JP6320278B2 - Color processing apparatus and method - Google Patents

Description

  The present invention relates to color processing for reproducing changes in local gradation and chromaticity of an image.

  When image data taken by an imaging device such as a camera is output by an output device such as a display or a printer, color gamut compression processing for correcting a color gamut difference between input and output devices is performed. In general, in color gamut compression processing, conversion parameters (lookup table (LUT), matrix, etc.) for converting color data of an input device into color data of an output device are defined in advance, and image data is converted using the conversion parameters. Is uniformly color-converted.

  However, uniform conversion of the entire image such as color gamut compression processing can suitably reproduce the color of the entire image, but may lose local gradation. For example, a visible striped pattern in the image data of the input device may not be visible because the gradation is compressed in the image data for the output device.

  As a method for solving the problem of losing local gradation, processing based on the spatial frequency characteristics of an image has been proposed. For example, the technique disclosed in Patent Document 1 separates input image data into a local contrast component and an overall brightness component, and only compresses the overall brightness component with gradation, thereby maintaining dynamic gradation of the input image data. Obtain an image with a compressed range. However, the technique of Patent Document 1 has the following problems.

  The first problem is that the difference in compression rate due to color coordinates is not taken into consideration. In the color gamut compression processing described above, lightness compression and saturation compression with different compression rates depending on chromaticity are performed, but the technique of Patent Document 1 does not consider the difference in compression rate due to chromaticity, and is local. Changes in gradation and chromaticity cannot be reproduced properly.

  The second problem is that the processing time is long. The processing based on the spatial frequency of the image generally has a high processing cost, and the processing time is very long compared to the conventional color gamut compression processing.

JP 2009-038504

  An object of the present invention is to improve the reproduction of changes in local gradation and chromaticity of an image. Another object of the present invention is to generate image data in which the color gamut is compressed by storing the local gradation and chromaticity change components of the image.

  The present invention has the following configuration as one means for achieving the above object.

The color processing apparatus of the present invention has the following configuration. That is,
Separating means for separating upper bit image data composed of a plurality of upper bits from input image data;
Calculating means for calculating a difference between the color represented by the input image data and the color represented by the upper bit image data as difference image data;
Based on conversion information corresponding to image forming conditions, color processing is performed on the upper bit image data, and color processing means for synthesizing the difference image data with the upper bit image data after the color processing,
The calculation means converts the input image data and the higher-order bit image data into image data in a device-independent color space, and calculates a difference between the image data as the difference image data .

  According to the present invention, it is possible to improve the reproduction of changes in local gradation and chromaticity of an image. In addition, it is possible to generate image data in which the color gamut is compressed by storing the local gradation and chromaticity change components of the image.

FIG. 3 is a block diagram illustrating a configuration example of an information processing apparatus that performs color processing according to an embodiment. FIG. 2 is a block diagram illustrating a processing configuration example of the color processing apparatus according to the first embodiment. 6 is a flowchart for explaining color processing in the color processing apparatus. The figure which shows an example of UI. The figure which shows the signal flow in the color processing of a color processing apparatus. The figure which shows an example of the conversion information and the correction coefficient table mentioned later. The flowchart explaining the acquisition process of a correction coefficient. The flowchart explaining the separation process of global change data and local change data. The flowchart explaining a correction process. The flowchart explaining a synthetic | combination process. FIG. 10 is a diagram illustrating an example of a UI according to the second embodiment. 9 is a flowchart for explaining separation processing by a separation unit according to the second embodiment. FIG. 10 is a diagram illustrating a configuration example of a color conversion profile according to the third embodiment. 10 is a flowchart for explaining correction coefficient acquisition processing according to the third embodiment. FIG. 10 is a block diagram illustrating a configuration example of a profile creation unit that creates a color conversion profile according to the third embodiment. The flowchart explaining a profile creation process. FIG. 10 is a block diagram illustrating a processing configuration example of a color processing apparatus according to a fourth embodiment. 10 is a flowchart for explaining color processing in the color processing apparatus according to the fourth embodiment. The figure which shows an example of UI. The flowchart explaining the production | generation process of difference image data. 5 is a flowchart for explaining processing of a color processing unit. The figure which shows an example of conversion information.

  Hereinafter, a color processing apparatus and a color processing method according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, an Example does not limit this invention concerning a claim, and all the combinations of the structure demonstrated in an Example are not necessarily essential for the solution means of this invention.

[Device configuration]
The block diagram of FIG. 1 shows an example of the configuration of an information processing apparatus that executes the color processing of the embodiment. The CPU 201 uses a main memory 202 such as a RAM as a work memory, executes a program stored in a storage unit 203 or a ROM 204 such as an HDD or an SSD, and controls a configuration to be described later via a system bus 205. Note that the storage unit 203 and the ROM 204 store programs and various data for realizing color processing described later.

  A general-purpose interface (I / F) 206 such as USB includes an instruction input unit 207 such as a keyboard and a mouse, a recording medium (computer-readable recording medium) 208 such as a USB memory and a memory card, and an image output device 209. Connected. Further, on the monitor 211 connected to the video card (VC) 210, the CPU 201 displays information indicating the user interface (UI), processing progress, and processing results.

  For example, the CPU 201 loads an application program (AP) stored in the ROM 204, the storage unit 203, or the recording medium 208 into a predetermined area of the main memory 202 in accordance with a user instruction input via the instruction input unit 207. Then, the AP is executed, and the UI is displayed on the monitor 211 according to the AP.

