JP2009033601A - Color processing device, color converting device, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure a color reproduction area having an extent to some degree while absorbing a difference in the color reproduction region occurring among a plurality of devices. <P>SOLUTION: A color converting device 10 has: a color correction information generation section 20; and a color correction section 30. The color correction information generation section 20 has a target color acquisition section 21 for acquiring a target color; a dependent color acquisition section 22 for acquiring information on the dependent color of each device; an average color gamut generation section 23 for generating an average color gamut in the color gamut of each device; a color gamut compression section 24 for converting the target color to that in the average color gamut; and a correction LUT generation section 26 for generating the correction LUT for each device, based on the information on the dependent color of each device and the average color gamut target color. The color correction section 30 has: an image acquisition section 31 for acquiring an image; first and second color conversion sections 32, 33 for converting color by referring to the correction LUT for each device; and first and second image output sections 34, 35 for outputting an image for each device after color conversion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color processing device, a color conversion device, and a program.

In recent years, color devices such as digital cameras, color scanners, color printers, and color displays have become widespread, and the market demand for colors has increased. Especially in a system used in DTP (Desk Top Publishing) or the like, the demand is high. Therefore, CMS (color management system) in each device has become indispensable, and a device calibration technique has been developed to stably maintain color reproduction in the device.
By the way, a problem with such a color device is that a difference occurs in the color reproduction gamut, that is, the color gamut in each device. For example, when comparing the color gamut between a color display and a color printer, the difference is obvious. Also, there is a difference in color gamut between similar devices (for example, printers of the same model), and it is difficult for current calibration techniques to completely match the color reproduction of a plurality of printers of the same model. Various attempts have been made to stabilize color reproduction by color gamut compression techniques such as minimum color difference, saturation preservation, and brightness preservation for each device gamut, but complete color matching is very difficult.

Here, as a technique described in the publication, there is a method using a color gamut common to devices (see, for example, Patent Document 1 and Patent Document 2).
In the technique of Patent Document 1, a common color reproduction range common to a plurality of image forming apparatuses is generated, an input image signal is compressed into a common color reproduction range, and an image signal compressed into the common color reproduction range is converted into an image signal. Delivered to a plurality of image forming apparatuses. Then, in each image forming apparatus, an image based on the distributed image signal is formed and output, so that common color reproducibility can be obtained in each image forming apparatus.
In the technique of Patent Document 2, source-side device color data input to a CMS is converted into a device-independent color space, and the converted data is converted into a color reproduction region of a destination-side device A and a destination-side device B. Mapping is performed in a common color reproduction region that overlaps the other color reproduction region. Then, the color data mapped in the common color reproduction region is converted into color data for the destination side device.

JP 2003-60925 A Japanese Patent Laid-Open No. 10-79865

Here, in general, when there is a difference in the color gamut between a plurality of apparatuses, if the difference is absorbed using the common part of these color gamuts, the common part becomes narrow and reproduced. There was a possibility that a defect occurred in the image.
It is an object of the present invention to ensure a color reproduction range having a certain extent while absorbing a difference in color reproduction range that occurs between a plurality of apparatuses.

