JP4935451B2 - Color correction device, profile creation device, and color correction method - Google Patents

Description

  The present invention relates to a color correction method in consideration of a difference in ground color of a recording medium.

  When color matching is performed under the condition that there is a difference in the ground color of the recording medium, it is necessary to attach ink to at least one of the recording media in order to reproduce the white (achromatic color and maximum brightness) of the image data. This is because, when reproducing white of the image data, it is necessary to correct the difference in the color of the exposed ground color by the color of the ink. According to such a color matching method, the colors can be matched absolutely, but there is a problem of graininess due to the use of a small amount of ink to reproduce the white of extremely light image data. In addition, there is a problem that even if white is specified on the image data in order to prevent the ink from being used, the ink is used when actually printing, and the user cannot be satisfied. .

On the other hand, there has been proposed a method for creating a correction curve that does not use ink for white reproduction of image data and also realizes absolute color matching to some extent (see Patent Document 1). In such a configuration, an arbitrary color between the reproduction paper white color and the reproduction destination (color matching target) paper white color is set as a target color for reproducing white of the image data in the correction curve. (Set by the constants a, b, and c in Equations 1 to 3 of the same document). Therefore, it is also possible to set the paper white color of the reproduction destination (color matching target) as a target color for reproducing the white of the image data (set constant a = b = c = 0). In this case, since the white of the image data is reproduced by the color of the paper white that is the reproduction destination (color matching target), it is possible to prevent ink from being used to reproduce the white of the image data.
JP 2006-103096 A

In the above-described literature, the correction curve is defined by a spline curve, and the size of the center point of the spline curve is adjusted so as to match the color of the reproduction source. However, if the correction rule for the entire area is defined by a uniform spline curve, the consistency between the area where the absolute color accuracy with respect to the reproduction source color should be emphasized and the paper white color to be color-matched is determined. There is a problem that an appropriate correction rule cannot be defined for each of the areas to be emphasized. In addition, in the above document, it is assumed that the color reproduction characteristics of the printing device at the reproduction destination are faithful to the device profile at the reproduction destination, and the device profile resulting from the machine error and the actual color reproduction characteristics of the printing device. There was also a problem that it was not possible to compensate for the deviation between the two.
In order to solve the above problems, an object of the present invention is to ensure absolute color accuracy while utilizing the ground color of a recording medium to be color-matched.

In order to achieve such an object, in the present invention, when performing color correction to match the color formed by attaching the color material to the recording medium with the color of a predetermined target, the region where the color material is attached in a large amount is described above. While following the color of the target, a correction target value that approaches the ground color of the recording medium to be color-matched is set as the adhesion amount of the coloring material decreases. In other words, in the correction target value, an area where the color material adhesion amount is large places importance on absolute color matching with the target color, and the color material adhesion target decreases as the color material adhesion amount decreases. It is important to maintain the ground color of the recording medium. Accordingly, it is possible to set a correction target value that makes use of the ground color of the recording medium to be color-matched for white that minimizes the amount of the color material attached while ensuring a certain degree of absolute color accuracy. The correction unit corrects the adhesion amount of the color material based on a deviation amount between the color actually obtained by printing and measuring the color recording target recording medium and the color indicated by the correction target value. To do. Since correction is performed based on the color obtained by actually printing and measuring the color-matching recording medium, the printing apparatus that performed the printing simultaneously with the color matching with the target color. Compensation for variations in color reproducibility can also be realized.

  Further, by confirming whether or not the correction is appropriate, it is possible to realize color correction with higher accuracy. For example, it is realized by correction by confirming that the amount of deviation between the color obtained by printing and measuring the color according to the corrected adhesion amount of the color material and the target color is smaller than a predetermined threshold value. It can be confirmed whether the color accuracy satisfies a certain standard. Further, since the amount of deviation between the actually printed color and the target color is confirmed, the absolute color accuracy with respect to the target color can be confirmed.

  Further, when the deviation amount is larger than a predetermined threshold and the correction is inappropriate or insufficient, the color obtained by printing and measuring the color according to the corrected color material adhesion amount and the correction target You may make it perform correction based on the deviation | shift amount with the color which a value shows. That is, correction with higher accuracy can be performed by correction based on the amount of deviation between the corrected print result and the correction target value. By repeating such processing, it is possible to achieve color accuracy that satisfies a predetermined standard.

