JP5028241B2 - Color processing apparatus and color processing method - Google Patents

Description

  The present invention relates to a color processing apparatus and a color processing method, and more particularly, to a color processing apparatus and a color processing method for creating a color conversion table between input / output devices.

  In general, color conversion processing is performed in order to maintain color reproducibility between an input device and an output device. As conventional color conversion processing, a table (LUT) having a correspondence relationship between an input color signal value input from an input device and an output color signal value to be output from an output device corresponding to the input color signal value is used as necessary. Interpolation processing was performed.

  However, the LUT does not always have preferable gradation characteristics depending on the creation conditions. The LUT creation conditions include, for example, the characteristics of the LUT creation algorithm installed in the application that created the LUT, the characteristics of the data that the application referred to when creating the LUT, and the presence of noise with respect to the color signal value. It is done. As described above, when the gradation characteristic of the LUT is not appropriate, a smoothing process using a Gaussian filter or the like may be required for the LUT.

  When the smoothing process is performed on the LUT in this way, the color reproduction characteristics of the LUT change. On the other hand, for a certain input color signal A (important color), there is a case where there is a demand for color reproduction particularly for an important color, for example, the output color signal is desired to be reproduced with B (reproduction color). In such a case, even if the LUT satisfies the requirement for color reproduction of an important color consisting of a single color or a set of colors, if the LUT is subjected to smoothing as described above, the requirement is It will not be satisfied.

  In order to minimize the change in color reproduction characteristics due to the smoothing of the LUT as described above, the following techniques have been proposed.

  First, there is a technique for selectively smoothing only a noise component to be smoothed by configuring so as not to locally smooth (or smooth) only around a certain chromatic color (for example, , See Patent Document 1).

  In addition, there is a technique for improving color reproducibility by enabling smoothing conditions to be controlled for each of a plurality of positions on a color space (see, for example, Patent Document 2).

By the way, the color reproduction of important colors is not limited to the color reproduction relationship between single colors such as skin color and blue pure color, but there is also a color reproduction relationship in which a set of colors is mapped. For example, color reproduction between gradations of white to yellow (primary color: shade of single color material), curved surface connecting white, yellow, and green (secondary color: bright color that does not include M in CMY subtractive color mixture) The color reproduction between each other can be considered.
Japanese Patent Laid-Open No. 2003-116012 Japanese Patent Laid-Open No. 2003-179764

  However, in the conventional LUT smoothing technique, only the case of single colors is considered as the color reproduction relationship of important colors. That is, when the important color is a set of colors, such as the color reproduction using the primary color and the secondary color described above, the color set and the mapping of the set are not sufficiently considered. Therefore, when a smoothing process is performed on an LUT that satisfies the requirements for color reproduction of an important color consisting of a single color or a set of colors, the color reproduction characteristics change and the requirement cannot be satisfied. It has not been fully resolved yet.

  SUMMARY An advantage of some aspects of the invention is that it provides a color processing apparatus and a color processing method that enable LUT smoothing to maintain color reproducibility for important colors. .

As a means for achieving the above object, the color processing apparatus of the present invention comprises the following arrangement. That is, in a color processing apparatus that adjusts color conversion conditions and creates a color conversion table, a color conversion unit that converts an input color signal using the color conversion condition and outputs the converted signal as a first output color signal; Smoothing means for smoothing one output color signal using a smoothing condition and outputting it as a second output color signal, and defining a plurality of important color information in a straight line in the color space of the input color signal Holding means for holding each type of a primary color as an area to be processed and a secondary color as an area defined by a plane in the color space of the signal of the input color, the input color, and the holding means Based on the distance between the plurality of important colors held in the weight, the weight calculation means for calculating the weight used for the weighting operation according to the type, and the weight among the weights calculated by the weight calculation means is the maximum Decision to determine weight And calculating a third output color signal by performing a weighting operation on the first output color signal and the second output color signal using the maximum weight determined by the determination unit and the determination unit. Weighting and synthesizing means, and table creating means for creating the color conversion table using the third output color signal.

  According to the present invention having the above configuration, it is possible to perform LUT smoothing so as to maintain color reproducibility for important colors.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<First Embodiment>
System Configuration FIG. 1 is a diagram illustrating a configuration example of a color processing system according to the present embodiment. Color conversion processing using a color conversion table (LUT) created in the present embodiment (device RGB → output of input device) Device RGB conversion).