  Next, the CPU 201 loads various data stored in the storage unit 203 and the recording medium 208 into a predetermined area of the main memory 202 in accordance with a user instruction. Then, predetermined arithmetic processing is performed on various data loaded into the main memory 202 in accordance with the AP. Then, the CPU 201 displays the calculation processing result on the monitor 211 according to the user instruction, stores it in the storage unit 203 or the recording medium 208, and outputs it to the image output device 209.

  Note that the CPU 201 can also send and receive programs, data, and arithmetic processing results to and from computer devices and server devices on a wired or wireless network via a network I / F (not shown) connected to the system bus 205. it can. The monitor 211 and the instruction input unit 207 may be a touch panel in which they are overlapped. In that case, the information processing apparatus is a computer device such as a tablet device or a smartphone.

[Processing configuration]
An example of the processing configuration of the color processing apparatus 101 of the first embodiment is shown in the block diagram of FIG. Note that the color processing apparatus 101 illustrated in FIG. 2 is realized by the CPU 201 executing the image processing AP, and the processing of the color processing apparatus 101 described later is executed by the image processing AP. Although not shown in FIG. 2, the processing of each unit is executed using a buffer allocated to the main memory 202.

  The UI unit 102 displays the UI on the monitor 211 and inputs a user instruction to the UI via the instruction input unit 207. The user instruction includes, for example, selection of an image output device, image forming conditions of the image output device, an instruction of image data to be output to the image output device, and the like.

  The image input unit 103 inputs image data (input image data) from the storage unit 203 or the recording medium 208 in accordance with a user instruction. The separation unit 104 performs filtering processing on the input image data as data representing changes in local gradation and chromaticity of the image (hereinafter referred to as local change data), and changes in global gradation and chromaticity of the image. The data to be represented (hereinafter referred to as global change data) is separated.

  The correction coefficient acquisition unit 105 acquires the conversion information for color processing specified by the selection of the image output device and the image forming conditions from the conversion information holding unit 106, and acquires the correction coefficient based on the conversion information. The correction processing unit 107 performs correction processing on the local change data based on the correction coefficient.

  The combining unit 108 combines the global change data and the corrected local change data. The color processing unit 109 performs color processing on the combined image data based on the conversion information for color processing acquired in the same manner as the correction coefficient acquisition unit 105. The output unit 111 outputs a print job including the color-processed image data to the image output device 209. The image output device 209 forms an image represented by the input image data on a recording medium in accordance with designated image forming conditions.

  Note that the color processing unit 109 acquires, for example, conversion information corresponding to a color gamut (hereinafter referred to as an output color gamut) in a specified image forming condition of the image output device 209 from the conversion information holding unit 106, and Performs color processing such as gamut mapping that maps the gamut to the output gamut.

  Further, the output unit 111 uses the color separation table corresponding to the designated image forming condition of the image output device 209 to convert the RGB signal value of the image data into a color material amount signal value CMYK that represents the color material amount. Perform the disassembly process. Further, the output unit 111 also executes halftone processing for reducing the number of gradations of the image data to the number of gradations that can be processed by the image output device 209. Of course, the image output device 209 that has received the RGB image data from the output unit 111 may perform color separation processing and halftone processing.

[Process flow]
The color processing in the color processing apparatus 101 will be described with reference to the flowchart of FIG. The UI unit 102 displays a UI for the user to input information necessary for the subsequent processing on the monitor 211 (S11). An example of the UI is shown in FIG.

  The user operates the instruction input unit 1001 to input or select information (for example, a model number) for specifying an image output device to which image data is output and a file name of the image data to be output. When image data to be output is designated (S12), the image input unit 103 inputs the image data (S13). The image display unit 1002 displays an image represented by image data (input image data) for which output is instructed.

  Next, the user operates the output mode selection unit 1003 to select the output mode of the image output apparatus when outputting an image. As an output mode, for example, photographic tone, monitor match for color matching with a monitor image, or the like can be selected. Note that the operation order of the instruction input unit 1001 and the output mode selection unit 1003 may be reversed, and the user may operate the instruction input unit 1001 after operating the output mode selection unit 1003.

  The conversion button 1005 is a button for instructing execution of color processing. When the conversion button 1005 is pressed (or touched) by the user, the input image data is mapped to the image display unit 1004 in the color gamut corresponding to the selected image output device and output mode (hereinafter, image forming conditions). An image is displayed. The output button 1006 is a button for giving an instruction to output the processing result by the color processing apparatus 101 to the image output apparatus 209. When the output button 1006 is pressed (or touched) by the user, the color processing apparatus 101 starts color processing for outputting input image data to the image output apparatus 209. Note that the operation of the conversion button 1005 is not essential, and the output button 1006 can be operated without operating the conversion button 1005.

  When the conversion button 1005 or the output button 1006 is pressed (S14), the correction coefficient acquisition unit 105 acquires conversion information (conversion information for color processing) corresponding to the image forming condition from the conversion information holding unit 106 (S15). . Then, a correction coefficient is acquired based on the conversion information for color processing (S16). Details of the correction coefficient acquisition process will be described later.

  Next, as will be described in detail later, the separation unit 104 separates the input image data into global change data and local change data by filtering (S17). Subsequently, as will be described in detail later, the correction processing unit 107 performs correction processing on the local change data based on the correction coefficient (S18).