  Further, in confirming whether or not the correction is appropriate, the threshold value suitable for each region may be set. In the present invention, the region where the color material adhesion amount is large follows the target color, and the color material adhesion amount is corrected so as to approach the ground color of the recording medium to be color-matched. This is because the correction policy is different in both areas. It is also possible to set the threshold value for the entire region while setting the threshold value for each region. In this case, it can be confirmed that the absolute color accuracy of the whole satisfies a certain standard. It should be noted that the threshold value should be reduced for an area where the color material adhesion amount is corrected so as to follow the color of the target, and is corrected so as to approach the ground color of the recording medium to be color-matched. The threshold value should be increased for the region where the amount of the coloring material is small. Further, for the entire area obtained by combining these areas, the value between both areas should be set as the threshold value.

Of course, the above invention can be realized not only by the apparatus but also by a color correction method, and can also be realized by a color correction program for executing processing according to the above method. The device according to the present invention, a method, a program to sometimes be performed independently, other devices in a state installed in a device such as a profile creation device For example, the implementation, with a program The idea of the invention is not limited to this and includes various aspects, and can be changed as appropriate.

  Further, it can be provided as a recording medium on which a program corresponding to the present invention is recorded. The recording medium for this program may be a magnetic recording medium, a magneto-optical recording medium, or any recording medium that will be developed in the future. In addition, the duplication stages such as the primary duplication product and the secondary duplication product are equivalent without any question. Further, even when a part is software and a part is realized by hardware, the idea of the invention is not completely different, and a part is stored on a recording medium and is appropriately changed as necessary. It may be in the form of being read. In addition, not all functions are necessarily realized by a single program, but may be realized by a plurality of programs. In this case, what is necessary is just to make each function implement | achieve in a some computer.

Here, embodiments of the present invention will be described in the following order.
(1) Color correction device:
(2) Color correction processing:

(1) Color Correction Device FIG. 1 shows a configuration of a computer 10 and its peripheral devices as a color correction device according to an embodiment of the present invention. The main part of the color correction apparatus of the present invention is actually executed by the computer 10. Specifically, the CPU 12 included in the computer 10 reads the program data 11a stored in the hard disk drive (HDD) 11 or the like, and executes the calculation according to the program data 11a while expanding the program data 11a on the RAM 13. . Then, by controlling the printer 20 and the colorimeter 30 via the USB interface (I / F) 14 and the like by the calculation, various means constituting the color correction apparatus of the present invention are realized. In the present embodiment, the printer 20 is an inkjet printer, and forms a printed image by ejecting and adhering a large number of ink particles as a color material to a printing paper. Further, a color image is formed by reducing and mixing a plurality of types (colors) of ink particles on a printing paper. The computer 10 and the printer 20 may be connected to other interfaces such as infrared rays and a wireless LAN. A keyboard 40 a and a mouse 40 b are connected to the computer 10 via an input interface (I / F) 16.

In the CPU 12 and RAM 13, a color correction program P1, a printer driver P2, and a colorimeter driver P3 are executed. The color correction program P1 includes modules of a target color acquisition unit P1a, a printer color acquisition unit P1b, a correction target value setting unit P1c, a correction profile creation unit P1d, and an accuracy confirmation unit P1e. The target color acquisition unit P1a acquires colorimetric values when a predetermined color patch is printed by the target printer 50. In the present embodiment, the color measurement values of the color patches printed by the target printer 50 based on the patch data CD in which the colors are represented by C (cyan) M (magenta) Y (yellow) K (black) are absolute colors. Acquired as the L ^* a ^* b ^* value of the CIELAB color space. The color acquired here is hereinafter referred to as a target color. The target printing machine 50 is, for example, a digital screen printing machine, and performs printing by attaching ink amounts based on CMYK included in image data to a printing target using each screen.

In the present embodiment, a target profile TP that prescribes a color (L ^* a ^* b ^* ) value when the target printer 50 performs printing on standard printing paper based on an arbitrary CMYK value is prepared. Therefore, by applying the CMYK value of the patch data CD to the target profile TP, the target printing machine 50 obtains the L ^* a ^* b ^* value when printing on standard printing paper based on the patch data CD. . Of course, the colorimeter printed by the target printer 50 based on the patch data CD may be actually measured by the colorimeter 30. As standard printing paper, for example, those approved by ISO or JAPANCOLOR are used.

The printer color obtaining unit P1b obtains an L ^* a ^* b ^* value by measuring the color of each color patch printed by the printer 20 on an arbitrary printing paper based on the patch data CD by the colorimeter 30. Hereinafter, the acquired color is expressed as a printer color. Here, by outputting the patch data CD to the printer driver P1b, the printer 20 executes color patch printing based on the patch data CD, and obtains the colorimetric values of each color patch from the colorimeter driver P3. . It is assumed that the patch data CD is provided with uncolored color patches and blanks to which at least any ink is not attached. Then, the colorimeter 30 also measures the L ^* a ^* b ^* value of the color (ground color) indicated by any printing paper in a state where no ink is attached.

