JP2002237958A - Color converter, color conversion profile generator and generating method, imaging device, program, recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert print use CMYK data for a color copying machine and a color printer into RGB data or the like, by which a display device or other color printer or the like can reproduce black characters with high quality. SOLUTION: A black character color discriminating section 151 discriminates whether or not a print use CMYK data have a color of a black character. When the CMYK data have the black character color, a colorimetry value correction processing section 154 uses a black color contrast conversion table to apply contrast correction, to emphasize the contrast to a colorimetric value converted from the CMYK data by a CMYK/photometric value conversion section 153. When the section 151 determines that the CMYK data are of non- black character color, the colorimetry value correction processing section 154 uses a non-black color contrast conversion table to apply contrast correction which does not emphasize the contrast so much to a colorimetric value converted from the YMCK data by the CMYK/photometric value conversion section 153. The colorimetric value after the correction is converted into RGB data by a colorimetric value/RGB conversion section 155.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color conversion technique for CMYK data, and more particularly, to CMYK data generated for printing by a specific image forming apparatus such as a color copying machine, a color printer, and a color facsimile. To convert data into color data of another format suitable for outputting to a display or another color printer.

[0002]

2. Description of the Related Art There are many conventional techniques for color conversion of CMYK data and the like. For example, as a general color conversion method of color data including four color components such as CMYK, there is a memory map interpolation calculation method using a four-dimensional lookup table (for example, Japanese Patent No. 2903808).
No., JP-A-57-208765). CMY for printing
To output K data on another color printer,
Convert YK data to device-independent Lab signal, and make corrections to reproduce ground color faithfully.
When the ground color is not reproduced, a method of performing contrast control for improving the visibility of the highlight and then converting the same to CMYK data for another color printer is known (Japanese Patent Application Laid-Open No. Hei 8-212324). . Since a hard copy image output from a color printer or the like and a soft copy image displayed on a CRT display or the like have completely different color reproduction methods, even images based on the same image data have different appearances. It is known to be perceived as color. Therefore, the dynamic range of the input color data and the dynamic range of the output color data are matched so that the appearance of the color perceived in the hard copy image and the soft copy image match, and the perceptual match using the color adaptation model A technique is known in which a color conversion profile is created so as to perform color conversion, and color conversion is performed using the color conversion profile (JP-A-11-112819).

[0003]

An image forming apparatus such as a color printer or a color copying machine has a function of accumulating CMYK data generated for printing in the apparatus in a storage device such as a hard disk and repeatedly using the same. There is. However, the stored CMYK data is simply color-converted into RGB data and sent to a computer, for example.
In some cases, high-quality images cannot be reproduced even if they are displayed on a display or output to another color printer. In particular, the reproduction quality of black characters is remarkably deteriorated.

[0004] The cause is the C generated by the image forming apparatus.
This is because MYK data has characteristics optimized for hard copy. For example, in the case of a color copying machine, if black characters are overprinted in four colors of CMYK, sharpness is reduced due to misregistration of each color, and readability is reduced. Therefore, the edge portion of the black character is extracted, and the edge of the black character is output in a single color of K.
A so-called image area separation process is often performed in which color separation is performed so as to use all of the four YK inks. Similarly, in the case of a color printer, for example, a drawing code is determined in a printer driver, black character portions are output in K single color, and non-black character portions are subjected to four-color separation in object adaptive color processing. It is often said. CMYK data with different color reproduction methods for black characters and other areas in this way can reproduce black characters with high quality even if they are simply converted to RGB data and output to a display or other color printer. Can not.

An object of the present invention is to convert CMYK data generated for printing in an image forming apparatus such as a color printer, a color copying machine, a color facsimile, etc., as described above, to a display or another color printer. An object of the present invention is to provide a color conversion device for performing color conversion into RGB data or the like capable of reproducing black characters of high quality, and a method and a device for creating a color conversion profile to be used by the color conversion device.

The technique disclosed in Japanese Patent Application Laid-Open No. H08-212324 is a technique for converting between hard copy output signals, so that a faithful color reproduction can be basically performed by converting the CMYK data into colorimetrically matched CMYK data. There will be. However,
In a case where the CMYK data is once converted into RGB data for display and output to a color printer through a printer driver, the dynamic range of the monitor is made to match the dynamic range of the color printer output on the printer driver side. Since color correction processing is often performed, simply matching the white reference of the CMYK data and the RGB data may cause insufficient black density in the printer output.

On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. H11-112819, the dynamic range of input color data and the dynamic range of output color data are matched, so that the data can be converted into color data suitable for screen display. Further, even when the image is output to another color printer via a printer driver, a decrease in black density can be prevented. However, since this conventional technique targets input color data read by a scanner or input by a digital camera, even if the prior art is applied to CMYK data on which the above-described image area separation processing and object adaptive color processing have been performed. Cannot be applied as it is, for example, because the user does not know how to determine the black point (darkest point).

[0008]

According to the present invention, there is provided a color conversion apparatus for converting input CMYK data into output color data of a predetermined other format.
As described in claim 1, CMYK corresponding to a non-black character color
A means for enhancing the contrast of output color data for CMYK data corresponding to a black character color, rather than output color data for data.

The color conversion apparatus of the present invention has two modes depending on the difference in the method of realizing the means for enhancing the contrast of the output color data for the CMYK color signal corresponding to the black character color.

[0010] The color conversion apparatus according to the first aspect is described in claim 2.
As described, the image processing apparatus includes: a color conversion profile indicating a correspondence relationship between CMYK data and output color data; and color conversion processing means for converting CMYK data into output color data with reference to the color conversion profile. The main feature is that the conversion profile has a characteristic of enhancing the contrast of the output color data for the CMYK data corresponding to the black character color more than the output color data for the CMYK data corresponding to the non-black character color.

According to a second aspect of the present invention, there is provided a color conversion apparatus.
As described, CMYK / CMYK data for converting CMYK data into colorimetric values when an image is formed using a specific image forming apparatus.
Colorimetric value converting means, black character color determining means for determining whether the CMYK data is a black character color, and CMYK data of the CMYK data determined to be a black character color by the black character color determining means.
/ Colorimetric values to which colorimetric values converted by the colorimetric value converting means are subjected to contrast correction for black character colors, and colorimetric values of CMYK data determined to be non-black character colors are subjected to contrast correction for non-black characters. Output color data for CMYK data corresponding to a non-black character color, comprising correction means, and colorimetric value / output color data conversion means for converting the colorimetric value corrected by the colorimetric value correction means into output color data. The main feature is that the contrast of the output color data with respect to the CMYK data corresponding to the black character color is enhanced.

