown;
The value of the first color level in the second image information is corrected so that the difference between the value of the first color level and the target value of the value of the first color level in the color of the reference image becomes small. First derivation means for deriving a first correction equation for the first correction expression using a difference between a value of the first color level and a first threshold value of the first color level ;
The value of the second color level in the second image information is corrected so that the difference between the value of the second color level and the target value of the value of the second color level in the color of the reference image is reduced. Second derivation means for deriving a second correction formula for the first correction using a difference between a value of the first color level corrected by the first correction formula and a second threshold value of the first color level ;
The first color level value is corrected based on the first correction formula, and the second color level value is calculated based on the second correction formula derived using the corrected first color level value. Correction means for correcting the value and correcting the image information of the image to be corrected by applying the corrected first color level value and the corrected second color level value;
A correction device comprising: Wherein each of the first derivation means and said second deriving means, the color of interest for correction, and using the first threshold value and said second predetermined threshold value for each color to be subjected to correction The correction device according to claim 1, wherein a correction target region that is a region of image information to be corrected is determined. The second deriving means, each different correction multiple corresponding to the target region of the correction equation correcting device according to claim 1 or claim 2 for deriving a second correction equation using. The second derivation means is at least a portion of the plurality of the correction target region is duplicated, in claim 3 of deriving one order-order second correcting equation using the derived result of the second correction equation preceding The correction apparatus as described. The second deriving means, each of the plurality of the correction target region is not overlapped, according to claim 3 in which each stage after deriving said first deriving means derives the second correction equation in parallel Correction device. Image reading means for reading the reference image and the image to be corrected;
The correction apparatus according to any one of claims 1 to 5 , which corrects image information obtained by the image reading unit;
An image reading apparatus comprising: An image reading apparatus according to claim 6 ;
Image forming means for forming an image based on image information corrected by the correction device of the image reading device;
An image forming apparatus. Computer
The first image information obtained by reading the reference image indicating the predetermined color is set to a first color level indicating the predetermined color and a color level different from the first color level. Conversion means for converting into second image information in a color space having a second color level shown;
The value of the first color level in the second image information is corrected so that the difference between the value of the first color level and the target value of the value of the first color level in the color of the reference image becomes small. First derivation means for deriving a first correction equation for the first correction expression using a difference between a value of the first color level and a first threshold value of the first color level ;
The value of the second color level in the second image information is corrected so that the difference between the value of the second color level and the target value of the value of the second color level in the color of the reference image is reduced. Second derivation means for deriving a second correction formula for the first correction using a difference between a value of the first color level corrected by the first correction formula and a second threshold value of the first color level ;
The first color level value is corrected based on the first correction formula, and the second color level value is calculated based on the second correction formula derived using the corrected first color level value. Correction means for correcting the value and correcting the image information of the image to be corrected by applying the corrected first color level value and the corrected second color level value;
Program to function as.