JP2022076858A - Color correction device and image forming system - Google Patents

Abstract

To efficiently correct read values of colors read by a reading device, the colors other than basic colors included in process colors.SOLUTION: A color correction device according to an aspect of the present invention is a color correction device that corrects read values of a reading device that reads the colors of an image formed on a recording medium, and has a reading characteristic correction unit that, based on color measurement values of the colors of a basic color image measured by a colorimeter, the basic color image formed on the recording medium by using the basic colors in the process colors, and read values of the colors of the basic color image read by the reading device, corrects the reading characteristics of colors other than the basic colors read by the reading device.SELECTED DRAWING: Figure 3

Description

The present invention relates to a color correction device and an image forming system.

In the image forming system, in order to match the color characteristics of an image formed on a recording medium between a plurality of image forming systems, a technique for adjusting the color of an image based on the reading value of the color of the image formed on the recording medium by a reading device. It has been known.

Further, in order to correct the reading value by the reading device even if there is no color-controlled reference chart, the reading value of the four basic colors included in the process color (CMYK) changes due to the variation in the total spectral sensitivity characteristics of the reading device. A configuration is disclosed in which a component is extracted from image data and the reading value of the color component is corrected to a reference density (see, for example, Patent Document 1).

However, in the configuration of Patent Document 1, when correcting the reading value by the reading device of the color other than the basic color included in the process color, the color chart used as the correction reference is used. Therefore, it takes time and effort to correct, and there is room for improvement in terms of correction efficiency.

An object of the present invention is to make it possible to efficiently correct the reading value by a reading device of a color other than the basic color included in the process color.

The color correction device according to one aspect of the present invention is a color correction device that corrects the reading value of the reading device that reads the color of the image formed on the recording medium, and uses the basic color of the process color on the recording medium. Based on the color measurement value of the formed basic color image by the colorimeter and the reading value of the color of the basic color image by the reading device, the reading characteristic of the color other than the basic color by the reading device is obtained. It has a reading characteristic correction unit for correction.

According to the present invention, it is possible to efficiently correct the reading value by the reading device of a color other than the basic color included in the process color.

It is a figure which shows the whole structure example of the image formation system which concerns on embodiment. It is a figure of the hardware configuration example of the image formation system which concerns on embodiment. It is a block diagram of the functional configuration example of the color correction apparatus which concerns on 1st Embodiment. It is a figure which shows the example of the chromaticity variation of a white LED light source. It is a figure of the spectral reflectance example of process color yellow and fluorescent yellow. It is a figure which shows the example of the color matching function of a CIE color measurement standard observer. It is a figure which shows the example of the variation of the total spectral sensitivity characteristic of an in-line sensor. It is a block diagram which shows the signal processing example of the color correction apparatus which concerns on embodiment. It is a figure of the masking coefficient calculation method example of a hue division method. It is a figure of the hue division masking color conversion hue division example. It is a figure of an example of a hue division masking color conversion parameter. It is a figure of the correction result example by the color unevenness correction part of the color correction apparatus which concerns on embodiment, (a) is a figure which shows before correction, (b) is a figure which shows after correction. It is a figure of the color chart example for color unevenness correction which concerns on embodiment. It is a block diagram of the processing example by the color unevenness correction part which concerns on embodiment. It is a figure of the internal pattern example used by the color unevenness correction part which concerns on embodiment. It is a figure of the correction coefficient calculation example by the color unevenness correction part which concerns on embodiment. It is a figure of the correction example of the reading characteristic correction part which concerns on 1st Embodiment. It is a figure of the high density color correction example of the reading characteristic correction part which concerns on 2nd Embodiment. It is a figure which shows the relationship example of the spectroscopic characteristic change and the reading characteristic on a high density side.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same components are designated by the same reference numerals, and duplicate description will be omitted as appropriate.

Further, the embodiments shown below exemplify a color correction device for embodying the technical idea of the present invention, and the present invention is not limited to the embodiments shown below. Unless otherwise specified, the shapes of the components, their relative arrangements, the values of the parameters, etc. described below are not intended to limit the scope of the present invention to that alone, but are intended to be exemplified. Is. In addition, the size and positional relationship of the members shown in the drawings may be exaggerated in order to clarify the explanation.

The color correction device according to the embodiment is a device that corrects the reading value of the reading device that reads the color of the image formed on the recording medium.

In the embodiment, the reading device is based on the color measurement value by the colorimeter of the basic color image formed on the recording medium using the basic color of the process color and the reading value by the color reading device of the basic color image. Corrects the reading characteristics of colors other than the basic colors.

For example, using a predetermined correspondence between the colorimetric value of the color of the basic color image by the colorimeter and the reading value of the color of the basic color image by the reading device of the color of the basic color image, the reading by the reading device of colors other than the basic color is used. Correct the characteristics. This makes it possible to efficiently correct the reading characteristics of the reader without using a reference color chart even for colors other than the basic colors.

Further, by adjusting the color of the image formed on the recording medium by the image forming system by using the reading device corrected for the reading characteristic, the color characteristic of the image formed on the recording medium can be adjusted among the plurality of image forming systems. Allows for more accurate alignment.

Here, the process color means a color expressed by a combination of four basic colors in a printed matter. The four basic colors are, for example, cyan, magenta, yellow and black.

In the embodiment, these are referred to as basic colors, and an image composed of one basic color is referred to as a basic color image. Hereinafter, in order to simplify the explanation, cyan may be referred to as C, magenta may be referred to as M, yellow may be referred to as Y, and black may be referred to as K. Further, a color image including a basic color image or the like may be referred to as a patch.

The colorimeter is, for example, a spectrocolorimeter that measures the color of an object by the reflection or transmittance of each wavelength. In the embodiment, the colorimetric value measured by the colorimeter is used as the color reference value.

Hereinafter, an embodiment will be described by taking as an example an image forming system including the color correction device according to the embodiment.

[Embodiment]
<Overall configuration example of image forming system 100>
First, with reference to FIG. 1, the overall configuration of the image forming system 100 according to the embodiment will be described. FIG. 1 is a diagram illustrating an example of the overall configuration of the image forming system 100.

As shown in FIG. 1, the image forming system 100 includes a scanner unit 101, an automatic document feeder (ADF) 102, a paper feeding unit 103, and an apparatus main body 104.

The apparatus main body 104 includes a tandem image forming unit 105, a resist roller 108 that supplies a recording medium from the paper feeding unit 103 to the image forming unit 105 via a transport path 107, an optical writing device 109, and a fixing transport unit 110. And a double-sided tray 111.

In the image forming unit 105, a total of five photoconductor drums are arranged side by side corresponding to four colors of Y, M, C and K, which are process colors, and a special color S including a fluorescent color which can be additionally set in the station. ing. Further, the image forming unit 105 arranges an image forming element including a charger, a developer 106, a transfer device, a cleaner, and a static eliminator around each photoconductor drum 112.

