JP6446898B2 - Image processing apparatus, image forming apparatus, image processing method, and program thereof - Google Patents

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, an image processing method, and a program thereof.

  In the color management system, there is an ICC (International Color Consortium) profile as an industry standard data format used for color conversion. In color conversion using an ICC profile, first, an input image signal from an input device such as a scanner or a digital camera is converted into a device-independent signal using an input device profile (input profile). Then, the device-independent signal is converted into an output image signal using an output device profile (output profile). An output device such as a printer or a multifunction peripheral performs output based on the output image signal.

Here, conversion to an output image signal for an output device is performed by, for example, ICC Specification ICC. 1: 2010 (Profile version 4.3.0.0), FIG. 2 d). The lattice points of the CLUT used in this conversion method are the entire L ^* a ^* b ^* color space (0 ≦ L ^* ≦ 100, −128 ≦ a ^* ≦ 127, −128 ≦ b ^* ≦ 127), or XYZ The entire color space (0 ≦ X ≦ 1.0, 0 ≦ Y ≦ 1.0, 0 ≦ Z ≦ 1.0) is arranged uniformly. For this reason, there is a problem that the number of grid points in the color gamut that can be reproduced by an existing input / output device is small, and the color reproduction accuracy is poor. Therefore, in order to realize good color reproduction, a technique for adjusting the arrangement of grid points used in an output profile LUT such as a CLUT is already known.

  Patent Document 1 discloses coordinate data of grid points (lattice points) in a color space of a color signal of an LUT and a color patch of a predetermined color for the purpose of providing a color image processing method with good color reproduction even with a plurality of light sources. The measurement data obtained by measuring colors is acquired, the coordinates of the grid points are converted into non-linearity, the coordinates of the device signal (output image signal) corresponding to the coordinates of the grid points are generated, and a new LUT is formed The structure made to do is disclosed. As disclosed in this patent document 1, as one of its features, for a grid point included in a color gamut obtained from measurement data, a predetermined interpolation process is performed using the coordinates of the grid point in the color gamut and the measurement data. To generate device signal coordinates corresponding to the coordinates of the grid points included in the color gamut. For grid points that are not included in the color gamut, a predetermined color gamut compression process is performed, and grid points that are not included in the color gamut. The above object is achieved by generating the coordinates of the device signal corresponding to the coordinates.

  However, with the conventional methods for adjusting the arrangement of the grid points as described above, the conversion accuracy of the color near the gray balance and the achromatic color axis can be improved by increasing the grid points inside the color gamut of the output device. However, the color reproduction at the end of the color gamut was not considered. In other words, in the conventional method, since the grid points are not arranged at the end of the gamut, the arrangement of the grid points after the color gamut compression is arranged so as to cut the end of the gamut, and the color at the end of the gamut There was a problem that the reproducibility deteriorated.

  The present invention has been made in view of the above, and provides an image processing apparatus, an image forming apparatus, an image processing method, and a program thereof that can perform good color reproduction even at the end of the color gamut of an output device. With the goal.

In order to solve the above-described problems and achieve the object, the present invention obtains the color value of the feature point at the end of the color gamut from the information on the color gamut of the output device , and calculates the point of the point in the device-independent color space. In the output profile for converting the color value to the color value of the corresponding point in the color gamut of the output device, so that the output value of the conversion table used for the conversion has the color value of the feature point at the end of the color gamut. A first table defining a relationship between input values and output values according to the number of gradations in a device-independent first color space; and the output profile. A grid point information acquisition unit that acquires information about grid points in the first color space included in the conversion table, and an output that acquires information on the color gamut in the first color space corresponding to the color gamut of the output device. A color gamut information acquisition unit; Based on the grid point information acquired by the grid point information acquisition unit and the color gamut information acquired by the output color gamut information acquisition unit, at least a primary color and a secondary color of the color gamut of the output device The color value of the feature point in the first color space corresponding to the feature point at the end of the color gamut of the output device including any of the output devices is used as the output value, and the color value of the lattice point closest to the feature point in the first color space The table generation unit that sets the relationship between the input value and the output value in the first table, and the color value of each grid point indicated by the information about the grid point acquired by the grid point information acquisition unit A grid point conversion unit that converts an output value corresponding to an input value sandwiching a color value of a grid point to be converted among the input values of the first table generated by the table generation unit; and the grid point conversion Each grid point converted by the unit within the color gamut of the output device A color gamut compression unit that performs color gamut compression to be arranged, and a color value in the first color space of each lattice point that has been color gamut compressed by the color gamut compression unit, and a color value in a second color space that depends on the output device A color space conversion unit for converting to the grid point, each grid point indicated by the information about the grid point acquired by the grid point information acquisition unit, and the second color space corresponding to each grid point obtained by the color space conversion unit. A profile generation unit that generates the output profile including a conversion table in which color values are associated with each other.

  According to the present invention, in an output device using an output profile, good color reproduction can be achieved even at the end of the color gamut.

