JP2002185804A - Color converter and color conversion method, parameter generator for color conversion and its method, image processing system and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color converter that can attain highly accurate color conversion without making the scale of hardware increase, even when receiving a color signal where only part of color spaces is substantially utilized. SOLUTION: The color converter is provided with a look-up table storage means 304, that stores interpolation arithmetic operation parameters, a partial color space information storage means 303 that stores range data in a partial color space, a color data generating means 301 for interpolation arithmetic operation that reads the range data of the partial color space from the partial color space information storage means 303 and that maps input color data onto the partial color space to generate the color data for interpolation arithmetic operation, and an interpolation arithmetic means 302, that reads the interpolation arithmetic operation parameter from the look-up table storage means 304, on the basis of interpolation arithmetic operation data and that applies an interpolation arithmetic operation to the interpolation arithmetic operation data for converting the data into color data for an image forming device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus (for example, a color facsimile,
The present invention relates to a color conversion device, a color conversion method, a color conversion parameter generation device, a color conversion parameter generation method, an image processing system, and a recording medium for performing color conversion on a color signal for a color printer.

[0002]

2. Description of the Related Art Conventionally, a memory map interpolation method using a three-dimensional look-up table (hereinafter referred to as a look-up table) has been proposed as a technique for easily and rapidly performing color conversion in the fields of color printing and color hard copy. ing. Here, the look-up table means that an input color space is divided into a plurality of unit interpolation solid groups, a unit interpolation solid including input color data is selected, and a plurality of vertices (hereinafter referred to as a grid) of the selected unit interpolation solid are selected. The output values corresponding to (points) are tabulated.

FIG. 17 is a diagram showing a configuration example of a conventional color conversion apparatus using a memory map interpolation method. Referring to FIG. 17, the color conversion apparatus performs a color conversion by performing an interpolation operation using a look-up table stored in a look-up table storage means 304 for storing a look-up table. And an interpolation operation means (memory map interpolation operation means) 302 for performing the operation.

In the color conversion apparatus shown in FIG.
02 divides the input color space into a plurality of unit interpolation solid groups,
Selecting a unit interpolation solid including the input color data, reading output values corresponding to a plurality of vertices (hereinafter referred to as lattice points) of the selected unit interpolation solid from the lookup table storage means 304, and performing a linear interpolation operation Thus, color conversion is performed over the entire color space.

[0005]

When document data on a computer is output by an image forming apparatus such as a printer, RGB color signals are converted to CMYK data or CMYK output signals of an image forming apparatus (for example, a printer). Generally, color conversion into color signals such as data or K data (monochrome output) is performed and transmitted to the image forming apparatus. As a typical RGB color signal, an sRGB color signal is known. In particular, when an RGB color signal is handled in a computer, it is often used after being converted into an sRGB signal. The relationship between the sRGB color signal and the XYZ tristimulus values is defined as in the following equation (Equation 1). However, in Equation 1, RO, GO, BO and R, G, B are each 0.
This is a value normalized to a value of １1.

[0006]

(Equation 1) If RO, GO, BO ≦ 0.00304, then R, G, B are R = 12.92 * ROG = 12.92 * GOB = 12.92 * BO, and RO, GO, BO> If it is 0.00304, then R, G, and B are R = 1.055 * RO ^{(1.0 / 2.4)} -0.0
55 G = 1.055 * GO ^{(1.0 / 2.4)} -0.0
55B = 1.055 * BO ^{(1.0 / 2.4)} -0.0
55.

However, the RGB color signals as described above generally have their color characteristics defined on the basis of the display in many cases. Therefore, the color reproduction range is limited, and there is an inconvenience in color conversion. Had occurred.

For example, consider a case where an image as input by a scanner is input to a computer and the input image is output by a printer. The document to be input by the scanner is generally photographic paper or printed matter. The color gamut of such a reflection original has a portion protruding from the sRGB color space. for that reason,
SRGB for easily handling scanner input images on a computer
If converted to color signals, information will be lost. For this reason, the missing information cannot be reproduced even when outputting to a printer, and the color cannot be faithfully reproduced.

In order to deal with such a problem, a new color space that can handle a wider color space has recently been developed as sR.
GB64 color signals have been proposed. The sRGB 64 color signal has the following features. That is, first, R, G, B
Each color is 16 bits and has a wide range from -4 to 4. Second, the color reproduction range is very wide, and all real colors can be handled.

The sRGB 64 color signal can handle a wider color reproduction range than the conventional RGB signal. Therefore, even when the above-described scanner input signal is output to the printer, the RGB color signal can be used.
It is possible to perform faithful color reproduction without causing information loss at the time of B conversion.

However, by expanding the range of Red, Green, and Blue so that all color spaces can be expressed, imaginary colors (colors that do not exist) are also included in the color reproduction range. Therefore, such an input color signal is
If a conventional color conversion device as shown in FIG. 17 attempts to perform color conversion on the entire input color space simply by a memory map interpolation method, grid points must be assigned to a color gamut that does not exist, and interpolation efficiency is reduced. As a result, the data size of the lookup table stored in the lookup table storage unit 304 becomes very large.

For example, when a general RGB signal is input, the number of divisions required for color conversion from RGB to CMYK is 16
, The size of the lookup table required for performing the interpolation operation is 19,652 (= 4 * 17 * 1).
7 * 17) bytes, whereas the data size of the lookup table for the sRGB 64 color data is 8,586,756 (= 4 * 129 * 129 * 12).
9) Bytes required.

Further, when the entire input color space is divided, it becomes difficult to obtain an output value corresponding to a lattice point assigned to an imaginary color. Therefore, the conventional color conversion device of FIG. 17 (that is, the conventional memory map interpolation method) cannot handle a color signal such as sRGB64.

The present invention can be applied to a case where a color signal that uses only a part of the color space, such as the sRGB 64 color signal, is input (that is, sRGB6).
(Even in a case where only a part of the color gamut of colors that can be represented by input color data is used, such as when converting four-color data into color data of an image forming apparatus), the hardware is not increased. It is an object of the present invention to provide a color conversion device, a color conversion method, a color conversion parameter generation device, a color conversion parameter generation method, an image processing system, and a recording medium capable of performing high-precision color conversion.

[0015]

In order to achieve the above object, according to the present invention, input color data represented by a first color system having three color components is converted into a second color system. In a color conversion apparatus for converting color data into color data for an image forming apparatus represented by a system, an input color on a grid point obtained by dividing a partial color space smaller than a color space that can be expressed by a first color system into unit cubes. Lookup table storage means for storing output color data corresponding to data as interpolation calculation parameters, partial color space information storage means for storing range data of the partial color space, and partial color space information storage means An interpolation color data generating means for reading the range data and mapping the input color data to the partial color space to generate interpolation color data; and the look-up table storage means based on the interpolation color data. Interpolation calculation means for reading interpolation calculation parameters from the image processing apparatus and performing interpolation calculation on the interpolation calculation color data using the read interpolation calculation parameters to convert the interpolation calculation color data into color data for an image forming apparatus. It is characterized by.

According to a second aspect of the present invention, in the color conversion device of the first aspect, the interpolation color data generating means converts the input color data when the input color data is not included in the partial color space. It is characterized by having mapping means for replacing with color data on the boundary surface of the partial color space.

According to a third aspect of the present invention, in the color conversion apparatus according to the second aspect, the mapping means converts the input color data when the input color data underflows or overflows the range of the partial color space. It is characterized in that mapping is performed by clipping on the boundary surface of the partial color space.