The correction target value setting unit P1c sets the correction target value DP based on the L ^* a ^* b ^* value of the ground color and the target color for the color patch printing paper printed by the printer 20. In the correction target value DP, color reproduction characteristics are set so as to follow the target color while maintaining the ground color of the printing paper of the color patch printed by the printer 20. The correction profile creation unit P1d acquires the correction target value DP and the printer color, and creates a correction profile MP based on the comparison between them. For the low-lightness area, a correction profile MP that defines a correction amount that causes the printer color when the printer 20 prints the patch data CD to be the same as the color defined by the correction target value DP is created. For the low-lightness area, a correction that defines a correction amount that causes the printer color when the printer 20 prints the patch data CD to gradually approach the color of the printing paper on which the patch data CD is printed as the lightness becomes high. A profile MP is created.

The accuracy confirmation unit P1e and the printer color acquisition unit P1b cause the printer 20 to print the patch data CD while performing correction using the correction profile MP, and newly set the colorimetric values (L ^* a ^* b ^* values). Acquired as the printer color. The accuracy confirmation unit P1e calculates a deviation amount between the obtained printer color and the target color, and determines whether or not the calculated deviation amount is smaller than a predetermined threshold value. If the amount of deviation between the printer color and the correction target value is larger than a predetermined threshold value, the correction profile creation unit P1d creates the correction profile MP again.

The printer driver P2 includes a color conversion unit P2a, a color separation processing unit P2b, and a print data generation unit P2c. The color conversion unit P2a converts the input image data into absolute color space image data based on the source profile including the target profile TP, and also converts the absolute color space image data into the printer based on the base profile BP. Color conversion is performed to image data of an ink amount of C′M′Y′K ′ at 20. In addition, in order to distinguish from CMYK which shows the ink amount in the target printing machine 50, the ink amount in the printer 20 shall be described as C'M'Y'K '. When the color conversion is performed based on the base profile BP, when the correction profile MP is prepared, the color conversion is performed while performing the correction using the correction profile MP. The base profile BP is a profile that defines a correspondence relationship between L ^* a ^* b ^* values and C′M′Y′K ′ values.

  The color separation processing unit P2b acquires ink amount image data, and performs color separation processing on the image data. In this embodiment, CMYK ink amount image data is acquired and converted into C′M′Y′K′lc ′ (light cyan) lm ′ (light magenta) image data by color separation processing. In the printer 20 of the present embodiment, it is possible to use C′M′Y′K′lc′lm ′ ink, and image data of the amount of ink that can be used by the printer 20 is obtained by the color separation process. And printing can be performed with each ink amount based on the image data.

The print data generation unit P2c performs a halftone process on the image data after the color separation process. Here, a dither method, an error diffusion method, or the like can be applied. Each pixel discharges / does not discharge ink, or discharges a large dot / discharges a medium dot / discharges a small dot / all. It is converted into halftone data having information specifying whether or not to discharge. Furthermore, the print data generation unit P2c performs microweave processing based on the halftone data. Specifically, print data specifying which ink nozzle at which main scanning / sub-scanning timing is assigned to each pixel of the halftone data is generated. Then, the print data generation unit P2c outputs the print data attached with the control information of the printer 20 such as print conditions to the printer 20 via the USB I / F 14. The colorimeter driver P3 acquires the colorimetric value obtained by the colorimeter 30 using the L ^* a ^* b ^* value.

(2) Color Correction Processing FIG. 2 shows the flow of color correction processing, and FIG. 3 schematically shows the overall configuration of color correction processing. In step S100, the target color acquisition unit P1a acquires the target profile TP and the patch data CD, and acquires the target color when the target printer 50 prints each color patch based on the patch data CD using the target profile TP. . In the patch data CD, the color of each color patch is expressed in CMYK, and the L ^* a ^* b ^* value corresponding to each CMYK is acquired with reference to the target profile TP. The target profile TP is given by, for example, a matrix conversion formula, and a corresponding L ^* a ^* b ^* value can be obtained by inputting a CMYK vector. Further, the target profile TP may be a lookup table, and an L ^* a ^* b ^* value corresponding to CMYK indicated by the patch data CD may be acquired by interpolation or the like. When C = M = Y = K = 0, white on the conversion source image data is expressed.