FIG. 1 is a block diagram illustrating a system configuration example including the image processing apparatus according to the first embodiment. FIG. 2 is a conceptual diagram of general color conversion. FIG. 3 is a functional block diagram illustrating a main part of the image processing apparatus according to the first embodiment. FIG. 4 is a diagram for explaining lattice points. FIG. 5A is a diagram illustrating an input table (initial state) of L ^* in the case of 11 gradations in the first embodiment. FIG. 5B is a diagram illustrating an a ^* input table (initial state) in the case of 11 gradation levels in the first embodiment. FIG. 5C is a diagram illustrating an input table (initial state) of b ^* in the case of 11 gradations in the first embodiment. FIG. 6A is a graph showing the input / output relationship of the input table of FIG. 5A. FIG. 6B is a graph showing the input / output relationship of the input table of FIG. 5B. FIG. 6C is a graph showing the input / output relationship of the input table of FIG. 5C. FIG. 7 is a diagram for explaining general color gamut compression. FIG. 8 is a block diagram illustrating a functional configuration of the input table generation unit in the first embodiment. FIG. 9 is a flowchart for describing input table generation processing according to the first embodiment. FIG. 10 is a diagram illustrating a feature point extraction result in the first embodiment. FIG. 11 is a diagram illustrating an input table generation method according to the first embodiment. FIG. 12 is a diagram illustrating an example in which an input table is adjusted and generated by the input table generation method according to the first embodiment. FIG. 13 is a diagram showing an example in which the arrangement of lattice points is adjusted by a conventional method. FIG. 14 is a functional block diagram of the input table generation unit in the second embodiment. FIG. 15 is a flowchart illustrating the flow of input table generation processing in the second embodiment. FIG. 16A is a diagram showing the input / output relationship of the input table in which the output values are concentrated near 0 as a solid line graph and the dotted line graph when the input / output relationship is equal. FIG. 16B is a diagram exemplifying lattice point intervals when the lattice point conversion unit performs conversion using the input table corresponding to the graph of FIG. 16A. FIG. 17A is a diagram for describing an example of the smoothing processing result. FIG. 17B is a diagram for describing an example of the smoothing processing result. FIG. 17C is a diagram for describing an example of the smoothing processing result. FIG. 18A is a diagram for describing an example of the smoothing processing result. FIG. 18B is a diagram for describing an example of the smoothing processing result. FIG. 18C is a diagram for describing an example of the smoothing processing result. FIG. 19A is a diagram for describing an example of the smoothing processing result. FIG. 19B is a diagram for describing an example of the smoothing processing result. FIG. 19C is a diagram for describing an example of the smoothing processing result. FIG. 20A is a diagram for describing an example of the smoothing processing result. FIG. 20B is a diagram for describing an example of the smoothing processing result. FIG. 20C is a diagram for describing an example of the smoothing processing result. FIG. 21 is a diagram illustrating a usage pattern of the image processing apparatus according to each embodiment. FIG. 22 is a block diagram illustrating an example of a hardware configuration of a multi-function peripheral equipped with an output profile generated by the image processing apparatuses according to the first and second embodiments.

  Hereinafter, embodiments of an image processing apparatus, an image forming apparatus, an image processing method, and a program thereof will be described in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram illustrating a system configuration example including an image processing apparatus according to the present embodiment. The system includes an image input device 10, an image processing device 20, and an image output device 30. The image processing apparatus 20 according to the present embodiment creates an output profile used in the color conversion shown in FIG.

  In the example of FIG. 1, the image input device 10, the image processing device 20, and the image output device 30 are shown as separate bodies, but these are integrated, for example, a multifunction device (MFP (Multi Function Printer)). It may be configured as follows. A multifunction peripheral is an apparatus having a plurality of image processing functions such as a copy, a printer, a scanner, and a facsimile. The image input device 10 is a device that inputs color image data to the image processing device 20 side, such as a color scanner, digital camera, personal computer (PC), and the image output device 30 is a color image of a printer, various displays, a projector, or the like. Is a device that outputs.

FIG. 3 is a functional block diagram showing the main part of the image processing apparatus of the present embodiment.
The image processing apparatus 20 of the present embodiment includes a grid point information acquisition unit 211, an output color gamut information acquisition unit 212, an input table generation unit 213, a grid point conversion unit 214, a color gamut compression unit 215, a color space conversion unit 216, and A processing unit 210 including a profile generation unit 217 is included. The image processing apparatus 20 has a hardware configuration using a normal computer including a storage device such as an HDD, a display device such as a display device, and an input device such as a keyboard and a touch panel, connected to the processing unit 210. Can be realized.

  Specifically, the processing unit 210 includes a control device such as a CPU and a memory such as a ROM and a RAM (none of which are shown). When the processing unit 210 is activated, the processing unit 210 expands a program (not shown) stored in a storage device such as a ROM or an HDD into a main memory RAM, thereby performing the functions of the above functional units. Realize. The RAM is also used as a work area for temporarily storing various data such as calculation results of the respective units of the image processing apparatus 20. The above-mentioned program is a file in an installable or executable format for the image processing apparatus 20 and is read by a computer such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). It can be provided by being recorded on a possible recording medium. Alternatively, the program may be stored on a computer connected to a network such as the Internet and provided or distributed via the network.