According to a fourth aspect of the present invention, in the color conversion apparatus according to the second aspect, the mapping means comprises a first conversion unit.
The area excluding the partial color space from the color space that can be expressed by the color system is divided into a plurality of truncated pyramid regions, and the input color data is included in any of the color spaces divided into the plurality of truncated pyramid regions. Is determined, and the input color data is converted into color data on the boundary surface of the partial color space by linear conversion means corresponding to the determination result.

According to a fifth aspect of the present invention, a color space that covers the color reproduction range of the image forming apparatus is defined as a partial color space, and input color data located outside the range of the partial color space is defined as a partial color space. To generate color data for an interpolation operation, perform a memory map interpolation operation on the color data for an interpolation operation, and convert the color data to color data for an image forming apparatus.

According to a sixth aspect of the present invention, there is provided color data for an image forming apparatus represented by a first color system having three color components and represented by a second color system. In the color conversion method, the input color data is converted so as to fall within the range of a partial color space narrower than the color space that can be expressed by the first color system, thereby generating interpolation calculation color data. Color data for interpolation calculation using output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a color space that can be expressed by the color system 1 into unit cubes as interpolation calculation parameters By performing an interpolation operation on the color data for the image forming apparatus.

According to a seventh aspect of the present invention, in the color conversion method according to the sixth aspect, the color data for the interpolation calculation is:
When the input color data is not included in the partial color space, the input color data is generated by mapping the input color data on the boundary surface of the partial color space.

According to an eighth aspect of the present invention, in the color conversion method of the seventh aspect, the color data for interpolation calculation is
When the input color data underflows or overflows the region of the partial color space, the input color data is generated by mapping by clipping the input color data onto the boundary surface of the partial color space.

According to a ninth aspect of the present invention, in the color conversion method of the seventh aspect, the color data for the interpolation operation is:
A region excluding the partial color space from the color space that can be expressed by the first color system is divided into a plurality of pyramid regions, and the input color data is divided into a plurality of pyramid regions. It is characterized by being determined by determining whether the input color data is included, and converting the input color data into color data on the boundary surface of the partial color space by linear conversion means corresponding to the determination result.

According to a tenth aspect of the present invention, the input color data is converted so as to fall within a range of a partial color space narrower than a color space that can be expressed by the first color system, and the color data for interpolation calculation is converted. Is generated, and output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes is used as an interpolation calculation parameter, A color for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system by performing an interpolation operation on the interpolation color data. A color conversion parameter generation device that generates a parameter used in a conversion process, wherein the color range calculation unit obtains a color range of the image forming apparatus on a first color system.
Comparing means for comparing the color range of the image forming apparatus with the predetermined color range in the first color system; and determining whether the color range of the image forming apparatus is not included in the predetermined color range. Means for calculating a range of the partial color space by expanding a predetermined color range, and an output color corresponding to input color data on a grid point obtained by dividing the range of the partial color space into unit cubes. Interpolating parameter generating means for generating data as an interpolating parameter.

The invention according to claim 11 is the first invention.
0, in the color conversion parameter generation device, the color gamut calculation means, when obtaining the color gamut of the image forming apparatus on the first color system, a plurality of images represented by the second color system. Converting the color data group for the forming apparatus into a color data group corresponding to the first color system, and obtaining the maximum value and the minimum value in the first color system for each color component from the converted color data group; It is characterized by.

The invention according to claim 12 is the first invention.
0, the partial color space calculation means defines a minimum value and a maximum value for each axis of the partial color space as integer multiples of 2 ⁿ (n = integer). It is characterized in that the range of the color space is calculated.

The invention according to claim 13 is the first invention.
5. The parameter conversion device according to claim 1, wherein the partial color space calculation unit sets the range of the calculated partial color space to the partial color space according to claim 1. 6. It is characterized in that it is set as space range data.

The invention according to claim 14 is the first invention.
5. The color conversion parameter generation device according to claim 1, wherein the interpolation calculation parameter generation unit looks up the generated interpolation calculation parameter into the color conversion device according to claim 1. 6. It is characterized in that it is set as a table.

[0029] The invention according to claim 15 provides the invention according to claim 1.
0, the parameter calculation means for interpolation calculation includes grid point generation means for generating grid points for a range of the partial color space calculated by the partial color space calculation means, and grid point generation means. Interpolating parameter calculation means for calculating output color data corresponding to the lattice points generated by the above as parameters for the interpolating operation.

[0030] Further, the invention according to claim 16 is based on claim 1.
5. The color conversion parameter generation device according to 5, wherein the grid point generation unit has at least one of a white point and a black point at a grid point obtained by dividing the partial color space calculated by the partial color space calculation unit into unit cubes. It is characterized in that lattice points are generated so as to be included.

According to a seventeenth aspect of the present invention, the input color data is converted so as to fall within the range of a partial color space narrower than the color space that can be expressed by the first color system, and the color data for interpolation calculation is converted. Is generated, and output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes is used as an interpolation calculation parameter, A color for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system by performing an interpolation operation on the interpolation color data. A color conversion parameter generation method for generating a parameter used in a conversion process, wherein a color range of an image forming apparatus is obtained on a first color system, and a color range of the image forming apparatus in the first color system is determined. Compare with specified color range and include in specified color range When there is no color gamut, a color range obtained by expanding a predetermined color range is obtained, the expanded color range is generated as a range of a partial color space, and the range of the partial color space is divided into unit cubes. It is characterized in that output color data corresponding to input color data on a grid point is generated as an interpolation calculation parameter.

Further, according to the present invention, the input color data represented by the first color system having three color components is converted into the second color data.
An image processing system that converts color data for an image forming apparatus represented by a color system and outputs the color data to the image forming apparatus,
5. The method according to claim 1, wherein input color data represented by a first color system having three color components is converted into color data for an image forming apparatus represented by a second color system. The color conversion device according to any one of the above is used.

According to a nineteenth aspect of the present invention, input color data represented by a first color system having three color components is converted into a second color data.
An image processing system that converts color data for an image forming apparatus represented by a color system and outputs the color data to the image forming apparatus,
A color conversion parameter generation device according to any one of claims 10 to 16 is used.

According to a twentieth aspect of the present invention, the input color data represented by the first color system having three color components is converted to the second color data.
In the color conversion processing for converting into color data for an image forming apparatus represented by the color system, the input color is set so as to fall within the range of a partial color space narrower than the color space that can be expressed by the first color system. An output color corresponding to input color data on grid points obtained by converting data to generate color data for interpolation calculation and dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes A computer-readable recording that records a program that causes a computer to perform a process of converting color data for an image forming apparatus by performing an interpolation operation on color data for an interpolation operation, using the data as parameters for the interpolation operation. Medium.

According to a twenty-first aspect of the present invention, the input color data is converted so as to fall within a range of a partial color space narrower than the color space in which the first color system can be expressed, and the color data for interpolation calculation is used. Is generated, and output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes is used as an interpolation calculation parameter, A color for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system by performing an interpolation operation on the interpolation color data. A color conversion parameter generation process for generating parameters used in the conversion process, wherein a color range of the image forming apparatus is obtained on a first color system, and a color range of the image forming apparatus in the first color system is determined. Compare with specified color range and include in specified color range When there is no color gamut, a color range obtained by expanding a predetermined color range is obtained, the expanded color range is generated as a range of a partial color space, and the range of the partial color space is divided into unit cubes. This is a computer-readable recording medium on which a program for causing a computer to execute a process of generating output color data corresponding to input color data on a grid point as interpolation calculation parameters is recorded.