The invention according to claim 1 is acquired by the color gamut information acquisition unit that acquires the color gamut information about the plurality of first color gamuts that are the color gamuts of the plurality of devices, and the color gamut information acquisition unit. Based on the color gamut information, a color gamut specifying means for specifying a second color gamut that is an color outline having an average outline of each of the plurality of first color gamuts, and the color gamut specifying means A reproduction color specifying means for specifying the reproduced color in the specified second color gamut and a dependent color depending on the characteristics of each of the plurality of devices corresponding to the reproduced color specified by the reproduction color specifying means are determined. And a dependent color determining means.
According to a second aspect of the present invention, the color gamut information obtaining unit obtains color information in the first color space depending on the device and color information in the second color space independent of the device for each of the plurality of devices. The associated color gamut information is acquired, and the dependent color determining unit is configured to determine the dependent color depending on characteristics of each of the plurality of devices based on the color gamut information acquired by the color gamut information acquiring unit. The color processing apparatus according to claim 1, wherein:
According to a third aspect of the present invention, the color gamut specifying unit is configured such that each of the plurality of devices associated with color information in the first color space in the color gamut information acquired by the color gamut information acquiring unit. An average color information is obtained by performing a predetermined average operation on a plurality of pieces of color information in the second color space, and the second color gamut is specified by prediction based on the average color information. The color processing apparatus according to Item 2.
According to a fourth aspect of the present invention, the color gamut specifying unit obtains the plurality of first color gamuts based on the color gamut information acquired by the color gamut information acquiring unit, and the plurality of first color gamuts. The color processing apparatus according to claim 1, wherein the second color gamut is specified by performing a predetermined average operation on a plurality of color information respectively included in and corresponding to the color information.
According to a fifth aspect of the present invention, the color gamut specifying unit performs an average operation on the plurality of first color gamuts according to the plurality of devices, thereby obtaining the second color gamut. The color processing apparatus according to claim 1, wherein the color processing apparatus is specified.
According to a sixth aspect of the invention, there is provided target color information acquisition means for acquiring target color information in which color information in the first color space depending on the device is associated with color information in the second color space not depending on the device. Further, the reproduction color specifying means specifies the reproduction color based on color information in the second color space included in the target color information acquired by the target color information acquisition means. The color processing apparatus according to claim 1.
According to a seventh aspect of the present invention, the color information in the first color space included in the target color information is used as a grid point, and the grid point corresponds to the reproduction color specified from the target color information. The color processing apparatus according to claim 6, further comprising a generating unit configured to generate a lookup table in which information about the dependent color is set as a correction coefficient.
According to an eighth aspect of the present invention, the generation unit sets information on the four-dimensional dependent colors of cyan, magenta, yellow, and black for the four-dimensional grid points of cyan, magenta, yellow, and black. The color processing apparatus according to claim 7, wherein the lookup table is generated.
The invention according to claim 9 is characterized in that the generation means further generates information for correcting a gradation of at least one of cyan, magenta, yellow, and black. Device.
The invention according to claim 10 is acquired by the color gamut information acquiring unit that acquires the color gamut information relating to the plurality of first color gamuts that are the color gamuts of the plurality of devices, and the color gamut information acquiring unit. Based on the color gamut information, a color gamut specifying means for specifying a second color gamut that is an color outline having an average outline of each of the plurality of first color gamuts, and the color gamut specifying means The reproduction color specifying means for specifying the reproduction color in the specified second color gamut, and the reproduction color corresponding to the reproduction color according to the input of the reproduction color specified by the reproduction color specification means A color conversion apparatus comprising correction means for correcting to dependent colors depending on the characteristics of a plurality of apparatuses.
The invention according to claim 11 is based on a function of acquiring color gamut information related to a plurality of first color gamuts, which is a color reproduction gamut of each of a plurality of devices, and the acquired color gamut information. A function of specifying a second color gamut, which is a color reproduction gamut having an average outline of each of the plurality of first color gamuts, and a function of specifying a reproduction color within the specified second color gamut; A program for realizing a function of determining a dependent color depending on characteristics of each of the plurality of devices corresponding to the specified reproduction color.

The invention of claim 1 has an effect that it is possible to secure a color gamut having a certain extent while absorbing a difference in color gamut generated between a plurality of apparatuses.
According to the second aspect of the present invention, as compared with the case where the present configuration is not provided, a process for securing a color reproduction range and determining a device-dependent color corresponding to a certain color in the color reproduction range is performed efficiently. Has the effect of being able to.
The invention of claim 3 has the effect that the process of ensuring a color reproduction range having a certain size can be performed at a high speed as compared with the case where this configuration is not provided.
According to the fourth aspect of the present invention, when a color gamut having a certain extent is ensured as compared with the case where the present configuration is not provided, there is an effect that it is possible to make it difficult for a step to be generated in the outline.
The invention of claim 5 has an effect that a color reproduction gamut close to the color reproduction gamut of any device can be secured.
The invention according to claim 6 can appropriately specify the color that is the basis for determining the device-dependent color within the color gamut having a certain extent as compared with the case where the present configuration is not provided. It has the effect of being able to.
The invention of claim 7 has an effect that colors output by a plurality of apparatuses having differences in color gamut can be matched to some extent.
The invention according to claim 8 has an effect that colors output by a plurality of apparatuses that express colors in four colors of cyan, magenta, yellow, and black and have different color gamuts can be matched to some extent.
According to the ninth aspect of the present invention, it is possible to increase the degree of coincidence of colors output by a plurality of apparatuses having different color gamuts in comparison with the case where the present configuration is not provided. Have
The invention according to claim 10 can secure a color gamut having a certain extent while absorbing a difference in color gamut generated between a plurality of apparatuses, and perform color conversion into the color gamut. It has the effect.
According to the eleventh aspect of the present invention, it is possible to secure a color gamut having a certain extent while absorbing a difference in color gamut generated between a plurality of apparatuses.

The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described in detail below with reference to the accompanying drawings.
First, an outline of the present embodiment will be described.
When there are a plurality of image output apparatuses (for example, printers), the color reproduction in the output product usually varies due to the difference in the color gamut due to machine differences. As one of the solutions, there is a method in which color gamuts of a plurality of image output apparatuses are obtained and color correction is performed within a common color gamut (AndGamut) which is a common part of all of these. However, when the color gamuts of a plurality of image output devices are greatly different, it is conceivable that the common color gamut becomes narrow and the color reproduction results are not good.
Therefore, in the present embodiment, an average color gamut is obtained from the color reproduction gamuts of a plurality of image output apparatuses, and color reproduction is performed within this average color gamut. As a result, even if the color gamut is different among a plurality of apparatuses, the color reproduction range of the output product can be secured while suppressing the machine difference.