Further, the apparatus main body 104 arranges an intermediate transfer belt 113 stretched between the drive roller and the driven roller while being sandwiched between the nips of the transfer device and the photoconductor drum 112. ..

The image forming system 100 writes light to the photoconductor drum 112 corresponding to each of the colors Y, M, C, K and S, develops each color with the toner of each color in the developing device 106, and puts it on the intermediate transfer belt 113. For example, primary transfer is performed in the order of Y, M, C, K and S.

Then, a full-color image and a special-color image superimposed in five colors by the primary transfer are secondarily transferred to a recording medium, and then fixed and ejected, whereby a full-color image can be formed on the recording medium.

Further, in the image forming system 100, an in-line sensor 114 and a white reference member 115 for shading correction of the in-line sensor 114 are arranged downstream of the fixing and conveying unit 110.

The in-line sensor 114 is an example of a reading device that reads the color of an image formed on a recording medium in order to correct the density of a printed image. The in-line sensor 114 includes a CCD (Charge Coupled Device) line sensor in which pixels that output an electric signal according to the received light intensity are arranged in a one-dimensional array. The pixel arrangement directions intersect the transport direction of the recording medium. Further, the line sensor includes a pixel array that receives red light (R), a pixel array that receives green light (G), and a pixel array that receives blue light (B), and reads RGB. Output the value.

The in-line sensor 114 outputs an electric signal according to the light intensity of the reflected light of the printed image formed on the recording medium by the pixel array of each color. The image forming system 100 uses the light intensity (density) of each color of the image read by the inline sensor 114 for color adjustment in the printed image.

Further, the in-line sensor 114 has a light source that irradiates the recording medium with light. The light source may be any light source as long as it irradiates the recording medium with light, but in the embodiment, it is, for example, a white LED (Light Emitting Diode) light source that irradiates white light.

By irradiating the recording medium with light from the white LED light source, the brightness of reading by the in-line sensor 114 can be ensured. Further, the in-line sensor 114 may include a CMOS (Complementary metal-oxide-semiconductor), a PD (Photo Diode) array or the like instead of the CCD.

<Hardware configuration example of image forming system 100>
Next, the hardware configuration of the image forming system 100 will be described with reference to FIG. FIG. 2 is a block diagram showing an example of the hardware configuration of the image forming system 100.

As shown in FIG. 2, the image forming system 100 includes a controller 910, a short-range communication circuit 920, an engine control unit 930, an operation panel 940, a network I / F (Interface) 950, and an inline sensor 114. Have.

Of these, the controller 910 includes a CPU (Central Processing Unit) 901, which is the main part of the computer, a system memory (MEM-P) 902, a north bridge (NB) 903, a south bridge (SB) 904, and an ASIC. It includes a (Application Specific Integrated Circuit) 906, a local memory (MEM-C) 907 as a storage unit, an HDD (Hard Disk Drive) controller 908, and an HD (Hard Disk) 909 as a storage unit. The HD909 may be an SSD (Solid State Drive). Further, the NB 903 and the ASIC 906 are connected by an AGP (Accelerated Graphics Port) bus 921.

The CPU 901 is a control unit that controls the entire image forming system 100. The NB903 is a bridge for connecting the CPU901, the MEM-P902, the SB904, and the AGP bus 921, and includes a memory controller that controls reading and writing to the MEM-P902, a PCI (Peripheral Component Interconnect) master, and an AGP target. Has.

The MEM-P902 is a ROM (Read Only Memory) 902a that is a memory for storing programs and data that realizes each function of the controller 910, and a RAM (Random) that is used as a memory for developing programs and data and a memory for drawing at the time of memory printing. Access Memory) 902b.

The program stored in the ROM 902a is configured to be recorded and provided as a file in an installable format or an executable format on a computer-readable recording medium such as a CD-ROM, CD-R, or DVD. You may.

The SB904 is a bridge for connecting the NB903 to a PCI device and a peripheral device. The ASIC 906 is an IC (Integrated Circuit) for image processing applications including hardware elements for image processing, and has a role of a bridge connecting the AGP bus 921, the PCI bus 922, the HDD 908, and the MEM-C907, respectively.

This ASIC906 is a PCI target and an AGP master, an arbiter (ARB) which is the core of the ASIC906, a memory controller which controls MEM-C907, and a plurality of DMACs (Direct Memory Access Controllers) which rotate image data by hardware logic and the like. , And a PCI unit that transfers data between the scanner unit 101 and the printer unit 932 via the PCI bus 922.

A USB interface or an IEEE 1394 (Institute of Electrical and Electronics Engineers 1394) interface may be connected to the ASIC 906.

The MEM-C907 is a local memory used as a copy image buffer and a code buffer. The HD909 is a storage for accumulating image data, accumulating font data used at the time of printing, and accumulating forms. The HD909 controls reading or writing of data to the HD909 according to the control of the CPU 901.

The AGP bus 921 is a bus interface for a graphics accelerator card proposed to accelerate graphic processing, and the graphics accelerator card can be accelerated by directly accessing the MEM-P902 with a high throughput. ..

Further, the short-range communication circuit 920 has a communication circuit 920a. The short-range communication circuit 920 is a communication circuit such as NFC and Bluetooth (registered trademark).

Further, the engine control unit 930 includes a scanner unit 101 and a printer unit 932. The operation panel 940 displays a current setting value, a selection screen, etc., and receives a panel display unit 940a such as a touch panel that accepts input from an operator, and a numeric keypad that accepts setting values of conditions related to image formation such as density setting conditions. It also has an operation panel 940b including a start key or the like for receiving a copy start instruction.

The controller 910 controls the entire image forming system 100, and controls, for example, drawing, communication, input from the operation panel 940, and the like. The scanner unit 101 or the printer unit 932 includes an image processing portion such as error diffusion and gamma conversion.

The image forming system 100 can sequentially switch and select the document box function, the copy function, the printer function, and the facsimile function by the application switching key of the operation panel 940.

When the document box function is selected, the document box mode is set, when the copy function is selected, the copy mode is set, when the printer function is selected, the printer mode is set, and when the facsimile mode is selected, the facsimile mode is set.

The network I / F950 is an interface for performing data communication using the network. The short-range communication circuit 920 and the network I / F 950 are electrically connected to the ASIC 906 via the PCI bus 922.

The in-line sensor 114 has a line sensor 121 and a white LED light source 122, and is electrically connected to the ASIC 906 via the PCI bus 922. The ASIC906 outputs a control signal and can drive and control the line sensor 121 and the white LED light source 122.