[0036]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of an image processing system according to the present invention. Referring to FIG. 1, the image processing system includes a display 100, a digital camera (digital still camera) 101, and a scanner 102.
, A computer 103, an image forming apparatus 104, and an image processing apparatus 200.

Here, software such as various applications and a printer driver can be mounted on the computer 103. In addition, the digital camera 10
1, a scanner 102 is an input device for capturing image data to be processed. The display 100
Is a display device for displaying image data, and the image forming device 104 is an output device for printing out the image data. Note that a color printer, a color copier, a color facsimile machine, or the like can be used as the image forming apparatus 104.

FIG. 2 is a diagram showing a configuration example of the computer 103 and the image processing device 200 in the image processing system of FIG. Referring to FIG. 2, the computer 10
Reference numeral 3 has a function of transmitting a drawing command to the image processing apparatus 200 through software such as an application and a printer driver.

On the other hand, the image processing apparatus 200 includes a rendering processing unit 201, a band buffer 202, a color conversion processing unit (color conversion device) 203, a gradation processing unit 204, and the like. Is converted into data that can be processed by the image forming apparatus 104. Note that the image processing apparatus 200 may include other functions such as a data compression process.

Next, the operation of the image processing system shown in FIGS. 1 and 2 will be described. First, an operation until the computer 103 generates a drawing command will be described. First, the operator takes image data into the computer 103 using an image input device such as the scanner 102, for example. Next, the operator edits the read image data while displaying it on a display by using an application or the like installed in the computer 103.
When the editing operation is completed, the operator instructs printing to output the image to the image forming apparatus 104.

When the computer 103 receives a print instruction from the application, the computer 103 transmits document data in the application to the printer driver. After converting the document data into a drawing command that can be received by the image processing apparatus 200, the printer driver
Send to 00.

Next, the operation of the image processing apparatus 200 will be described. The image processing apparatus 200 includes a computer 103
Rendering processing unit 2
In step 01, the command format data is converted into raster format image data (for example, RGB image data) and stored in the band buffer 202. Color conversion processing unit (color conversion device)
A color conversion unit 203 performs color conversion on the image data (for example, RGB image data) read from the band buffer 202, converts the image data into color data (for example, CMYK) suitable for the image forming apparatus (output apparatus) 104, Key processing unit 204
Send to Then, the gradation processing unit 204 applies dither processing or the like to convert the data into gradation data that can be processed by the image forming apparatus 104, and transmits the generated gradation data to the image forming apparatus (output apparatus) 104. As a result, the image forming apparatus 104 can perform printing.

In the examples shown in FIGS. 1 and 2, the image processing apparatus 200 is provided separately from the computer 103 and the image forming apparatus 104.
03 or the image forming apparatus 1
04 may be implemented. Alternatively, the image forming apparatus 1
It may be implemented in a printer control device (not shown) provided independently of the printer controller 04. That is, the image processing device 20
0 or some functions of the computer 10
3 or the image forming apparatus 104 or the printer control device.

The image processing apparatus 200 of the present invention can be realized by software. For example, the functions of the image processing apparatus 200 can be realized by a printer driver that exists as a program in the computer 103.

In the configuration example of FIG. 2, the present invention
The feature of the configuration of the color conversion processing unit (color conversion device) 203 is that prior to describing this, a known memory map interpolation calculation will be described first.

As a memory map interpolation method using a three-dimensional lookup table (hereinafter, referred to as a lookup table), various memory map interpolation methods such as tetrahedral interpolation, triangular prism interpolation, and cubic interpolation have been proposed. . In addition,
In the present invention, any of the above-described interpolation methods may be used in the interpolation calculation means 302 described later. Here, a memory map interpolation method using a triangular prism interpolation method will be described as an example.

In the triangular prism interpolation method, as shown in FIG. 3, the input color space X, Y, Z (R, G, B) is divided into a plurality of unit triangular prisms. Then, when calculating the value of the output P at the input X, Y, Z coordinates, a unit triangular prism including the input X, Y, Z coordinates is selected, and the selected unit triangular prism 6 is selected.
The output value at the output P is obtained by linear interpolation based on the output values of the vertices (= lattice points).

Here, when applied to color conversion, X, Y,
Z corresponds to the input signals R (red), G (green), B (blue),
The output P is Y for controlling the ink in the case of a four-color printer.
(Yellow), M (magenta), C (cyan), Bk
(Black) signal. It is also assumed that the output values of the respective grid points are obtained in advance by calculation as interpolation calculation parameters, and are constructed as a three-dimensional lookup table (lookup table).

The selection of the unit triangular prism in the triangular prism interpolation method will be described. In this type of interpolation method, as shown in FIG. 3, each coordinate of the input color space X, Y, Z is divided into 2 n pieces (in the example of FIG. 3, n = 2), The space X, Y, Z is divided into 2 3n cubes. Now, let the bit width of X, Y, Z be f bits (for example,
X, Y, Z are represented as X = x + Δx, Y = y + Δy, Z = z + Δz, and f bits (eg, 8 bits) are upper n bits (eg, 2 bits) and lower bits (eg, 2 bits). fn) bits (for example, 6 bits), the upper n bits of X, Y, and Z are x, y, z, and the lower (fn) bits are Δx, Δ
When corresponding to y and Δz, one of the cubes divided into 2 3n powers is selected by the upper n bits of X, Y and Z. The divided cube is divided into two triangular prisms, and the lower (f−n) bits indicate the relative positions Δx, Δy, and Δz in the selected cube. Can be determined as belonging to the triangular prism.

The interpolation operation of the triangular prism interpolation method is performed as follows. FIG. 4 is a diagram for explaining the interpolation calculation on the side of the triangular prism. Referring to FIG. 4, the output value at each vertex coordinate of the triangular prism is Pi (i = 1 to 6, the value is known), and the coordinates at the intersection of the triangular surface 31 and the triangular prism 32 including the coordinates of the output P to be obtained are given. When the output values are Pa, Pb, and Pc, respectively, the value of Pa is P1 and P2.
Is obtained by linear interpolation using the line segment ratio of Similarly, the value of Pb is obtained from P3 and P4 by linear interpolation, and the value of Pc
Is obtained from P5 and P6 by linear interpolation.

More specifically, for example, P1-P2
Assuming that = P4-P2 = P6-P4 = [Delta], Pa is determined by the following expression: Pa = ([Delta] z * P2 + ([Delta]-[Delta] z) * P1) / [Delta]. Pb and Pc are similarly obtained.

Next, on the triangular surface 31, by linearly interpolating the output values Pa, Pb, and Pc of the vertexes obtained above in accordance with the following equation (Equation 2), the value of the output P can be obtained.

[0053]

P = Pa + (Pb−Pa) × ＝ x / （+ (Pc
−Pb) × {y / △

As described above, in the memory map interpolation method,
If each color in the input color space is divided into 2 n, the selection of the divided solid and the interpolation operation can be processed with the upper and lower bits, so that the configuration of the color conversion device can be simplified.

A three-dimensional look-up table (look-up table) used for the memory map interpolation method
Is constructed as follows: FIG. 5 is a flowchart illustrating an example of a procedure for constructing a look-up table used for a memory map interpolation operation.

