JP4641959B2 - Image processing device - Google Patents

Description

  The present invention relates to an image processing apparatus that performs color conversion processing on RGB color value data read by a scanner or the like or displayed on a computer screen into CMYK color value data handled by a color printer or the like. In particular, the present invention holds the set specific input color value data as key color color value data, and for the input color value data that matches the key color color value data, the input color value data as it is is used as the key color color data. The present invention relates to an image processing apparatus in which input color value data that does not match value data is subjected to color reduction processing by the color reduction processing means.

  Normally, RGB color value data that is read by a printer device or a scanner or displayed on a computer screen is gradation data for each pixel of RGB (Red Green Blue) color, and the image is an image of a printer or the like. When printing with a processing apparatus, it is necessary to perform color conversion into a CMYK (Cyan Magenta Yellow blacK) image corresponding to the print engine. In the color conversion process, RGB three-dimensional data is converted into CMYK four-dimensional data. The color conversion is performed using a color conversion table (LUT) indicating the relationship between RGB gradation data and CMYK gradation data.

  In this case, if each of the RGB color value data has 256 gradations, the color conversion is performed on 2563 colors which are combinations of all RGB gradation data, that is, combinations of CMYK gradation data corresponding to about 16.77 million colors. Giving a table a huge amount of data. Therefore, normally, for example, as in the image processing apparatus disclosed in Patent Document 1 (Japanese Patent No. 3603766), conversion values for hundreds to tens of thousands of grid points out of 16.77 million colors are color conversion tables. Therefore, CMYK values are obtained by interpolation processing at the intermediate part of these lattice points.

  The image processing apparatus disclosed in Patent Document 1 converts input gradation data in the RGB color space into gradation data in the CMYK color space, and converts the gradation data in the CMYK color space into image reproduction data by halftone processing. In the image processing apparatus for converting to RGB, the output density gamma characteristic A with respect to the gradation in the RGB color space and the output density gamma characteristic B with respect to the gradation in the CMYK color space in the halftone process are made equal to each other. It is a thing. If printing is performed using this image reproduction data, the color of the designed image can be faithfully reproduced, and a high-quality image can be printed.

  However, even if a color conversion table having conversion values for grid points is used, interpolation processing of intermediate portions of the grid points is complicated and time consuming, and high processing speed cannot be obtained. Accordingly, the present applicant has already filed a patent application concerning the invention of Japanese Patent Application No. 2005-266978 (hereinafter referred to as “Prior Application 1”) or Japanese Patent Application No. 2005-266969 (hereinafter referred to as “Prior Application 2”). ing. The image processing apparatus according to the invention disclosed in the prior application 1 or the prior application 2 stores the output color value data converted from the input color value data by the color conversion table in the cache table together with the input color value data. By using it for the conversion process, the color conversion process is speeded up.

That is, in the image processing device disclosed in the above-mentioned prior application 1 or prior application 2, the output color value data converted from the input color value data immediately before is stored in the cache table together with the input color value data, and the following When the input color value data of the pixel matches the input color value data stored in the cache table, the output color value data stored in the cache table is directly used as the output color value data without performing the conversion process using the color conversion table. To do. On the other hand, if the input color value data of the next pixel does not match the input color value data stored in the cache table, a conversion process using the color conversion table is performed to obtain output color value data from the input color value data. It is configured.

  Generally, there is a high possibility that adjacent pixels in the image have the same color, so the probability that the input color value data of the previous pixel and the input color value data of the next pixel will be the same increases. Therefore, according to the above, the ratio that the input color value data of the next pixel matches the input color value data stored in the cache table increases, and the conversion to the cache table is not performed by the color conversion table. The stored output color value data can be used as output color value data as it is. As a result, the processing speed can be increased.

Japanese Patent No. 3603766

  However, even the image processing apparatus using the cache table as described above has a problem that the processing speed is still insufficient. If such a problem is simply dealt with, the gradation of the color value data may be coarsened, and accordingly, high-speed processing becomes possible. However, there is a problem in that the image quality of the printed image is degraded by the coarser gradation.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to further increase the speed of color conversion processing while ensuring necessary image quality in an image processing apparatus.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present application includes color conversion means for performing color conversion from RGB data as input color value data to CMYK data as output color value data based on a color conversion table. A cache table for storing the input color value data and output color value data immediately converted by the color conversion unit, and a key color holding unit for holding the set specific input color value data as key color color value data. A key color comparing means for comparing the key color color value data with the input color value data, and a color reduction processing means for extracting data up to a predetermined upper digit of the input color value data, and comparing with the key color comparing means For the input color value data that matches the key color color value data, the input color value data as it is is changed to the input color value that does not match the key color color value data. The color value data after the color reduction processing by the color reduction processing means is compared with the input color value data of the cache table, and the color value data and the cache table after the color reduction processing are performed. If the input color value data of the cache table match, the output color value data of the cache table is set as output color value data, and the color value data after the color reduction processing and the input color value data of the cache table do not match The color value data color-converted by the color conversion means is used as output color value data.