  Next, the synthesizing unit 108 synthesizes the global change data and the corrected local change data (S19). Subsequently, the color processing unit 109 acquires conversion information for color processing corresponding to the image forming condition from the conversion information holding unit 106 (S20), and based on the conversion information for color processing, the color processing unit 109 adds color information to the combined image data. Processing is performed (S21). At this time, an image obtained by color-gamut mapping the input image data is displayed on the image display unit 1004. When the output button 1006 is pressed, the output unit 111 outputs the image data after color processing to the image output device 209 (S22).

  FIG. 5 shows a signal flow in the color processing of the color processing apparatus 101. The correction coefficient acquisition unit 105 acquires conversion information for color processing (S15) and calculates a correction coefficient (S16). On the other hand, the separation unit 104 generates a brightness signal Lm and a saturation signal Cm of global change data by RGB → LC conversion (S17a) and smoothing filter processing (S17b). Then, the LC value of the input image data is divided by the global change data LmCm (S17c) to generate local change data L′ C ′. In other words, local change data L'C 'is generated by dividing the lightness signal L of the input image data by the lightness signal Lm after filtering and dividing the saturation signal C of the input image data by the saturation signal Cm after filtering. To do.

  Next, the correction processing unit 107 performs correction processing on the local change data L′ C ′ based on the correction coefficient (S18). The synthesizing unit 108 performs a synthesizing process (S19a) by multiplication of the corrected local change data LcCc and the global change data LmCm and LC → RGB conversion (S19b) (S19b). The color processing unit 109 acquires conversion information for color processing (S20), and performs color processing on the combined image data (S21).

  FIG. 6 shows an example of conversion information and a correction coefficient table described later. The conversion information shown in FIG. 6 (a) is a lookup table (LUT) in which device RGB values of the image output device corresponding to each grid point (RGB value) of a uniform grid obtained by slicing the range of RGB values, for example, 17 slices. It is. The format of the conversion information is not limited to the LUT, but may be a determinant such as a matrix or a gamma table format.

  In this way, by performing correction processing before color processing based on color processing conversion information applied to image forming conditions (image output device and output mode, etc.), changes in gradation and chromaticity in input image data Can be appropriately reproduced in the image output device 209.

Correction coefficient acquisition unit Correction coefficient acquisition processing (S16) will be described with reference to the flowchart of FIG. The correction coefficient acquisition unit 105 calculates a lightness compression rate and a saturation compression rate for each lattice point of the acquired conversion information. In other words, using the following formula, the input value (input RGB value) of the grid point is converted to the Lab value Lab _in (S61), and the output value (device RGB value) of the grid point is converted to the Lab value Lab _out (S62). ).
R _Linear = R ^γ ;
G _Linear = G ^γ ;
B _Linear = B ^γ ;
X = 0.4124 × R _Linear + 0.3576 × G _Linear + 0.1805 × B _Linear ;
Y = 0.2126 × R _Linear + 0.7152 × G _Linear + 0.0722 × B _Linear ;
Z = 0.0193 × R _Linear + 0.1192 × G _Linear + 0.9505 × B _Linear ;
;
if (X> 0.008856)
fx = (X / Xw) ^1/3 ;
else
fx = 903.3 × (X / Xw) / 116;
if (Y> 0.008856)
fy = (Y / Yw) ^1/3 ;
else
fy = 903.3 × (Y / Yw) / 116;
if (Z> 0.008856)
fx = (Z / Zw) ^1/3 ;
else
fx = 903.3 × (Z / Zw) / 116;
;
L = 116 x fy-16;
a = 500 × (fx-fy);
b = 500 × (fy-fz);… (1)
Here, γ = 2.2 for sRGB,
XwYwZw is the XYZ value of the white point. For D65, Xw = 95.05, Yw = 100.0, Zw = 108.91.

Next, the correction coefficient acquisition unit 105 converts the Lab value of the lattice point into an LC value using Equation (2) (S63), and the lightness compression rate Lratio and saturation compression rate for each lattice point using Equation (3). Cratio is calculated (S64).
C = √ (a ² + b ² );… (2)
;
Lratio = L _in / L _out ;
Cratio = C _in / C _out ;… (3)

Next, the correction coefficient acquisition unit 105 calculates the brightness correction coefficient k _L and the saturation correction coefficient k _C used for the correction processing based on the calculated compression rate using the following formula (S65), and calculates these correction coefficients. Store in the buffer (S66).
k _Li = 1 / Lratio;
k _Ci = 1 / Cratio;… (4)
Where i is the number of the grid point.

As shown in FIG. 6 (b), the correction coefficient is stored in association with the RGB value of the grid point, and the RGB value is input, and the brightness correction coefficient k _L and the saturation correction coefficient k _C are output (hereinafter referred to as a table). , Correction coefficient table). In addition, the correction coefficient table once created can be stored in the conversion information holding unit 106 in association with the image forming conditions (image output apparatus and output mode). In this case, if the correction coefficient table corresponding to the image forming condition is stored in the conversion information holding unit 106, it is not necessary to calculate the correction coefficient.

Separation unit The separation process (S17) of global change data and local change data will be described with reference to the flowchart of FIG. The separation unit 104 converts the input image data into Lab values according to the equation (1) (S31), calculates the phase h = a / b of each pixel (S32), and uses the equation (2) to input image data The Lab value is converted into an LC value (S33).