  The “average color gamut” here is not limited to the color gamut obtained by performing a normal average operation on the color reproduction gamuts of a plurality of apparatuses, and a weight is set for each apparatus. It may be a color gamut obtained by an average calculation according to a weight (weighted average calculation). Alternatively, for example, an “average color gamut” may be set using a regression model without using an average calculation. In the following, for convenience, the “average color gamut” is simplified and referred to as “average color gamut”, but this “average color gamut” is similarly obtained based on the average calculation (including the weighted average calculation). It shall include the color gamut and the color gamut obtained using the regression model.

Hereinafter, specific embodiments for realizing such an outline will be described.
FIG. 1 is a block diagram showing a functional configuration of the color conversion apparatus according to the present embodiment.
The color conversion apparatus 10 according to the present embodiment is connected to a plurality of image output apparatuses via, for example, a network (not shown). Here, for simplicity, the first device and the second device are used as the image output apparatuses. Consider two of the devices. The color conversion apparatus 10 is roughly divided into a color correction information generation unit 20 and a color correction unit 30.

Among these, the color correction information generation unit 20 includes a target color acquisition unit 21, a dependent color acquisition unit 22, an average color gamut generation unit 23, a color gamut compression unit 24, an average color gamut target color storage unit 25, And a correction LUT generation unit 26.
The target color acquisition unit 21 acquires target color information as a target value indicating the ideal state of the target device, for example. In the present embodiment, the target color acquisition unit 21 is provided as an example of the target color information acquisition unit.
The dependent color acquisition unit 22 acquires device-dependent color information reflecting the color output characteristics of each device. In the present embodiment, the dependent color acquisition unit 22 is provided as an example of the color gamut information acquisition unit.
The average color gamut generator 23 generates an average color gamut that is an average color gamut of the color gamut of each device based on the device-dependent color information acquired by the dependent color acquisition unit 22. However, here, the “average color gamut” does not mean only a complete average as described above. For example, it may be a color gamut obtained by a predetermined average calculation such as an average obtained by weighting the color gamut of each device. Alternatively, a color gamut obtained by, for example, a calculation using a regression model may be used without using the average calculation. In the present embodiment, an average color gamut generating unit 23 is provided as an example of the color gamut specifying means.

The color gamut compression unit 24 converts the target color into a target color within the average color gamut (hereinafter referred to as “average color gamut target color”) based on the target color information acquired by the target color acquisition unit 21. In this embodiment, the average color gamut target color is used as an example of the reproduction color, and the color gamut compression unit 24 is provided as an example of the reproduction color specifying unit.
The average color gamut target color storage unit 25 stores information on the average color gamut target color generated by the color gamut compression unit 24.
The correction LUT generation unit 26 performs color correction based on the device-dependent color information acquired by the dependent color acquisition unit 22 and the average color gamut target color information stored in the average color gamut target color storage unit 25. A lookup table (hereinafter referred to as “correction LUT”) is generated. This correction LUT is referred to in the color correction processing of the color correction unit 30, and a correction LUT for the first device and a correction LUT for the second device are generated. In the present embodiment, the correction LUT generation unit 26 is provided as an example of the dependent color determination unit and as an example of a generation unit that generates a lookup table.

The color correction unit 30 includes an image acquisition unit 31, a first color conversion unit 32, a second color conversion unit 33, a first image output unit 34, and a second image output unit 35.
The image acquisition unit 31 acquires an image from, for example, a network (not shown).
The first color conversion unit 32 refers to the correction LUT for the first device, and converts color information in the image acquired by the image acquisition unit 31. In the present embodiment, the first color conversion unit 32 is provided as an example of a correction unit that corrects a reproduced color to a dependent color.
The second color conversion unit 33 refers to the correction LUT for the second device and converts the color information in the image acquired by the image acquisition unit 31. In the present embodiment, the second color conversion unit 33 is provided as an example of a correction unit that corrects a reproduced color to a dependent color.
The first image output unit 34 outputs the image whose color information has been converted by the first color conversion unit 32 to the first device.
The second image output unit 35 outputs the image whose color information has been converted by the second color conversion unit 33 to the second device.

Next, the operation of the color conversion apparatus 10 in the present embodiment will be described.
FIG. 2 is a flowchart showing the operation of the color correction information generation unit 20 of the color conversion apparatus 10.
In the color correction information generation unit 20, the target color acquisition unit 21 first acquires target device color data (hereinafter referred to as "target device base data") (step 201). The target device base data is an example of target color information. Next, the dependent color acquisition unit 22 performs color data representing the color output characteristics of the first device (hereinafter referred to as “first device base data”) and color data representing the color output characteristics of the second device. (Hereinafter referred to as “second device base data”) (step 202). These device base data are examples of color gamut information. Then, the average color gamut generation unit 23 is an average color that is an average color gamut of the color gamut of the first device and the color gamut of the second device based on the first device base data and the second device base data. A region is generated (step 203). Further, the color gamut compression unit 24 converts the target device base data acquired in step 201 into data related to the target color in the average color gamut generated in step 203 (hereinafter referred to as “average color gamut base data”). This is stored in the gamut target color storage unit 25 (step 204). Further, the correction LUT generation unit 26 generates the correction LUT for the first device using the first device base data and the average color gamut base data, and generates the second device base data and the average color gamut base data. Using this, a correction LUT for the second device is generated (step 205).