  In FIG. 1, reference numeral 101 denotes a central processing unit (CPU). A read-only memory (ROM) 102 is connected to the CPU 101 via a bus 104 together with a random access memory (RAM) 103. The CPU 101 can directly execute a program stored in the ROM 102 or the RAM 103.

  In addition, an input interface 105, an HDD interface 107, a video interface 109, and an output interface 111 are also connected to the bus 104. A part or all of the bus 104 may be configured by a high-speed network device such as Ethernet (registered trademark) or a peripheral device interface such as PCI.

  An input device 106 such as a keyboard, mouse, digital camera, or scanner can read information from the CPU 101 via the input interface 105. At this time, device information unique to the digital camera such as a model name and color information of the digital camera can also be read.

  A secondary storage device (HDD) 108 such as a hard disk device or an optical disk device can read and write via the HDD interface 107. Data stored on the HDD 108 can be expanded in the RAM 103 by using an appropriate means. Similarly, the data developed in the RAM 103 can be stored in the HDD 108 by using an appropriate means. As described above, the CPU 101 can execute the data expanded in the RAM 103 as a program. In this embodiment, color conversion processing is executed by expanding the LUT held in the HDD 108 in the RAM 103. The ROM 102, the RAM 103, and the HDD 108 may be devices shared by a network such as a telephone line or Ethernet (registered trademark), and the form is not particularly limited in the present embodiment.

  Arbitrary characters or images can be displayed on the monitor 110 by causing the CPU 101 to control the video interface 109.

  An output device 112 such as a printer or plotter can exchange information via the output interface 111. The CPU 101 can read device information unique to the printer such as the model name and color gamut information of the output device 112 via the output interface 111. Similarly, in the case of the input device 106, the CPU 101 can read the device information of the input device 106 through the input interface 105. Note that the input device 106 and the output device 112 may be shared over a network.

LUT Generation Processing Hereinafter, generation processing of a color conversion table (LUT) for input device RGB → output device RGB conversion used in the color processing system shown in FIG. 1 will be described.

  FIG. 2 is a block diagram showing a configuration for generating a color conversion LUT in this embodiment. The LUT generated here has a configuration as shown in FIG. 3, for example. In the present embodiment, an example is shown in which the color signal is an RGB value that can take an integer value of 0 to 255, but a color system other than RGB or a color space, such as CIE-L * a * b * or CIECAM02 or the like may be used.

  In FIG. 2, the color signal generation unit 201 determines an input device RGB value as an input of the LUT, and sequentially sends it to a color conversion unit 202, a weight calculation unit 204, and an LUT creation unit 209 described later. In this embodiment, the color signal generated by the color signal generation unit 201 includes a color signal necessary for realizing color reproduction of important colors in addition to the color signals arranged to cover the RGB space. It is.

  The color conversion unit 202 converts the input device RGB value from the color signal generation unit 201 with reference to the color conversion condition 203 which is a conversion control parameter, and converts the output device RGB value which is the first output color signal. Generate. The color conversion condition 203 is, for example, an LUT that holds a pair of an input device RGB value and a corresponding output device RGB value. The output device RGB values generated by the conversion in the color conversion unit 202 are sent to the subsequent synthesis unit 208 and the smoothing unit 206. The details of the color conversion unit 202 and the color conversion condition 203 are not described in detail, but the color reproduction conditions described in the important color condition 205 described later are sufficiently satisfied in the conversion result by the color conversion unit 202. To do. The content of the LUT created in this embodiment is controlled by adjusting the color conversion condition 203 as the original LUT.

  The smoothing unit 206 receives the output device RGB value (first output color signal) from the color conversion unit 202 described above, and performs the smoothing process according to the smoothing condition 207 to convert it into the second output color signal. Thereafter, the data is sent to the composition unit 208 in the subsequent stage. As a specific smoothing process in the smoothing unit 206, for example, a general smoothing process such as a smoothing process using a Gaussian filter can be applied. Further, as the smoothing condition 207, for example, the strength and range of smoothing are stored. However, since the present embodiment is not particularly limited, details thereof will not be described in detail.

  The weight calculation unit 204 receives the input device RGB value from the color signal generation unit 201, calculates the weight with reference to the important color condition 205, and sends the calculation result to the synthesis unit 208. Details of this weight calculation will be described later.