The target color obtained in step S100 is stored in the HDD 11 or RAM 13. The target profile TP is an L ^* a ^* b ^* value obtained when the target printer 50 actually prints a color patch on standard printing paper based on the CMYK value, and the colorimeter 30 measures the color patch. It is prepared in advance by associating with the original CMYK value. Therefore, the target color obtained by the target profile TP indicates the color when the target printer 50 prints the color patch on the standard printing paper.

  In step S110, the printer color acquisition unit P1b acquires the patch data CD, and causes the printer 20 to print a color patch based on the patch data CD. As shown in FIG. 3, the patch data CD is CMYK image data used by the target printer 50, and the color conversion unit P2a sequentially applies the target profile TP and the base profile BP, whereby the C used by the printer 20 is used. It is converted into image data of “M” Y ”K”. The color separation processing unit P2b converts the image data of C'M'Y'K 'into image data of C'M'Y'K'lc'lm' by the separation process. For example, a process of replacing a part of C ′ with lc ′ such as a double amount is performed.

  Next, the print data generating unit P2c generates print data by sequentially executing halftone processing and microweave processing on the image data after the color separation processing, and outputs the print data to the printer 20 via the USB I / F 14. As a result, the printer 20 prints the color patch CP on the color matching target printing paper set in the printer 20. The printing paper to be color-matched here may be any type, but is basically different from the standard printing paper on which the color patch is printed when the target profile TP for the target printer 50 is created. Printing paper is set. This is because the owner of the printer 20 does not always have the same printing paper as the standard printing paper, and the user does not always want to match colors to the same printing paper as the standard printing paper. The patch data CD is preferably set so that each color of the color patch CP uniformly covers the entire color reproduction gamut of the target printer 50 or the printer 20. Further, in the color patch CP, an uncolored patch is formed in which the printer 20 does not eject any ink.

  In step S120, color measurement of the printed color patch CP and uncolored patch is performed by the colorimeter 30, and the colorimetric value is acquired as a printer color from the colorimeter driver P3 by the printer color acquisition unit P1b. In step S130, the correction target value setting unit P1c sets the correction target value DP. Here, the correction target value DP is set based on the colorimetric value (ground color of the printing paper) of the non-colored patch obtained in step S120 and the target color obtained in step S100.

FIG. 4 is a graph showing an example of the correction target value DP. In the figure, the horizontal axis represents the input lightness L ^* in indicated by the achromatic color (a ^* , b ^* = 0) patch data CD (from the CMYK value of the patch data CD to the L ^* a ^* b ^* value by a known conversion formula). The vertical axis represents the output lightness L ^* out (the lightness L ^* t, L ^* p of the target color and the printer color) on the vertical axis. As shown in the figure, even when the white color (C = M = Y = K = 0) on the image data with the input lightness L ^* in = 100 is input, both the target color and the printer color have the highest lightness. Is not the maximum brightness L ^* = 100. This is because the paper ground of the standard printing paper on which the color patch is printed when creating the target profile TP and the paper ground of the color matching target printing paper on which the color patch CP is printed in step S110 are complete. This is because colors that are not white and lighter than the paper cannot be reproduced.
However, if a conversion table unique to the printer is sandwiched between the color conversion unit and the color separation processing unit in the printer driver, L ^* = 100 may be obtained.

In the present embodiment, the standard L-printing method in which the lightness L ^* pw of the printing paper to be color-matched on which the color patch CP is printed in step S110 is printed when the target profile TP is created. It is brighter than the lightness L ^* tw of the paper. In this embodiment, the input / output characteristics are linear, and the intermediate output lightness L ^* t, L ^* p is distributed on the straight lines Sp, St connecting the lightness L ^* pw, L ^* tw of each paper and the origin. ing. The straight lines Sp and St are shown by broken lines in FIG.

In FIG. 4, the correction target value DP is indicated by a solid line. The correction target value DP follows the straight line St indicating the color reproduction of the target printing machine 50 in the low lightness region, and gradually increases away from the straight line St in the high lightness region brighter than the predetermined input lightness L ^* in. It approaches Sp and reaches the lightness L ^* pw at the highest lightness. By doing so, it is possible to set a correction target value DP that absolutely matches the color reproduction of the target printing machine 50 in a region where the lightness is low and the amount of attached ink is large. On the other hand, in areas where the lightness is high and the amount of ink to be deposited is small, the correction is made with an emphasis on the relative gradation with respect to the color of the paper background by making the color close to the ground color of the exposed print paper for color matching. A target value DP can be set.