Hereinafter, the processing contents of each step will be described in detail.
In step 201, the target color acquisition unit 21 calculates an absolute target color that is a target color in the present system. The absolute target color here is, for example, a target value indicating the ideal state of the target device, and its color reproduction range is preferably larger than the color reproduction range of a general device. This is because when the target value is narrower than the color gamut, the ability of the device to be corrected cannot be fully used by calibration or color correction. Here, color correction such as calibration is performed based on the correction LUT. This correction LUT is generated by setting a device-independent target value (for example, L * a * b *) for the input grid point, and obtaining a value in the color space of the device that satisfies this target value as the output grid point. Is done.
The simplest system configuration in this case is one-dimensional color correction (single-color calibration), and its chromaticity value and density value for the device color space of a single-color gradation indicated by a one-dimensional LUT (TRC: Tone Reproduction Curve). Or the thing according to it becomes a target value. Similarly, in calibration and color correction for three dimensions (for example, CMY and RGB) and four dimensions (for example, CMYK), the chromaticity values (for example, L * a * b *) for multidimensional grid points of CMY (K) are used. It will be assigned as a target value.

Note that this target value may be held and stored in advance. However, for example, when the correction grid points will have a 4-bit grid point data to CMYK4 colors, the 17 ^four the number of data. In such a case, every time the target color is changed, it is very laborious and inefficient to output the data by the target device and measure the color. Therefore, a method for obtaining the target color by holding the target device color data (target device base data) more than a certain number (for example, about 1000 patches) and predicting the grid point data from the target device base data is considered. It is done. As a result, it is not necessary to previously hold all target colors for the grid points, and color correction values can be determined efficiently even when the target color (target device) is changed.

Here, the target device base data is data indicating the output color of the target device when performing color correction.
FIG. 3 shows an example of the target device base data. This is an example of a CMYK four-color printer. In this case, the target device base data is a set of data pairs (base data) of device-dependent data (CMYK) and corresponding device-independent data (L * a * b *). However, regarding device-independent data, a general L * a * b * is taken as an example here, but the present invention is not limited to this. For example, data in a color system classified into tristimulus values XYZ, uniform color space L * u * v *, etc., or data expressed by polynomial approximation such as (Lab) = F (CMYK) In addition, data represented by Neugebauer, Kubelka-Munk, Lambert Bale, etc. as physical model formulas, or data converted by an ICC profile, etc. may be used, and a data pair indicating the characteristics of the device can be generated Anything is acceptable. In general, the number of data pairs is not limited, but a data number of about 200 to 1600 is desirable as a problem in color accuracy and system configuration. Thus, the output characteristics of the target device can be grasped, and the output color of the device with respect to the correction target point can be predicted.

Next, in step 202, the dependent color acquisition unit 22 acquires, for each of the first device and the second device, the first device base data and the second device base data that clarify the color output characteristics of each device. To do. The first device base data and the second device base data may be acquired by measuring a patch output from each device, or may be acquired from profile information of each device.
FIG. 4A shows an example of the first device base data, and FIG. 4B shows an example of the second device base data. These are examples of a CMYK four-color printer. Further, as can be seen from the figure, the format of the first device base data and the second device base data is the same as the format of the target device base data. In this case, the first device base data and the second device base data include CMYK and the like that are similar to the device-dependent color space, and L * a * b * and the like that are similar to the device-independent color space that is paired therewith. Necessary and sufficient number of data pairs (base data) as combinations are prepared. As described in the description of the target color base data, the type of the base data is not limited to this, and any data can be used as long as a data pair indicating the characteristics of the device can be generated. The number is not limited, but a data number of about 200 to 1600 is desirable as a problem in color accuracy and system configuration.

  Subsequently, in step 203, the average color gamut generation unit 23 calculates an average color gamut of the color gamut of the first device and the color gamut of the second device based on the first device base data and the second device base data. Find the average color gamut. Here, all base data acquired by the target device is used. The average color gamut generated here represents an average outline of the color gamut of the first device and the color gamut of the second device.

FIG. 5 is a diagram showing an average color gamut generation method by the average color gamut generation unit 23.
Of these, (a) performs a predetermined average operation on each device base data acquired by the dependent color acquisition unit 22 to obtain an average value (average color information), and obtains an average color gamut by prediction based on the average value. Shows how. That is, the average color gamut is specified by taking an average of the first device base data and the second device base data and predicting a point between the average points.
Further, (b) obtains the color gamut for each apparatus from the device base data acquired by the dependent color acquisition unit 22, obtains an average value by performing a predetermined average operation on the points included in and corresponding to each color gamut, A method is shown in which a color gamut composed of these average values is used as the average color gamut. That is, the average of the points corresponding to the color gamut of the first device and the color gamut of the second device is taken and the average point is connected to specify the average color gamut.