According to the present invention, there is provided an apparatus for creating a color conversion profile used to convert CMYK data into output color data of another predetermined format. The color conversion profile creation device may include a CMYK data generation unit and a CMYK data generated by the CMYK data generation unit, the CMYK data being used as a colorimetric value when an image is formed by a specific image forming apparatus. A colorimetric value converting means for converting, a black character color determining means for determining whether or not the CMYK data generated by the CMYK data generating means corresponds to a black character color; and a CMYK determined to be a black character color by the black character color determining means. The colorimetric value of the data converted by the colorimetric value conversion means is subjected to contrast correction for black character color, and the CMYK data determined to be non-black character color.
Colorimetric value correcting means for performing contrast correction for non-black characters on the colorimetric values of the data, and color conversion setting means for setting a color conversion profile using the colorimetric values corrected by the colorimetric value correcting means. And CMYK corresponding to a non-black character color
The main feature is to create a color conversion profile having a characteristic of enhancing the contrast of output color data for CMYK data corresponding to a black character color, rather than output color data for data.

According to the present invention, there is provided a method of creating a color conversion profile used to convert CMYK data into output color data of another predetermined format. This method comprises the steps of: generating CMYK data; converting the CMYK data generated by the CMYK data generating step into colorimetric values when an image is formed by a specific image forming apparatus; A black character color determining step for determining whether or not the CMYK data generated in the generating step corresponds to a black character color; and CMY determined to be a black character color in the black character color determining step.
The colorimetric values of the K data converted in the colorimetric value conversion step are subjected to contrast correction for black character colors, and the colorimetric values of CMYK data determined to be non-black character colors are
A colorimetric value correction step of performing contrast correction for non-black characters, and a color conversion setting step of setting a color conversion profile using the colorimetric values corrected by the colorimetric value correction step. CMYK corresponding to the black character color, rather than the output color data for the corresponding CMYK data
The main feature is to create a color conversion profile having a characteristic of enhancing the contrast of output color data with respect to data.

Next, the features of the present invention described above and other features will be described in detail with reference to the embodiments.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

<Example of Image Processing System> FIG. 1 shows an example of an image processing system according to the present invention. In FIG.
An image forming apparatus 100 forms an image using CMYK data and outputs a hard copy, and specifically includes a color printer, a color copying machine, a color facsimile apparatus, and the like. The image forming apparatus 101 includes a CMYK
Data can be output to the color conversion device 104 of the present invention. The color conversion device 104 converts the CMYK data into RG
It has a function of color conversion into B data. Reference numeral 102 denotes a computer such as a personal computer, on which various applications and software such as a printer driver can be installed. The computer 102 displays the RGB data sent from the color conversion device 104 on the display 103,
1 can be output to the color printer 101 by operating the printer driver corresponding to 1. The color printer 101 receives drawing data in RGB format from the computer 102 and outputs a hard copy. The color printer 101 includes a computer 10
Printer control device 1 for converting the drawing data in RGB format received from printer 2 into CMYK data for printing
05 is built-in.

Note that the printer control device 105 can be a device independent of the color printer 101.
Further, it is also possible to adopt a form in which a part of the function is executed by a printer driver of the computer 102 or the like.

Similarly, the color conversion device 104 of the present invention can be realized as an independent device. For example, the color conversion device 104 can be realized by software on the computer 102. 100 may be adopted. As described above, the image forming apparatus 100 on which the color conversion device 104 of the present invention is mounted is also included in the present invention.

The overall operation of the image processing system is as follows. The image forming apparatus 100 accumulates CMYK data generated in the process of outputting a hard copy on a built-in hard disk or the like. The hard copy output operation means, for example, a printing operation using a color printer or a copying operation using a color copier. The CMYK data generated in the image forming apparatus 100 is
It is transferred to the color conversion device 104 when it is generated or when instructed. The color conversion device 104 performs a color conversion process on the CMYK data to convert the CMYK data into RGB data.
Send to 2. The computer 102 stores the RGB data in a storage medium such as an internal hard disk.
The operator of the computer 102 displays the RGB data stored in the computer 102 on the display 103 as needed to view the image, processes the RGB data using an appropriate application, or processes the original RGB data or The processing data is transferred to the color printer 10
1 for printing.

<Description of Image Forming Apparatus 100: As a Color Printer> With reference to FIG. 2, a configuration related to an operation of generating CMYK data when the image forming apparatus 100 is a color printer will be described.

In FIG. 2, reference numeral 200 denotes the image forming apparatus 10.
This is a computer that sends a drawing command to the image forming apparatus 100 and is connected to the image forming apparatus 100 via an interface cable or a network. This computer 200 is shown in FIG.
Computer 102 in some cases. Reference numeral 210 denotes a printer control device of the image forming apparatus 100, which may have the same configuration as the printer control device 105 of the color printer 101 in FIG. 1, and includes, for example, a color conversion processing unit 211, a rendering processing unit 212, a band buffer 213, and a floor control unit. Key processing unit 2
14, a storage device 215. Such a printer control device 210 may be mounted on the image forming apparatus 100 or may be an independent device. Also,
A part of the function may be executed by a printer driver of the computer 200 or the like.

An operator of the computer 200 edits and creates the document data 204 by using an application 201 or the like mounted on the computer 200. Then, when the document creation is completed, a print instruction is issued to output using the image forming apparatus 100. Computer 200
Receives the instruction to instruct printing from the application 201, transmits the document data in the application to the printer driver 202. The printer driver 202 converts the document data into a drawing command in an RGB format that can be received by the printer control device 210 and temporarily stores the command in a recording medium 203 such as a hard disk as needed. It is transmitted to the printer control device 210.

When the printer control unit 210 receives the drawing command, the color conversion processing unit 211
The drawing command in the B format is color-converted into a drawing command in the CMYK format. At this time, the color conversion processing unit 211 performs color conversion processing suitable for the attribute of the drawing object while interpreting the drawing command, and sends the processed CMYK format drawing command to the rendering processing unit 212. The rendering processing unit 212 converts the command format data into raster format CMYK data and stores it in the band buffer 213. The rasterized CMYK data is read from the band buffer 213 and
In step 4, gradation conversion is performed. The gradation processing unit 204 converts the CMYK data into print data of a number of gradations that can be processed by the image forming engine of the image forming apparatus 100 by applying dither processing or the like, and temporarily stores the print data in a storage device 215 such as a hard disk. save. For example, when the image forming engine of the image forming apparatus 100 forms a hard copy using C (cyan), M (magenta), Y (yellow), and K (black) inks, the density of 256 gradations of each color is if possible,
Raster CMYK data in which each color of C, M, Y, and K is represented by 8 bits is stored as print data in the storage device 2.
15 will be stored. In the case where binarization is performed by dither processing, binary CMYK data in raster format in which each color of C, M, Y, and K is represented by one bit is stored in the storage device 215. After that, the storage device 21 is adjusted according to the printing speed of the image forming apparatus 100.
5, CMYK data is read out, printed by the image forming engine, and a hard copy is output.