In the example of FIG. 4, the correction target value DP that follows the straight line St indicating the reproduction color of the target printer 50 is set for the region up to the boundary value L ^* u near the input lightness L ^* in = 70. In the present embodiment, the output brightness L ^* t and L ^* p are both linear. However, they may have non-linear characteristics. For example, when the lightness L ^* t of the target color is linear and the lightness L ^* p of the printer color is non-linear, the correction target value DP is set so that the lightness L ^* p of the printer color is linear. It becomes. On the contrary, when the lightness L ^* t of the target color is non-linear, a correction target value DP is set so that the lightness L ^* p of the printer color is non-linear. In particular, since the color reproduction characteristic of the lightness L ^* p of the printer color varies depending on the model and machine of the printer 20, the correction profile MP that follows the color reproduction characteristic of the target printing machine 50 also for the purpose of compensating for these variations. Need to be set. On the other hand, a correction target value DP that gradually approaches the ground color of the printing paper to be color-matched is set in an area having a higher brightness than the boundary value L ^* u. In addition, at a lightness higher than the boundary value L ^* u, the degree of emphasizing the ability to follow the straight line Sp is monotonically increased as the input lightness L ^* in increases. Moreover, as the correction profile MP in the boundary value L ^* u is smoothly bent, the slope of the straight line St than the boundary value L ^* u is the slope of the curve of the corrected target value DP in the high brightness in the vicinity of the boundary value L ^* u Have been to match. When the correction target value DP is represented by an equation, it is represented by the following equation (1).
(Equation 1)
L ^* opt = L ^* t (1−κl) + L ^* p · κl (1)
However, when L ^* in <L ^* u, κl = 0
When L ^* in ≧ L ^* u, κl = f (L ^* in)
L ^* opt represents the brightness value of the correction target value DP. κl means an adjustment coefficient, and κl = f (L ^* in) indicates that the adjustment coefficient κl is expressed by a function of L ^* in. As shown in FIG. 4, f (L ^* in) may be a monotonically increasing function that satisfies f (L ^* u) = 0 and f (100) = 1. For example, f (L ^* in) can be a linear function, a spline function, an exponential function, or the like that satisfies f (L ^* u) = 0 and f (100) = 1. Further, in order to make the correction target value DP bend smoothly at L ^* in = L ^* u, it is desirable that the first derivative of f (L ^* in) gradually approaches 0 when L ^* in → L ^* u. .

FIG. 5 shows characteristics relating to the color of the correction target value DP. In the figure, the vertical axis indicates the target color a ^* t and the printer color a ^* p with respect to the input value a ^* in on the horizontal axis. Neither the target color a ^* t nor the printer color a ^* p is 0 at the input value a ^* in = 0. Neither the standard printing paper on which the color patch is printed when creating the target profile TP nor the printing paper on which the color patch CP is printed in step S110 is completely white. Because it has a slight color. In the high saturation region where the amount of ink adhering is relatively large and the exposure of the paper background is suppressed, there is no difference between the target color a ^* t and the printer color a ^* p. The b ^* value has almost the same characteristics. The correction target value DP for the a ^* b ^* value is expressed by the following equation (2).
(Equation 2)
a ^* opt = a ^* t (1−κa) + a ^* p · κa (2)
However, when | a ^* in |> a ^* u, κa = 0
When | a ^* in | ≦ a ^* u, κa = f (a ^* in)
b ^* opt = b ^* t (1−κb) + b ^* p · κb
However, when | b ^* in |> b ^* u, κb = 0
When | b ^* in | ≦ b ^* u, κb = f (b ^* in)
Here, in the high saturation region where the ink adhesion amount is large, the color values a ^* opt and b ^* opt of the correction target value DP are made to follow the color values a ^* t and b ^* t of the target color, and the ink adhesion amount In the small low saturation region, the color values a ^* opt and b ^* opt of the correction target value DP are gradually brought closer to the color values a ^* p and b ^* p of the printer color by the adjustment coefficients κa and κb.

When the correction target value DP is set as described above, in step S140, the correction profile creation unit P1d creates a correction profile MP that defines a correction rule that matches the printer color with the color of the correction target value DP. Correction profile MP is, when the color conversion unit P2a converts the L ^* a ^* b ^* values and C'M'Y'K 'values by a base profile BP, pre L ^* a ^* b ^* value correction for correcting the A lookup table that defines rules. In the example of FIG. 4, since the lightness L ^* p of the printer color is larger than the lightness L ^* opt of the correction target value DP, the L ^* value to be input to the base profile BP is preliminarily shifted according to the difference (L ^*). By correcting downward by opt−L ^* p), the lightness L ^* opt of the correction target value DP can be corrected so as to be reproduced. In the high lightness region, the amount of deviation (L ^* opt−L ^* p) between the base profile BP and the lightness L ^* pw of the printer color gradually decreases, so that the correction amount for gradually downward correction is reduced. Rules are defined in the correction profile MP. At the highest lightness, the lightness L ^* opt of the correction target value DP matches the lightness L ^* pw of the printer color (L ^* opt−L ^* pw = 0), so the correction amount is set to zero.