The grid point information acquisition unit 211 stores grid point information (hereinafter referred to as grid point information) in the output profile generated by the profile generation unit 217 described below, or a storage device of the image processing apparatus 20 that stores this information. Obtain from outside. As described above, the lattice points are in the L ^* a ^* b ^* color space (0 ≦ L ^* ≦ 100, −128 ≦ a ^* ≦ 127, −128 ≦ b ^* ≦ 127), or the XYZ color space (0 ≦ X ≦ 1). .., 0 ≦ Y ≦ 1.0, 0 ≦ Z ≦ 1.0) are equally arranged according to an arbitrary number of divisions set by the user. For example, if the number of divisions is set to 9 by the user in the L ^* a ^* b ^* color space, L ^* is 0, 12.5, 25.0, 37.5, ..., 87.5, 100.0. In this way, 100 / (9-1) = 12.5 is divided, and a ^* and b ^* are 256 / (9−, like −128, −96, −64,..., 96, 127. 1) It is divided in 32 steps (however, the maximum value of a ^* and b ^* is 127). Then, the points of all the division positions in the L ^* a ^* b ^* space shown in FIG. 4 are lattice points. In the following, the L ^* a ^* b ^* color space will be described as an example, but the same can be considered for the XYZ color space.

The output color gamut information acquisition unit 212 stores information on the color gamut (output color gamut) that can be reproduced by the output device (hereinafter referred to as output color gamut information). Or obtain from the outside. In the present embodiment, the output color gamut information (hereinafter referred to as output color gamut information) includes a plurality of points (including feature points) indicating the output color gamut in the L ^* a ^* b ^* color space, and corresponding to them. The output device-dependent color information is included. Furthermore, it is assumed that the priority order when the later-described addition target grid point position extraction unit 2133 extracts grid point positions is included for the feature points. For example, if the output color gamut is a patch corresponding to a feature point of the output color gamut in the L ^* a ^* b ^* color space, for example, Yellow of a CMYK printer, {C, M, Y, K} = {0 , 0, 100, 0} (%) patches are output from the output device to actually measure colors, or a well-known color prediction model such as Neugebauer, Yule-Nielsen, or a neural network is constructed, and the color of each point is determined. It can be obtained by prediction.

The input table generation unit 213 generates an input table using the grid point information acquired by the grid point information acquisition unit 211 and the output color gamut information acquired by the output color gamut information acquisition unit 212. This input table is a table that defines the input / output relationship of an arbitrary number of gradations for each of L ^* , a ^* , and b ^* . FIG. 5A to FIG. 5C illustrate L ^* , a ^* , and b ^* tables (initial state) in the case of 11 gradations. 6A to 6C are graphs showing the input / output relationship of each table. In the example of FIGS. 5A to 5C, the input side is set at equal intervals in an easy-to-understand manner, but in practice it can be set freely. The input table generation unit 213 generates a final input table by adjusting each such table using the lattice point information and the output color gamut information. Details of the generation of the input table will be described later.

The lattice point conversion unit 214 converts lattice points using the input table generated by the input table generation unit 213. Specifically, the grid point conversion unit 214 first compares the input values of the input table with the L ^* , a ^* , and b ^* values of the grid points, and determines the input values of the input table that sandwich the grid point values. look for. For example, for lattice points {L ^* , a ^* , b ^* } = {12.5, −128, −96}, it is found that L ^* = 12.5 is between 10 and 20 in the input table. From this, the converted value of L ^* = 12.5 is (48.12−35.11) × (12.5−10) / (20−10) +35 by linear interpolation of the output values of 10 and 20 in the input table. .11 = 38.36. If a ^* and b ^* are obtained in the same manner, the converted values are {L ^* , a ^* , b ^* } = {38.36, −128, −69.21}. When the input value of the input table matches the L ^* , a ^* , and b ^* values of the grid point, the grid point conversion unit 214 sets the output value corresponding to the input value as the value after conversion. In this way, the L ^* , a ^* , and b ^* values of all grid points are converted using the input table. The same can be done for the XYZ color space.

The color gamut compression unit 215 uses the grid point information converted by the grid point conversion unit 214 and the output color gamut information acquired by the output color gamut information acquisition unit 212 to convert each grid point outside the output color gamut. Color gamut compression is performed so that the grid points fall within the output color gamut. Color gamut compression is a process of moving the L ^* a ^* b ^* values of each grid point so that they fall within the output color gamut, which is a range that can be reproduced by the output device. As a specific example of this color gamut compression, as illustrated in FIG. 7, the output color gamut is represented by a polygon, a vector is drawn from the lattice point toward the surface of this polygon, and the intersection is color gamut compressed. There is a method as a later point. There is no particular rule as to which direction the vector is directed, and it depends on the idea of the designer. For example, the orientation of the vector here is a ^* , b ^* (XYZ) so that the grid point outside the output color gamut moves toward the nearest surface on the polygon or the color is not changed. In the case of a color space, it can be determined to move to the surface on the polygon while maintaining the ratio of Y, Z).

In the color space conversion unit 216, the output color gamut information acquisition unit 212 acquires the L ^* a ^* b ^* value after the color gamut compression processing of each lattice point obtained by the color gamut compression by the color gamut compression unit 215. Based on the output color gamut information, the output value for the output device (for example, CMYK value) is converted. For points after color gamut compression that do not include a corresponding point in the output color gamut information, the color space conversion unit 216 firstly has an L ^* a ^* b ^* color space included in the color gamut information. Among the points, a point surrounding the point to be converted is searched for at a point near the point to be converted. Then, the color space conversion unit 216 uses the output device-dependent color information (for example, YMCK value) corresponding to the found point, and performs interpolation of the point to be converted by an interpolation calculation using Equation (1) described later. Find the output value for the output device.