Referring to FIG. 5, first, a color prediction formula is constructed (step S101). Note that the color prediction formula is a model in which the output characteristics of the image forming apparatus are modeled by mathematical expressions, and a calorimetric value can be obtained from the output color data by calculation. For example, XYZ tristimulus values can be obtained from CMYK output values. As a general method for constructing a color prediction formula, a color patch is output by an image forming apparatus, the output color patch is measured by a spectrophotometer, and then,
Color patch colorimetric data and output color data (= C, M, Y,
K value) is approximated to construct a color prediction formula.

Next, output values corresponding to the RGB values of the grid points are obtained based on the color prediction formula constructed in step S101 (step S102). To calculate an output value for a grid point Pi (R, G, B), first, Lab values are calculated from RGB values.
Device-independent colors such as values (for example,
Lab value). This conversion is based on a relational expression between RGB and XYZ. Next, gamut mapping (gamut compression) is performed to replace device-independent colors such as Lab values with colors that can be output by the image forming apparatus (step S103).

The input RGB color data contains many colors that cannot be reproduced by an image forming apparatus such as a printer. For example, a pure color green cannot be reproduced with a printer. The output values for such color data are mapped to colors as close as possible to perform color reproduction with less discomfort. Various schemes have been proposed for this gamut mapping, but generally, an input Lab signal is subjected to brightness compression, saturation compression, and the like to output a color (for example, L'a'b '). A mapping method is used.

After performing the gamut mapping, an output CMYK value corresponding to the Lab value after the mapping (that is, L'a'b 'value) is calculated (step S104,
S105). However, since the conversion from Lab to CMYK cannot be uniquely calculated, first, K is obtained according to a predetermined black generation condition (step S104), and then the remaining CMY is calculated (step S105).

Next, it is determined whether or not the output values of all the grid points have been calculated (step S106). When the output values of all the grid points have been calculated, they are used as interpolation calculation parameters, that is, three-dimensional look-up values. As an up table (lookup table), the data is written to the ROM or stored in a data file.

As described above, in the memory map interpolation operation, the interpolation solid to which the input color data belongs is selected using the upper bits and the lower bits of the input data, and the output value at the vertex (= grid point) of the interpolation solid is selected. Is read from a three-dimensional lookup table (look-up table), and an interpolation operation is performed using the lower bits of the input data and the grid point output value read from the three-dimensional lookup table (look-up table) to output the input color data. The value can be calculated.

When color conversion is performed using the above-described memory map interpolation method, generally, the more the number of divisions to the input RGB color space, the more accurate the color conversion can be realized. The data amount of the look-up table (look-up table) increases. Therefore, in the memory map interpolation method, it is important to divide the input color space as efficiently as possible.

On the other hand, when a color space that can express even non-existent colors (= imaginary colors) is used as input color data, such as the sRGB 64 color space, there is a possibility that it can be actually input even if it can be expressed numerically. There is no color space at all. Therefore,
When such a color space is used as the input color data, it is necessary to increase the efficiency by performing the memory map interpolation calculation only for the effective color space.

Therefore, in the present invention, a color space that covers the color reproduction range of an image forming apparatus (eg, a printer) is defined as a partial color space, and input color data located outside the range of the partial color space is defined as the partial color space. A memory map interpolation operation is performed after mapping to a space, thereby enabling efficient color conversion.

FIG. 6 is a diagram showing a configuration example of the color conversion apparatus (color conversion processing unit 203 in FIG. 2) according to the present invention. Referring to FIG. 6, this color conversion device is represented by a first color system (for example, sRGB64) having three color components (for example, red (R), green (G), and blue (B)). Color data (for example, CMYK, CMY, or K) for an image forming apparatus (for example, a color printer or a monochrome printer) in which input color data is represented by a second color system
Output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes (that is, an interpolation operation). Lookup table storage means 304 for storing parameter data, a partial color space information storage means 303 for storing partial color space range data, and a partial color space range data read from the partial color space information storage means 303 for input. Interpolation color data generation means 3 for mapping color data to a partial color space to generate interpolation calculation color data
01 and the interpolation calculation parameters are read out from the look-up table storage means 304 based on the interpolation calculation color data, and the interpolation calculation is performed on the interpolation calculation color data using the read interpolation calculation parameters. And an interpolation calculating means 302 for converting the color data into color data for the device.

Here, the interpolation calculation color data generating means 30
1 if the input color data is not included in the partial color space,
There is a mapping means 305 for replacing the input color data with the color data on the boundary surface of the partial color space.

FIG. 7 is a diagram for explaining a partial color space. Referring to FIG. 7, the partial color space 92 is a color space in which the input color data can be expressed, that is, a cubic space representing a part of the input color space 93 (for example, sRGB64 color space). Is the RGB of P0 and P1
It can be described by coordinates. Therefore, the partial color space is
RP _min , RP _max , GP _min , GP _max , BP _min , BP
_{Defined by} the value of _max . That is, RP _min , RP
_{max, GP min, GP max,} BP min, the value of BP _max is the partial color space information.

FIG. 8 is a diagram for explaining the concept of setting the range of the partial color space. For simplicity of description, in FIG. 8, the R, G, and B color spaces are replaced with a two-dimensional RG space. In the example of FIG. 8, a standard RGB color space (for example, sRGB color space) 91 is a color space that takes values of 8 bits (0 to 255) on each axis. In the standard RGB color space (for example, sRGB color space) 91, a value obtained by converting a color that can be output by the image forming apparatus into the above-described RGB color signal is plotted by ●.

As shown in FIG. 8, some of the colors that can be output by the image forming apparatus may take a negative value, and the standard RGB
It cannot be expressed in the color space 91. Although not shown in FIG. 8, some of the colors that can be output by the image forming apparatus are 25.
It may exceed five. Therefore, the ranges RP _min , RP _max , GP _min , and GP of the partial color space 92 are so set that all the color data that can be output by the image forming apparatus can be represented in this way.
_max , BP _min and BP _max are set.

However, a standard RGB color space (for example, s
Even if there is a color gamut in which the output colors of the image forming apparatus are not distributed in the (RGB color space) 91, it is necessary to convert the drawing color artificially created on the computer into a color and output the converted color. The range of 92 is a standard RGB color space 9
The range of 0 to 255 is included. That is, RP _min , GP _min , BP _min ≦ 0 RP _max , GP _max , BP _max ≧ 255.

In the partial color space range setting method described above, the partial color space range is determined based on the color reproduction range of a predetermined image forming apparatus. However, the color reproduction range of an image forming apparatus is changing with the progress of devices, and considering the versatility of a color conversion apparatus, some output values can be output even in a color space that excludes a partial color space from an input color space. You have to be as required. For example, given CMYK
Assuming that the partial color space is determined according to the color reproduction range of the printer, it is easy to imagine that the color reproduction range of a printed matter using a special color (for example, a special color such as red or yellow) is further expanded.

Therefore, according to the present invention, when input color data outside the range of the partial color space is input, the input color data is generated by the mapping means 305 of the interpolation calculation color data generating means 301 as shown in FIG. The data (R, G, B) is mapped to the boundary surface of the partial color space to obtain interpolation calculation color data (R ′, G ′, B ′).

Next, the processing operation of the color conversion apparatus shown in FIG. 6 will be described. First, color data generation means 301 for interpolation calculation
Reads the range data of the partial color space from the partial color space information storage means 303 and determines whether or not the input color data (input RGB data) is included in the partial color space. As a result, if the input color data (RGB) is out of the range of the partial color space, the interpolation calculation color data generating means 301 maps the input color data (RGB) on the boundary surface of the partial color space by the mapping means 305. And converts the data into color data for interpolation calculation (R′G′B ′), and gives the data to the interpolation calculation means 302. Upon receiving the interpolation calculation color data (R′G′B ′) from the interpolation calculation color data generation unit 301, the interpolation calculation unit 302 uses the interpolation calculation parameters stored in the lookup table storage unit 304. Interpolation is performed on the interpolation calculation color data, and an output value (for example, CM
YK data).