  FIG. 6 shows the relationship among the average color gamut generated by such a method, the color gamut of the first device, and the color gamut of the second device. Also from this figure, it can be seen that the average color gamut has an average outline of the color gamut of the first device and the color gamut of the second device.

  Subsequently, in step 204, the color gamut compressing unit 24 sets the target color for the correction point when performing the calibration and color correction calculated in step 201 within the average color gamut (including the boundary) obtained in step 203. Convert to color. This conversion may be realized by using various proposed color gamut compression methods. In the present embodiment, a minimum color difference GMA (Gamut Mapping Algorithm) for converting from a target color point to a point in the average color gamut that minimizes the color difference is used, but the present invention is not limited to this. Depending on the intended use, it may be realized by a color gamut compression method based on saturation preservation and lightness preservation.

FIG. 7 is a diagram illustrating a target color conversion method by the color gamut compression unit 24.
As described above, since the color gamut of the target color is set sufficiently wide, the color gamut of the target color is compressed to the average color gamut. An arrow indicates the conversion direction of the color on the boundary of the target color gamut to the color within the average color gamut.

Further, by performing such color gamut compression, the target device base data is converted into base data relating to the average color gamut target color (hereinafter referred to as “average color gamut base data”).
FIG. 8 shows an example of average color gamut base data. As can be seen from the figure, the format of the average color gamut base data is the same as the format of the target device base data, the first device base data, and the second device base data. The content of the average color gamut base data is obtained by changing the value of L * a * b * in the target device base data. For example, for (C, M, Y, K) = (0, 0, 0, 0), in the target device base data, (L *, a *, b *) = (L01, a01, b01). However, in the average color gamut base data, (L *, a *, b *) = (L01 ′, a01 ′, b01 ′). Here, (L01 ′, a01 ′, b01 ′) indicates a point where (L01, a01, b01) is converted by color gamut compression. When the color difference minimum GMA is used, (L01 ′, a01 ′, b01 ′) is determined by (L01, a01, b01). Therefore, (L01 ′, a01 ′, b01 ′) = f (L01 , A01, b01).

  In step 205, the correction LUT generation unit 26 generates a correction LUT. Specifically, a device-dependent color in each device for the average color gamut target color is obtained. That is, CMYK that reproduces the average color gamut target color in the first device is predicted for all target grid points based on the first device base data. Various proposals have been made for this prediction method. Although it does not specifically limit, it is good to predict using the method of Unexamined-Japanese-Patent No. 10-262157, for example. The device-dependent color predicted here becomes a correction value (correction coefficient in the correction LUT for the first device) for each lattice point. The second device performs the same process as the first device to obtain a correction LUT for the second device.

FIG. 9 shows an example of the correction LUT. (A) is a correction LUT for the first device, and (b) is a correction LUT for the second device.
In the correction LUT for the first device shown in (a), C-in, M-in, Y-in, and K-in are C, M, Y, and K of the average color gamut base data shown in FIG. Corresponding to As C-out, M-out, Y-out, and K-out, C in the first device for reproducing L *, a *, and b * in the average color gamut base data shown in FIG. M, Y, and K are set. That is, (C11, M11, Y11, K11) is (C, M, Y, K11) in the first device for reproducing (L *, a *, b *) = (L01 ′, a01 ′, b01 ′). K). This is obtained from the first device base data of FIG.

  Further, in the correction LUT for the second device shown in (b), C-in, M-in, Y-in, and K-in are C, M, and C of the average color gamut base data shown in FIG. It corresponds to Y and K. As C-out, M-out, Y-out, and K-out, C in the second device for reproducing L *, a *, and b * in the average color gamut base data shown in FIG. M, Y, and K are set. That is, (C21, M21, Y21, K21) is (C, M, Y, K) in the second device for reproducing (L *, a *, b *) = (L01 ′, a01 ′, b01 ′). K). This is obtained from the second device base data of FIG.

  The correction LUT obtained in this way realizes correction for each device for performing color reproduction in the average color gamut. That is, the image acquisition unit 31 acquires the input image. Then, the first color conversion unit 32 performs color conversion with reference to the correction LUT for the first device obtained here, thereby generating an image for the first device. In addition, the second color conversion unit 33 generates an image for the second device by referring to the correction LUT for the second device. Thereafter, the first image output unit 34 outputs an image for the first device to the first device, and the second image output unit 35 outputs an image for the second device to the second device. In this way, by outputting an image for each device by each device, color reproduction within the average color gamut is theoretically achieved in the printed matter output from the first device and the second device.

  However, when referring to the correction LUT, interpolation processing is performed for colors between grid points, but nonlinearity of output characteristics between grid points becomes a problem, and in this sense, color reproduction is incomplete. As a countermeasure, it is conceivable to reduce the lattice point interval of the correction LUT so as to make the color reproduction range finer and have more correction values. However, since the amount of memory and the amount of calculation of correction values are large, it is desirable to select appropriately for each target system for color correction in a balance between processing accuracy and processing cost. Further, by performing reproduction in the average color gamut for each point of the input image in the same manner as in the present method, more accurate color correction can be performed. On the other hand, by applying feedback that reproduces the average color gamut to the correction LUT, it can be configured with a realistic processing time, and not only software processing but also application to hardware calibration and color correction mounting is conceivable.