  The profile generation unit 217 generates an LUT indicating the relationship between each grid point indicated by the grid point information and the output value for the output device converted by the color space conversion unit 216, and generates a profile to generate an output profile.

  FIG. 8 is a block diagram illustrating a functional configuration of the input table generation unit 213.

  The input table generation unit 213 includes a feature point setting unit 2131, a difference value calculation unit 2132, an addition target grid point position extraction unit 2133, and a control point addition unit 2134.

  Here, input table generation processing by the feature point setting unit 2131, the difference value calculation unit 2132, the addition target grid point position extraction unit 2133, and the control point addition unit 2134 of the input table generation unit 213 will be described. FIG. 9 is a flowchart illustrating the input table generation process.

The feature point setting unit 2131 extracts feature point information of the output color gamut from the output color gamut information acquired by the output color gamut information acquisition unit 212 and sets it in the work area (S100). FIG. 10 is a diagram illustrating a feature point extraction result. The feature point setting unit 2131 sets feature points in the L ^* a ^* b ^* color space as illustrated in FIG. This feature point corresponds to a primary color, secondary color, or black and white point that is likely to exist near the end of the output color gamut, and the feature point extraction result includes the L ^* a ^* b ^* value of those points. The priority order when the following addition target grid point position extraction unit 2133 extracts grid point positions is stored.

  Note that the feature points are not limited to those illustrated in FIG. 10. For example, {C, M, Y, K} corresponding to a middle point between R and Y = {0, 50, 100, 0} (%) points and {C, M, Y, K} = {0, 0, 50, 0} (%) points that are intermediate between W and Y. Accordingly, it can be appropriately adjusted.

  Also, with regard to the priority order, in this embodiment, the priority is given to the primary color that is conspicuous when other colors are mixed. The order may be changed as appropriate according to the aim.

  Next, in S110, the difference value calculation unit 2132 first acquires the color value of one feature point from the feature point information set by the feature point setting unit 2131 in S100.

Subsequently, in S120, the difference value calculation unit 2132 excludes the color values of the feature points acquired for a ^* and b ^* and the points of a ^* = 0 and b ^* = 0 acquired by the grid point information acquisition unit 211. A difference value from the color value at each grid point position (hereinafter referred to as a grid point position) (for example, the difference between the values of a ^* and b ^* is obtained as a sum) is calculated (S120). At this time, if there is a desire to move a specific grid point, the position of the grid point may be excluded from the calculation target. In addition, it may replace with the said difference value and may employ | adopt the distance between two points of a feature point and each lattice point.

  Subsequently, in S <b> 130, the addition target grid point position extraction unit 2133 extracts the grid point position having the smallest difference value among the values calculated by the difference value calculation unit 2132 as the addition target grid point position. When the same grid point position is extracted for different feature points, the addition target grid point position extraction unit 122 applies the grid point position to the feature point with the higher priority according to the above-described priority order. And the feature point with the lower priority is extracted by excluding the position of the lattice point. Here, for the feature point with the lower priority, the grid point position with the next smallest difference value is set as the extraction target.

Further, in S140, the addition target grid point position extraction unit 2133 determines whether or not a control point having the color value of the extracted grid point position as an input value has been set in the input table. Here, a set of input / output values of the L ^* , a ^* , and b ^* tables of the input table is referred to as a control point.

  As a result of the determination, if a control point having the input color value of the already extracted grid point position has already been set (Yes in S140), in S150, the addition target grid point position extracting unit 2133 The output value corresponding to the control point is changed to the color value of the feature point. Thereafter, in S160, the grid point position is excluded and the process returns to S130, and the grid point position having the next smallest difference is extracted. In S130, S140, S150, and S160, (1): extraction of grid point position, (2): determination of whether or not the extracted grid point position has been set in the input table, (3): (1 The process of excluding the grid point positions extracted in step) is sequentially performed until it is determined that there is no control point whose input value is the value of the extracted grid point position for the grid point positions that are not excluded.

  If it is determined in S140 that there is no control point whose input value is the color value of the extracted grid point position (No in S140), in S170, the control point adding unit 2134 determines the color value of the extracted grid point position. A control point having the input value and the color value of the feature point as an output value is added to the input table.

  After this additional change, the process proceeds to S180, and if all the feature points have already been processed (Yes in S180), the series of processes ends. If there is a feature point that has not yet been processed (No in S180), the process returns to S110, and the subsequent processing is repeated until all the feature points have been processed. In this way, a final input table is generated.

  Next, the generation of the input table will be described with a specific example. FIG. 11 is a diagram for explaining an input table generation method.

The number of control points in the input table can be arbitrarily set between 2 and the maximum value (256 for 8 bits and 65536 for 16 bits) independently of the number of divisions in the arrangement of grid points. Moreover, in practice L ^*, a ^*, b ^* directed to a three-dimensional color space, L ^{*, a *,} b ^* of but adjustment of the input table by adding the above-described processing is performed for each of the following Then, for the sake of simplicity, the description will be made in a two-dimensional space of a ^* and b ^* .

First, the a ^* b ^* value {ap, bp} of the feature point P in the output color gamut is acquired, and the closest lattice point position is searched. Here, G {ag, bg} is extracted as the position of the lattice point closest to the feature point P (see the upper left graph in FIG. 11).

  Next, a search is made in the input table for control points whose positions ag and bg of the extracted nearest lattice points are input values.