As for the a ^* b ^* values, the deviations between the color values a ^* p, b ^* p of the printer color and the color values a ^* opt, b ^* opt of the correction target value DP (a ^* opt−a ^* p, b ^* opt) A correction amount corresponding to -b ^* p) is defined in the correction profile MP. At the smallest saturation, the color values a ^* opt, b ^* opt of the correction target value DP coincide with the color values a ^* p, b ^* p of the printer color (a ^* opt−a ^* p, b ^* opt). −b ^* p = 0), the correction amount is set to 0. For example, the correction profile MP can be created as three one-dimensional look-up tables in which the correction amount is individually defined for each of L ^* a ^* b ^* . Of course, the correction profile MP may be created as a three-dimensional lookup table in which the correction amount is simultaneously defined for L ^* a ^* b ^* .

Further, it is sufficient that the correction can be reflected in the C′M′Y′K ′ value finally obtained by the conversion by the base profile BP, and C′M′Y′K on the output side of the base profile BP is more directly applied. 'A correction profile MP for correcting a value may be created. Further, it may be created as a correction profile MP for correcting the L ^* a ^* b ^* value on the output side of the target profile TP for converting the CMYK value into the L ^* a ^* b ^* value. In the present embodiment, a correction profile MP is created as a profile for correcting the L ^* a ^* b ^* value on the input side of the base profile BP. Thereafter, when the color conversion unit P2a performs conversion using the base profile BP, correction is performed. The L ^* a ^* b ^* value on the input side is corrected in advance by the profile MP. A correction profile MP that realizes color matching with the target printer 50 can be shared by a plurality of printers 20 in which calibration (compensation for machine-to-machine error) for the base profile BP is executed in advance. Therefore, after the correction profile MP is created, the correction profile MP may be exported via a network or the like so that it can be used by another printer.

  Further, the correction profile MP is not limited to the one created alone, and the correction profile MP may be combined with the base profile BP or the target profile TP used by the color conversion unit P2a. Of course, by combining the base profile BP, the correction profile MP, and the target profile TP, it is possible to create a link profile in consideration of color matching. In this case, by converting the CMYK image data with the link profile, the corrected C′M′Y′K ′ image data can be obtained directly, and color conversion can be performed efficiently.

When the correction profile MP is created as described above, the accuracy confirmation unit P1e prints the color patch CP in step S150. Here, similarly to step S110, printing based on the patch data CD is performed by the printer 20. However, when the color conversion unit P2a performs conversion based on the base profile BP, the L ^* a ^* b ^* value on the input side is corrected in advance by the correction profile MP, and then C′M is calculated from the L ^* a ^* b ^* value. Conversion to a 'Y'K' value is performed. That is, the color patch reflecting the correction profile MP created in step S140 is printed. In the subsequent step S160, the printer color is acquired by the color measurement of the color patch CP as in step S120. In step S170, the accuracy confirmation unit P1e calculates the amount of deviation between the printer color and the correction target value.

FIG. 6 is a graph showing the amount of deviation between the printer color and the target color. As shown in the figure, the lightness L ^* p of the printer color is close to the lightness L ^* opt of the correction target value DP in all lightnesses as compared with FIG. Also, the boundary value L ^* u and lightness L ^* p of the printer color in the low brightness area to follow the lightness L ^* t of the target color, the correction target value in the high-lightness region than the boundary value L ^* u Corresponding to the separation of the lightness L ^* opt of the DP from the lightness L ^* t of the target color, the lightness L ^* p of the printer color is also separated from the lightness L ^* t of the target color. In step S170, for each lightness L ^* in, a lightness difference ΔL ^* between the lightness L ^* p of the printer color and the lightness L ^* t of the target color is calculated. The lightness difference ΔL ^* corresponds to the color difference ΔE (CIE DE1976) when it is assumed that there is no deviation in the ^* a ^* b ^* values. Then, the average lightness difference [Delta] L ^* 1 of lightness difference [Delta] L ^* for all brightness, the average lightness difference [Delta] L ^* 2 of lightness difference [Delta] L ^* for the low-lightness region than the boundary value L ^* u, the boundary value L ^* u Also, the average brightness difference ΔL ^* 3 of the brightness difference ΔL ^* for the high brightness area is calculated as the shift amount.