The color conversion process according to the attribute of the object in the color conversion processing unit 211 will be specifically described below. Generally, in order to obtain a high-quality hard copy output, it is necessary to use a different color reproduction method for each attribute of an object. In particular, even if the RGB data is black (R = G = B = 0), the color reproduction method is different between the case of reproducing a black character and the case of reproducing a gradation image such as a photographic image. Is common. In other words, when trying to reproduce black characters with four colors of CMYK, there is a problem in that the positions of dots of each color are displaced at the time of hard copy output, and characters are blurred and difficult to read. In addition, when four colors are superimposed, it is difficult to maintain a color balance, and there is a problem that the color tends to be tinged. On the other hand, if black is reproduced only with K ink in a shadow portion of a photographic image, it becomes difficult to maintain gradation continuity with chromatic portions other than black, causing a problem that gradation is discontinuous. Therefore, a color reproduction method is often used in which black characters are reproduced with a single color of K, and a photographic image portion is reproduced with four colors.

The CMYK data optimized for hard copy output by such object adaptive color processing is simply color-converted into, for example, RBG data, provided to the computer 102, and output to the display 103.
Re-output to another color printer 101 cannot reproduce high quality black characters. Therefore, the color conversion device 1 of the present invention
04 is CMYK subjected to the above-mentioned object adaptive color processing.
Data (or CMYK data subjected to image area separation processing in a color copying machine described later in detail) is subjected to a color conversion process to, for example, RGB data which can reproduce high-quality black characters on a display or another color printer.

<Embodiment 1 of Color Conversion Apparatus 104> FIG. 3 is a block diagram showing an embodiment of the color conversion apparatus 104 according to the present invention. In the figure, reference numeral 120 denotes a color conversion processing unit, and 121 denotes a color conversion profile storage unit. The color conversion profile storage unit 121 stores a color conversion profile that represents a correspondence between input CMYK data and RGB data that is output color data. The color conversion processing unit 120 converts the input CMYK data to RGB data with reference to the color conversion profile, and outputs the RGB data.

According to the present invention, C corresponding to the non-black character color
The RGB data (output color data) corresponding to the MYK data has a smaller RGB value than the RGB data (output color data) for the CMYK data corresponding to the black character color.
Since the color conversion profile having the characteristic of enhancing the contrast of the B data is stored in the color conversion profile storage unit 121, the CMYK data corresponding to the black character color is converted into RGB data with enhanced contrast. Therefore, like CMYK data for printing of a color printer, CMYK data subjected to object adaptive color processing is used.
If RGB data obtained by color-converting the data by the color conversion device 104 of this embodiment is sent to the computer 102 and displayed on the display 103 or output to the color printer 101, high-quality black characters can be reproduced. It should be noted that for colors other than the black text color, the contrast is not emphasized so much as to achieve faithful color reproduction.

In the color conversion device 104 of the present embodiment, a widely known four-dimensional lookup table (4D-LU) is used.
The memory map interpolation calculation method using T) is adopted. Therefore, the color conversion profile is stored in the color conversion profile storage unit 121 as a four-dimensional lookup table. The color conversion processing unit 120
Using the upper bits and the lower bits of the MYK data (for example, 8 bits for each color), the vertices of the interpolated solid to which the input color belongs (representative points in a four-dimensional color space represented by CMYK4 components);
A grid point address generation unit 123 that generates an address of a grid point) and provides the address to the color conversion profile storage unit 121
By performing an interpolation operation using the grid point output value (interpolation parameter) read from the color conversion profile storage unit 121 and the lower n bits of the CMYK data,
And an interpolation operation unit 124 for obtaining RGB data values corresponding to the YK data.

Known documents relating to the memory map interpolation calculation method employed in this embodiment include, for example, JP-A-57-208765 and JP-A-2903808. In these publications, four colors represented by four color components are used.
Divides the dimensional color space into a plurality of five-vertex bodies, selects a five-vertex body that includes the input color using upper bits of the input data,
A five-point interpolation method has been disclosed which realizes high-precision color conversion over the entire color space by reading a corresponding interpolation operation strength from a four-dimensional lookup table and performing a linear interpolation operation. The interpolation operation method in the color conversion processing unit 120 of the present embodiment may have the same contents, and the characteristic of the embodiment lies in the characteristics of the color conversion profile used for the interpolation operation. The above description is omitted.

<Embodiment of Color Conversion Profile Creation Apparatus and Method> Next, the color conversion profile storage unit 121 shown in FIG.
A method and an apparatus for creating a color conversion profile (four-dimensional look-up table) having the above-described characteristics to be stored in the profile will be described.

FIG. 4 is a block diagram showing an embodiment of a color conversion profile creating apparatus according to the present invention. FIG.
6 is a flowchart illustrating an example of a color conversion profile creation procedure according to the color conversion profile creation method of the present invention. The procedure from step S102 in FIG. 5 is processing executed by the color conversion profile creation device in FIG.

The color conversion profile creation device may be mounted on the color conversion device 104 or the image forming device 100, or may be an independent device. The color conversion device 104 or the image forming device 100 on which the color conversion profile creation device of the present invention is mounted is also included in the present invention.

In FIG. 4, reference numeral 300 denotes a CMYK data generation unit, which is means for executing step S102 in FIG. In the present embodiment, the CMYK data generation unit 30
0 is a grid point address generation unit 301 and a CMYK calculation unit 30
Consists of two. The grid point address generation unit 301 uses the CMYK
A counter for generating an index (ID) of a grid point, which is a representative point in a four-dimensional color space represented by four color components,
Here, the number of grid points is 625, counting is performed from 0 to 624, and each count value is sequentially output as a grid point ID. The CMYK calculation unit 302 calculates the C
Calculate and output the MYK value. For example, when the four-dimensional lookup table of the color conversion profile divides each CMYK color component into 16, the CMYK values of each grid point are generated as values of 16 steps for each color. That is, the grid point I
According to D = 0, 1, 2, 3 ,,,,,,, [C, M, Y, K] = [0,0,0,0], [0,0,0,16] , [0,0,0,32], ..., [0,0,0,255], [0,0,16,0], [0,0,16,16], [0,0,16, 32], ..., [0,0,16,255],:: Generate CMYK data such as [255,255,255,0], [255,255,255,16], [255,255,255,32], ..., [255,255,255,255] . When the color conversion profile creation processing is executed by software using a computer, the CMYK data of one grid point is prepared from a list of CMYK data of all grid points prepared in advance.
Processing such as taking in MYK data can also be performed.