  When the corresponding control point is found, the output value of the control point is changed to the color values ap and bp of the feature point P (see the lower right graph in FIG. 11). If no corresponding control point is found in the search, control point addition processing is performed as described above.

  This process is performed for all feature points, and an adjusted input table is generated.

  When the input table generated in this way is applied, the lattice points of the upper left graph in FIG. 11 are converted into the lattice points of the lower right graph. In addition, the lower right figure in FIG. 11 is rotated 90 degrees clockwise.

  FIG. 12 is a diagram for explaining an example in which the input table is adjusted and generated by the above method. In the present embodiment, the grid point conversion unit 214 converts grid points using the adjusted input table obtained as described above, and the color gamut compression unit 215 performs color conversion on the grid points after the conversion. In the example of FIG. 12, P → P ′, G1 → G1 ′, so that the position of the grid point near the end of the output color gamut matches the point corresponding to the end of the output color gamut. Conversion is performed as G2 → G2 ′. For this reason, the color gamut compression by the color gamut compression processing does not occur at the lattice points near the end of the output color gamut. As a result, the occurrence of scraping at the end of the output color gamut can be suppressed, and more accurate color reproduction is possible.

  FIG. 13 shows an example in which the arrangement of grid points is adjusted by a conventional method for reference. In the prior art, there is a possibility that scraping may occur at the end of the output color gamut, as indicated by the hatched area in FIG.

Here, the difference in processing results between the method of the present embodiment and the conventional method will be described by taking as an example the case where the signal at the point P outside the output color gamut described above is input. The interpolation calculation method depends on CMM (Color Management Module), but here, linear interpolation is used as a general example. In addition, the actual calculation is performed in a three-dimensional space of L ^* , a ^* , and b ^*. However, for the sake of simplicity, it will be described as a two-dimensional space of a ^* and b ^* .

  The point P is a point surrounded by the lattice points G0 to G3. In the conventional method, the grid points G0 and G1 existing outside the color gamut are subjected to color gamut compression to become G0 'and G1', respectively.

  The CMYK values corresponding to the respective lattice points are as follows because G0 'is on the line between Green and Yellow, G1' is on the line between Green and Cyan, and G2 and G3 are inside the color gamut.

G0 ′: {C, M, Y, K} = {c0, 0, 100, 0} (c0 ≠ 100)
G1 ′: {C, M, Y, K} = {100, 0, y1, 0} (y1 ≠ 100)
G2: {C, M, Y, K} = {c2, m2, y2, 0} (c2 ≠ 100, m2 ≠ 100, y2 ≠ 100)
G3: {C, M, Y, K} = {c3, m3, y3, 0} (c3 ≠ 100, m3 ≠ 100, y3 ≠ 100)

  On the other hand, according to the method of the present embodiment, the grid point G1 exists outside the color gamut and the color gamut compression is performed to become G1 ', but G0 does not move because it is on the color gamut boundary. Therefore, the CMYK values corresponding to the respective grid points are as follows because G1 ′ is on the line between Green and Yellow, G0 ′ = G0 is on Green, and G2 and G3 are inside the color gamut. .

G0 ′: {C, M, Y, K} = {100, 0, 100, 0}
G1 ′: {C, M, Y, K} = {c0 ′, 0, 100, 0} (c0 ′ ≠ 100)
G2: {C, M, Y, K} = {c2 ′, m2 ′, y2 ′, 0} (c2 ′ ≠ 100, m2 ′ ≠ 100, y2 ′ ≠ 100)
G3: {C, M, Y, K} = {c3 ′, m3, “y3”, 0} (c3 ′ ≠ 100, m3 ′ ≠ 100, y3 ′ ≠ 100)

Here, the a ^* b ^* values of the grid points G0 to G3 are {a0, b0}, {a0, b1}, {a1, b1}, {a1, b0}, respectively, and the a ^* b ^* value of the input point P Is {a, b}, the CMYK value corresponding to P is calculated by the following equation (equation (1)).

P: {C, M, Y, K} = db × {da × G0 ′ + (1-da) × G3} + (1-db) × {da × G1 ′ + (1-da) × G2}
However, da = (a−a1) / (a0−a1),
db = (b−b0) / (b1−b0)

  As can be seen from the above, in the conventional method, {C, M, Y, K} = {C0,0,100,0} → {100,0,100,0} → {100,0, Y0,0} (However, the point on the line of c0 <C0 <100, y0 <Y0 <100, c0 ≠ 100, y0 ≠ 100) cannot be taken. However, in the method of this embodiment, the point on Green, that is, {a, b } Is input, da = db = 0, and the accuracy that is effectively utilized up to the end of the color gamut, such as being reproduced as {C, M, Y, K} = {100, 0, 100, 0}. Good color reproduction.

(Second Embodiment)
In the first embodiment described above, it is possible to generate an output profile with good color reproduction even at the end of the output color gamut by generating the input table so that the grid points match the feature points. However, there is a bias in the size of each surface of the polyhedron (polygon) formed by the lattice points after color gamut compression, so that there is a difference in color reproduction accuracy for each surface on this polyhedron.

  In the second embodiment, the input table is smoothed (described below) based on the values of the control points of the input table obtained in the first embodiment. Reduce bias and suppress differences in color reproduction accuracy between surfaces.