[First Embodiment]
<Example of functional configuration of color correction device 300>
Next, the functional configuration of the color correction device 300 will be described with reference to FIG. FIG. 3 is a block diagram showing an example of the functional configuration of the color correction device 300. As shown in FIG. 3, the color correction device 300 includes a reading value correction unit 301, a color unevenness correction unit 302, an estimation unit 303, a reading characteristic correction unit 304, and an internal pattern information storage unit 305.

Each part of the reading value correction unit 301, the color unevenness correction unit 302, the estimation unit 303, and the reading characteristic correction unit 304 follows a program in which any of the components shown in FIG. 2 is developed from the ROM 902a onto the RAM 902b. It is a function or a functioning means realized by operating by a command from the CPU 901. Further, the internal pattern information storage unit 305 is a function constructed by the RAM 902b and HD909 shown in FIG. Although FIG. 3 shows the main configurations of the color correction device 300, the color correction device 300 may have a configuration other than these.

The reading correction unit 301 corrects the reading of the inline sensor 114 that reads the color of the printed image. The color unevenness correction unit 302 corrects color unevenness according to the reading position information in the plane of the recording medium. Here, the reading value of the color of the image by the in-line sensor 114 may differ depending on the reading position even if the color has the same image density due to the unevenness of the brightness of the illumination light, the unevenness of the transport of the recording medium, and the like. .. Such a difference in reading value (individual difference) of the in-line sensor 114 is called color unevenness. The color unevenness correction unit 302 corrects this color unevenness.

The estimation unit 303 describes the color measurement value of the basic color image formed on the recording medium by the image formation system 100 using the process color by the colorimeter, and the RGB reading value read by the inline sensor 114 of the basic color image. Based on the above, the reading characteristics of the in-line sensor 114 for colors other than the basic colors are estimated.

The reading characteristic correction unit 304 corrects the reading characteristic by the in-line sensor 114 of a color other than the basic color based on the estimation result by the estimation unit 303. The internal pattern information storage unit 305 stores internal pattern information (for example, area ratio) for each color plate used for color adjustment in the image forming system 100.

The color correction device 300 is based on the relationship between the color components of the standard (observer) RGB cone signal such as the tristimulus value (CIE1931XYZ) (straight line connecting the white color and the solid color of the standard recording medium) and the CMYK basic color image. The relationship between the basic color of CMYK in the high density range and the special color such as a mixed color or a fluorescent color in which the basic color of CMYK is mixed is calculated in advance. For example, the variation range of the chromaticity (spectral energy characteristic) of the white LED light source is calculated in advance from the spectral reflectance of the color of the recording medium and the total spectral sensitivity characteristic of the in-line sensor 114. The internal pattern information storage unit 305 stores the calculation result. CIE is an abbreviation for the International Commission on Illumination.

The color unevenness correction unit 302 corrects the color unevenness of the read value according to the reading position due to the influence of the illuminance unevenness of the white LED light source 122, the transport unevenness of the recording medium, and the like. After that, the estimation unit 303 estimates the reading characteristics of the inline sensor 114 from the relationship between the reading value of the basic color image of CMYK and the color measurement value. This reading characteristic includes reading characteristics such as basic colors, mixed colors, and spot colors of CMYK in a high density region. The reading characteristic correction unit 304 corrects the reading characteristic of the inline sensor 114 according to the estimation result of the estimation unit 303.

In the following, the reading characteristics of the inline sensor 114 are estimated from the reading characteristics of the basic color image of [n1] process color CMYK, the reading value of the process color whose spectral characteristics change in the high density range, and the color mixture formed by the process color CMYK. Each component will be described with reference to an example of correcting the reading value and the reading value of the spot color.

<Example of chromaticity variation of white LED light source 122>
FIG. 4 is a diagram illustrating an example of chromaticity variation of the white LED light source 122 included in the inline sensor 114. The plurality of graphs shown in FIG. 4 show the variation in the chromaticity of the plurality of white LED light sources, and show the individual difference in the chromaticity among the plurality of white LED light sources. The chromaticity can also be referred to as a spectral energy characteristic.

As shown in FIG. 3, there are individual differences in the white LED light source 122. In particular, the variation in the peak frequency of blue, which has a peak near 450 nm, affects the reading characteristics of the basic color image. The estimation unit 303 estimates the characteristics of the white LED light sources 122 having different chromaticities as shown in FIG. 4, for example.

<Example of spectral reflectance of process color yellow and fluorescent yellow>
Next, FIG. 5 is a diagram showing an example of the spectral reflectance of process color yellow and fluorescent yellow. Further, FIG. 6 is a diagram showing an example of the CIE colorimetric standard observer color matching function. The CIE colorimetric standard observer color-blind function is a numerical representation of the color vision response of a standard observer, which is generally used to quantitatively represent color. Further, the area (integral value) of the region overlapping with the spectral radiance obtained from the spectral reflectance for an arbitrary light source is defined as the tristimulus value XYZ.

In the short wavelength region (400 nm to 500 nm) in FIGS. 5 and 6, since the process color yellow absorbs the light in the short wavelength region, the Z value (reflectance) which is approximately a blue component becomes smaller.

<Example of variation in total spectral sensitivity characteristics of in-line sensor 114>
Next, FIG. 7 is a diagram showing an example of variation in the total spectral sensitivity characteristics of the in-line sensor 114. The total spectral sensitivity characteristic of FIG. 7 shows the case where the peak wavelength of the white LED light source 122 in FIG. 4 has the minimum and maximum variation, and is in the short wavelength region (400 nm to 500 nm) through the color filter (blue). It is a schematic representation of the overall sensitivity characteristics.

Since the total spectral sensitivity characteristic of the in-line sensor 114 (chromaticity MAX) whose peak wavelength is shifted to the long wavelength side has a larger region overlapping with the reflectance of the process color yellow, it has the spectral reflectance characteristic shown in FIG. Even when the same color is read, the reading value becomes large.

<Example of signal processing by the color correction device 300>
Next, FIG. 8 is a block diagram [n2] showing an example of signal processing by the color correction device 300. The color correction device 300 converts the RGB reading of the inline sensor 114 into the CIEXYZ color space with high accuracy, and uses the standard definition formula to input the output image (internal pattern) of the image forming system 100 to the CIELab as an input color. Can be converted to a color space.

When correcting the color conversion parameters of the image formation system 100 using the basic colors of the process colors formed on the recording medium and the color mixing test gradation pattern, the reading value of the inline sensor 114 is color-converted and output to the γ conversion table. Adjust the 3D-LUT. As a result, even if the image output density of the image forming system 100 changes due to long-term use, it can be corrected to an appropriate target output density, and the color reproducibility of the output image can be ensured.

The in-line sensor 114 outputs RGB digital image data based on the shading information of the image of the recording medium that reads the internal pattern formed in the process color.