  The synthesizing unit 208, according to the calculation result of the weight calculation unit 204, the first output color signal from the color conversion unit 202 and the second output color obtained by smoothing the first output color signal by the smoothing unit 206 As a weighting calculation with the signal, for example, a weighted average is taken. A third output color signal is generated by this weighting calculation and is sent to the LUT creation unit 209 at the subsequent stage. At this time, the weight value input from the weight calculation unit 204 is 0 to 1. In the synthesis unit 208, when the weight value is 1, the device RGB value from the color conversion unit 202 (unsmoothed) is set to 100%, and when the weight value is 0, the device RGB value from the smoothing unit 206 is (smoothed). ) Synthesis is performed with a device RGB value of 100%.

  The LUT creation unit 209 forms an LUT as shown in FIG. 3 by using the input RGB values from the color signal generation unit 201 and the output device RGB values from the synthesis unit 208, and stores this as an LUT 210. Thereby, the final color conversion table creation process in the present embodiment is performed.

Weight calculation process Hereinafter, the weight calculation process in the present embodiment will be described in detail.

  First, FIG. 4 shows two example tables held as the important color condition 205. The important color condition 205 may include conditions other than the two tables shown in FIG. In FIG. 4, 401 is an important color table in which important colors to be considered in the present embodiment are registered. The important color table 401 has a “type” of an important color that is an index for searching a weight calculation table to be described later and determining a weight calculation method. Here, examples of “single color”, “primary color”, “secondary color”, and “gray axis” are shown as “types” of important colors. The important color table 401 further includes input color information in the input device and reproduction color information in the output device corresponding to the input color information as important color information necessary for weight calculation for each type. FIG. 4 shows input color information “RGB0in”, “RGB1in”, “RGB2in” and reproduction color information “RGB0out”, “RGB1out”, and “RGB2out” as important color information for each type.

  Here, if the important color is a specific “single color”, a pair of “RGB0in” and “RGB0out” is registered as the input color and the reproduction color.

  Further, according to the important color table 401, it is possible to set even when the important color is not a specific single color. For example, as an important color, it is possible to describe a primary color as an area defined by a straight line in the color space of the input color signal. That is, if the important color is “primary color” or “gray axis”, two pairs of “RGB0in” and “RGB0out”, “RGB1in” and “RGB1out” may be registered as important color information. Thus, for example, it is possible to describe a constraint (primary color compensation) that a white-yellow gradation at the input must lie on a white-yellow straight line at the output.

  As an important color, it is also possible to describe a secondary color as an area defined by a plane in the color space of the input color signal. That is, if the important color is “secondary color”, three pairs of “RGB0in” and “RGB0out”, “RGB1in” and “RGB1out”, and “RGB2in” and “RGB2out” may be registered as important color information. Thus, for example, a constraint (secondary color compensation) is described in which a color that exists on a white-green-yellow surface in the input must also exist on a white-green-yellow surface in the output. be able to.

  In this embodiment, in order to simplify the description, an example in which only three colors are designated as important color information is shown. However, the present invention is not limited to this example, and for example, a line segment (curve) with an arbitrary number of colors. ) May be defined, and a surface (curved surface) may be defined with an arbitrary number of colors.

  In FIG. 4, reference numeral 402 denotes a weight calculation table, in which “type” similar to the important color table 401 and “weight calculation method” corresponding thereto are registered. The function registered as the “weight calculation method” in the present embodiment has a part or all of RGB values designated as important color data in the important color table 401 as arguments, and values of 0 to 1 as calculation results return it. Which information described in the important color table 401 is referred to calculate the weight depends on the specification of the specified function.

  Hereinafter, a specific weight calculation method in the weight calculation unit 204 will be described. Of the weight calculation methods registered in the weight calculation table 402 of FIG. 4, the processing of f0 corresponding to “monochrome” is shown in FIG. 5, and the processing of f1 corresponding to “primary color” is shown in FIG.

  First, for f0, as shown in FIG. 5, first, in step S501, a distance D from the input color is calculated. The distance D calculated here is a Cartesian distance in the RGB space between the input color signal RGB and RGB0in extracted from the important color table 401. Next, in step S502, it is checked whether or not the input color signal is far from RGB0in by determining whether or not the calculated distance D is greater than 10. If the distance D is within 10 as a result of the determination, the distance D is linearly mapped between 0 and 1 in step S503, the result is set to the weight W, and the process is terminated. On the other hand, if the distance D is greater than 10, the weight W is set to 0 and the process is terminated.

  Similarly, for f1, as shown in FIG. 6, first, the distance D is calculated in step S601. The distance D here is a distance between the input color signal RGB and a straight line having both ends of RGB0in and RGB1in, that is, a Cartesian distance between a point and a line segment. In step S602, the distance D is determined. If it is within 7, the distance D is linearly mapped between 0 and 1 in step S603. Thereafter, in step S604, the result of W conversion (in this example, non-linear conversion by square) is set as the weight W, and the process is terminated. On the other hand, if the distance D is greater than 7, the weight W is set to 0 and the process is terminated.