  FIG. 14 is a functional block diagram of the input table generation unit 213b according to the second embodiment. The same parts as those in the first embodiment will be omitted as appropriate.

  The input table generation unit 213b includes an input table smoothing unit 2135 in addition to the configuration of the first embodiment. Other configurations are the same as those of the first embodiment.

  Here, the input table generation processing in the present embodiment will be described with reference to FIG. FIG. 15 is a flowchart for explaining the flow of input table generation processing in the present embodiment.

  In S100 to S180, the same processing as in the first embodiment is performed.

  After a series of processing has been completed for all feature points in S180 (Yes in S180), in S290, the input table smoothing unit 2135 smoothes the curve to be applied to each control point of the adjusted input table as described below. The control points are smoothed so that As described above, the grid points are converted by linear interpolation using the input table by the grid point conversion unit 214. For this reason, for example, in the case of an input table in which output values are concentrated near 0 as illustrated in the graph of FIG. 16A, the converted grid points are also concentrated near 0, and the solid line in FIG. 16B. As shown by, the lattice point interval is narrow on the inside and wide on the outside, and the transformed lattice points are biased. When the control points of the input table that cause such a bias are brought closer to the line indicated by the dotted lines in FIG. 16A by smoothing the curve applied to the control points, the intervals between the grid points are evenly approached. The bias will be reduced.

  Here, a specific example of the smoothing process will be described.

  Here, an example in which smoothing is performed using a well-known LOESS is shown. LOESS is a method of fitting a curve to a plurality of points (in this case, control points) by a local weighted polynomial regression method. Specifically, a polynomial f (x) that minimizes the following equation (1) is obtained recursively. Note that the number of dimensions of the polynomial f (x) can be set to a desired value according to the curve shape to be obtained.

  Here, x is the input value of the control point of interest, y is the output value of the control point of interest, xi is the input of each control point existing in the local region span near the control point of interest. The value f (xi) is a value obtained when xi is included in the polynomial, and w (dx) is determined according to the distance from x, and represents a weight that increases as the distance becomes shorter.

  In addition, the above span is a value representing the local region with the entire input value being 1.0. For example, in the case of an 8-bit input signal, the range in which the input value can be taken is 0 to 256, so span = 0.25. If there is, the process is performed on ± 32 control points of interest.

FIGS. 17A to 17C, FIGS. 18A to 18C, FIGS. 19A to 19C, and FIGS. 20A to 20C show the results of smoothing by switching span. In FIGS. 17A, 18A, 19A, 20A, 17B, 18B, 19B, and 20B, a ^* _in and b ^* _in in the graphs indicated by solid lines are control points after smoothing. An input value is indicated, and b ^* _out and a ^* _out indicate output values of control points after smoothing (dotted line graphs are before smoothing). 17C, FIG. 18C, FIG. 19C, and FIG. 20C are polyhedrons formed by the grid formed by the smoothed control points in the a ^* b ^* space and the grid points after the color gamut compression corresponding to the output color gamut. (Here, in the a ^* b ^* space).

  As shown in these figures, it can be seen that as the span (shown in the upper left in the figure) is increased, the smoothing is performed and the intervals between the lattice points become more uniform. That is, the unevenness of the surface size on the polyhedron formed by each lattice point after color gamut compression is reduced. That is, by using the input table smoothed as described above, it is possible to suppress a difference in color reproduction accuracy for each surface of the polyhedron formed by each lattice point after color gamut compression corresponding to the output color gamut. Here, LOESS is used as the smoothing processing method, but various other methods such as LOWESS and spline interpolation may be used.

(Usage form)
Next, usage modes of the image processing apparatus according to each of the above-described embodiments will be described. FIG. 21 is a diagram illustrating a usage pattern of the image processing apparatus according to each embodiment.

  As the usage form of the image processing apparatus 20 that generates the output profile of each embodiment described above, there are a case where it is used on the manufacturer side and a case where it is used on the user side (office, printing factory, etc.). When used on the manufacturer side, it is used when a designer designs an output profile to be mounted by default in the image forming apparatus, or when an output profile is modified in response to a customization request from a customer. In this case, the output color gamut information acquisition unit 212, the grid point conversion unit 214, the color gamut compression unit 215, and the like are provided separately by the image forming apparatus and the information processing apparatus, respectively, and the designer can follow the procedure. Thus, each apparatus may be configured to read necessary data, execute processing, and store processing result data.

  On the other hand, when used on the user side, it is used to create an output profile that matches the current machine state in response to machine differences such as printing devices and temporal variations. In this case, the image processing apparatus 20 is provided as one system or is provided as software and is installed in the image processing apparatus or the information processing apparatus. In addition, when the processing units included in the image processing apparatus 20 are provided in separate devices, it is preferable to operate the processing units provided in the devices in cooperation with each other.

(Other embodiments)
The output profile generated by the image processing apparatus 20 according to the first and second embodiments is mounted on an image forming apparatus such as a multifunction peripheral, and the engine unit (360) of the image forming apparatus converts this output profile. And can be configured to perform color conversion and output an image. The image forming apparatus configured as described above is an image forming apparatus capable of excellent color reproduction even at the end of the color gamut. Hereinafter, an example of the hardware configuration of the multifunction peripheral will be described.