Various types of mapping means 305 can be considered. As one example, as the mapping means 305, when the input color data underflows or overflows the range of the partial color space, one that maps the input color data on the boundary surface of the partial color space by clipping may be used. it can.

That is, in this example, the mapping means 3
05 is RP for R of input color data (RGB).
_{If max} >R> RP _min , R ′ = R, and R <R
If P _min , R ′ = RP _min, and R> RP _max
Then, R is converted to R 'by setting R' = RP _max .

Similarly, G and B of the input color data (RGB) are converted into G 'and B'.

As another example, the mapping means 30
5 is a color obtained by excluding the partial color space from the color space that can be expressed by the first color system into a plurality of quadrangular pyramid regions, and input color data divided into a plurality of quadrangular pyramid regions. It is possible to use one that determines which one of the spaces is included and converts the input color data into color data on the boundary surface of the partial color space by linear conversion means corresponding to the determination result.

FIG. 10 shows an example in which a color space outside the range of the partial color space is divided into six truncated pyramid regions. In this example, the mapping unit 305 divides the color space outside the range of the partial color space into six truncated quadrangular pyramids and calculates the input color data on the boundary surface of the partial color space by calculation corresponding to the truncated quadrangular pyramid. Map to data.

FIG. 11 is a diagram for explaining this mapping method. FIG. 11 is a two-dimensional drawing of one of the truncated pyramids taken out. FIG.
In FIG. 1, the input color data is M, and the color data after mapping is Mo. Referring to FIG. 11, first, a plane (M1-M2-M3-M4) including the input color data M is obtained. For example, M1 can be obtained by the following linear operation of T1 and P1. _{R M1 = (B M -BP max} ) * RT min + (BT max -B M) * RP min G M1 = (B M -BP max) * GT max + (BT max -B M) * GP max B M1 = B _M

The other M2, M3, and M4 can be obtained by the same linear operation.

When M1, M2, M3 and M4 are obtained, M
A plane surrounded by 1, M2, M3, and M4 is represented by P1-
R _Mo , G _Mo , and B _Mo are obtained by performing similarity conversion to the boundary surface of the partial color space surrounded by P2-P3-P4. That is, R _Mo , G _Mo , and B _Mo are given by: R _Mo = (R _M2 −R _M ) * RP _min + (R _M −R _M4 ) * RP _max G _Mo = (G _M2 −G _M ) * GP _min + (G _M -G _M4) * obtained as a GP _max B _Mo = BP _max.

Next, a color conversion method by the color conversion apparatus shown in FIG.
Will be described with reference to the flowchart of FIG. Figure
Referring to FIG. 12, first, a color gamut for performing an interpolation operation is determined.
For this purpose, the range data of the partial color space (ie, RP
_min, RP_max, GP_min, GP_{m ax}, BP_min, BP_maxof
Is read (step S201).

When the range data of the partial color space is read, the color conversion process is executed while reading the input color data (steps S202 to S206). That is, when the input color data Din (for example, RGB) is read in step S202, it is converted to interpolation calculation color data D'in (for example, R'G'B ') in step S203. next,
In step S204, an interpolation calculation parameter (output value of a grid point) corresponding to the interpolation calculation color data D'in is read from the lookup table. And step S
In step 205, the above-described interpolation calculation is performed on the interpolation calculation color data D'in using the interpolation calculation parameters, and output color data is calculated. In step S206,
It is checked whether or not the interpolation operation has been completed for all the input color data. If the interpolation operation has not been completed for all the input color data, step S20 is performed.
Steps S2 to S205 are repeated, and when it is determined in step S206 that the interpolation calculation processing has been completed for all the input color data, the color conversion processing ends.

In step S203, the conversion from the input color data Din to the color data D′ in for interpolation calculation is performed based on whether or not the input color data Din is within the range of the partial color space. That is, the input color data Di
If n is data in the partial color space, D'in = Din
And execute the interpolation operation as it is. On the other hand, if the input color data Din is not within the range of the partial color space, a mapping process to the boundary surface of the partial color space is executed.

As described above, in the color conversion apparatus of FIG.
Lookup table storage that stores output color data (that is, interpolation calculation parameters) corresponding to input color data on grid points obtained by dividing a partial color space narrower than the color space that can be expressed by the color system into unit cubes. Means 304 and partial color space information storage means 3 for storing range data of the partial color space
03; an interpolation calculation color data generation unit 301 that reads the range data of the partial color space from the partial color space information storage unit 303 and maps the input color data to the partial color space to generate interpolation calculation color data; Based on the calculation color data, the interpolation calculation parameters are read from the look-up table storage unit 304, and the interpolation calculation is performed on the interpolation calculation color data using the read interpolation calculation parameters to obtain the color for the image forming apparatus. Since there is provided the interpolation calculation means 302 for converting the data into data, even when color data that substantially uses only a part of the color space such as sRGB 64 color data is input (ie, As in the case of converting sRGB 64 color data into color data for an image forming apparatus, the color gamut of a part of the color that can be expressed by the input color data Even when not being used), without increasing the hardware, it is possible to perform highly accurate color conversion.

In particular, interpolation calculation color data generating means 301
Has mapping means 305 that replaces the input color data with color data on the boundary surface of the partial color space when the input color data is not included in the partial color space. Even when color data is input, color conversion can be performed.

When the mapping means 305 maps the input color signal on the boundary surface of the partial color space by clipping when the input color signal underflows or overflows the area of the partial color space. Even when color data that cannot be interpolated is input, color conversion can be performed while maintaining continuity of gradation.

Further, the mapping means 305 divides the area excluding the partial color space from the color space that can be expressed by the first color system into a plurality of quadrangular pyramid regions, and the input color signal is When it is determined which of the color spaces divided into regions is included in the color space, and when the data is converted into color data on the boundary surface of the partial color space by the linear conversion means corresponding to the determination result, the interpolation is also performed. When a color signal that cannot be calculated is input, color conversion can be performed while maintaining the continuity of gradation.

As described above, in the present invention, a color conversion system (for example, conversion from sRGB64 to a printer color signal) that substantially uses only a part of the color gamut of a color space in which an input color signal can be expressed is assumed. It has only a look-up table corresponding to a predetermined color gamut, and for an input signal not included in the predetermined color gamut, converts the input signal to a color signal of a predetermined color gamut, performs interpolation, and outputs an output value. I try to calculate.

That is, in the present invention, mapping is performed only when input color data located in a color space outside the partial color space is input, and color data in the partial color space is subjected to only interpolation calculation processing. Perform color conversion. Thereby, the processing speed can be improved.

FIG. 13 shows the partial color space information stored in the partial color space information storage means 303 and the lookup table stored in the lookup table storage means 304 of the color conversion apparatus shown in FIG. FIG. 2 is a diagram illustrating a configuration example of a color conversion parameter generation device that generates a color conversion parameter;

Referring to FIG. 13, the color conversion parameter generation device 400 includes a colorimetric data storage unit 401,
GB data generation unit 402 and partial color space setting unit 403
And a lattice point generation unit 404 and a lookup table calculation unit 405. Further, a colorimeter for measuring the color patches output from the image forming apparatus is connected to the outside. This color conversion parameter generation device 400 includes:
For example, it can be provided in the image processing apparatus 200 shown in FIGS.