In addition, although the configuration of a four-dimensional LUT (CMYK) is assumed here, the number of memories considered to be a problem in the four-dimensional LUT can be reduced and the amount of calculation can be reduced by the configuration of the three-dimensional LUT (CMY) and K single color. Therefore, color correction can be realized with a lower cost process.
Furthermore, in addition to the multi-dimensional table, by providing a one-dimensional LUT (TRC) for each color in the subsequent stage, it is possible to compensate for the gradation that is a problem in the LUT processing and to perform more accurate color conversion processing. .
In the present embodiment, a color printer is assumed as the image output device. However, for example, a color display may be used, and in this case, an LUT having RGB three-dimensional lattice points may be used. Further, the lattice points of the LUT may be four-dimensional or more lattice points using special colors.
Furthermore, LUT lattice points that conform to the ICC profile standard may be adopted.

  In this embodiment, the color correction information generation unit 20 generates a correction LUT, and the color correction unit 30 performs color conversion with reference to the correction LUT. However, the present invention is not limited to this mode. . That is, based on the first device base data, the second device base data, and the average color gamut target color acquired by the color correction information generation unit 20, the color correction unit 30 performs direct color conversion for each input pixel of the image. Various configurations may be adopted.

By the way, some of the colors included in the average color gamut generated in the present embodiment are not included in the color gamut of the first device or the second device.
FIG. 10 is a diagram for explaining this.
Among these, (a) shows the relationship between the average color gamut and the color gamut of the first device. A color that is included in the average color gamut and is not included in the color gamut of the first device needs to be converted into a color in the color gamut of the first device by prediction, as indicated by an arrow. If a common color gamut of the color gamut of the first device and the color gamut of the second device is used, such prediction is not necessary. However, when the average color gamut is used as in the present embodiment, a wider color gamut than the common color gamut can be obtained as shown by the hatched lines in the figure.
(B) shows the relationship between the average color gamut and the color gamut of the second device. A color that is included in the average color gamut and not included in the color gamut of the second device needs to be converted into a color in the color gamut of the second device by prediction, as indicated by an arrow. If a common color gamut of the color gamut of the first device and the color gamut of the second device is used, such prediction is not necessary. However, when the average color gamut is used as in the present embodiment, a wider color gamut than the common color gamut can be obtained as shown by the hatched lines in the figure.

  Although the configuration for two devices has been described here, it is not necessary to have two devices, and a configuration for a plurality of devices is also conceivable. Similarly, when there are a plurality of devices, an average color gamut of the plurality of devices may be obtained and color correction may be performed within the average color gamut. As an application example, a deployment to a cluster printing system in which a plurality of printers are connected to a network can be considered.

FIG. 11 is a diagram showing a configuration example of such a cluster printing system.
As shown in the figure, this cluster printing system is configured by connecting a print server 40 and printers 41a, 41b, 41c,..., 41f via a network. In this configuration, the print server 40 functions as the color conversion device 10 of FIG. That is, the average color gamut is obtained based on the color gamuts of the printers 41a, 41b, 41c,..., 41f, and the colors output from the printers 41a, 41b, 41c,. As a result, the colors of the output products in the printers 41a, 41b, 41c,.

As another system configuration, development to a multi-engine printer having two engines in one printer housing is also conceivable.
FIG. 12 is a diagram showing a configuration example of such a multi-engine printer.
As shown in the figure, the multi-engine printer 50 includes a first image forming unit 51 and a second image forming unit 52, which have the same configuration. Therefore, the first image forming unit 51 will be described. The first image forming unit 51 includes an image forming unit including a photosensitive drum 61, a charger 62, a laser exposure unit 63, a developing device 64, a primary transfer roll 65, and a drum cleaner 66. A unit, an intermediate transfer belt 67, a secondary transfer roll 68, and a fixing device 69 are provided. The image forming units are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 67 in the order of yellow (Y), magenta (M), cyan (C), and black (K). The first image forming unit 51 includes a laser control device 71, a toner amount detection sensor 72, and a calculation device 73. Furthermore, as a configuration common to the first image forming unit 51 and the second image forming unit 52, the multi-engine printer 50 includes a paper tray 53, a colorimetric sensor 54, a color processing device 55, an unevenness correction device 56, An image processing device 57 is provided.

  The image forming process of the multi-engine printer 50 shown in FIG. 12 is roughly as follows. That is, when image data is input to the image processing device 57 from a PC or the like, the image processing device 57 performs predetermined image processing on the image data, and the first image forming unit 51 or the second image forming unit 52 creates the image data. Perform image work. Here, since the image forming processes of the first image forming unit 51 and the second image forming unit 52 are the same, the first image forming unit 51 will be described. The image processing device 57 converts the image data into Y, M, C, K. Are converted into color material gradation data of the four colors and output to the laser control device 71. The laser control device 71 converts the color material gradation data of the four colors Y, M, C, and K to laser exposure corresponding to each color. Output to the device 63.