  FIG. 7 is a graph showing an outline of the relationship between distance and weight in the calculation method f0 corresponding to “monochrome” and the calculation method f1 corresponding to “primary color” described with reference to FIGS. As can be seen from FIG. 7, the characteristics of f0 and f1 are greatly different from each other, although the weight increases as the distance decreases.

  In the present embodiment, the input device RGB values and the colors (or line segments and planes on which the colors extend) stored in the important color information “RGB0in”, “RGB1in”, and “RGB2in” on the important color table 401 are used. An example of calculating the weight based on the distance was shown. However, the present invention is not limited to this example, and it is not always necessary to calculate weights by the same method for all types. This is because the optimal calculation method differs between “single color”, which only requires point-to-point distance calculation, and “primary color”, which considers the positional relationship between at least two points that make up the line segment. It is. Further, it is considered that the ideal weight is different between the case of “single color” for which reproduction of a specific color is desired to be controlled and the case of “primary color” that is not limited to a specific color.

  FIG. 8 is a flowchart showing the entire weight calculation process in the weight calculation unit 204. As described above, the weight calculation unit 204 receives one input device RGB value from the color signal generation unit 201, calculates the weight with reference to the important color condition 205, and sends the calculation result to the synthesis unit 208. The important color condition 205 includes at least the important color table 401 and the weight calculation table 402 described above.

  When the weight calculation unit 204 receives the input device RGB value from the color signal generation unit 201, the processing shown in FIG. 8 is started. First, in step S801, internal variables including a variable Wmax that holds the maximum weight value are initialized, and in step S802, output device RGB values from the color conversion unit 202 are captured.

  Next, in steps S803 to S807, the weight W is calculated for all the important colors registered in the important color table 401, and the maximum value is adopted as the final weight Wmax. For this purpose, first, in step S803, it is determined whether or not the processing has been completed for all the important colors on the important color table 401. If there is an unprocessed important color, the process proceeds to step S804. If completed, the process proceeds to step S808.

  In step S804, one unprocessed important color information is extracted from the important color table 401. In step S805, one weight calculation method for the important color is determined by searching the weight calculation table 402 by the type of the important color. In step S806, using the determined weight calculation method, the weight is calculated as described above, and the calculation result is stored in the weight W. The weight calculation process in step S806 corresponds to the process shown in the flowchart of FIG. 5 or FIG.

  In step S807, the weight W calculated in step S806 is compared with the variable Wmax holding the maximum weight value, and Wmax is updated with the value of W only when W> Wmax. Thereafter, the processing returns to step S803, and the processing up to step S807 is repeated for all the important colors registered in the important color table.

  On the other hand, in step S808 after the processing of all important colors is completed, the value of the variable Wmax that holds the maximum weight value is sent to the synthesis unit 208, and the weight calculation processing in the weight calculation unit 204 is completed.

  As described above, the weight calculation unit 204 obtains only one weight value Wmax corresponding to the input color for realizing color reproduction of a plurality of important colors. Wmax will be sent. Then, the combining unit 208 uses the single Wmax sent to calculate a weighted average of the device RGB value before smoothing from the color conversion unit 202 and the output device RGB value smoothed by the smoothing unit 206. By taking it, smoothing processing in consideration of a plurality of important colors becomes possible.

  As described above, according to this embodiment, in order to prevent the color reproduction of the important color before the LUT smoothing from being affected by the smoothing, the input color is weighted according to the distance from the important color. And weighted average the results before and after smoothing according to the weight. The distance (weight) calculation method used at that time is prepared for each type of important color (monochrome, primary color, secondary color, etc.), and by using this separately, the color reproduction part of the important color that is not smoothed, Control can be performed so that the color reproduction characteristics change smoothly with the color reproduction portion of the important color to be smoothed. That is, smoothing of the LUT is realized while maintaining color reproduction matching for a plurality of important colors. Furthermore, by preparing a set of colors such as a primary color and a secondary color as important color types, it is possible to perform LUT smoothing considering color reproduction of not only a single color but also a set of colors.