Reference numeral 303 denotes a colorimetric value calculation unit which converts the CMYK data of each grid point generated by the CMYK calculation unit 302 into
This is a means for processing (corresponding to step S103 in FIG. 5) for converting it into a colorimetric value when an image is formed using the image forming apparatus 100. This conversion includes the CM of the grid point.
The YK data may be output from the image forming apparatus 100 and the result of the color measurement may be used as it is, or the color prediction formula (CMY
(A method of calculating a colorimetric value from an K data using an approximation function) may be used. As the colorimetric value, a Lab value, an XYZ value, or the like can be used. In the present embodiment, the Lab value is used as the colorimetric value.

FIG. 5 shows the procedure for obtaining the color prediction formula as step S101. A general method of constructing a color prediction formula is to output a color patch in the image forming apparatus 100 serving as a source of CMYK data, measure the output patch with a spectral colorimeter, and then measure the colorimetric data of the color patch. This is a method of constructing a color prediction equation by approximating the relationship between the output color data and the output color data (= CMYK values). The work of constructing such a color prediction formula is not new and can be performed manually or semi-automatically. When the procedure shown in FIG. 5 is executed by software using a computer, the construction of the color prediction formula is completed in advance, and only the process of setting the color prediction formula is performed in step S101. Good.

Now, in order to improve the reproducibility of black characters, it is necessary to recognize whether or not the CMYK data corresponds to a black character color. The means for performing this recognition is the black character color determination unit 304 (corresponding to step S108 in FIG. 5). In the CMYK data of the above-described color printer, color processing is performed so that black characters are reproduced in K single color. Therefore, it can be determined whether or not the CMYK data is K single color by checking whether or not the CMYK data is black. That is, when the CMYK data satisfies C ≦ th, M ≦ th, Y ≦ th, and K> 0, the black character color determination unit 304 determines that the black character color. th is a predetermined threshold value, and may be set to th = 0 in the present embodiment.

Reference numeral 305 denotes a colorimetric value correction processing unit which determines a colorimetric value correction method according to the determination result of the black character color determining unit 304 and corrects the colorimetric value (corresponding to step S104 in FIG. 5). Specifically, when the CMYK data is determined to be a black character color, contrast correction is performed to enhance the contrast in order to enhance the reproducibility. Perform contrast correction. In this embodiment,
The colorimetric value correction processing unit 305 includes a storage unit 306 storing a contrast conversion table for black character colors and a contrast conversion table for non-black character colors, and a storage unit 306 selected according to the determination result of the black character color determination unit 304. It comprises a colorimetric value correction unit 307 that performs a colorimetric value contrast correction using a contrast conversion table.

Reference numeral 309 denotes a color conversion profile setting unit which uses the colorimetric values L'a'b 'corrected by the colorimetric value correction processing unit 305 to convert colors from CMYK data to RGB data. Set the conversion profile.
In this embodiment, the color conversion profile setting unit 309 converts the corrected colorimetric values L'a'b 'into RGB data.
an ab / RGB conversion unit 310 and the converted RGB data as an output value of a grid point, a grid point address generation unit 301
And a color conversion profile temporary storage unit 311 that stores in the form of a four-dimensional look-up table at an address corresponding to the grid point ID generated in step (1). The conversion process by the Lab / RGB conversion unit 310 corresponds to step S105 of FIG. 5, and the operation of storing the converted RGB data in the color conversion profile temporary storage unit 311 is step S10 of FIG.
Equivalent to 6. In the above configuration, the process is repeated for all grid points (in FIG. 5, the end of the repetition is determined in step S107).

The color conversion profile created as a four-dimensional look-up table in the color conversion profile temporary storage unit 311 in this manner is written in the color conversion profile storage unit 121 of the color conversion device 104 according to the present invention shown in FIG. As described with reference to FIG. 3, the CMYK data corresponding to the black character
It is converted to B data.

Next, a specific colorimetric value correction method in the colorimetric value correction processing unit 305 will be described with reference to FIG. In FIG. 6, the horizontal axis represents the brightness L before correction, the vertical axis represents the brightness L ′ after correction, the solid line represents the input / output relationship for black character colors, and the dotted line represents the input / output relationship for non-black character colors. I have.
When the CMYK data is determined to be a black character color by the black character color determination unit 304, the colorimetric value correction unit 307 sets the lightness L range [Bpt-Wp] to [0-1] as shown by the solid line.
00], the colorimetric value Lab is corrected to a colorimetric value L′ a′b ′ with enhanced contrast. Here, Wp is the white point of CMYK data (lightness when C = M = Y = K = 0) and generally corresponds to the lightness of the ground color. Bpt is the black point, C = M = Y =
It corresponds to the output brightness when 0, K = 255. On the other hand, when the CMYK data is determined to be a non-black character color, the colorimetric value correction unit 307, as indicated by the dotted line, displays the lightness L range [0-W
p] is linearly converted to [0-100]. By applying such contrast correction, it is possible to create a color conversion profile that can reproduce black characters and non-black characters in a dynamic range suitable for each.

More specifically, in the above-described contrast correction by the linear conversion, since the brightness of the white point of the CMYK data is converted to 100, the ground color of the paper is converted to white on the display, and the image having good visibility is displayed. Can be reproduced. Also, when outputting to another color printer,
Since no ink is applied to the ground color portion, ink can be saved, and high-quality color reproduction can be performed without causing background roughness. [C, M, Y, K] = [0,0,0,255]
Is converted to L ′ = 0, and the black point is not corrected for the non-black character color. Therefore, the black character can be reproduced with enhanced contrast and excellent readability. In other cases, faithful color reproduction can be performed in the shadow portion without deteriorating the gradation.

The contrast conversion table storage unit 306 stores two types of contrast conversion tables corresponding to the solid line and the dotted line in FIG. 6 as a one-dimensional look-up table. One of the contrast conversion tables can be selected for use, but is not limited to this. That is, since only the white point Wp and the black point Bpt are necessary values for the conversion of the colorimetric values, only the values of the white point Wp and the black point Bpt are stored in the contrast conversion table storage unit 406, and the black character color is stored. Sometimes the value of Bpt stored is selected, and B
Alternatively, 0 may be selected as the value of pt, and contrast correction may be performed by performing linear conversion in each dynamic range.

Note that K used in a color printer or the like is used.
Since the ink may have a slight tint, the colorimetric value Lab of the CMYK data corresponding to the black character color is represented by a = b
= 0 may not be achieved. In this case, [L ', a', b '] = [0, 0, 0] simply by setting the lightness L' of the black character color to 0
However, it becomes an imaginary color signal (a color that does not exist), and conversion to RGB data cannot be guaranteed. In order to cope with this, it is effective to forcibly make the color achromatic.