Then, global change data LmCm is generated by smoothing the lightness value L and the saturation value C using a Gaussian filter shown in the following equation (S34). Note that the LC value and phase h of the input image data and the global change data LmCm are stored in a buffer.
G (x, y) = 1 / (2πσ ² ) exp {-(x ² + y ² ) / 2σ ² }… (5)

  As the kernel size σ of the Gaussian filter, for example, the size of 1/10 of the input image is used, but the size is not limited to this, and is determined to be the kernel size σ based on the actual observation distance as described later. Also good. In addition to the Gaussian filter, other smoothing filters such as a moving average filter and a bilateral filter may be used, or global change data may be generated by performing processing in the frequency domain using Fourier transform. Good.

  Next, for each pixel of the input image data, the separation unit 104 divides the lightness value L by the lightness value Lm of the corresponding pixel of the global change data, and the saturation value C is the saturation of the corresponding pixel of the global change data The local change data L′ C ′ divided by the value Cm is generated (S35). The local change data L′ C ′ is stored in the buffer.

  The brightness value L ′ (= L / Lm) of the local change data represents the ratio of the brightness of each pixel when the brightness value Lm of the global change data is 1 (global tone) and is brighter than the global tone. Pixels are L ′> 1, and pixels darker than the global gradation are L ′ <1. Similarly, the saturation value C ′ (= C / Cm) of the local change data represents the ratio of the saturation of each pixel when the saturation value Cm of the global change data is 1 (global saturation). Pixels with higher saturation than saturation are C ′> 1, and pixels with lower saturation than global saturation are C ′ <1.

Correction Processing Unit Correction processing (S18) will be described with reference to the flowchart of FIG. The correction processing unit 107 acquires the RGB value of the input image data of the target pixel from the buffer (S41). Then, the lightness correction coefficient k _L and the saturation correction coefficient k _C of the pixel of interest are calculated by interpolation calculation referring to the correction coefficient table with the RGB values as input (S42).

Next, the correction processing unit 107 acquires the local change data L′ C ′ of the target pixel from the buffer (S43), and performs correction processing on the L′ C ′ value using the following equation (S44). Note that the local change data LcCc after the correction processing is stored in a buffer.
Lc = k _L × L ';
Cc = k _C × C ';… (6)

  Compared to the color gamut (input color gamut) of an input device such as a digital camera, the color gamut (output color gamut) of an output device such as an image output device is narrow, and conversion information uses the input color gamut as the output color gamut. This is information for compression, and the compression ratio <1 calculated by the equation (3). On the other hand, as shown in Equation (4), the correction coefficient is the reciprocal of the compression ratio (> 1), and correction processing for emphasizing changes in gradation and saturation is applied to the local change data by the calculation of Equation (6). Will be.

  Next, the correction processing unit 107 determines whether or not the correction value LcCc has been calculated for all pixels (S45). If there is an incomplete pixel, the process returns to step S41 to repeat the calculation of the correction value LcCc. .

Synthesizing Unit The synthesizing process (S19) will be described with reference to the flowchart of FIG. The synthesizing unit 108 acquires the local change data LcCc of the target pixel from the buffer (S51), and acquires the global change data LmCm of the target pixel (S52). Then, the corrected brightness value Lc is multiplied by the brightness value Lm of the global change data, the corrected saturation value Cc is multiplied by the saturation value Cm of the global change data, and the corrected LC value of the target pixel is calculated. Calculate (S53).

Next, the synthesizing unit 108 acquires the phase h of the target pixel from the buffer (S54), and calculates the corrected ab value of the target pixel using the following equation (S55).
a = √ {h ² C ² / (1 + h ² )};
b = √ {C ² / (1 + h ² )};… (7)
Here, h is the hue of the target pixel calculated in step S32,
C is the saturation value of the target pixel calculated in step S53.

  Next, the synthesizing unit 108 converts the Lab value after correcting the pixel of interest into an RGB value in the same format as the input image data by performing the inverse operation of Expression (1) (S56). Then, it is determined whether or not corrected RGB values have been calculated for all pixels (S57). If there is an incomplete pixel, the process returns to step S51, and the calculation of corrected RGB values is repeated.

  In this way, with reference to the conversion information according to the image forming conditions (image output device and output mode, etc.), the correction processing according to the brightness and saturation of the pixel is applied to the local brightness component and saturation component of the pixel. Apply. Therefore, even when brightness compression and saturation compression with different compression rates depending on chromaticity are performed, it is possible to appropriately reproduce local gradation and chromaticity changes of the image.

  A color processing apparatus and color processing method according to a second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof may be omitted.

  In the first embodiment, the input image data is separated into the local change data and the global change data, and based on the lightness compression rate and the saturation compression rate of the conversion information, a correction process that emphasizes the local change data is performed. Explained how to properly reproduce typical gradation and chromaticity changes. At that time, the parameters of the filter used for the separation processing of the local change data and the global change data are set based on the image size. For example, if the size of 1/10 of the input image is set to the kernel size σ of the filter, the global change data indicates the average gradation and chromaticity in the region of 1/10 size of the input image.

  In the second embodiment, a method for setting filter parameters based on actual print observation conditions will be described. In the following, the UI and separation processing (S17), which are the differences from the first embodiment, will be described, and description of other configurations and processing will be omitted.