The in-line sensor 114 includes a CIS (contact image sensor) composed of a white LED light source 122 and a photoelectric conversion element, an A / D (Analog / Digital) converter, and a drive circuit for driving them. Digital image data of 8 bits each for RGB is generated and output from the shading information of the recording medium.

At this time, the digital image data is corrected for shading and other color unevenness generated on the mechanism of the inline sensor 114.

The controller 910 (see FIG. 2) acquires the output reading value (the average value of each RGB value in the reading area) with respect to the RGB digital image data (scanner reading value) for the gradation pattern. The RGB calibration (ACC) readings thus obtained are color-converted to XYZ chromaticity values.

For example, according to the process color CMYK data from the internal pattern information storage unit 305, it is divided into the following 15 color categories, and the color conversion from the device RGB to the XYZ chromaticity value is performed.
(Color category 1: Hue_1) Primary color: C single color (Color category 2: Hue_2) Primary color: M single color (Color category 3: Hue_3) Primary color: Y single color (Color category 4: Hue_4) Primary color: K single color (color category 5: Hue_5) Secondary color: CM color mixture (color category 6: Hue_6) Secondary color: MY color mixture (color category 7: Hue_7) Secondary color: YC color mixture (color category 8: Hue_8) secondary color Color: CK color mixture (color category 9: Hue_9) Secondary color: MK color mixture (color category 10: Hue_10) Secondary color: YK color mixture (color category 11: Hue_11) Tertiary color: CMY color mixture (color category 12: Hue_12) Tertiary color: CMK mixed color (color category 13: Hue_13) Tertiary color: MYK mixed color (color category 14: Hue_14) Tertiary color: YCK mixed color (color category 15: Hue_15) Fourth color: CMYK mixed color

Here, with respect to the color category 15, the color category may be further divided according to the mixing ratio of the CMYK color mixture as described below, and the set of color conversion parameters may be switched for color conversion.
MIN (CMY) / K> 1.0 (color category 15-1)
1.0 ≧ MIN (CMY) / K ＞ 0.75 (color category 15-2)
0.75 ≧ MIN (CMY) / K ＞ 0.5 (color category 15-3)
0.5 ≧ MIN (CMY) / K ＞ 0.25 (color category 15-4)
MIN (CMY) / K ≤ 0.25 (color category 15-5)

When performing more color area division according to the CMYK data of the process color (the version in which the preset CMYK data is not 0 in the embodiment) used for the color correction of the color mixture, the mixture is mixed at the output level after the γ characteristic correction of the printer unit 932. Perform the ratio calculation. The color area determination unit 306 in FIG. 8 can execute the color area division process.

In this embodiment, color correction of mixed colors using a gradation pattern will be described. The color stabilization control test chart is a gray gradation patch pattern, which is the most important color for color balance. The color stabilization control test chart is composed of a gray gradation patch containing only K and a process gray gradation patch in which Y, M, and C are mixed. Here, the patch is an example of a color image formed on a recording medium with a single color.

In the image forming system 100, a gray gradation patch of only K having the same chromaticity and a process gray gradation patch are arranged in a pair. The chromaticity of this patch is detected by a color sensor, and feedback is given to the color correction table so that the color difference between the paired K-only gray gradation patch and the process gray gradation patch disappears.

When converting the RGB output, which is the reading value of the inline sensor 114, to the device-independent CIEXYZ chromaticity value or sRGB, the masking coefficient is switched for each color category based on the combination of the internal pattern CMYK values, and linear conversion is performed. ..

In the present embodiment, since the color conversion is performed for the internal pattern of the discrete CMYK values, it is not necessary to consider the continuity at the boundary of each color category. Therefore, it is possible to obtain the masking coefficient by the least squares method or the like using RGB reading data and color measurement values such as CIEXYZ for each color category.
Rout = coef_rr [Hue_x] * Rin + coef_rg [Hue_x] * Gin + coef_rb [Hue_x] * Bin + const [Hue_x]
Gout = coef_gr [Hue_x] * Rin + coef_gg [Hue_x] * Gin + coef_gb [Hue_x] * Bin + const [Hue_x]
Bout = coef_br [Hue_x] * Rin + coef_bg [Hue_x] * Gin + coef_bb [Hue_x] * Bin + const [Hue_x]
Kout = coef_kr [Hue_x] * Rin + coef_kg [Hue_x] * Gin + coef_kb [Hue_x] * Bin + const [Hue_x]

(input)
Rin: R output of the scanner (R component reading of the scanner device)
Gin: G output of the scanner (G component reading of the scanner device)
Bin: Scanner B output (scanner device B component reading)

(output)
Rout: R output (standard R component: for example CIEXYZ_X)
Gout: G output (standard G component: for example CIEXYZ_Y)
Bout: B output (standard B component: for example CIEXYZ_Z)
Kout: K output (K component CIEXYZ_Y)

(coefficient)
coef [Hue_x]: Masking coefficient for color conversion in the color category Hue_x
const [Hue_x]: Constant in color category Hue_x

Further, for color category 11 (tertiary color: CMY color mixture), the hue changes greatly according to the ratio of each color component, so by performing hue division masking color conversion, highly accurate color prediction becomes possible. ..

In order to reduce the influence of the spectral sensitivity of the RGB output of the in-line sensor 114 and the XYZ chromaticity defined by the International Commission on Illumination that are not in a completely linear relationship, the in-line sensor is used instead of linear masking for process gray. It is also possible to use an equation that uses up to the third-order term of the RGB output of 114.

It is an average value of the difference between the XYZ chromaticity value obtained by converting the RGB output of the in-line sensor 114 and the XYZ chromaticity value determined by the International Commission on Illumination. Both XYZs are converted to L * a * b * according to the definition defined by the International Commission on Illumination, and then calculated as the color difference (ΔE).

It is better to change the matrix A for each attribute of the patch according to the type of color material used, such as whether the measured patch is a black-only gray gradation patch or a process gray gradation patch, to convert the RGB output of the sensor. It is shown that the color difference (ΔE) generated between the XYZ chromaticity value obtained in the above process and the XYZ chromaticity value determined by the International Commission on Illumination can be reduced.

This is because the influence of the spectral sensitivity of the RGB output of the inline sensor 114 and the non-linearity on the color matching function of the XYZ chromaticity defined by the International Commission on Illumination can be reduced by changing the matrix A for each patch attribute. ..

Therefore, by adopting a color conversion method in which the matrix A is set for each patch attribute, it occurs between the XYZ chromaticity value obtained by converting the RGB output of the sensor and the XYZ chromaticity value set by the International Commission on Illumination. It can be seen that the color difference can be reduced.