Therefore, according to another embodiment, the colorimetric value correction unit 307 sets the colorimetric value Lab to [L ',
[0, 0] to make the saturation 0. This is also one of the features of the present invention. By performing such forced achromaticization, high-quality black characters can be reproduced even when the color printer 101 uses K ink having a slight color tone. This is the same in the embodiment described below.

<Second Embodiment of Color Conversion Device 104> In the first embodiment of the color conversion device 104 described with reference to FIG. 3, the input CMYK data is an 8-bit signal for each color (generally a multi-level signal). )Met.

FIG. 7 shows CMY binarized by dither processing.
FIG. 2 is a block diagram illustrating an embodiment of a color conversion device 104 for performing a color conversion process on K data. The color conversion device 104 according to the present embodiment stores buffer memories 125c, 125m, 125y, and CMYK color components in the color conversion processing unit 120 and the color conversion profile storage unit 121 illustrated in FIG.
125k, binary / multi-value conversion units 126c, 126m, 1
26y and 126k are added. The operation is as follows.

As the input binary CMYK data, a predetermined number of consecutive pixels are temporarily stored in buffer memories 125c to 125k corresponding to the respective color components. Binary CMYK data temporarily stored here, are sequentially input to the binary / multi-level conversion unit 126c~126k corresponding. In the binary / multi-value conversion units 126c to 126k, first, the binary C
"0" of the MYK data is converted into an 8-bit signal of "0",
1 "is replaced by an 8-bit signal of" 255 ", respectively.
Next, by performing a smoothing filtering process on the 8-bit signal, CMY expressed by 8 bits for each color is obtained.
The K data is generated and sent to the color conversion processing unit 120.

The operation of the color conversion processing unit 120 is as described in the first embodiment.
However, the contents of the color conversion profile (four-dimensional lookup table) stored in the color conversion profile storage unit 121 are changed. This change will be described with reference to FIGS.

Since the binary / multi-value converters 126c to 126k perform the smoothing filtering process, the high-frequency components of the binary CMYK data are removed. As a result, the character portion is blurred, and the readability is reduced. Characters are difficult to read. This phenomenon will be described with reference to FIG.

FIG. 8 illustrates a change in pixel value due to the smoothing filtering process of binary CMYK data.
(A) shows a pixel value change around a black character, and (b) shows a pixel value change in a picture area. However, only the horizontal direction 5 pixels are represented in a simplified manner. (A) and (b)
Is the binary CM before smoothing filtering
Represents a pixel value of YK data, arrow right represents the pixel values of the 8-bit CMYK data after the smoothing filtering. However, in order to make the levels of the binary CMYK data and the 8-bit CMYK data uniform, “1” of the binary CMYK data and “255” of the 8-bit CMYK data are represented by the same height.

In (a), the center is a black character pixel ([C, M, Y,
K] = [0,0,0,1]). Also, assuming paper white around black characters, ([C, M, Y, K] = [0, 0, 0, 0]). In the 8-bit CMYK data obtained by performing the smoothing filtering process on the binary CMYK data, as shown on the right side, the pixel value of the black character pixel decreases and the density of the surrounding image increases, so that the black character is blurred. It becomes an image.

In (b), 8-bit CMY after the binary CMYK data shown on the left is subjected to smoothing filtering processing.
The K data has pixel values as shown on the right. Binary CMY
Since the K data is binarized by dither processing,
Originally, it has the property that CMYK inks are struck off and on. In the case of such a pattern, the multi-valued CMYK data before the dither processing does not contain much high-frequency components. Therefore, the 8-bit CMYK data obtained by performing the smoothing filtering processing on the binary CMYK data almost returns to the state before the dither processing. And the deterioration due to the smoothing filtering process is smaller than that of the character portion.

Therefore, in this embodiment, when the color conversion profile stored in the color conversion profile storage unit 121 is created by the color conversion profile creation device (FIG. 4),
The colorimetric value correction processing unit 305 performs nonlinear contrast conversion only on the black character color to perform strong contrast enhancement. By using the color conversion profile created in this way, the reproducibility of a black character portion where blur is likely to occur due to the smoothing filtering process can be dramatically improved. However, if a non-character contrast pattern portion is subjected to non-linear contrast conversion, the color will greatly change. Therefore, the same linear contrast conversion as in the first embodiment is applied.

Also, when creating a color conversion profile for the present embodiment, the black character color determination unit 304 can make a determination in the same manner as described above. However, if there is any color pixel around the black character, C = M = Y = 0 is not satisfied, so that the above-described determination threshold th is a value other than 0 (for example, 16).
Is used. Actually, black characters are frequently drawn on a white background or on a highlight color. Therefore, even if the determination is made only by the balance of C, M, Y, and K, the black character color and the non-black character color can be accurately determined. It is identifiable.

A specific example of nonlinear contrast conversion for creating a color conversion profile used in this embodiment will be described with reference to FIG. In FIG. 9, similarly to FIG. 6, the horizontal axis is the brightness L before correction, and the vertical axis is the brightness L ′ after correction.
The solid line represents the input / output relationship when the color is black, and the dotted line represents the input / output relationship when the color is non-black. The input / output relationship of the non-black character colors is the same as in FIG.

In the case of a black character color, the colorimetric value correction unit 307
As shown by the solid line, the contrast [Bpt-Wp] of the lightness L is nonlinearly converted to [0-100] to perform strong contrast enhancement. If the color conversion is performed using the color conversion profile created in this way, the contrast of the black character portion is greatly enhanced, so that the blurred character can be restored to a considerably readable RGB image by the smoothing filtering process. it can.

Even in the case of multi-valued CMYK data, depending on its characteristics, it is effective to perform strong contrast enhancement correction on the black character color by nonlinear conversion as shown in FIG.

<Third Embodiment of Color Conversion Device 104> FIG.
FIG. 9 is a block diagram showing another embodiment of the color conversion device 104 according to the present invention. The color conversion device 104 according to the present embodiment includes a data buffer 150, a black character color determination unit 151, a contrast conversion table storage unit 152, a CMYK / colorimetric value conversion unit 153, a colorimetric value correction processing unit 154, and a colorimetric value / RGB conversion. 155.

CMY input from image forming apparatus 100
The K data is temporarily stored in the data buffer 150 and sequentially sent to the black character color determination unit 151 and the CMYK / colorimetric value conversion unit 153. The black character color determination unit 151 is a unit that determines whether the CMYK data corresponds to the black character color by the same method as the black character color determination unit 304 in FIG. The contrast conversion table storage section 152 stores contrast conversion tables for black character colors and non-black character colors as shown in FIG. 6 (or FIG. 9), and one of the contrast conversion tables is determined by the black character color determination section 151. Selected according to the result.