The laser exposure device 63 irradiates the photosensitive drum 61 with an exposure beam in accordance with the input color material gradation data. After the surface of the photosensitive drum 61 is charged by the charger 62, the surface is scanned and exposed by the laser exposure device 63 to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of Y, M, C, and K by the developing device 64.
The toner image formed on the photosensitive drum 61 in this way is primarily transferred to the intermediate transfer belt 67 by the primary transfer roll 65. On the other hand, the residual toner on the photosensitive drum 61 is scraped off by the drum cleaner 66.
The toner image primarily transferred to the intermediate transfer belt 67 is conveyed to a secondary transfer position as the intermediate transfer belt 67 rotates. At this time, the toner amount detection sensor 72 detects the toner amount on the intermediate transfer belt 67, the arithmetic device 73 performs arithmetic operations such as image quality adjustment, and the result is output to the laser control device 71. On the other hand, a predetermined size of paper is supplied from the paper tray 53 and conveyed to the secondary transfer position. At the secondary transfer position, the toner image held on the intermediate transfer belt 67 is electrostatically transferred to the sheet by the pressing of the secondary transfer roll 68.
Thereafter, the sheet on which the toner image has been transferred is conveyed to the fixing device 69, and the toner image is fixed on the sheet by receiving a fixing process with heat and pressure by the fixing device 69. The sheet on which the fixed image is formed is discharged outside the multi-engine printer 50 by a discharge roll (not shown).

  In such a multi-engine printer 50, in the present embodiment, the color processing device 55 functions as the color correction information generation unit 20 in FIG. 1, and the image processing device 57 functions as the color correction unit 30 in FIG. . That is, the colorimetric sensor 54 performs colorimetry on the patch printed by the first image forming unit 51 and the patch printed by the second image forming unit 52, and the colorimetric results are respectively measured as the first device base data and the second This is transmitted to the color processing device 55 as device base data. Accordingly, the color processing device 55 generates a correction LUT for matching the color of the first image forming unit 51 and the color of the second image forming unit 52. The unevenness correction device 56 also performs unevenness correction based on the color measurement result. Then, the image processing device 57 refers to the correction LUT generated by the color processing device 55 and converts the input color signal into the color signal for the first image forming unit 51 and the color signal for the second image forming unit 52. And convert to

  For example, when printing even-numbered pages and odd-numbered pages alternately with different engines using such a multi-engine printer 50, the color difference between the engines is more severe than when using other color printing systems. It becomes. In the present embodiment, by using the average color gamut, the color difference between the engines can be easily suppressed. Therefore, an effect can be expected even in the configuration of the multi-engine printer 50. Moreover, if the color gamut of a certain device is small or a common color gamut is obtained for various devices, the common part may become extremely narrow. In this case, it has been a problem that the reproduced color gamut becomes narrow, but a certain degree of improvement can be expected by using the average color gamut. Furthermore, in this configuration, since there are two types of engines, a situation where only one engine is replaced due to a failure or the like can be considered. The method according to the present embodiment can cope with the output difference due to the change over time caused by such an old and new engine, and can be expected as a technique for extending the life of the machine. In addition, it has an advantage in terms of processing cost compared to a method for obtaining a common color gamut, and can be expected, for example, as a real-time color correction method.

By the way, the color correction information generation processing and color conversion processing in this embodiment may be realized by a general-purpose computer. Therefore, the hardware configuration will be described assuming that these processes are realized by the computer 90.
FIG. 13 is a diagram illustrating a hardware configuration of the computer 90.
As shown in the figure, the computer 90 includes a CPU (Central Processing Unit) 91 as a calculation means, a main memory 92 as a storage means, and a magnetic disk device (HDD: Hard Disk Drive) 93. Here, the CPU 91 executes various types of software such as an OS (Operating System) and applications to realize the above-described functions. The main memory 92 is a storage area for storing various software and data used for execution thereof, and the magnetic disk device 93 is a storage area for storing input data for various software, output data from various software, and the like. .
Further, the computer 90 includes a communication I / F 94 for performing communication with the outside, a display mechanism 95 including a video memory and a display, and an input device 96 such as a keyboard and a mouse.

  It should be noted that the program for realizing the present embodiment may be provided by being stored in a recording medium such as a CD-ROM, as well as provided by communication means.