  FIG. 22 is a block diagram illustrating an example of a hardware configuration of a multi-function peripheral equipped with an output profile generated by the image processing apparatus 20 according to the first and second embodiments. As shown in the figure, this multifunction device has a configuration in which a controller 310 and an engine unit (Engine) 360 are connected by a PCI (Peripheral Component Interface) bus. The controller 310 is a controller that controls the entire MFP, drawing, communication, and input from an operation unit (not shown). The engine unit 360 is a printer engine that can be connected to a PCI bus, and is, for example, a monochrome plotter, a 1-drum color plotter, a 4-drum color plotter, a scanner, or a fax unit. The engine unit 360 includes an image processing unit that performs error diffusion, gamma conversion, color conversion using an input profile and an output profile, in addition to a so-called engine unit such as a plotter.

  The controller 310 includes a CPU 311, a north bridge (NB) 313, a system memory (MEM-P) 312, a south bridge (SB) 314, a local memory (MEM-C) 317, and an ASIC (Application Specific Integrated Circuit). 316 and a hard disk drive (HDD) 318, and the North Bridge (NB) 313 and the ASIC 316 are connected by an AGP (Accelerated Graphics Port) bus 315. The MEM-P 312 further includes a ROM (Read Only Memory) 312a and a RAM (Random Access Memory) 312b.

  The CPU 311 performs overall control of the multifunction peripheral, has a chip set including the NB 313, the MEM-P 312 and the SB 314, and is connected to other devices via the chip set.

  The NB 313 is a bridge for connecting the CPU 311 to the MEM-P 312, SB 314, and AGP 315, and includes a memory controller that controls reading and writing to the MEM-P 312, a PCI master, and an AGP target.

  The MEM-P 312 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, a memory for drawing printers, and the like, and includes a ROM 312a and a RAM 312b. The ROM 312a is a read-only memory used as a memory for storing programs and data, and the RAM 312b is a writable and readable memory used as a program and data development memory, a printer drawing memory, and the like.

  The SB 314 is a bridge for connecting the NB 313 to a PCI device and peripheral devices. The SB 314 is connected to the NB 313 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 316 is an IC (Integrated Circuit) for image processing having hardware elements for image processing, and has a role of a bridge for connecting the AGP 315, the PCI bus, the HDD 318, and the MEM-C 317, respectively. The ASIC 316 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 316, a memory controller that controls the MEM-C 317, and a plurality of DMACs (Direct Memory) that rotate image data using hardware logic. (Access Controller) and a PCI unit that performs data transfer between the engine unit 360 via the PCI bus. The ASIC 316 is connected to an FCU (Facile Control Unit) 330, a USB (Universal Serial Bus) 340, and an IEEE 1394 (the Institute of Electrical and Electronics 13) interface via an PCI bus. The operation display unit 320 is directly connected to the ASIC 316.

  A MEM-C 317 is a local memory used as a copy image buffer and a code buffer, and an HDD (Hard Disk Drive) 318 is a storage for storing image data, programs, font data, and forms. It is.

  The AGP 315 is a bus interface for a graphics accelerator card that has been proposed to speed up graphics processing, and speeds up the graphics accelerator card by directly accessing the MEM-P 312 with high throughput. .

DESCRIPTION OF SYMBOLS 10 Image input apparatus 20 Image processing apparatus 30 Image output apparatus 210 Processing part 211 Grid point information acquisition part 212 Output color gamut information acquisition part 213, 213b Input table generation part 214 Grid point conversion part 215 Color gamut compression part 216 Color space conversion part 217 profile generation unit 2131 feature point setting unit 2132 difference value calculation unit 2133 addition target grid point position extraction unit 2134 control point addition unit 2135 input table smoothing unit

JP 2002-152530 A

Claims (6)