In this embodiment, it is premised that the mixing ratio of CMYK patches can be determined at the time of patch detection. In the image forming system 100 equipped with the inline sensor 114, patches are detected in the order of image formation, so that the attributes of the patches detected by the inline sensor 114 can be determined.

Further, here, the case of converting the RGB output of the inline sensor 114 to the XYZ chromaticity value is described, and the application of this embodiment is preferable when the color matching functions of two different color system have non-linearity. be.

The attributes are classified into two types, a gray gradation patch containing only K and a process gray gradation patch in which Y, M and C are mixed, but the attribute classification method is not limited to this.

Further, as a method of converting the RGB output of the inline sensor 114 into an XYZ chromaticity value, there are a method of linear conversion using a matrix, a method of using a polynomial conversion, a method of using a neural network, a method of using a look-up table, and the like.

In either method, if the attributes of the patch can be determined, the weight of the connection between the neurons used in the neural network may be changed or the lookup table used may be changed for each attribute of the patch. This makes it possible to reduce the difference between the XYZ chromaticity value obtained by converting the RGB output of the inline sensor 114 and the XYZ chromaticity value determined by the International Commission on Illumination.

As described above, in the present embodiment, various parameters used when converting the RGB output of the inline sensor 114 into the XYZ chromaticity value are changed for each patch attribute. This makes it possible to reduce the difference between the XYZ chromaticity value obtained by converting the RGB output of the inline sensor 114 and the XYZ chromaticity value determined by the International Commission on Illumination. Then, it becomes possible to improve the accuracy of the color stabilization control using the XYZ chromaticity value.

<Example of masking processing by the color correction device 300>
Next, the masking process by the color correction device 300 will be described. FIG. 9 is a diagram showing an example of a method for calculating the masking coefficient of the hue division method according to the embodiment. Further, FIG. 10 is a diagram showing an example of hue division in the hue division masking color conversion.

As shown in FIG. 9, the hue division for the RGB data is performed on a plane extending radially around the achromatic color axis (Dr = Dg = Db) with respect to the entire three-dimensional RGB color space.

For specific hue determination, the image signal (snpr, snpg, snpb) is converted into a hue signal (HUE) and compared with the hue boundary value (HUE00-11), and the hue region (12 divisions) is determined based on the result. This is performed by outputting a hue region signal (Huejo).

(Color difference signal generation)
A color difference signal (X, Y) is generated from the difference (for example, G component-R component and B component-G component) of the image signal (snpr, snpg, snpb).

(Wide area hue detection)
A wide-area hue signal (HUEH) is generated from the color difference signals (X, Y). The wide area hue signal (HUEH) indicates the position (see FIG. 7) when the XY signal plane is divided into eight.

(Color difference signal rotation)
A color difference signal (XA, YA) is generated according to a wide area hue signal (HUEH). The color difference signal (XA, YA) is the coordinate when the color difference signal plane (X, Y) is rotated and moved to the region of "HUEH = 0".

(Narrow range hue detection)
A narrow-range hue signal (HUEL) is generated from a color difference signal (XA, YA). The narrow-range hue signal (HUEL) is the slope of the color difference signal plane coordinates (HUEL / 32 = YA / XA).

(Hue boundary register)
The hue boundary register (HUE00 to HUE11) set value is output.

(Hue area judgment)
A hue region (HUE) is generated by comparing the magnitude relationship between the hue boundary signal (HUE00 to HUE11: 8bit) and the hue signal (HUELH, HUEL}).

(Hue division masking)
Hue region Based on the determined hue HUE, a masking operation according to the hue is performed. In this embodiment, the masking operation from the scanner RGB to the unified RGB is performed. When performing the product-sum calculation of the linear masking of the 12-hue division, the processing is performed independently for each color of the RGB and IR (infrared) components. Based on the hue determination signal HUE calculated by the hue region determination, the color correction coefficient and the color correction constant are selected and calculated.

The masking coefficient of each hue is of (Dr, Dg, Db, Dir) and (Dc, Dm, Dy, Dk) of 2 points on the achromatic color axis and 2 points (4 points in total) on both boundary planes. It can be determined by the correspondence.

In the embodiment, the input color is defined as RGB (scanner vector) and the output color (corresponding color) is defined as CMYK (printer vector), but the attributes of the input / output data can be set arbitrarily and a general-purpose color is used. Conversion is possible, and masking operations from scanner RGB to CIEXYZ, sRGB, etc. are also possible.

In FIG. 9, the correspondence between (Dr, Dg, Db, Dir) and (Dc, Dm, Dy, Dk) at four points is the following equation (1).

The masking coefficient that connects the correspondence of the determinants that summarize the equations (1) is calculated by calculating the product of the inverse matrix of the matrix that summarizes the right sides of colors 1 to 4 and the matrix that summarizes the left sides in equation (1). can.

If the relationship between the two points on the achromatic axis (white and black) and the two points on both boundary planes (four points in total) is determined in this way, the masking coefficient can be obtained. Therefore, as a parameter design for color conversion, the right side of Eq. (1) is defined as the scanner vector and the left side is defined as the printer vector regardless of the attributes of the input / output data, and the scanner vector and printer vector at each division point are obtained. become.

In the hue division masking color conversion, as shown in FIG. 10, the division points of the color space are two points for each of the primary color (C, M, Y) and the secondary color (R, G, B), for a total of 12 points. Divide by points.

FIG. 11 is a diagram showing an example of a color conversion parameter in the hue division masking according to the present embodiment. As shown in FIG. 11, after setting 14 final scanner vectors and printer vectors including white and black dots on the achromatic color axis, the masking coefficient can be calculated for each hue region. Even in this case, the continuity at the boundary of each hue region is maintained.
Rout = coef_rr [hue] * Rin + coef_rg [hue] * Gin + coef_rb [hue] * Bin + const
Gout = coef_gr [hue] * Rin + coef_gg [hue] * Gin + coef_gb [hue] * Bin + const
Bout = coef_br [hue] * Rin + coef_bg [hue] * Gin + coef_bb [hue] * Bin + const
Kout = coef_kr [hue] * Rin + coef_kg [hue] * Gin + coef_kb [hue] * Bin + const

(input)
Rin: R output of the scanner (R component reading of the scanner device)
Gin: G output of the scanner (G component reading of the scanner device)
Bin: Scanner B output (scanner device B component reading)

(output)
Rout: R output (standard R component: for example CIEXYZ_X)
Gout: G output (standard G component: for example CIEXYZ_Y)
Bout: B output (standard B component: for example CIEXYZ_Z)
Kout: K output (K component CIEXYZ_Y)

(coefficient)
coef_ [hue]: Masking coefficient for color separation in the hue hue region
const: constant

<Example of color unevenness correction by the color unevenness correction unit 302>
Next, FIG. 12 is a diagram illustrating an example of a color unevenness correction result by the color unevenness correction unit 302 of the color correction device 300. FIG. 12 (a) is a diagram showing before correction, and FIG. 12 (b) is a diagram showing after correction.