In step S180, the accuracy confirmation unit P1e compares the average lightness differences ΔL ^* 1, ΔL ^* 2, ΔL ^* 3 with the threshold values T1, T2, T3, and the average lightness differences ΔL ^* 1, ΔL ^* 2, It is confirmed that ΔL ^* 3 is smaller than the threshold values T1, T2, and T3, respectively. In the present embodiment, the threshold values T1, T2, and T3 are set to 0.7, 0.5, and 2.0, respectively. In a lightness area lower than the boundary value L ^* u, correction is performed so that the lightness L ^* p of the printer color matches the lightness L ^* t of the target color. Therefore, the threshold value T2 corresponding to the area is a value that requires high accuracy. Set to On the other hand, since the correction is performed such that the lightness L ^* p of the printer color gradually deviates from the lightness L ^* t of the target color in the lightness area higher than the boundary value L ^* u, the threshold value T3 corresponding to the area is It is set to a value that requires relatively low accuracy. That is, the threshold value T3 is set so as to allow the difference between the correction target value DP and the target color in a lightness area higher than the boundary value L ^* u. The whole is set to a value between threshold values T2 and T3.

Having described the color accuracy determination for lightness L ^* is in the above, for the color values a ^* b ^* values in step S180, the printer color color values a ^* p, b ^* p and the target color of the color value a ^* t , B ^* t and a threshold value for each region delimited by the boundary values a ^* u, b ^* u, and the same accuracy determination is performed. In this embodiment, the accuracy of the L ^* a ^* b ^* values is individually determined. However, the color difference ΔE between the target color and the printer color for each color patch CP is calculated based on the Euclidean distance in the CIELAB space. The color difference ΔE may be determined as a threshold value. Of course, the shift amount may be grasped by other color difference formulas such as a color difference ΔE ₀₀ (CIE DE2000). In step S180, if color accuracy satisfying the threshold values T1, T2, T3, etc. is not obtained, the process returns to step S140, and the deviation amount between the current printer color acquired in step S160 and the correction target value DP. Then, the correction profile MP is created again. On the other hand, in step S180, if color accuracy satisfying the threshold values T1, T2, T3, etc. is obtained, the process is terminated.

  By executing the above loop processing, the color gamut where the amount of ink adhering is small and the exposure of the ground color is unavoidable, while allowing a certain amount of color difference from the target color, the amount of ink adhering is large. For a color gamut with less exposure, color deviation from the target color can be minimized. In addition, a certain color accuracy can be ensured as a whole. Accordingly, it is possible to create a correction profile MP that compensates for differences in color reproduction characteristics between the target printing machine 50 and the printer 20 and machine errors unique to the printer 20. The printer 20 itself simultaneously with color matching with the target printing machine 50. Calibration can also be realized. In white (C = M = Y = K = 0) on the CMYK image data, correction is performed so as to match the ground color of the print paper to be color-matched. The fact that the printer color matches the ground color of the printing paper means that none of the ink adheres to the printing paper. Therefore, white on the CMYK image data can be reproduced without attaching any ink. it can. As a result, even though a white portion is provided in the image data in anticipation of non-coloration, the impression that the ink is attached when the printing is actually performed and a grainy feeling is generated or the ink is wasted. Can be prevented.

In the above, the correction is repeated so that the predetermined color accuracy can be satisfied. However, the processing may be terminated when the predetermined number of repetitions is repeated. Further, based on the color difference ΔE between the paper of the printing paper to be color-matched on which the color patch CP is printed in step S110 and the paper of the standard printing paper on which the color patch is printed when the target profile TP is created. Alternatively, a threshold value T3 for a region with a higher brightness than the boundary value L ^* u may be set. This is because the magnitude of the shift amount of the area is largely controlled by the color difference ΔE between the two paper bases. Further, since the magnitude of the shift amount of the region is also governed by the adjustment coefficient κl = f (L ^* in), the threshold T3 may be set according to the function form of f (L ^* in). On the contrary, if the color accuracy satisfying the threshold value T3 is not obtained even if the correction is repeated a predetermined number of times, the function form of f (L ^* in) may be changed. Basically, if it is changed to f (L ^* in), which emphasizes the ability to follow the target color, color accuracy that satisfies the threshold value T3 can be easily obtained. Further, the boundary value L ^* u may be adjusted when color accuracy satisfying the threshold value T3 cannot be obtained even after repeating the correction a predetermined number of times.