The invention according to claim 2 of the present application is the invention according to claim 1, characterized in that the key color color value data is data set by a key color color value and a predetermined range value .

  The image processing apparatus of the present invention has the following effects. That is, in the invention according to the first aspect, the input color value data as compared with the key color color value data compared with the key color comparison means does not match the input color value data as it is with the key color color value data. For the input color value data, the color value data after color reduction processing is compared with the input color value data in the cache table. If the two match, the output color value data in the cache table is used as the output color value data. If they do not match, the color value data color-converted by the color conversion means is set as output color value data. As a result, it is possible to further increase the speed of the color conversion process while ensuring the necessary image quality.

  Further, in the invention according to claim 2, in the image processing apparatus according to claim 1, since the key color color value data has a data width, the ratio of determination as the key color increases, Color reproducibility can be improved.

  Hereinafter, specific examples of the present invention will be described in detail with reference to examples and drawings. However, the embodiments shown below exemplify an image processing apparatus for embodying the technical idea of the present invention, and are not intended to identify the present invention as this image processing apparatus. The present invention is equally applicable to image processing apparatuses of other embodiments included in the scope of claims.

  FIG. 1 is a block diagram showing a schematic configuration of an image processing apparatus according to the present invention. A control code is sent from the host computer 10 to the image processing apparatus 20. The image processing apparatus 20 includes an input buffer 21 that receives input data, a CPU 23 that controls the operation of the entire printer, a program ROM 22 that contains a program describing the operation of the CPU 23, image data extracted from the control code, and calculation data. A data RAM 24 for storing data, a print image transfer unit 25 for converting image data converted for output into data for the final process and transferring it to the printer engine unit 26, and the like. Note that the HDD 30 may be adopted as an additional option for the processing area.

  The program ROM 22 includes a key color comparison unit 221 that compares key color color value data and input color value data, and an input color value analysis unit 222 that determines whether the input color values of the current pixel and the cache table pixel match. A color conversion unit 223 for obtaining an output color value with respect to an input color value using a color conversion table, a cache table information updating unit 224 for updating cache table information with the obtained input color value and output color value, and an input color It is composed of a color reduction processing unit 225 and the like that extract data up to a predetermined upper digit of value data.

  Here, the color reduction processing by the color reduction processing unit 225 will be described with reference to FIG. There are three input color values, R, G, and B. In FIG. 2, only one of them is shown. The input color value has a gradation of 8 bits. For example, when 6 bits (64 gradations) are set as the color reduction level value, the upper 6 bits are extracted from the 8-bit input color value. Then, the 6 bits are compared with the upper 6 bits of the input color value held in the cache table.

  In this way, if only the upper few bits are extracted from the 8-bit input color value and compared, the input color value of the cache table can be obtained as long as the upper bits match regardless of the lower bits. Therefore, the probability of adopting the output color value of the cache table increases. As a result, the number of color conversion processes using the color conversion table is reduced, and the processing speed can be increased.

  The data RAM 24 includes a cache table 241 for storing color-converted input color value data and output color value data, input image data obtained from control codes, an image data buffer 242 for output image data obtained later, and input color values. The color conversion table 243, which is a reference table for obtaining output color values, a color reduction level buffer 244 for storing user-specified color reduction level values, a key color buffer 245 for storing color values of key colors, and the like.

  As shown in FIG. 4, the cache table 241 is divided into a key color type and a non-key color type other than the above, and the input color value data color-converted immediately before by the color conversion unit so as to perform high-speed processing. Stores output color value data. As shown in FIG. 5, the color conversion table 243 holds conversion values of input RGB values versus output CMYK values at grid points of several hundreds to tens of thousands of colors out of 2,563 colors, that is, about 16.77 million colors. . As shown in FIG. 6, the key color buffer 245 stores the color value of the key color and its range value, and these values are set by the user. The range value may be set for each color of RGB as a partial designation, or may be set as a total value of the deviation of each color of RGB as a whole designation.