FIG. 12 schematically shows the relationship between the reading value obtained by reading a single color patch having a uniform density on the entire surface with the in-line sensor 114 and the color difference converted from the paper white of the recording medium using the color measurement value CIELAB. It is shown in. The horizontal axis indicates the position in the main scanning direction. The main scanning direction means a direction that intersects with the transport direction of the recording medium in the image forming system 100.

As shown in FIG. 12A, the reading level of the color patch by the in-line sensor 114 differs depending on the reading position even for the color patch having the same image density. There are various factors such as uneven illuminance (illumination depth) in the main scanning direction and uneven transfer of paper as factors that cause a difference in the reading value of the color patch by the in-line sensor 114. Even if shading correction or the like is performed on a white plate mounted in the image forming system 100, color unevenness with different reading values may occur depending on the nature of the recording medium to be conveyed.

Since the color unevenness is reproduced according to the position, the color unevenness correction unit 302 corrects the reading value of the inline sensor 114 according to the position for the purpose of performing the color correction with high accuracy. The correction coefficient is calculated in advance from the difference between the reading values of the colorimeter and the in-line sensor 114, and the reading value is corrected according to the position of the image (internal pattern). As a result of the correction by the color unevenness correction unit 302, as shown in FIG. 12B, a uniform reading value can be obtained regardless of the position in the main scanning direction.

Although the correction of the color unevenness in the main scanning direction is shown in the present embodiment, the color unevenness in the sub-scanning direction due to the transport unevenness of the recording medium can be similarly corrected.

Here, FIG. 13 is a diagram showing an example of a color chart used for color unevenness correction. Further, FIG. 14 is a block diagram showing an example of processing by the color unevenness correction unit 302.

FIG. 13 shows an example of the internal pattern 131 read by the inline sensor 114 in order to perform color correction of the output γ characteristic for each basic color (CMYK). This internal pattern 131 has the following features.
The internal pattern 131 has 21 gradations (including white paper) of the basic color CMYK.
Twelve patches are arranged in the main scanning direction of the image forming system 100.
-A total of four patch groups with the same color and gradation value are arranged over multiple pages and different main / sub positions.
The internal pattern 131 is image data of a pre-designed internal pattern CMYK version, and position information necessary for reading by the inline sensor 114 can be added according to the internal pattern 131.

(1) The RGB colors of the inline sensor 114 are r_ave0 to r_ave11, g_ave0 to g_ave11, and b_ave0 to b_ave11, which are R, G, and B data averaged for each region of the 12 patches arranged in the main scanning direction. Input to the correction block.
[Sensor RGB color correction block input data]
r_ave0, r_ave1, ..., r_ave10, r_ave11
g_ave0, g_ave1, ..., g_ave10, g_ave11
b_ave0, b_ave1, ..., b_ave10, b_ave11

(2) The correction coefficients wsh_c0 to wsh_c11, wsh_m0 to wsh_m11, wsh_y0 to wsh_y11, and wsh_k0 to wsh_k11 according to the output color and the main scanning position are given by the correction coefficient calculation unit 307 at any time during the calculation. The correction coefficient is an integer of 12 bits in the present embodiment, and is calculated by dividing by 2048 ( ²¹¹ ) as shown below at the time of calculation.
[Correction coefficient]
wsh_c0, wsh_c1, ..., wsh_c10, wsh_c11
wsh_m0, wsh_m1, ..., wsh_m10, wsh_m11
wsh_y0, wsh_y1, ..., wsh_y10, wsh_y11
wsh_k0, wsh_k1, ..., wsh_k10, wsh_k11
Here, 12 bits have an integer of 1 bit and a decimal number of 11 bits. The setting range is, for example, 0.7 to 1.3.

(3) Multiply the reading by the correction coefficient for each area.
In the embodiment, conversion to CMYK image density is assumed for color correction of the basic color in the subsequent stage, and correction is performed by multiplying the reading channel having a complementary color relationship by the correction coefficient calculation.
[Color unevenness correction calculation]
r_ave0 * wsh_c0, r_ave1 * wsh_c1, ..., r_ave10 * wsh_c10, r_ave11 * wsh_c11
g_ave0 * wsh_m0, g_ave1 * wsh_m1, ..., g_ave10 * wsh_m10, g_ave11 * wsh_m11
b_ave0 * wsh_y0, b_ave1 * wsh_y1, ..., b_ave10 * wsh_y10, b_ave11 * wsh_y11
g_ave0 * wsh_k0, g_ave1 * wsh_k1, ..., g_ave10 * wsh_k10, g_ave11 * wsh_k11

In the present embodiment, regarding G, the correction coefficients wsh_m and wsh_k are different for M and K.
[Operation example]
wsh_c0 = 0.915, wsh_c1 = 0.897, ..., wsh_c63 = 0.875
r_ave0 = 179.18, r_ave1 = 180.23, ..., r_ave63 = 181.34
r_ave0 × wsh_c0 = 163.95, r_ave1 × wsh_c1 = 161.67, ・ ・ ・, r_ave63 × wsh_c63 = 158.67

The correction coefficient calculation unit 307 outputs a correction value in 12 bits (integer 8 bits, decimal 4 bits) to the estimation unit 303, the reading characteristic correction unit 304, and the color conversion unit.

FIG. 15 is a diagram showing an example of an internal pattern used by the color unevenness correction unit 302. Further, FIG. 16 is a diagram showing an example of the calculation result of the correction coefficient by the color unevenness correction unit 302.

The internal pattern 151 is an image forming system 100 that outputs a CMYK monochromatic solid as a uniform image, and is read by an in-line sensor 114 and a colorimeter at intervals of each patch (see FIG. 13) included in the internal pattern 131.

FIG. 16 shows the reading value and the color measurement value of the inline sensor 114, which has a complementary color relationship with a certain color plate, converted into a color difference from paper white.

In FIG. 16, the image formation system uses the input / output relationship in which the reading value and the color measurement value of the inline sensor 114 are approximated by a linear equation for the variation characteristic of the color difference from the paper white by the least square method or the like as the target characteristic of the reading value correction. The correction coefficient for 100 and the color information (any of the basic colors CMYK in this embodiment) is calculated.

For example, when the approximate characteristic is y = ax + b and the coordinate value of the color difference from the paper white is P (m, n) for the reading value and the color measurement value of the inline sensor 114 at the position where the uniform pattern is present, the color difference from the paper white is used. The target value Xt of the reading value correction for is expressed by the following equation.
Xt = (n-b) / a

The correction coefficient wsh_** calculated by the correction coefficient calculation unit 307 is a ratio of the reading values as follows.
wsh_** = Xt / m = (n-b) / (akakerum)

Since this embodiment is a correction example for the process color (CMYK) of the basic color, there are four types of color information, and the relationship between the reading value and the color measurement value by the above-mentioned inline sensor 114 may be obtained for each color.