The CMYK / colorimetric value converter 153 converts the CMYK data into the colorimetric values (here, Lab values) of the image forming apparatus 100 and performs the colorimetric measurement similarly to the colorimetric value calculator 303 in FIG. The value is given to the value correction processing unit 154. The colorimetric value correction processing unit 154 uses the contrast conversion table selected according to the black character color determination result in the contrast conversion storage unit 152 to perform the colorimetric value Lab on the colorimetric value correction unit 307 of FIG. The same contrast correction is performed, and the corrected colorimetric values L'a'b 'are output.

As described in connection with the colorimetric value correction unit 307 in FIG. 4, a colorimetric value correction process is performed to cope with a case where the K ink used in a color printer or the like has a slight tint. In the section 154, CMY corresponding to the black character color
For the K data, the colorimetric value Lab may be converted to [L ', 0, 0] to forcibly achromaticize.

The colorimetric value / RGB conversion unit 155 converts the colorimetric values L′ a′b ′ corrected by the colorimetric value correction processing unit 154 to R
Convert to a GB color signal.

With such a configuration, the first embodiment can be used.
It is clear that color conversion from CMYK data equivalent to the above to RGB data is possible.

Although not shown, the binary /
Means corresponding to the multi-value conversion units 126c to 126k are provided on the output side or the input side of the data buffer 150,
A configuration is also possible in which a non-linear contrast conversion table for black characters as shown by the solid line in FIG. 9 is stored in the contrast conversion table storage unit 152. According to the color conversion device 104 having such a configuration, it is possible to generate RGB data with good black character reproduction quality from CMYK data binarized by dither processing or the like, as in the second embodiment. This is clear from the above description.

<Description of Image Forming Apparatus 100: As Color Copier> FIG. 11 is a block diagram showing a schematic configuration of a general color copier. Referring to this block diagram, CM in the case where image forming apparatus 100 is a color copying machine
The operation of generating YK data and the configuration related thereto will be described.

In FIG. 11, reference numeral 401 denotes an image input device (scanner) for reading an image of a document. Since the RGB data input from the image input device 401 is data that is substantially linear in reflectance, the log data is subjected to logarithmic conversion by the Log conversion circuit 402 to be converted into data that is substantially linear in density. The data after logarithmic conversion is applied to a filter circuit 403, an edge separation circuit 407 for image area separation, and a dot separation circuit 4
08 and the color separation circuit 409. These circuits 4
The result of separation by 07, 408, 409 is determined by the decision circuit 410.
And is separated into image areas such as black characters / photographs / halftone dots. For example, when the separation result of the edge separation circuit 407 is “edge” and the separation result of the color separation circuit 409 is “black pixel”, “black character” is set. Such an image area separation result is provided to the filter circuit 403, the color correction circuit 404, the UCR circuit 405, and the dither circuit 406. The data after logarithmic conversion is subjected to filter processing according to the image area by the filter circuit 403, and furthermore, the color correction circuit 4
04 performs color correction according to the image area. The CMYK data output from the color correction circuit 404 is
The image data is passed through U05, subjected to UCR (under color removal) processing according to the image area, sent to a dither circuit 406, and subjected to dither processing using a dither matrix according to the image area. The CMYK data after the dither processing is sent to an image output device 414 (an imaging engine such as a laser printer) and printed.

By the way, since the above-described image area separation is performed while judging the characteristics of the local image, the pixels around the edge of the black character are accurately determined to be the black character. In the case of a black character having a small size, the entire character is eventually identified as a black character. However, in a large black character such as a title character, only its edge portion is determined to be a black character, and the inside of the character is regarded as a photograph. Pixels determined as black characters are converted into K-monochromatic data at the pixel level corresponding to the edge strength in color correction and UCR processing and are printed with only K ink, while pixels determined as photographs or halftone dots are , And CMYK four-color data, and printing is performed by overprinting four-color inks. Therefore, FIG.
As schematically shown in FIG. 2, in the case of a large character, only the edge portion is reproduced with a single color of K, and the inside of the character is reproduced with four colors of CMYK. However, in recent color copiers, the density level is adjusted so as to match the inside of the edge and the edge, so that unnaturalness does not occur at the edge portion.

Now, for a CMYK image in which a single black color portion and a portion where four colors are overprinted are adjacent to each other as in the case of the above-described large characters, the color conversion device 104 of the first or third embodiment will be described. As described above, if the image is converted into an RGB image by changing the contrast between the black single-color portion and the other portions, when the RGB image is displayed on the display 103 or output to the color printer 101, the black image may not be bordered. This may result in a natural image. on the other hand,
In the case of small black characters, the reproduction quality when output to another color printer is improved by performing contrast enhancement. An embodiment of the color conversion device 104 taking this point into consideration will be described below.

<Fourth Embodiment of Color Conversion Device 104> FIG.
Is a block diagram showing another embodiment of the color conversion device 104. The color conversion device 104 according to the present embodiment is, for example, as shown in FIG.
UCR circuit 405 of the color copier having the structure shown in FIG.
The output CMYK data is input via the storage device 415 as shown in FIG. The present invention also includes a color copying machine in which the color conversion device 104 of the present embodiment is internally connected as shown in FIG. Similarly, an image forming apparatus such as a color printer incorporating the color conversion device 104 according to the first, second, or third embodiment is also included in the present invention.

Referring to FIG. In the figure, reference number 150
155 are the same parts as the elements of the same number in FIG. 10, and the only newly added elements are the non-black character color judgment unit 160 and the comprehensive judgment unit 161. CMYK data (for example, 8 bits for each color) input from the color copier is temporarily stored in the data buffer 150. At the same time when the CMYK data of the target pixel is input from the data buffer 150 to the CMYK / colorimetric value converter 153, the CMYK around the target pixel is
The K data is input to the non-black character color determination unit 160, where it is determined whether or not there is a low-blackness non-black character color pixel around the target pixel. For example, 8 × around the pixel of interest
The CMYK data of the pixels other than the pixel of interest in the 8-pixel area is checked. If any of the C, M, and Y color values exceeds a predetermined value, a non-black character color pixel with low brightness exists around the pixel of interest. It is determined. This determination result and the black character color determination unit 1
The determination result of 51 is input to the overall determination unit 161. The comprehensive determination unit 161 determines that the pixel of interest is a black character color by the black character color determination unit 151, and that the non-black character color determination unit 160
Only when it is determined that there is no low brightness non-black character color pixel around the target pixel, the target pixel is determined to be a black character color, and the black character color contrast conversion table in the contrast conversion table storage unit 152 is selected. That is, whenever the non-black character color determination unit 160 determines that a non-black character color exists, the colorimetric value correction processing unit 154 performs contrast correction using the contrast conversion table for non-black characters. When the colorimetric value correction processing unit 154 performs contrast correction using the black character color contrast conversion table, the colorimetric value L′ a′b ′ is forcibly made achromatic. You may. The present invention also includes a color conversion device configured to forcibly achromaticize.