If the resolution (output resolution) of the printed matter to be output to the image output device 209 is Ro [dpi], the observation distance of the printed matter is D [mm], and the viewing angle is θ (for example, 10 °), the printed matter enters the observer's field of view. The number of pixels tp is expressed by the following equation. In the following description, the field of view is described as a square, but a circle with a radius tp may be used as the field of view.
tp = Ro / 25.4 × D × 2, tanθ / 2 (8)

If the resolution of the input image data is Ri, the pixel number td of the input image data corresponding to the pixel number tp of the printed material is expressed by the following equation.
td = tp × Ri / Ro (9)

From Expressions (8) and (9), the number of pixels td in the input image data that enters the viewer's field of view is expressed as follows by the viewing angle θ and the viewing distance.
td = Ro / 25.4 × D × 2, tanθ / 2 × Ri / Ro
= Ri / 25.4 × D × 2, tanθ / 2 (10)

  If the global change data is generated based on the number of pixels td entering the observer's visual field, the global gradation and chromaticity recognized by the observer can be acquired more accurately. The local change data generated by the separation process can more accurately represent local gradation and chromaticity changes recognized by the observer.

  FIG. 11 shows an example of the UI in the second embodiment. The user operates the resolution selection unit 1011 to select the resolution Ri [dpi] of the input image data, and inputs the observation distance D (unit: millimeters, for example) when observing the printed matter to the observation distance input unit 1012. Needless to say, the printed material is a printed material to be output from the image output device 209.

  The separation process (S17) by the separation unit 104 of the second embodiment will be described with reference to the flowchart of FIG. The processing from step S31 to S33 is the same as that in the first embodiment, and a description thereof will be omitted. When Lab → LC conversion (S33) is completed, the separation unit 104 acquires the observation distance D and the resolution Ri from the UI unit 102 (S341). Then, the number of pixels of the input image data that falls within a predetermined viewing angle θ (for example, 10 °) is calculated as the viewing size td (S342). Note that the resolution Ri of the input image data may be acquired from header information of the image data, for example.

  Next, the separation unit 104 smoothes the LC value of the input image data to obtain the global change data LmCm in the same manner as in the first embodiment (S343), but at this time, as the kernel size σ of the Gaussian filter, in step S342 The calculated visual field size td is used. Then, the local change data L′ C ′ is generated as in the first embodiment (S35).

  As described above, it is possible to more appropriately reproduce changes in local gradation and chromaticity of an image in consideration of viewing conditions.

  The color processing apparatus and color processing method according to the third embodiment of the present invention will be described below. Note that the same reference numerals in the third embodiment denote the same parts as in the first and second embodiments, and a detailed description thereof may be omitted.

  In the first and second embodiments, the lightness compression rate and the saturation compression rate are calculated from the conversion information corresponding to the image forming conditions, and the local change data is corrected (emphasized). In the third embodiment, a configuration example of a color conversion profile that can be used to improve the efficiency of the correction process will be described.

Color conversion profile configuration The color processing device 101 that converts input image data into image data to be output to the image output device 209 converts an input image signal, represented by an ICC profile, into an output color signal (device color signal). A color conversion profile is provided. Then, a color conversion profile corresponding to the image forming condition is selected, and color processing is performed using the color conversion profile.

  In Example 1, the input value (input RGB value) of the grid point of the color conversion profile is converted to an LC value, the output value (device RGB value) of the grid point is converted to an LC value, and the brightness of each grid point is converted. A compression rate and a saturation compression rate are calculated, and a correction coefficient is calculated from the compression rate. This processing requires the calculations of equations (1) to (4). In the third embodiment, in order to reduce the cost of these calculations, the lightness compression rate and the saturation compression rate corresponding to the grid points are stored in the color conversion profile.

  FIG. 13 shows a configuration example of the color conversion profile in the third embodiment. The color conversion profile shown in FIG. 13 (a) is an LUT in which an output value (device RGB value), a lightness compression rate, and a saturation compression rate are recorded corresponding to an input value (input RGB value) of a grid point. . Of course, the lightness compression rate and the saturation compression rate are calculated in advance by the procedure described in the first embodiment and recorded in the color conversion profile.

  Although FIG. 13 shows a color conversion profile including a LUT that converts an input RGB value into a device RGB value, a color conversion profile including an LUT that stores a color coordinate value typified by Lab may be used. In that case, the input RGB value may be converted into an Lab value, and the lightness compression rate and the saturation compression rate corresponding to the Lab value may be acquired.

  The correction coefficient acquisition process (S16) of the third embodiment will be described with reference to the flowchart of FIG. The correction coefficient acquisition unit 105 acquires the color conversion profile from the conversion information holding unit 106 in step S15, and then refers to the LUT stored in the color conversion profile to record the lightness compression rate and the saturation recorded corresponding to the lattice points. The degree compression rate is acquired (S123). Then, based on the acquired compression rate, a correction coefficient for each lattice point is calculated by Equation (4) (S124), and the calculated correction coefficient is stored in the buffer as a correction coefficient table (S125). According to the correction coefficient acquisition process of FIG. 14, the RGB → Lab conversion (S21, S22) of the grid points in the calculation of the correction coefficient shown in FIG. 7 becomes unnecessary, and the processing speed can be increased.