Obtain the color value of the feature point at the end of the color gamut from the color gamut information of the output device, and convert the color value of the point in the device-independent color space to the color value of the corresponding point in the color gamut of the output device An output profile for generating the output profile so that an output value of a conversion table used for the conversion has a color value of a feature point at the end of the color gamut,
With
The generator is
A first table defining a relationship between input values and output values according to the number of gradations in a device-independent first color space;
A grid point information acquisition unit that acquires information about grid points in the first color space included in the conversion table of the output profile;
An output color gamut information acquisition unit that acquires information on the color gamut in the first color space corresponding to the color gamut of the output device;
Based on the grid point information acquired by the grid point information acquisition unit and the color gamut information acquired by the output color gamut information acquisition unit, at least a primary color and a secondary color of the color gamut of the output device. The color value of the feature point in the first color space corresponding to the feature point at the end of the color gamut of the output device including any of the output devices is used as the output value, and the color value of the lattice point closest to the feature point in the first color space A table generation unit that sets a relationship between the input value and the output value in the first table,
The color value of each grid point indicated by the grid point information acquired by the grid point information acquisition unit is sandwiched with the color value of the grid point to be converted among the input values of the first table generated by the table generation unit. A grid point conversion unit for converting using an output value corresponding to the input value;
A color gamut compression unit that performs color gamut compression to place each grid point converted by the grid point conversion unit in the color gamut of the output device;
A color space conversion unit that converts a color value in the first color space of each lattice point subjected to color gamut compression by the color gamut compression unit into a color value in a second color space depending on the output device;
A conversion table in which each grid point indicated by the grid point information acquired by the grid point information acquisition unit is associated with a color value in the second color space corresponding to each grid point obtained by the color space conversion unit. A profile generator that generates the output profile including
An image processing apparatus comprising: The table generator is
A feature point setting unit that acquires and sets the feature point from the information on the color gamut of the output device acquired by the output color gamut information acquisition unit;
The difference value between the color value in the first color space of each grid point indicated by the grid point information acquired by the grid point information acquisition unit and the color value of each feature point set by the feature point setting unit is calculated. A difference value calculator,
An additional target grid point position extraction unit that extracts a position of a grid point at which the difference value calculated by the difference value calculation unit is minimum for each of the feature points as a grid point position to be added to the first table;
When the color value of the grid point position extracted by the addition target grid point position extraction unit is not in the input value of the first table, the color value is set as the input value, and the difference value between the grid point and the grid point position is minimum. A control point whose output value is the color value of the feature point is added to the first table, and the color value of the grid point position extracted by the addition target grid point position extraction unit is already input as the input value of the first table. If there is, a control point addition unit that changes an output value corresponding to the input value to a color value of the feature point that minimizes the difference value between the grid points;
The image processing apparatus according to claim 1 , further comprising: The table generation unit further smoothes the control points by adjusting the control points of the first table by smoothing the curves applied to the control points of the first table based on the generated information of the control points of the first table. The image processing apparatus according to claim 2 , further comprising a processing unit. In an image forming apparatus that performs color conversion according to an output profile and outputs an image,
Equipped with output profile generated by the image processing apparatus as claimed in any one of claims 3, an image forming apparatus and executes the color conversion in accordance with the output profile. An image processing method in an image processing apparatus for generating an output profile for converting a color value of a point in a device-independent color space into a color value of a corresponding point in a color gamut of an output device,
The color value of the feature point at the end of the color gamut is acquired from the color gamut information of the output device, and the output value of the conversion table used for the conversion of the output profile is the color value of the feature point at the end of the color gamut. Generating the output profile to have:
Providing a first table that defines a relationship between an input value and an output value in a device-independent first color space according to the number of gradations;
A grid point information acquisition unit acquiring information regarding grid points in the first color space included in the conversion table of the output profile;
An output color gamut information obtaining unit obtaining information on a color gamut in the first color space corresponding to the color gamut of the output device;
Based on the grid point information acquired by the grid point information acquisition unit and the color gamut information acquired by the output color gamut information acquisition unit by the table generation unit, at least a primary color of the color gamut of the output device The color value of the feature point in the first color space corresponding to the feature point at the end of the color gamut of the output device including any of the secondary colors is used as the output value, and is closest to the feature point in the first color space. The relationship between the input value and the output value with the color value of the grid point as the input value is set in a first table that defines the relationship between the input value and the output value according to the number of gradations in the first color space. Process,
The grid point conversion unit converts the color value of each grid point indicated by the grid point information acquired by the grid point information acquisition unit, among the input values of the first table generated by the table generation unit, to be converted Converting using the output value corresponding to the input value sandwiching the color value of the point;
A step of performing color gamut compression in which the color gamut compression unit arranges each grid point converted by the grid point conversion unit in the color gamut of the output device;
A step of converting a color value in the first color space of each lattice point subjected to color gamut compression by the color gamut compression unit into a color value of a second color space depending on the output device;
Each profile point indicated by the grid point information acquired by the grid point information acquisition unit and a color value in the second color space corresponding to each grid point obtained by the color space conversion unit are generated by the profile generation unit. Generating the output profile including the associated conversion table;
An image processing method comprising: The color value of the feature point at the end of the color gamut is obtained from the color gamut information of the output device, and the color value of the point in the device-independent color space is changed to the color value of the corresponding point in the color gamut of the output device. Generating the output profile so that the output value of the conversion table used for the conversion of the output profile for conversion has the color value of the feature point at the end of the color gamut;
Providing a first table that defines a relationship between an input value and an output value in a device-independent first color space according to the number of gradations;
A grid point information acquisition unit acquiring information regarding grid points in the first color space included in the conversion table of the output profile;
An output color gamut information obtaining unit obtaining information on a color gamut in the first color space corresponding to the color gamut of the output device;
Based on the grid point information acquired by the grid point information acquisition unit and the color gamut information acquired by the output color gamut information acquisition unit by the table generation unit, at least a primary color of the color gamut of the output device The color value of the feature point in the first color space corresponding to the feature point at the end of the color gamut of the output device including any of the secondary colors is used as the output value, and is closest to the feature point in the first color space. The relationship between the input value and the output value with the color value of the grid point as the input value is set in a first table that defines the relationship between the input value and the output value according to the number of gradations in the first color space. Process,
The grid point conversion unit converts the color value of each grid point indicated by the grid point information acquired by the grid point information acquisition unit, among the input values of the first table generated by the table generation unit, to be converted Converting using the output value corresponding to the input value sandwiching the color value of the point;
A step of performing color gamut compression in which the color gamut compression unit arranges each grid point converted by the grid point conversion unit in the color gamut of the output device;
A step of converting a color value in the first color space of each lattice point subjected to color gamut compression by the color gamut compression unit into a color value of a second color space depending on the output device;
Each profile point indicated by the grid point information acquired by the grid point information acquisition unit and a color value in the second color space corresponding to each grid point obtained by the color space conversion unit are generated by the profile generation unit. Generating the output profile including the associated conversion table;
A program that causes a computer to execute.