It is a block diagram which shows schematic structure of a color correction apparatus. It is a flowchart which shows the flow of a color correction process. It is explanatory drawing which shows the outline | summary of a color correction process. It is a graph which shows the correction | amendment target value regarding a brightness. It is a graph which shows the correction | amendment target value regarding a color. It is a graph which shows the amount of color shift.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Computer, 11 ... HDD, 11a ... Program data, 12 ... CPU, 13 ... RAM, 14 ... USB I / F, 16 ... Input I / F, 20 ... Printer, 30 ... Colorimeter, 50 ... Target printer, P1 ... Color correction program, P1a ... Target color acquisition unit, P1b ... Printer color acquisition unit, P1c ... Correction target value setting unit, P1d ... Correction profile creation unit, P1e ... Accuracy confirmation unit, P2 ... Printer driver, P3 ... Colorimetry Machine driver, CP ... color patch, BP ... base profile, TP ... target profile, DP ... correction target value, MP ... correction target value.

Claims (5)

In a color correction apparatus that matches a color formed by attaching a coloring material to a recording medium to a predetermined target color,
In the low brightness area where the brightness is low compared to the predetermined first threshold, the color matching with the first threshold is performed in the high brightness area where the brightness is higher than the first threshold while following the color of the target. By interpolating between the lightness of the ground color of the target recording medium and obtaining each value, the lightness becomes closer to the lightness of the ground color as the lightness becomes higher, and the saturation is higher than the predetermined second threshold value. The high saturation area follows the target color, and in the low saturation area where the saturation is lower than the second threshold value, interpolation is performed between the second threshold value and the saturation of the ground color. By obtaining each value, a correction target value setting means for setting a correction target value that approaches the saturation of the ground color as the saturation decreases ,
Based on the amount of deviation between the color indicated by the color measurement value obtained by printing and measuring the color-matching recording medium and the color indicated by the correction target value obtained by the correction target value setting means A color correction apparatus comprising: correction means for correcting the adhesion amount of the material.   The correction means is configured such that a deviation amount between a color indicated by a color measurement value obtained by printing and colorimetry according to the corrected adhesion amount of the color material and a color indicated by the correction target value is smaller than a predetermined threshold value. The color correction apparatus according to claim 1, wherein the color correction apparatus is confirmed. The correction means is configured such that a deviation amount between the color indicated by the color measurement value obtained by printing and measuring the color according to the corrected adhesion amount of the color material and the color indicated by the correction target value is larger than a predetermined threshold value. The correction is performed based on the amount of deviation between the color indicated by the color measurement value obtained by printing and measuring the color according to the corrected adhesion amount of the color material and the color indicated by the correction target value. 2. The color correction apparatus according to 2. In a profile creation device that matches a color formed by attaching a coloring material to a recording medium to a predetermined target color,
In the low brightness area where the brightness is low compared to the predetermined first threshold, the color matching with the first threshold is performed in the high brightness area where the brightness is higher than the first threshold while following the color of the target. By interpolating between the lightness of the ground color of the target recording medium and obtaining each value, the lightness becomes closer to the lightness of the ground color as the lightness becomes higher, and the saturation is higher than the predetermined second threshold value. The high saturation area follows the target color, and in the low saturation area where the saturation is lower than the second threshold value, interpolation is performed between the second threshold value and the saturation of the ground color. By obtaining each value, a correction target value setting means for setting a correction target value that approaches the saturation of the ground color as the saturation decreases ,
Based on the amount of deviation between the color indicated by the color measurement value obtained by printing and measuring the color-matching recording medium and the color indicated by the correction target value obtained by the correction target value setting means A profile creation device comprising means for creating a correction profile for correcting the amount of adhesion of a material. In a color correction method for matching a color formed by attaching a color material to a recording medium with a predetermined target color,
In the low brightness area where the brightness is low compared to the predetermined first threshold, the color matching with the first threshold is performed in the high brightness area where the brightness is higher than the first threshold while following the color of the target. By interpolating between the lightness of the ground color of the target recording medium and obtaining each value, the lightness becomes closer to the lightness of the ground color as the lightness becomes higher, and the saturation is higher than the predetermined second threshold value. For the high saturation region, the value of each value is obtained by interpolating between the second threshold value and the saturation of the ground color in the low saturation region which is lower than the second threshold value while following the target color. By finding the correction target value that approaches the saturation of the ground color as the saturation decreases ,
Correcting the adhesion amount of the coloring material based on the amount of deviation between the color indicated by the colorimetric value obtained by printing and measuring the color-matching recording medium and the color indicated by the correction target value. Characteristic color correction method.

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