The parameter generation device 40 for color conversion shown in FIG.
At 0, the colorimetric data storage unit 401 is for storing the colorimetric data received from an externally connected colorimeter. Note that the colorimetric data includes Lab values, XYZ values, and the like.

The RGB data generation unit 402 converts the colorimetric data stored in the colorimetric data storage unit 401 into RGB data.
It has a function of converting into B color data. This conversion is
For example, assuming sRGB64 as an RGB color space,
sRGB 64 color data can be calculated from the XYZ tristimulus values according to the following equation.

[0095]

(Equation 3)

Further, the partial color space setting unit 403 outputs
The range of the partial color space is set based on the RGB data calculated by the data generation unit 402. here,
To calculate the range of the partial color space, first, the maximum value and the minimum value of the RGB conversion data are obtained for each of the R, G, and B color components. For example, the minimum value of the R signal is 20 and the maximum value is 2
40, the minimum value of the G signal is -10, and the maximum value is 240.
Assuming that the minimum value of the B signal is −30 and the maximum value is 255, the range of the partial color space is determined by comparing a predetermined range with the above-mentioned maximum value and minimum value. Here, the predetermined range includes, for example, a general RGB space range (0 to 2).
55) is used. When a general range of RGB space (0 to 255) is used as the predetermined range, in the above example,
Since the minimum value of the G signal is 0 or less, the minimum value of the G coordinate in the partial color space is set to -10. If other considerations are similarly considered, the range of the partial color space can be calculated as _RPmin = 0, _RPmax = 255 _GPmin = −10, _GPmax = 255 _BPmin = −30, and _BPmax = 255.

However, if the partial color space is set within the above range, the black point (0, 0, 0) will not pass when the partial color space is divided by a cube having one side length of 16. As a result, the memory map interpolation calculation becomes complicated. Therefore, if the range of the partial color space is set so that the grid points always include either the white point WP or the black point BP as shown in FIG. 14 (in the example of FIG. 14, the length of one side is = 64), which makes it easy to implement the interpolation operation with hardware. _{That, RP min, RP max, GP} min, G
The values of P _max , BP _min , and BP _max are raised to the power of 2 (n = integer)
(That is, 16 in the above example) (that is, the minimum and maximum values for each axis of the partial color space are defined as integer multiples of 2 ⁿ (n = integer). As described above, by calculating the range of the color space), the memory access can be performed using the upper bits and the lower bits, and the interpolation operation can be performed using only the lower bits, thereby simplifying the circuit. That is, in the above _{example, RP min = 0, RP max} = 255 GP min = -16, GP max = 255 BP min = -32, had better be as BP _max = 255.

The range data of the partial color space calculated in this manner is supplied to the image processing device 200 (color conversion device 203).
And stored in the partial color space information storage means 303 of the color conversion device 203 as partial color space information.

In the color conversion parameter generation device 400 shown in FIG. 13, the grid point generation section 404 generates RGB values of grid points included in the range of the partial color space set by the partial color space setting section 403. This is given to the lookup table calculation unit 405. Further, the lookup table calculation unit 405 calculates an output value corresponding to the grid point generated by the grid point generation unit 404 (calculates an output value of the grid point by performing the processing shown in FIG. 5), The output value corresponding to the grid point is stored as a lookup table in the lookup table storage unit 304 of the color conversion device.

FIG. 15 is a flowchart for explaining the color conversion parameter generation method of the present invention. Referring to FIG. 15, first, predetermined patch data is output from an image forming apparatus (for example, a color printer) (Step S).
301). As the predetermined patch data, for example, CM
The color data obtained by arranging the YK color signals in 16 steps is output. The finer the steps, the better, but not particular. Even if not all combinations are output, the number of output patches can be reduced by fixing three of the four colors to the maximum value or the minimum value and setting the remaining one color in several steps.

[101] For example, CMYK = [0,0,0,0], [0,0,0,16], [0,0,0,32] ... [0,0,
[0,255], [0,0,255,0], [0,0,255,16], [0,0,255,32],…,
[0,0,255,255],:: [255,255,255,0], [255,255,255,16], [255,255,255,32],
…, [255,255,255,255] output a combination of patches.

Next, the color patch output in step S301 is measured by a colorimeter, and the XYZ value or Lab value of the output color patch is obtained (step S302).

Next, the colorimetric data is converted into RGB color data (for example, sRGB64 color system color data) which is a color signal of the input color space (step S303). Next, a distribution range of the converted RGB color data is obtained (Step S).
304), the range of the partial color space is determined by comparing the distribution range of the RGB color data with a predetermined color space range (step S3).
05). The range of the partial color space obtained in this way is set as one parameter for color conversion in the color conversion device.

When the range of the partial color space is determined in step S305, the partial color space is divided into unit solids to generate grid points (step S306), and the output values of the generated grid point positions (for example, CMYK values) are calculated as described above (step S307). The output value corresponding to the grid point thus obtained is set in the color conversion device as another parameter for color conversion, that is, as a look-up table (parameter for interpolation calculation).

FIG. 16 is a diagram showing an example of a hardware configuration of the image processing system of the present invention. Referring to FIG.
This image processing system is realized by, for example, a workstation or a personal computer, and controls the entire CPU 21; a ROM 22 storing a control program of the CPU 21; a RAM 23 used as a work area of the CPU 21; 24,
Digital camera 10 for inputting RGB image data
1 and a scanner 102, a display 100 for displaying image data, and an image forming apparatus 104 such as a color printer.

Here, CPU 21, ROM 22, RAM
23 and the hard disk 24 have a function as the computer 103 in FIGS. In this case,
The functions of the image processing apparatus 200 shown in FIGS.
Can be given. That is, the CPU 21 can be provided with a function as a color conversion device and a color conversion method of the present invention, and a function as a color conversion parameter generation device and a color conversion parameter generation method.

The functions of the CPU 21 such as the color conversion device and the color conversion method, the color conversion parameter generation device and the color conversion parameter generation method are as follows.
For example, a software package (specifically, a CD-R
16 can be provided in the form of an information recording medium such as an OM. For this reason, in the example of FIG. 16, when the information recording medium 30 is set, a medium drive device 31 that drives the information recording medium 30 is provided.

In other words, the color conversion device and the color conversion method, the color conversion parameter generation device and the color conversion parameter generation method of the present invention are applied to a general-purpose computer system having an image scanner, a display, and the like. Read the program recorded on the information recording medium of
The present invention can also be implemented in an apparatus configuration in which a microprocessor of the general-purpose computer system executes a color conversion process and a color conversion parameter generation process. In this case, the program for executing the color conversion processing and the color conversion parameter generation processing of the present invention (that is, the program used in the hardware system) is provided in a state recorded on a medium. The information recording medium on which a program or the like is recorded is not limited to a CD-ROM.
An OM, a RAM, a flexible disk, a memory card, or the like may be used. The program recorded on the medium is
When installed in a storage device incorporated in the hardware system, for example, the hard disk 24, this program can be executed to realize the color conversion processing function and the color conversion parameter generation processing.

A program for realizing the color conversion device and the color conversion method, the color conversion parameter generation device and the color conversion parameter generation method of the present invention is provided not only in the form of a medium but also by communication. For example, it may be provided by a server.