  In the present embodiment, examples of “monochromatic”, “primary color”, and “secondary color” are shown as the important color types to which the weight calculation method is assigned. However, the present invention is not limited to this. For example, in addition to the “primary color” even for the same line segment, a calculation method such as “achromatic color axis” is added, and weight calculation on the achromatic color axis (saturation 0 line), which is generally easy to understand for human eyes, It may be distinguished from the weight calculation in other “primary colors”.

<Other embodiments>
Although the embodiment has been described in detail above, the present invention can take an embodiment as a system, apparatus, method, program, recording medium (storage medium), or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, an imaging device, a web application, etc.), or may be applied to a device composed of a single device. good.

  The present invention also provides a software program that realizes the functions of the above-described embodiments directly or remotely to a system or apparatus, and the system or apparatus computer reads out and executes the supplied program code. Achieved. The program in this case is a computer-readable program that corresponds to the flowchart shown in the drawing in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Recording media for supplying the program include the following media. For example, floppy disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As a program supply method, the following method is also possible. That is, the browser of the client computer is connected to a homepage on the Internet, and the computer program itself (or a compressed file including an automatic installation function) of the present invention is downloaded to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to make it. That is, the user can execute the encrypted program by using the key information and install it on the computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, and then executed, so that the program of the above-described embodiment can be obtained. Function is realized. That is, based on the instructions of the program, the CPU provided in the function expansion board or function expansion unit can perform part or all of the actual processing.

It is a figure which shows the structural example of the color processing system in one Embodiment which concerns on this invention. It is a block diagram which shows the structure for producing | generating the LUT for color conversion in this embodiment. It is a figure which shows the structural example of the LUT produced | generated in this embodiment. It is a figure which shows the example of a table hold | maintained as important color conditions in this embodiment. It is a flowchart which shows the weight calculation method regarding the single color in this embodiment. It is a flowchart which shows the weight calculation method regarding the primary color in this embodiment. It is a graph which shows the outline of the relationship between distance and weight in the single color and primary color in this embodiment. It is a flowchart which shows the whole weight calculation process in this embodiment.

Claims (7)

A color processing apparatus that adjusts color conversion conditions and creates a color conversion table,
Color conversion means for converting an input color signal using a color conversion condition and outputting as a first output color signal;
Smoothing means for smoothing the first output color signal using a smoothing condition and outputting it as a second output color signal;
A primary color as a region defined by a straight line in the color space of the input color signal and a secondary color as a region defined by a plane in the color space of the input color signal. Holding means for holding each type , and
A weight calculating means for calculating a weight used for a weighting operation according to the type based on a distance between the input color and a plurality of important colors held in the holding means;
Of the weights calculated by the weight calculation means, a determination means for determining the maximum weight;
Weighting synthesis for calculating a third output color signal by performing a weighting operation on the first output color signal and the second output color signal using the maximum weight determined by the determining means. Means,
Table creating means for creating the color conversion table using the third output color signal;
A color processing apparatus comprising: 2. The color processing according to claim 1 , wherein the weight calculation unit calculates the weight so that the smaller the distance between the input color and the important color held in the holding unit is, the larger the weight is. apparatus. The holding means holds a pair of information indicating a calculation method for calculating the weight for each of the plurality of important colors,
It said weight calculation means, for each of a plurality of important color held by the holding means, which comprises using the weight calculation method is a pair, the color processing apparatus according to claim 1 or 2. The weighting synthesis means calculates the third output color signal by taking a weighted average of the first output color signal and the second output color signal according to the weight. The color processing apparatus according to any one of claims 1 to 3 . The color processing apparatus according to any one of claims 1 to 4 wherein the color conversion condition is characterized by represented as a table. A color processing method for adjusting a color conversion condition and creating a color conversion table,
A color conversion step of converting an input color signal using a color conversion condition and outputting as a first output color signal;
Smoothing the first output color signal using a smoothing condition and outputting as a second output color signal;
A primary color as a region defined by a straight line in the color space of the input color signal and a secondary color as a region defined by a plane in the color space of the input color signal. A holding step for holding each holding type in the holding means;
A weight calculation step of calculating a weight used for a weighting operation according to the type based on a distance between the input color and a plurality of important colors held in the holding unit ;

A determination step for determining a maximum weight among the weights calculated by the weight calculation step;
Weighting synthesis for calculating a third output color signal by performing a weighting operation on the first output color signal and the second output color signal using the maximum weight determined in the determination step. Steps,
A table creation step of creating the color conversion table using the third output color signal;
A color processing method characterized by comprising: A computer program for causing a computer to function as each unit of the color processing apparatus according to any one of claims 1 to 5 by being executed by the computer.

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