Further, in the color unevenness correction for the basic color of the process color, the internal pattern 151 is not limited to the solid image only. A pattern having a plurality of gradations including a halftone may be used for each color, and a color correction coefficient according to the gradation level may be used, or a correction coefficient common to all gradations may be used by averaging.

Regarding color correction for secondary color or higher readings used for color correction of mixed colors, not only complementary colors but also RGB readings are based on the following relationship instead of the color difference from paper white, depending on the patch formation position. The correction coefficient is calculated using the distribution of the reading value and the color measurement value (three stimulation values) obtained by the in-line sensor 114.
Read by in-line sensor 114 R: X (CIEXYZ)
Reading by in-line sensor 114 G: Y (CIEXYZ)
Read by in-line sensor 114 B: Z (CIEXYZ)

For example, when correcting the reading value of R (a mixture of M and Y) which is a secondary color, an image is formed of the internal pattern 151 of the layout as shown in FIG. 15 with 100% of M plate and 100% of Y plate. do. Assuming a color chart for color correction, r_ave0 to r_ave 9, g_ave0 to g_ave9, and b_ave0 to b_ave9 of each data of R, G, and B averaged for each area of 10 patches arranged in the main scanning direction in advance. The correction coefficient is input to the correction coefficient calculation unit 307, and the correction coefficient is calculated from the reading value and the color measurement value by the inline sensor 114.

[Input data to the correction coefficient calculation unit 307]
r_ave0, r_ave1, ..., r_ave8, r_ave9
g_ave0, g_ave1, ..., g_ave8, g_ave9
b_ave0, b_ave1, ..., b_ave8, b_ave9

At any time during reading value correction, correction coefficients wsh_rr0 to wsh_rr9, wsh_rg0 to wsh_rg9, and wsh_rb0 to wsh_rb9 according to the output color and the main scanning position are given by the correction coefficient calculation unit 307.

The correction coefficient is an integer of 12 bits, and the calculation is performed using the value divided by 2048 ( ²¹¹ ) as shown below.

[Correction coefficient]
wsh_rr0, wsh_rr1, ..., wsh_rr8, wsh_rr9
wsh_rg0, wsh_rg1, ..., wsh_rg8, wsh_rg9
wsh_rb0, wsh_rb1, ..., wsh_rb8, wsh_rb9

Multiply the input data and the correction factor for each area. In the present embodiment, conversion to CIELAB (CIEXYZ) is assumed for the secondary color R pattern (color category 6: MY color mixing) of the color correction of the color mixture, and the RGB reading channel is multiplied by the correction coefficient calculation as follows. Make corrections to.
[Example of correction operation for color category 6]
r_ave0 * wsh_rr0, r_ave1 * wsh_rr1, ..., r_ave8 * wsh_rr8, r_ave11 * wsh_rr9
g_ave0 * wsh_rg0, g_ave1 * wsh_rg1, ..., g_ave10 * wsh_rg8, g_ave11 * wsh_rg9
b_ave0 * wsh_rb0, b_ave1 * wsh_rb1, ..., b_ave10 * wsh_rb8, b_ave11 * wsh_rb9

<Correction example by reading characteristic correction unit 304>
Next, FIG. 17 is a diagram illustrating an example of correction processing by the reading characteristic correction unit 304. FIG. 17 schematically shows the relationship between the CIE tristimulus value (Z component) and the in-line sensor 114 in the images of paper white and process color yellow and fluorescent yellow of the standard recording medium. Here, fluorescent yellow is an example of a spot color that is a color other than a mixing color.

Since the color unevenness correction unit 302 corrects the color unevenness according to the reading position information in the plane, the reading value for the white color of the standard recording medium is the same under all conditions, and the characteristic values of the white point and the process color yellow are set. The slope of the passing straight line corresponds to the chromaticity of the inline sensor 114. Therefore, the reading value of the inline sensor 114 can be estimated from the slope of a straight line (dotted line P in FIG. 17) from the reading value of the process color yellow which is an arbitrary color measurement value Z.

The process of calculating the slope of this straight line is the process of the estimation unit 303. Since the reading characteristics of each color change linearly between the chromaticity MAX and the chromaticity MIN, the straight line (dotted line F in FIG. 17) with respect to the fluorescent yellow is the chromaticity MAX from the chromaticity of the inline sensor 114. It can be obtained by mapping from the relationship with the chromaticity MIN, and a reading estimated value (Bout in FIG. 16) of fluorescent yellow, which is an arbitrary color measurement value Z (Zin in FIG. 16), can be calculated.

The process of correcting the above-mentioned reading value of fluorescent yellow is the process of the reading characteristic correction unit 304.

<Action and effect of color correction device 300>
As described above, in the present embodiment, the color measurement value by the colorimeter of the basic color image formed on the recording medium using the basic color of the process color and the in-line sensor 114 of the color of the basic color image ( Based on the reading value by the reading device), the reading characteristics of colors other than the basic colors by the inline sensor 114 are corrected.

For example, the reading characteristic by the in-line sensor 114 is corrected by using the correspondence between the colorimetric value by the colorimeter of the color of the basic color image and the reading value by the color reading device of the basic color image. This correspondence relationship is predetermined and stored in the internal pattern information storage unit 305.

By doing so, even if the color is other than the color included in the plurality of basic color images, the reading characteristic by the reading device can be efficiently corrected without using the reference color chart.

Further, by adjusting the color of the image formed on the recording medium by the image forming system 100 by using the in-line sensor 114 whose reading characteristic is corrected, the color characteristic of the image formed on the recording medium can be adjusted between several image forming systems. Can be adjusted more accurately.

Further, in the present embodiment, the color unevenness correction unit 302 for correcting the color unevenness in the reading value is provided, and the reading characteristic correction unit 304 is included in the plurality of basic color images corrected by the color measurement value and the color unevenness correction unit 302. The reading characteristics are corrected based on the reading value of the color.

As a result, even when color unevenness occurs in the reading value of the in-line sensor 114 due to uneven illuminance, uneven paper transfer, or the like, it is possible to reduce the influence of the color unevenness on the correction of the reading characteristic.

[Second Embodiment]
Next, the color correction device 300a according to the second embodiment will be described. In the present embodiment, the reading characteristics of the in-line sensor 114 can be accurately corrected even when the standard recording medium has white and solid density fluctuations and the spectral characteristics change in the high density range of the color of the image.

FIG. 18 is a diagram illustrating processing by the reading characteristic correction unit 304. FIG. 18 schematically shows the relationship between the reflectance corresponding to the image density (C component) of process cyan and the inline sensor 114 (R component).