[0110]

As described above, according to the first to ninth aspects of the present invention, the input color data represented by the first color system having three color components is converted into the second color data. When converting into color data for an image forming apparatus represented by a color system, the input color data is converted so as to fall within a range of a partial color space narrower than a color space that can be expressed by the first color system. To generate interpolation calculation color data, and perform interpolation calculation on output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than the color space that can be expressed by the first color system into unit cubes. The sRGB 64 data is converted into color data for the image forming apparatus by performing interpolation on the color data for the interpolation calculation by using the data as the parameters for the interpolation calculation. Color gamut of some colors that can be represented by input color data Even when not being used, without increasing the hardware, it is possible to realize a highly accurate color conversion.

In particular, according to the second, fourth, seventh, ninth, eighteenth, and twentieth aspects of the present invention, the color data for interpolation calculation is such that the input color data is in a partial color space. If not included, the input color data is generated by mapping it on the boundary surface of the partial color space. Therefore, even when color data that cannot be interpolated is input, color conversion can be performed.

According to the third and eighth aspects of the present invention, when the input color data underflows or overflows the region of the partial color space, the input color data is converted to the partial color space. Since it is generated by mapping by clipping on the boundary surface of, even if color data that cannot be interpolated is input,
Color conversion can be performed while maintaining the continuity of gradation.

According to the fourth and ninth aspects of the present invention, the color data for interpolation calculation includes a plurality of quadrangular truncated pyramids in a region excluding a partial color space from a color space that can be expressed by the first color system. It is determined whether the input color data is included in the color space divided into the plurality of quadrangular frustum regions, and the input color data is divided into the boundary of the partial color space by the linear conversion means corresponding to the determination result. Since the color data is generated by converting the color data on the surface, even when color data that cannot be interpolated is input, it is possible to perform color conversion while maintaining the continuity of gradation.

According to the tenth to seventeenth, nineteenth, and twenty-first aspects of the present invention, the first color system falls within a range of a partial color space narrower than a color space that can be expressed. In this manner, the input color data is converted to generate interpolation calculation color data, and the partial color space narrower than the color space that can be expressed by the first color system is divided into unit cubes into input color data on grid points. By using the corresponding output color data as interpolation calculation parameters and performing interpolation calculation on the interpolation calculation color data, the input color data represented by the first color system is converted by the second color system. When generating a parameter used in a color conversion process for converting color data to be represented into color data for an image forming apparatus, a color range of the image forming apparatus is obtained on a first color system, and The color range of the image forming apparatus is compared with a predetermined color range, and If the color gamut that is not included in the color range is present determines the color range obtained by enlarging a predetermined color range, and generates a color range that extends as a range of the partial color space, also,
Since output color data corresponding to input color data on grid points obtained by dividing the range of the partial color space into unit cubes is generated as an interpolation calculation parameter, sRGB 64 color data is converted into color data for an image forming apparatus. Even when only a part of the gamut of colors that can be represented by the input color data is used, it is possible to create efficient color conversion parameters suitable for the color reproduction range of the image forming apparatus. it can.

In particular, according to the eleventh aspect of the present invention, in the color conversion parameter generating apparatus according to the tenth aspect,
The color gamut calculating means, when determining the color gamut of the image forming apparatus on the first color system, divides a number of image forming apparatus color data groups represented by the second color system into a first color system. Since the color data is converted into a color data group corresponding to the color system, and the maximum value and the minimum value in the first color system are obtained for each color component from the converted color data group, the color reproduction range of the image forming apparatus can be effectively set. The utilized color conversion parameters can be generated.

According to the twelfth aspect of the present invention, in the color conversion parameter generating device according to the tenth aspect,
The partial color space calculation means calculates the range of the partial color space by defining the minimum value and the maximum value for each axis of the partial color space as integer multiples of 2 ⁿ (n = integer). Can be used to select a unit solid and to perform an interpolation operation using lower bits, thereby enabling high-speed processing.

According to the sixteenth aspect of the present invention, in the color conversion parameter generating device according to the fifteenth aspect,
The grid point generation unit is a grid point obtained by dividing the partial color space calculated by the partial color space calculation unit into unit cubes,
Since the grid points are generated so as to include at least one of the white point and the black point, there is a case where only a lookup table corresponding to a part of the color reproduction range that can be represented by the input color data is provided. However, it is possible to satisfactorily control the output color for a specific color such as white or black.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an image processing system according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of a computer and an image processing device in the image processing system of FIG. 1;

FIG. 3 is a diagram for explaining a triangular prism interpolation method.

FIG. 4 is a diagram for explaining an interpolation operation on a side of a triangular prism.

FIG. 5 is a flowchart showing an example of a procedure for constructing a look-up table used for a memory map interpolation operation.

FIG. 6 is a diagram illustrating a configuration example of a color conversion device according to the present invention.

FIG. 7 is a diagram illustrating a partial color space.

FIG. 8 is a diagram for explaining a concept of setting a range of a partial color space.

FIG. 9 is a diagram for explaining mapping of input color data to a boundary surface of a partial color space.

FIG. 10 is a diagram illustrating an example in which a color space outside the range of the partial color space is divided into six truncated pyramid regions.

FIG. 11 is a diagram for explaining mapping of input color data to a boundary surface of a partial color space.

FIG. 12 is a flowchart for explaining a color conversion method by the color conversion device of FIG. 6;

FIG. 13 is a diagram showing a configuration example of a color conversion parameter generation device according to the present invention.

FIG. 14 is a diagram illustrating an example in which a grid point is set to always include either a white point WP or a black point BP.

FIG. 15 is a flowchart illustrating a color conversion parameter generation method according to the present invention.

FIG. 16 is a diagram illustrating a hardware configuration example of an image processing system according to the present invention.

FIG. 17 is a diagram illustrating a configuration example of a conventional color conversion device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 display 101 digital camera 102 scanner 103 computer 104 image forming device 200 image processing device 21 CPU 22 ROM 23 RAM 24 hard disk 30 information recording medium 31 medium drive device 201 rendering processing unit 202 band buffer 203 color conversion processing unit 204 gradation processing unit 301 Interpolation calculation color data generation means 302 Interpolation calculation means 303 Partial color space information storage means 304 Lookup table storage means 305 Mapping means 400 Color conversion parameter generation apparatus 401 Colorimetric data storage section 402 RGB data generation section 403 Partial color space Setting unit 404 Grid point generation unit 405 Lookup table calculation unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 BA02 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CE17 CE18 CH07 DA17 5C077 LL17 LL19 MP08 NP05 PP31 PP32 PP33 PP37 PP38 PQ12 PQ20 PQ22 PQ23 RR19 SS01 H06 5TT02B01 H05 LA28 LB02 MA01 MA04 MA11 NA03 NA09 NA29

Claims (21)