With the above configuration, if the RGB data output from the color conversion device 104 of this embodiment is sent to the computer 102 and output to the display 103 or the printer 101, the configuration described with reference to FIG. High quality black character reproduction can be performed while preventing the occurrence of such large character borders (pseudo contours).

The output of the black character color determination unit 154 and the output of the non-black character color determination unit 160 are directly supplied to the colorimetric value correction processing unit 154, and the colorimetric value correction processing unit 154 performs contrast conversion in accordance with the state of the output. A table may be selected.

<Implementation of the present invention using a computer>
As already mentioned, the present invention can be implemented by software on a general computer or on an image forming apparatus.

For example, a color conversion profile (four-dimensional look-up table) stored in the color conversion profile storage unit 121 shown in FIG. 3 is stored in a memory of a computer or an image forming apparatus, and corresponds to the grid point address generation unit 123. By executing a program including a processing step corresponding to the
A color conversion device equivalent to the color conversion device having the configuration shown in FIG. 3 or a color conversion process thereof can be realized. The color conversion apparatus having the configuration shown in FIG. 7 or the color conversion processing thereof can also be realized by software. However, in this case, the processing steps corresponding to the binary / multi-level conversion units 126c to 126k, and if necessary, the buffer memory 125
Processing steps for securing c to 125k on the memory and controlling buffering using the memory are added to the program.

Similarly, the color conversion device having the configuration shown in FIG. 10 or FIG. 13 or the color conversion processing thereof can be realized by software. In this case, the contrast conversion table stored in the contrast conversion table storage unit 152 is stored in the memory, and the functional units (151, 153, 154, 155, 160, and 161) illustrated in FIG. 10 or FIG.
A processing step of corresponding the data buffer 150 if necessary and reserved in the memory, and executes a program including the process steps for controlling buffering using it.

Further, the color conversion profile creating apparatus shown in FIG. 4 or its processing can be realized by software. The program for this includes processing steps corresponding to the elements denoted by reference numerals 300, 303, 304, 305, and 310 shown in FIG.
And storing the converted RGB values in a four-dimensional lookup table on a memory.

The programs described above are also included in the present invention. Further, various recording media such as a magnetic disk, an optical disk, a magneto-optical disk, and a semiconductor storage element on which the program is recorded are also included in the present invention.

In the above description, the output color data is RG
Although the B data is used, it is apparent from the above description that the present invention can be similarly applied to a case where output color data in other formats is used.

[0079]

As described in detail above, according to the present invention, black characters such as print data of an image forming apparatus such as a color printer or a color copying machine are subjected to object adaptive color processing and image area separation processing. CMYK data to which different color reproduction methods are applied for non-black characters and color data of another format is appropriately converted, and high-quality black characters can be reproduced on a display or another color printer. In the color conversion process or in the process of creating the color conversion profile, by performing appropriate contrast correction on the black character color and the non-black character color, black characters are prevented from lacking in density and reproduced with excellent readability, and For non-black characters, faithful color reproduction can be performed without impairing the gradation of the shadow portion. In the color conversion process or in the color conversion profile creation process, by performing a correction for achromatic color on the black character color, the black character can be reliably reproduced in a single black color. Even in the case of a black character color pixel, if a non-black character color low brightness pixel is present in the vicinity of the pixel, the large black character can also be processed by treating the black character color pixel as a non-black character color pixel and performing color conversion processing. It is possible to obtain effects such as high-quality reproducibility without generating a pseudo contour.

[Brief description of the drawings]

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

FIG. 2 is a block diagram for explaining a print data generation process of a color printer and a configuration of a printer control device.

FIG. 3 is a block diagram illustrating an example of a configuration of a color conversion device according to the present invention.

FIG. 4 is a block diagram illustrating an example of a configuration of a color conversion profile creation device according to the present invention.

FIG. 5 is a flowchart showing an example of a color conversion profile creation procedure according to the present invention.

FIG. 6 is a diagram illustrating an example of a contrast conversion table.

FIG. 7 is a block diagram showing another configuration of the color conversion device according to the present invention.

FIG. 8A is a diagram showing binary CMYK data of a black character portion and its multi-valued CMYK data in comparison. (B) Binary CMYK data of a picture area and its multi-value CM
It is a figure which shows YK data in comparison.

FIG. 9 is a diagram for explaining another example of the contrast conversion table.

FIG. 10 is a block diagram illustrating another configuration example of the color conversion device according to the present invention.

FIG. 11 is a schematic block diagram showing a general configuration of a color copying machine.

FIG. 12 is a diagram schematically illustrating a large character image output by a color copying machine.

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

[Explanation of symbols]

 100 Image forming apparatus as a source of CMYK data 101 Color printer 102 Computer 103 Display 104 Color conversion apparatus 120 Color conversion processing section 121 Color conversion profile storage section 123 Grid point address generation section 124 Interpolation operation section 125 Buffer memory 126 Binary / many Value conversion unit 150 Data buffer 151 Black character color determination unit 152 Contrast conversion table storage unit 153 CMYK / colorimetric value conversion unit 154 Colorimetric value correction unit 155 Colorimetric / RGB conversion unit 160 Non-black character color determination unit 161 General determination unit 300 CMYK data generation unit 301 Grid point address generation unit 302 CMYK calculation unit 303 Colorimetric value calculation unit 304 Black character color determination unit 305 Colorimetric value correction processing unit 306 Contrast conversion table storage unit 307 Colorimetric value correction unit 309 Color conversion profile setting unit 310 Color conversion profile temporary storage unit

Continuation of the front page F term (reference) 2C262 AA24 AA26 AA27 AB11 AC03 BA01 BA12 BA19 BC03 BC05 BC19 DA02 EA04 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE17 CE18 CH07 CH08 5C077 LL19 MM27 MP08 PP33 PP27 PP27 PP27 PP PP53 PQ08 PQ12 PQ23 SS02 TT02 5C079 HB01 HB03 HB08 HB12 LA02 LA12 LA21 LB02 MA11 NA03 NA05 PA01 PA02 PA03 PA05

Claims (23)