It is the block diagram which showed the function structure of the color conversion apparatus in embodiment of this invention. It is the flowchart which showed the operation example of the color correction information generation part of the color conversion apparatus in embodiment of this invention. It is the figure which showed an example of the target device base data used by embodiment of this invention. It is the figure which showed an example of the 1st device base data and 2nd device base data which are used by embodiment of this invention. It is a figure for demonstrating the production | generation method of the average color gamut in embodiment of this invention. It is a figure for demonstrating the average color gamut produced | generated in embodiment of this invention. It is a figure for demonstrating compression to the average color gamut of the target color in embodiment of this invention. It is the figure which showed an example of the average color gamut base data obtained when the target color is compressed to the average color gamut in the embodiment of the present invention. It is the figure which showed an example of the correction | amendment LUT for 1st devices and the correction | amendment LUT for 2nd devices produced | generated by embodiment of this invention. It is a figure for demonstrating the relationship between the average color gamut produced | generated by embodiment of this invention, the color gamut of a 1st device, the color gamut of a 2nd device, and a common color gamut. It is the figure which showed the structural example of the cluster printing system with which embodiment of this invention is applied. 1 is a diagram illustrating a configuration example of a multi-engine printer to which an embodiment of the present invention is applied. It is a hardware block diagram of the computer which can apply embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Color conversion apparatus, 20 ... Color correction information generation part, 21 ... Target color acquisition part, 22 ... Dependence color acquisition part, 23 ... Average color gamut generation part, 24 ... Color gamut compression part, 25 ... Average color gamut target color Storage unit 26 ... correction LUT generation unit 30 ... color correction unit 31 ... image acquisition unit 32 ... first color conversion unit 33 ... second color conversion unit 34 ... first image output unit 35 ... second Image output unit

Claims (11)

Color gamut information acquisition means for acquiring color gamut information relating to a plurality of first color gamuts that are respective color gamuts of a plurality of devices;
Based on the color gamut information acquired by the color gamut information acquisition unit, a color gamut that specifies a second color gamut that is an color reproduction gamut having an average outline of each of the plurality of first color gamuts Specific means,
Reproduction color specifying means for specifying a reproduction color in the second color gamut specified by the color gamut specifying means;
A color processing apparatus comprising: dependent color determining means for determining a dependent color depending on characteristics of each of the plurality of apparatuses corresponding to the reproduced color specified by the reproduced color specifying means. The color gamut information acquisition unit acquires the color gamut information in which the color information in the first color space depending on the device and the color information in the second color space independent of the device are associated with each of the plurality of devices. And
2. The dependent color determining unit determines the dependent color depending on characteristics of each of the plurality of devices based on the color gamut information acquired by the color gamut information acquiring unit. The color processing apparatus as described.   The color gamut specifying unit includes a plurality of units in the second color space for each of the plurality of devices associated with color information in the first color space in the color gamut information acquired by the color gamut information acquiring unit. 3. The color processing apparatus according to claim 2, wherein average color information is obtained by performing a predetermined average operation on the color information, and the second color gamut is specified by prediction based on the average color information.   The color gamut specifying unit obtains the plurality of first color gamuts based on the color gamut information acquired by the color gamut information acquiring unit, and includes a plurality of corresponding ones respectively included in the plurality of first color gamuts. The color processing apparatus according to claim 1, wherein the second color gamut is specified by performing a predetermined average operation on the color information.   The said color gamut specification means specifies the said 2nd color gamut by performing the average calculation which weighted according to the said several apparatus with respect to these 1st color gamut. The color processing apparatus according to 1. A target color information acquisition unit configured to acquire target color information in which the color information in the first color space depending on the device is associated with the color information in the second color space not depending on the device;
2. The reproduction color specifying unit specifies the reproduction color based on color information in the second color space included in the target color information acquired by the target color information acquisition unit. The color processing apparatus as described.   Color information in the first color space included in the target color information is set as a grid point, and information regarding the dependent color corresponding to the reproduced color specified from the target color information is set as a correction coefficient for the grid point. 7. The color processing apparatus according to claim 6, further comprising generating means for generating the look-up table.   The generation means generates the lookup table in which information about the dependent colors of cyan, magenta, yellow, and black is set for the four-dimensional grid points of cyan, magenta, yellow, and black. 8. The color processing apparatus according to claim 7, wherein   The color processing apparatus according to claim 8, wherein the generation unit further generates information for correcting a gradation of at least one of cyan, magenta, yellow, and black. Color gamut information acquisition means for acquiring color gamut information relating to a plurality of first color gamuts that are respective color gamuts of a plurality of devices;
Based on the color gamut information acquired by the color gamut information acquisition unit, a color gamut that specifies a second color gamut that is an color reproduction gamut having an average outline of each of the plurality of first color gamuts Specific means,
Reproduction color specifying means for specifying a reproduction color in the second color gamut specified by the color gamut specifying means;
Correction means for correcting the reproduced color to a dependent color depending on the characteristics of each of the plurality of devices corresponding to the reproduced color in response to the input of the reproduced color identified by the reproduced color identifying unit. A color conversion device characterized by that. On the computer,
A function of acquiring color gamut information relating to a plurality of first color gamuts that are color reproduction gamuts of a plurality of devices;
A function for specifying a second color gamut, which is a color reproduction gamut having an average outline of each outline of the plurality of first color gamuts, based on the acquired color gamut information;
A function for specifying a reproduction color within the specified second color gamut;
A program for realizing a function of determining a dependent color depending on characteristics of each of the plurality of devices corresponding to the specified reproduction color.

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