[Claims] 1. A color conversion apparatus for converting input color data represented by a first color system having three color components into color data for an image forming apparatus represented by a second color system, Lookup table storage means for storing output color data corresponding to input color data on lattice points obtained by dividing a partial color space smaller than a color space that can be expressed by the first color system into unit cubes as interpolation calculation parameters A partial color space information storage means for storing the partial color space range data; a partial color space range data read from the partial color space information storage means; An interpolation calculation color data generation unit for generating data; and an interpolation calculation parameter read from the lookup table storage unit based on the interpolation calculation color data. A color conversion device comprising: an interpolation operation unit that performs an interpolation operation on the color data for the interpolation operation by using the interpolation data to convert the color data into color data for an image forming apparatus. 2. The color conversion apparatus according to claim 1, wherein said interpolation calculation color data generation means converts the input color data on a boundary surface of the partial color space when the input color data is not included in the partial color space. A color conversion device comprising mapping means for replacing color data. 3. The color conversion device according to claim 2, wherein said mapping means places the input color data on a boundary surface of the partial color space when the input color data underflows or overflows the range of the partial color space. A color conversion device characterized in that mapping is performed by clipping. 4. The color conversion device according to claim 2, wherein the mapping unit divides a region obtained by removing a partial color space from a color space that can be expressed by the first color system into a plurality of truncated pyramid regions. Determining whether the input color data is included in a color space divided into a plurality of truncated pyramid regions, and converting the input color data to a color on a boundary surface of the partial color space by linear conversion means corresponding to the determination result. A color conversion device characterized by converting the data into data. 5. A color space that covers a color reproduction range of an image forming apparatus is defined as a partial color space, and input color data located outside the range of the partial color space is mapped to the partial color space to perform interpolation calculation. A color conversion method comprising: generating data; performing a memory map interpolation operation on the interpolation calculation color data; and converting the data into color data for an image forming apparatus. 6. A color conversion method for converting input color data represented by a first color system having three color components into color data for an image forming apparatus represented by a second color system. The input color data is converted so as to fall within the range of a partial color space narrower than the color space that can be expressed by the first color system, and color data for interpolation calculation is generated, so that the first color system can be expressed. Interpolation is performed on interpolation color data using output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than a simple color space into unit cubes, as interpolation calculation parameters. A color conversion method for converting the color data into color data for an image forming apparatus. 7. The color conversion method according to claim 6, wherein the input color data is mapped onto a boundary surface of the partial color space when the input color data is not included in the partial color space. A color conversion method characterized by being generated by performing 8. The color conversion method according to claim 7, wherein the color data for interpolation calculation is obtained by dividing the input color data into a boundary of the partial color space when the input color data underflows or overflows a region of the partial color space. A color conversion method characterized by being generated by mapping by clipping on a surface. 9. The color conversion method according to claim 7, wherein the interpolation calculation color data includes a plurality of quadrangular truncated pyramid regions excluding a region excluding a partial color space from a color space that can be expressed by a first color system. The input color data is determined to be included in any of the color spaces divided into the plurality of quadrangular frustum regions, and the input color data is converted to the boundary surface of the partial color space by the linear conversion means corresponding to the determination result. A color conversion method characterized by being generated by converting the above color data. 10. An interpolation operation color data is generated by converting input color data so as to fall within a partial color space narrower than a color space that can be expressed by a first color system. The output color data corresponding to the input color data on the grid points obtained by dividing the partial color space narrower than the color space that can be expressed by the color system into unit cubes is used as the interpolation calculation parameter. By performing an interpolation operation, a parameter used in a color conversion process for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system is generated. A color conversion parameter generating device for calculating a color range of the image forming apparatus on a first color system, and a color range of the image forming apparatus and a predetermined color in the first color system. Comparing means for comparing the range and the color of the image forming apparatus When a color gamut that is not included in the predetermined color range exists in the range, a predetermined color range is extended to calculate a range of the partial color space; A parameter generating means for generating, as interpolation parameters, output color data corresponding to the input color data on the grid points obtained by dividing the range into unit cubes. apparatus. 11. The color conversion parameter generation device according to claim 10, wherein said color range calculation means determines a color range of the image forming apparatus on a first color system. Are converted into a color data group corresponding to the first color system, and the maximum value and the minimum value in the first color system are converted from the converted color data group. Is calculated for each color component. 12. The color conversion parameter generation device according to claim 10, wherein said partial color space calculation means sets a minimum value and a maximum value for each axis of the partial color space to an integral multiple of 2 ⁿ (n = integer). A color conversion parameter generation device, wherein the parameter conversion device calculates a range of a partial color space by defining the range with a value. 13. The color conversion parameter generation device according to claim 10, wherein said partial color space calculation means sets the range of the calculated partial color space to any one of claims 1 to 4. A color conversion parameter generation device, which is set in a color conversion device as range data of a partial color space. 14. The color conversion parameter generation device according to claim 10, wherein said interpolation calculation parameter generation means outputs the generated interpolation calculation parameter. A color conversion parameter generation device, which is set as a look-up table in the color conversion device. 15. The color conversion parameter generation device according to claim 10, wherein the interpolation calculation parameter generation means generates grid points for a range of the partial color space calculated by the partial color space calculation means. Means for calculating color conversion parameters, the output color data corresponding to the grid points generated by the grid point generating means being calculated as interpolation calculation parameters. . 16. The color conversion parameter generation device according to claim 15, wherein the grid point generation unit includes at least a white point at a grid point obtained by dividing the partial color space calculated by the partial color space calculation unit into unit cubes. And generating a grid point so as to include any one of a black point and a black point. 17. An interpolation operation color data is generated by converting input color data so as to fall within a range of a partial color space narrower than a color space that can be expressed by a first color system. The output color data corresponding to the input color data on the grid points obtained by dividing the partial color space narrower than the color space that can be expressed by the color system into unit cubes is used as the interpolation calculation parameter. By performing an interpolation operation, a parameter used in a color conversion process for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system is generated. A color conversion parameter generation method for determining a color range of an image forming apparatus on a first color system and comparing the color range of the image forming apparatus with the predetermined color range in the first color system. , If there is a color gamut that is not included in the predetermined color range A color range obtained by expanding a predetermined color range, generating an expanded color range as a range of a partial color space, and corresponding to input color data on a grid point obtained by dividing the range of the partial color space into a unit cube. A color conversion parameter generation method, wherein output color data to be generated is generated as interpolation calculation parameters. 18. An image forming apparatus which converts input color data represented by a first color system having three color components into color data for an image forming apparatus represented by a second color system, In an output image processing system, input color data represented by a first color system having three color components is converted into color data for an image forming apparatus represented by a second color system. An image processing system using the color conversion device according to claim 1. 19. An image forming apparatus which converts input color data represented by a first color system having three color components into color data for an image forming device represented by a second color system, An image processing system for outputting, wherein the color conversion parameter generation device according to any one of claims 10 to 16 is used. 20. A color conversion process for converting input color data represented by a first color system having three color components into color data for an image forming apparatus represented by a second color system, First
The input color data is converted so as to fall within a range of a partial color space narrower than the color space that can be expressed by the first color system, and color data for interpolation calculation is generated. By performing, as an interpolation calculation parameter, output color data corresponding to input color data on grid points obtained by dividing a partial color space smaller than the space into unit cubes, and performing interpolation calculation on the interpolation calculation color data. A computer-readable recording medium in which a program for causing a computer to execute a process of converting color data for an image forming apparatus is recorded. 21. Interpolation color data is generated by converting input color data so as to fall within a range of a partial color space narrower than a color space that can be expressed by a first color system. The output color data corresponding to the input color data on the grid points obtained by dividing the partial color space narrower than the color space that can be expressed by the color system into unit cubes is used as the interpolation calculation parameter. By performing an interpolation operation, a parameter used in a color conversion process for converting input color data represented by a first color system into color data for an image forming apparatus represented by a second color system is generated. In the color conversion parameter generation processing, a color range of the image forming apparatus is obtained on a first color system, and the color range of the image forming apparatus in the first color system is compared with a predetermined color range. , If there is a color gamut that is not included in the predetermined color range A color range obtained by expanding a predetermined color range, generating an expanded color range as a range of a partial color space, and corresponding to input color data on a grid point obtained by dividing the range of the partial color space into a unit cube. A computer-readable recording medium in which a program for causing a computer to execute a process of generating output color data to be used as an interpolation calculation parameter is recorded.