[Claims] 1. A color conversion apparatus for converting input CMYK data into output color data of a predetermined other format, wherein the CMYK data corresponding to a black character color is output more than the CMYK data corresponding to a non-black character color. A color conversion device comprising means for enhancing the contrast of output color data with respect to data. 2. A color conversion device for converting input CMYK data into output color data of a predetermined other format, comprising: a color conversion profile representing a correspondence between CMYK data and output color data; And color conversion processing means for converting CMYK data into output color data with reference to the color conversion profile.
A color conversion device having a characteristic of enhancing the contrast of output color data for CMYK data corresponding to a black character color, rather than output color data for YK data. 3. A color conversion apparatus for converting input CMYK data into output color data of a predetermined other format, wherein the CMYK data is converted into a colorimetric value when an image is formed using a specific image forming apparatus. CMYK / colorimetric value conversion means to be converted, black character color determination means for determining whether or not the CMYK data is a black character color, CM which has been determined to be a black character color by the black character color determination means
The colorimetric values of the YK data converted by the CMYK / colorimetric value conversion means are subjected to black character color contrast correction, and the CMYK data colorimetric values determined as non-black character colors are subjected to non-black character contrast correction. And a colorimetric value / output color data converting means for converting the colorimetric value corrected by the colorimetric value correcting means into output color data, and CMYK corresponding to a non-black character color A color conversion apparatus, wherein the contrast of output color data for CMYK data corresponding to a black character color is enhanced more than output color data for data. 4. The method according to claim 1, wherein the colorimetric value correction unit performs contrast correction by linearly converting a dynamic range of a brightness component set for a black character color or a non-black character color into a predetermined dynamic range. Claim 3
The color conversion device as described in the above. 5. The colorimetric value correction unit according to claim 1, wherein the colorimetric value of the CMYK data determined to be a black character color has a non-linear dynamic range of a brightness component set for the black character color in a predetermined dynamic range. By performing the conversion, the contrast correction is performed, and for the colorimetric values of the CMYK data determined to be the non-black character color, the dynamic range of the brightness component set for the non-black character color is linearly converted to a predetermined dynamic range. 4. The color conversion apparatus according to claim 3, wherein contrast correction is performed by performing the correction. 6. The color conversion apparatus according to claim 3, wherein said colorimetric value correcting means corrects the colorimetric value of the CMYK data determined as the black character color so that the saturation becomes zero. 7. A means for determining whether or not there is a pixel of a non-black character color having a predetermined brightness or less in the vicinity of the pixel of interest from CMYK data around the pixel of interest. 4. The color conversion apparatus according to claim 3, wherein the colorimetric value correction unit performs contrast correction for the non-black character color on the pixel of interest determined to have a non-black character color pixel. . 8. An apparatus for creating a color conversion profile used to convert CMYK data into output color data of another predetermined format, comprising: CMYK data generating means; and CMYK data generating means. Generated CMYK
Colorimetric value conversion means for converting data into colorimetric values when an image is formed by a specific image forming apparatus; and CMYK generated by the CMYK data generating means
A black character color determining unit that determines whether the data corresponds to a black character color; and a CM that is determined to be a black character color by the black character color determining unit.
The colorimetric values of the YK data converted by the colorimetric value converting means are subjected to black character color contrast correction, and the colorimetric values of the CMYK data determined to be non-black character colors are subjected to non-black character contrast correction. Output color data for CMYK data corresponding to a non-black character color, comprising: colorimetric value correction means; and color conversion setting means for setting a color conversion profile using the colorimetric values corrected by the colorimetric value correction means. A color conversion profile creating apparatus for creating a color conversion profile having a characteristic of enhancing the contrast of output color data with respect to CMYK data corresponding to a black character color. 9. The colorimetric value correction means performs contrast correction by linearly converting a dynamic range of a brightness component of a colorimetric value set for a black character color or a non-black character color into a predetermined dynamic range. 9. The color conversion profile creation device according to claim 8, wherein: 10. The colorimetric value correction unit according to claim 1, wherein the colorimetric value of the CMYK data determined to be a black character color has a non-linear dynamic range of a brightness component set for the black character color in a predetermined dynamic range. CMYK that has been subjected to contrast correction by conversion and determined to be a non-black character color
9. The color correction method according to claim 8, wherein contrast correction is performed on the colorimetric values of the data by linearly converting a dynamic range of a brightness component set for a non-black character color into a predetermined dynamic range. Conversion profile creation device. 11. The color conversion profile creation method according to claim 8, wherein said colorimetric value correcting means corrects the colorimetric value of the CMYK data determined to be a black character color so that the saturation becomes zero. apparatus. 12. The CMYK data generating means generates CMYK data corresponding to a plurality of representative points in a four-dimensional color space represented by four components of CMYK, and the color conversion profile setting means sets the color conversion profile as 9. The color conversion profile creation device according to claim 8, wherein a four-dimensional lookup table in which each representative point is associated with an output color data value is created. 13. A method for creating a color conversion profile used to convert CMYK data into output color data of another predetermined format, comprising: a CMYK data generating step; and a CMYK data generating step. CM
A colorimetric value conversion step of converting YK data into a colorimetric value when an image is formed by a specific image forming apparatus; and a CM generated by the CMYK data generating step
A black character color determination step of determining whether the YK data corresponds to a black character color; and a colorimetric value converted by the colorimetric value conversion step of the CMYK data determined to be a black character color by the black character color determination step, A colorimetric value correction step of performing contrast correction for black character color and performing contrast correction for non-black character with respect to the colorimetric values of the CMYK data determined to be the non-black character color; A color conversion setting step of setting a color conversion profile using the colorimetric values, wherein the contrast of the output color data for the CMYK data corresponding to the black character color is made higher than that for the CMYK data corresponding to the non-black character color. A method for creating a color conversion profile that creates a color conversion profile with characteristics to enhance. 14. A color conversion device according to claim 2, wherein a color conversion profile created by the color conversion profile creation device according to any one of claims 8 to 12 is used. 15. A color conversion apparatus according to claim 2, wherein a color conversion profile created by the color conversion profile creation method according to claim 13 is used. 16. An image forming apparatus for forming an image using CMYK data, for converting CMYK data generated in the apparatus into output color data of a predetermined other format. An image forming apparatus, comprising the color conversion device according to any one of the preceding claims. 17. An image forming apparatus for forming an image using CMYK data, wherein a color conversion profile used for converting CMYK data generated in the apparatus into output color data of another predetermined format is created. Claims 8 to 1
3. An image forming apparatus comprising the color conversion profile creation device according to any one of 2. 18. A color conversion device according to claim 14, comprising the color conversion profile creation device according to claim 8. Description: 19. A program for causing a computer to execute a color conversion profile creation process comprising processing steps corresponding to the functions of each means of the color conversion profile creation device according to claim 8. 20. A program for causing a computer to execute a color conversion process comprising processing steps corresponding to the functions of each means of the color conversion device according to claim 3. 21. A program for causing a computer to execute a process of converting CMYK data into output color data with reference to a color conversion profile created by the color conversion profile creating device according to any one of claims 8 to 12. Program. 22. A program for causing a computer to execute a process of converting CMYK data into output color data with reference to a color conversion profile created by the color conversion profile creating method according to claim 13. 23. A recording medium readable by a computer, wherein the program according to claim 19, 20, 21, or 22 is recorded.