  In this way, by using the color conversion profile having the configuration shown in FIG. 13 (a), it becomes possible to simplify the process of calculating the lightness compression ratio and the saturation compression ratio, and to improve the efficiency of the correction process of the local change data. Can be achieved.

● Support for intents Color conversion profiles include monitor match profiles and colorimetric (colorimetric) profiles for faithful color reproduction as the types of color reproduction characteristics (intents) of hue and saturation. There is. In addition, there is a perceptual profile that preferably reproduces hue and saturation.

  The colorimetric profile is a profile that matches Lab in input RGB and Lab in output RGB. Therefore, depending on the selection of the intent at the time of image output, the enhancement of the local change data by the correction process may not be desirable. Therefore, it is conceivable to configure the LUT according to the intent of the color conversion profile.

  FIG. 13B shows the relationship between the intent and the correction target, “0” indicates the non-correction target and “1” indicates the correction target. For example, when the color conversion profile shown in FIG. 13A is a perceptual profile, only the lightness compression rate is stored in the LUT of the color conversion profile (or the saturation compression rate is all set to 1). Then, when a perceptual is designated as an intent, the correction processing unit 107 may correct only the brightness value L ′ of the local change data.

  When monitor match is specified as the intent, the correction processing unit 107 uses the color conversion profile having the LUT storing the lightness compression rate and the saturation compression rate, so that the correction processing unit 107 uses the lightness value L ′ and the saturation value C of the local change data. Correct '.

  In addition, when colorimetric is specified as the intent, the correction processing unit 107 substantially corrects the lightness value L ′ and the saturation value C ′ of the local change data by the color conversion profile having the LUT that does not store the compression rate. Do not do that. Instead of storing the compression rate, all of the lightness compression rate and the saturation compression rate may be set to 1.

  In this way, it is possible to control the correction target corresponding to the intent, and it is possible to form an image that realizes the color reproducibility desired by the user.

Creation of a color conversion profile including a compression rate table In addition, the color conversion profile stored in the conversion information holding unit 106 of the color processing apparatus 101 is a general color conversion profile in which the lightness compression rate and the saturation compression rate are not recorded. There are cases. Therefore, a new color conversion profile shown in FIG. 13 (a) including a table of brightness compression ratio and saturation compression ratio created by referring to the color conversion profile stored in the conversion information holding unit 106 is created and converted. It is conceivable to store the information in the information holding unit 106.

  A block diagram of FIG. 15 shows a configuration example of the profile creation unit 110 that creates the color conversion profile of the third embodiment. The color conversion unit 1101 refers to the color conversion profile stored in the conversion information holding unit 106, converts the input value (input RGB value) of each grid point of the color conversion LUT into an LC value, and outputs the output value (device RGB) Value) into an LC value. The compression rate calculation unit 1102 calculates the lightness compression rate and the saturation compression rate from the LC value input from the color conversion unit 1101. The table creation unit 1103 creates a compression rate table that records the lightness compression rate and the saturation compression rate corresponding to the grid points. The profile creation unit 1104 creates a color conversion profile by combining the created compression rate table and the color conversion table of the color conversion profile referred to by the color conversion unit 1101, and stores the created color conversion profile in the conversion information holding unit 106. Store.

  The profile creation process will be described with reference to the flowchart of FIG. The profile creation unit 110 acquires a color conversion profile from the conversion information holding unit 106 (S201), and determines whether the color conversion profile is a color conversion profile having a compression rate table (S202).

  In the case of a color conversion profile having a compression rate table, the profile creation unit 110 ends the profile creation process. In the case of a color conversion profile having no compression rate table, the profile creation unit 110 executes the processing from step S203 onward.

  The color conversion unit 1101 converts the input value (input RGB value) of each grid point of the color conversion LUT of the color conversion profile into an LC value (S203), and converts the output value (device RGB value) into an LC value (S204). ). Next, the compression rate calculation unit 1102 calculates a lightness compression rate and a saturation compression rate from the LC values input from the color conversion unit 1101 (S205). The processing of steps S203 to S205 is repeated until the lightness compression rate and saturation compression rate of all grid points are calculated by the determination of step S206.

  When the calculation of the brightness compression rate and the saturation compression rate of all grid points is completed, the table creation unit 1103 creates a compression rate table in which the brightness compression rate and the saturation compression rate corresponding to the grid points are recorded (S207). . Next, the profile creation unit 1104 synthesizes the compression rate table with the created compression rate table and the color conversion LUT of the color conversion profile referenced by the color conversion unit 1101 to create a color conversion profile including the compression rate table. (S208). Then, the created color conversion profile is stored in the conversion information holding unit 106 (S209).

  Note that the profile creation unit 110 may execute profile creation processing when a color conversion profile is stored in the conversion information holding unit 106, or may execute profile creation processing according to a user instruction.

  Hereinafter, a color processing device and a color processing method according to a fourth embodiment of the present invention will be described. Note that the same reference numerals in the fourth embodiment denote the same parts as in the first to third embodiments, and a detailed description thereof may be omitted.

  In Example 1-3, the input image data is separated into the local change data and the global change data by the filter process, and the local gradation and chromaticity changes are appropriately performed by the correction process that emphasizes the local change data. Explained how to reproduce. In the fourth embodiment, a method for appropriately reproducing changes in local gradation and chromaticity of an image with a simpler configuration will be described.