FIG. 18 shows an example in which the reading characteristic (slope of a line) of the inline sensor R changes from the vicinity of the Cyan solid pattern (point O, point P', point Q in FIG. 18) formed in the image under standard image formation conditions. There is.

FIG. 19 is a diagram showing an example of the relationship between the change in spectral characteristics corresponding to the amount of toner adhered on the high concentration side and the reading characteristics of the in-line sensor 114. Up to standard image formation conditions, the reflectance of 550 nm to 650 nm corresponding to the image density (C component) decreases, and when an image is formed with an adhesion amount higher than that, the hue tends to bend in the red direction, 550 nm to 650 nm. The change in reflectance of is small.

Since the decrease in reflectance on the short wavelength side is different from that from paper white to the cyan solid image formed under standard image formation conditions, the wavelength is shorter than the wavelength range corresponding to the image density (C component) (for example, 550 nm to 650 nm). The relationship between the R readings of the inline sensor 114, which also has sensitivity on the side, changes. As a result, the reading characteristic (slope of a line) of R of the inline sensor 114 changes from the vicinity of the cyan solid pattern formed in the image under the standard image formation conditions.

Since the color unevenness correction unit 302 corrects the color unevenness of the reading according to the reading position information in the plane, the reading value for the white color of the standard recording medium is the same under all conditions, and the white point (W) and the standard image drawing are the same. The slope of the straight line passing through the characteristic value of the process cyan solid under the condition corresponds to the chromaticity of the inline sensor 114.

In the total spectral sensitivity characteristics of the in-line sensor 114, as the reading characteristics of the process cyan solid under the standard image formation conditions of the chromaticity MAX and the chromaticity MIN, the straight line L and the straight line with respect to the slope of the line segment WO and the line segment WP in FIG. 18 are obtained in advance. The relationship of M is calculated from the total spectral sensitivity characteristics of the measured or in-line sensor 114 and the spectral reflectance characteristics of the process cyan solid with the image formation conditions changed.

Here, the R reading characteristic (slope of the line segment WO) of the inline sensor 114 of the chromaticity variation MAX with respect to the process cyan under the standard image formation condition is set to SL_A. Further, the R reading characteristic (slope of the line segment WP) of the inline sensor 114 of the chromaticity variation MIN with respect to the process cyan under the standard image formation condition is set to SL_B. The R reading characteristic (slope of the straight line L) of the inline sensor 114 of the chromaticity variation MAX with respect to the process cyan under the high density output condition is set to SL_C. Further, the in-line sensor R reading characteristic (slope of the straight line M) of the chromaticity variation MIN with respect to the process cyan under the high concentration output condition is set to SL_D.

High density output condition from the reflectance corresponding to the measured image density C (Cin in FIG. 18) of the process cyan solid patch under the standard image formation condition of the inline sensor 114 and the reading value R (Rin in FIG. 18) of the inline sensor 114. The reading characteristic of the in-line sensor 114 with respect to the process cyan in the above can be obtained, for example, as the inclination SL_F of the straight line (straight line N in FIG. 18) shown below from the reading characteristic with respect to the chromaticity MAX and the chromaticity MIN.
SL_F = (SL_E-SL_B) / (SL_A-SL_B) × (SL_C-SL_D) + SL_D

However, the R reading characteristic (slope of the line segment WQ) of the inline sensor 114 with respect to the process cyan under the standard image formation condition is set to SL_E, and the R reading characteristic (slope of the straight line N) of the inline sensor 114 with respect to the process cyan under the high density output condition. ) Is SL_F.

<Action and effect of color correction device 300a>
As described above, in the present embodiment, the relationship between the total spectral sensitivity characteristic of the in-line sensor 114 and the spectral reflectance characteristic of the image in which the image formation conditions are changed is determined in advance, and the in-line sensor 114 is used by utilizing the relationship. Correct the reading characteristics. By doing so, it is possible to accurately correct the reading characteristics of the in-line sensor 114 even when the white and solid density of the standard recording medium fluctuates and the spectral characteristics change in the high density range of the color of the image. can.

Although the embodiments have been described above, the present invention is not limited to the above-described embodiments specifically disclosed, and various modifications and changes can be made without departing from the scope of claims. ..

Further, in the above-described embodiment, the electrophotographic image forming system has been described, but the present invention can also be applied to other image forming systems such as an inkjet system.

Further, each function of the embodiment described above can be realized by one or more processing circuits. Here, the "processing circuit" as used herein is a processor programmed to perform each function by software, such as a processor implemented by an electronic circuit, or a processor designed to execute each function described above. It shall include devices such as ASIC (Application Specific Integrated Circuit), DSP (digital signal processor), FPGA (field programmable gate array) and conventional circuit modules.

100 Image formation system 114 In-line sensor 121 Line sensor 122 White LED light source 300 Color correction device 301 Reading value correction unit 302 Color unevenness correction unit 303 Estimating unit 304 Reading characteristic correction unit 305 Internal pattern information storage unit 306 Color area determination unit 307 Correction coefficient Calculation unit

Japanese Unexamined Patent Publication No. 2018-007123

Claims (7)

A color correction device that corrects the reading value of a reading device that reads the color of an image formed on a recording medium.
The reading is based on the color measurement value of the color of the basic color image formed on the recording medium using the basic color of the process color by the colorimeter and the reading value of the color of the basic color image by the reading device. A color correction device having a reading characteristic correction unit that corrects the reading characteristics of colors other than the basic colors by the device. Further, it has a color unevenness correction unit for correcting color unevenness in the read value, and has a color unevenness correction unit.
The color correction according to claim 1, wherein the reading characteristic correction unit corrects the reading characteristics based on the color measurement value and the reading value of the color of the basic color image corrected by the color unevenness correction unit. Device. The color correction device according to claim 1 or 2, wherein the color other than the basic color includes a color having a higher image density than the basic color image. The color correction device according to any one of claims 1 to 3, wherein the color other than the basic color is a color mixture in which a plurality of the basic colors included in the process color are mixed. The color correction device according to any one of claims 1 to 3, wherein the color other than the basic color includes a spot color which is a color other than a mixed color in which a plurality of the basic colors included in the process color are mixed. The reading characteristic correction unit passes through the reading value of the color of the basic color image and the reading value of the color of the recording medium in the graph showing the relationship between the reading value and the color measurement value. The color correction device according to any one of claims 1 to 5, which corrects the reading characteristic based on the inclination of a straight line. An image forming system that forms the image on the recording medium.
With the reading device
The color correction device according to any one of claims 1 to 6 is provided.
An image forming system that adjusts the color of an image based on the reading value of the reading device whose reading characteristics have been corrected by the color correction device.

Images