  The color value of key color and the range value can be set by displaying the setting screen and entering the numerical value directly with the keyboard, or by using a pointing device such as a mouse on the screen where the image is displayed. And the color value of the color displayed in that portion may be used as the key color color value. Further, not only one type of color value but also a plurality of types of colors may be set as the key color.

  Next, the processing operation of the image forming apparatus of the present invention will be described with reference to the flowchart of FIG. When a print command is sent from the host computer 10, the print command is temporarily stored in the input buffer 21. The CPU 23 extracts the image data from the print command stored in the input buffer 21 according to the command of the program ROM 22 and stores it in the image data buffer 242 of the data RAM 24.

When the image data is stored in the image data buffer 242, first, the number of processed pixel image data is checked to determine whether or not the color conversion processing for all the pixels of the processing target image has been completed (step S1). If not completed, the input color value of the next target pixel is acquired from the image data buffer 242 (step S2).

  It is determined whether or not the acquired input color value is within the range set from the color value of the key color held in the key color buffer 245 and the value (step S3). If the color value of the key color is not within the range set from the value, the color reduction processing unit 225 performs color reduction processing of the input color value (step S4).

  The input color value subjected to the color reduction processing is compared with the input color value stored in the cache table 241 to determine whether or not they match (step S5). If they match, the output color value is taken out from the cache table 241 (step S5). S6).

  If it does not match the input color value of the cache table 241 in step S5, the color conversion table 243 is referred to, and if necessary, an interpolation operation is performed to obtain an output color value (step S7). Then, the value of the cache table 241 is updated with the input color value and output color value at that time (step S8).

  The output color values obtained in steps S6 and S7 are stored in the image data buffer 242 (step S9), and the number of processed pixels is counted up by one (step S10).

  In step S3, if the input color value is within the range set from the color value of the key color and the value, the input color value is compared with the input color value stored in the cache table 241 to determine whether they match. If it matches, the output color value is extracted from the key color cache table 241 (step S12).

  If it does not coincide with the input color value of the key color cache table 241 in step S11, the color conversion table 243 is referred to, and if necessary, an interpolation operation is performed to obtain an output color value (step S13). Then, the value of the key color cache table 241 is updated with the input color value and output color value at that time (step S14).

  As described above, in the image processing apparatus according to the present invention, the set specific input color value data is held as the key color color value data, and the input color value data that matches the key color color value data is Since the input color value data as it is is not matched with the key color color value data, the color reduction processing is performed by the color reduction processing means. As a result, while ensuring the required image quality, the color The conversion process can be further speeded up.

It is a block diagram which shows schematic structure of the image processing apparatus of this invention. It is explanatory drawing of a color reduction process. 3 is a flowchart showing color conversion processing of the image processing apparatus of the present invention. It is a figure which shows the content of a cache table. It is a figure which shows the content of the color conversion table. It is a figure which shows an example of key color setting data.

10.... Host computer 20... Image processing device 21... Input buffer 22.
23 ... CPU
24..Data RAM
25... Print image transfer unit 26... Printer engine 30.
221 ... Key color comparison unit 222 ... Input color value analysis unit 223 ... Color conversion unit 224 ... Cache table information update unit 225 ... Color reduction processing unit 241 ... Cache table 242 ... Image data buffer 243 Color conversion table 244 Color reduction level buffer 245 Key color buffer

Claims (2)

Color conversion means for performing color conversion from RGB data as input color value data to CMYK data as output color value data based on the color conversion table, and input color value data and output color that have been color converted immediately before by the color conversion means A cache table for storing value data, key color holding means for holding set specific input color value data as key color color value data, and a key color for comparing the key color color value data with the input color value data A comparison unit, and a color reduction processing unit that extracts data up to a predetermined upper digit of the input color value data,
The input color value data as compared with the key color color value data compared by the key color comparison means is used as it is, and the input color value data that does not match the key color color value data as described above. The color value data after the color reduction processing by the means is compared with the input color value data of the cache table, and the color value data after the color reduction processing and the input color value data of the cache table are If they match, the output color value data of the cache table is set as output color value data. If the color value data after the color reduction processing and the input color value data of the cache table do not match, the color conversion means An image processing apparatus characterized in that the converted color value data is used as output color value data. The image processing apparatus according to claim 1, wherein the key color color value data is data set by a key color color value and a predetermined range value .

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