[Processing configuration]
A block diagram of FIG. 17 shows a processing configuration example of the color processing apparatus 101 of the fourth embodiment. Note that the color processing apparatus 101 shown in FIG. 17 is realized by the CPU 201 executing the image processing AP, and the processing of the color processing apparatus 101 described later is executed by the image processing AP. Although not shown in FIG. 17, the processing of each unit is executed using a buffer allocated to the main memory 202. The same components as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The separation unit 301 separates upper bit image data composed of a plurality of upper bits from the image data input by the image input unit 103. The difference calculation unit 302 generates difference image data indicating a difference between the color represented by the input image data and the color represented by the higher-order bit image data, details of which will be described later. In the fourth embodiment, the upper bit image data corresponds to “global change data”, and the difference image data corresponds to “local change data”. The bit position for separating the upper bit image data will be described later.

  The color processing unit 303 includes a color gamut mapping unit 304, an image composition unit 305, and an inverse conversion unit 306, and performs color conversion processing of input image data. The color gamut mapping unit 304 acquires conversion information corresponding to the image forming conditions from the conversion information holding unit 106, and performs color gamut mapping on the upper bit image data. The image synthesis unit 305 synthesizes the image data subjected to color gamut mapping and the difference image data. The inverse conversion unit 306 converts the combined image data into image data in the device RGB space of the image output device 209, for example.

[Process flow]
Color processing in the color processing apparatus 101 of the fourth embodiment will be described with reference to the flowchart of FIG. The UI unit 102 displays a UI for the user to input information necessary for subsequent processing on the monitor 211 (S401). FIG. 19 shows an example of the UI. Note that components similar to those of the UI shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  When the image data to be output is designated (S402), the image input unit 103 inputs the image data (S403). The image display unit 1002 displays an image represented by image data (input image data) for which output is instructed. Input image data is stored in a buffer.

  The user operates the bit number instruction unit 1021 to specify the number of upper bits considered to represent the overall gradation and chromaticity change (global change) of the image. For example, when it is considered that the upper 5 bits represent a global change, the user designates “5” using the bit number instruction unit 1021. Note that the operation order of the instruction input unit 1001 and the bit number instruction unit 1021 may be reversed, and the user may operate the instruction input unit 1001 after operating the bit number instruction unit 1021. Note that the UI unit 102 may display the default number of upper bits (for example, 5 bits or 6 bits) each time it is activated, or may display the number of bits specified last time.

  When the conversion button 1005 or the output button 1006 is pressed (S404), the separating unit 301 separates the upper bit image data from the input image data according to the designated bit number input from the UI unit 102 (S405). When the input image data is 8 bits for each color and the designated bit number is 5 bits, for example, the input image data can be shifted 3 bits to the right and then shifted left by 3 bits to create upper bit image data. The upper bit image data is stored in the buffer.

  Next, although the details will be described later, the difference calculation unit 302 generates difference image data from the input image data and the higher-order bit image data (S406). Subsequently, as will be described in detail later, the color processing unit 303 uses the upper bit image data and the difference image data to generate image data after color gamut mapping corresponding to the image forming conditions (S407). At this time, an image obtained by color-gamut mapping the input image data is displayed on the image display unit 1004. If the output button 1006 is pressed, the output unit 111 outputs the color-processed image data to the image output device 209 (S408).

[Difference calculation unit]
The difference calculation unit 302 generates difference image data corresponding to local conversion data representing changes in local gradation and chromaticity of the input image data. Therefore, the input image data and the higher-order bit image data are each converted into device-independent color space (DIC) image data, and the difference is calculated on the DIC.

  Difference image data generation processing (S406) will be described with reference to the flowchart of FIG. The difference calculation unit 302 acquires input image data (S501), and converts the input image data into DIC image data (S502). Subsequently, upper bit image data is acquired (S503), and the upper bit image data is converted into DIC image data (S504).

  Assuming that the input image data and upper bit image data are sRGB image data specified by the International Commission on Illumination (CIE) and DIC is CIELAB space, the image data of each pixel is CIE tristimulus value XYZ as shown in Equation (1). Then converted to CIELAB values.

Next, the difference calculation unit 302 generates difference image data from the input image data converted into the CIELAB value and the higher-order bit image data by the following equation (S505). The generated difference image data is stored in a buffer.
D (i, j) = I (i, j)-H (i, j)… (11)
Where I (i, j) is the input image data,
H (i, j) is the upper bit image data,
(i, j) are pixel coordinates.

[Color processing section]
The color processing unit 303 uses the higher-order bit image data H and the difference image data D to perform color processing for appropriately reproducing the local gradation and chromaticity change of the input image data. Therefore, the color gamut mapping unit 304 maps the upper bit image data H to the color gamut corresponding to the image forming condition on the DIC. Then, the image synthesis unit 305 synthesizes the difference image data with the higher-order bit image data after the color gamut mapping, and the inverse conversion unit 306 converts the synthesized image data from DIC into, for example, a device RGB space.

  The processing of the color processing unit 303 will be described with reference to the flowchart of FIG. The color gamut mapping unit 304 acquires conversion information corresponding to the image forming conditions from the conversion information holding unit 106 (S601). FIG. 22 shows an example of conversion information.

  As shown in FIG. 22, the conversion information includes the input value of the grid point (input RGB value) obtained by, for example, slicing the input RGB range along each axis, for example, and the CIELAB value in the color gamut of the image output device 209 corresponding to the grid point. LUT that describes the relationship of The conversion information is the color that converts the color gamut of the input device (input color gamut) and the color gamut of the output device (output color gamut) to CIELAB space, and associates the input color gamut with the output color gamut in CIELAB space. It can be created in advance by performing area compression. A known method may be used as the color gamut compression method, and the description thereof is omitted.

Next, the color gamut mapping unit 304 inputs the upper bit image data H (S602), refers to the LUT of the acquired conversion information, and performs color gamut mapping of the upper bit image data H (S603). Note that interpolation calculation is used for color gamut mapping. Subsequently, the image composition unit 305 inputs the difference image data D (S604), and adds the upper bit image data H ′ that has been color gamut mapped and the difference image data D according to the following formula to obtain the composite image data C. Generate (S605).
C (i, j) = H '(i, j) + D (i, j)… (12)

  Next, the inverse conversion unit 306 acquires the color gamut data of the image output device 209 from, for example, the conversion information holding unit 106 (S606). The color gamut data has the same format as the LUT shown in FIG. 22, and the grid points of the device RGB values of the image output device 209 and the patches formed by outputting the RGB values of the grid points to the image output device 209 are measured. Indicates the correspondence between color values (CIELAB values).

  Next, the inverse conversion unit 306 refers to the color gamut data and converts the composite image data C into device RGB values of the image output device 209 (S607). Interpolation calculation is used for this conversion. At this time, an image obtained by color-gamut mapping the input image data is displayed on the image display unit 1004.

  In this way, the upper bits of the input image data are used as image data representing changes in the overall gradation and chromaticity of the image, and only the upper bit image data is subjected to color processing, and the local gradation and chromaticity of the image are processed. Are stored as difference image data. This makes it possible to save the local gradation and chromaticity change components of the image in a short time and to obtain image data with a compressed color gamut without performing complicated processing such as frequency conversion or filtering. Can do.

[Modification]
In the fourth embodiment, the CIELAB space has been described as an example of the DIC. However, the present invention is not limited to this, and other color spaces such as CIE tristimulus values XYZ and CIELUV space may be used. Color appearance spaces such as CIECAM97, CIECAM97s, and CIECAM02 may be used for DIC.

  In the fourth embodiment, the example in which the color processing unit 303 outputs the device RGB signal of the image output device 209 has been described. However, the signal output by the color processing unit 303 represents an image such as CMYK, XYZ, or CIELAB. Any signal can be used as long as it is possible. For example, when the image output device 209 can input a CIELAB signal, the processing of the inverse conversion unit 306 may be passed through.

  In the fourth embodiment, the example in which the image data after the color gamut mapping of the upper bit image data and the difference image data are combined, converted into a device color signal, and output is described. As a process after conversion to the device color signal, a smoothing unit 307 that smoothes the device color signal may be added to the color processing unit 303. The smoothing process has an effect of reducing pseudo contours (artifacts) that may occur when the difference image data is synthesized.

  Further, the color processing apparatus 101 in each of the above embodiments can be connected to a laser beam printer, an inkjet printer, a thermal printer, or the like as the image output apparatus 209. A configuration in which the color processing apparatus 101 is incorporated in these printers is also within the scope of the present invention.

[Other Examples]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program It can also be realized by processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  104: Separation unit, 105 ... Correction coefficient acquisition unit, 107 ... Correction processing unit, 108 ... Composition unit, 109 ... Color processing unit

Claims (10)

Separating means for separating upper bit image data composed of a plurality of upper bits from input image data;
Calculating means for calculating a difference between the color represented by the input image data and the color represented by the upper bit image data as difference image data;
Based on the conversion information corresponding to the image forming condition, performing a color process to the upper-bit image data, have a color processing means for synthesizing processing said difference image data with the upper-bit image data after the color processing,
The color processing apparatus , wherein the calculation means converts the input image data and the higher-order bit image data into image data in a device-independent color space, and calculates a difference between the image data as the difference image data . The color processing apparatus according to claim 1 , wherein the color processing unit performs color gamut mapping on the upper bit image data as the color processing. It said color processing means color processing apparatus according to claim 1 or claim 2 for converting the image data after the combining process in the device color signal. The color processing apparatus according to claim 3 , wherein the color processing unit performs a smoothing process on the device color signal. It said color processing means, as the synthesis process, color processing apparatus according to any one of claims 1 to 4 for adding processing said difference image data with the upper-bit image data after the color processing. Furthermore, color processing apparatus according to any one of claims 1 to 5 comprising means for inputting a user instruction indicating the number of bits of the plurality of upper bit. Furthermore, color processing apparatus according to any one of claims 1 to 6 having a means for inputting a user instruction indicating the image forming condition. The color processing apparatus according to claim 7 , further comprising means for outputting image data output by the color processing means to an image output apparatus indicated by the image forming conditions. A separation step of separating upper bit image data composed of a plurality of upper bits from input image data ;
A calculation step of calculating a difference between the color represented by the input image data and the color represented by the upper bit image data as difference image data;
Based on the conversion information corresponding to the image forming condition, the upper-bit image data subjected to the color processing, the and a color processing step of the difference image data and the upper-bit image data after the color processing for synthesizing processing,
In the color processing method , the calculating step converts the input image data and the higher-order bit image data into image data in a device-independent color space, and calculates a difference between the image data as the difference image data . A program for causing a computer to function as each unit of the color processing device according to any one of claims 1 to 8 .

Images