JP2009246666A - Color data generating method, color data generator, and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a high-quality image with a good reproducibility by generating precise black data according to a primary color of a color image. <P>SOLUTION: When three-color color data consisting of C1, M1, and Y1 is input, a first parameter selecting section 11 selects the minimum data value min_K from among the three color values and a second parameter selecting section 12 selects the maximum data value max_K from among the three color values. A UCRγ table for calculating black data based on the minimum data value and corresponding to the color of the maximum data value max_K is prepared for each of the three colors. When the color associated with the table is the color of the maximum data value max_K, the table is used for calculating black data. A section 13 for calculating UCRγ, which corresponds to the color of the maximum data value max_K, selects a table associated with the color of the selected max_K from among the UCR<SB>γ</SB>tables corresponding to the color of the maximum data value max_K and generates black data K1 with respect to the min_K using the selected table. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  According to the present invention, in a color image forming apparatus, three color data including C (cyan), M (magenta), and Y (yellow) representing a color image to be formed is converted into four color data including black ink data. The present invention relates to a color data generation method and apparatus for generating color data for color image formation by conversion.

  Conventionally, in a color image forming apparatus such as a printer or a copying machine, when a color image is formed on a recording medium such as a printing paper, it is composed of C (cyan), M (magenta), Y (yellow), and K (black). It is common to use four colors of ink or toner.

  For this reason, in this type of color image forming apparatus, for example, when image data composed of three color data of R (red), G (green), and B (blue) is input from a computer, a scanner, or the like, This image data is first converted into image data composed of three color data of CMY, and further, part or all of the overlapping portion of the color data of these three colors is converted into K (black) data. Four-color data for image formation is generated. The generated CMYK color data is used to determine the amount of each color ink or toner used to form a color image.

  As a method for generating color data, for example, Patent Document 1 discloses that color data of three colors converted from RGB is C1 (cyan), M1 (magenta), and Y1 (yellow), and these color data of C1, M1, and Y1 are used. The minimum data value is set to the value of black data K, and black data K is subtracted from each color data of C1, M1, and Y1 to correct them, thereby correcting C2 (= C1-K) and M2 (= M1). -K), a technique for obtaining Y2 (= Y1-K) is disclosed. Thereby, the total amount of each color ink can be controlled to an appropriate amount.

  However, in the technique disclosed in Patent Document 1, the black data K is determined by the minimum data value among the color data of C1, M1, and Y1 regardless of the main color of the image. Depending on the main color of the image, the black color may appear too strong and the image may appear dirty, or the black color may be too weak to reproduce the contrast of the image, resulting in loss of image reproducibility and quality. There was a fear.

  Therefore, even if the main color of the color image is changed, the applicant of the present application cannot reproduce the contrast of the image sufficiently because the black color is too strong and the image looks dirty or the black color is too weak. We proposed a technology that would never be That is, a conversion table is prepared for each CMY color data by converting the minimum data value of each CMY color data into black data. Then, a minimum data value is selected from CMY, and a color conversion table corresponding to the minimum data value is selected. Then, the selected minimum data value is converted into black data using the selected conversion table.

  The conversion table for each color is set so that the input data area where black data is not generated differs depending on the color. For example, in the conversion table selected when C (cyan) is the minimum data value, black data is not generated when the input data value (minimum data value) is a predetermined value (for example, 72 in 255 gradations) or less. On the other hand, the conversion table selected when Y (yellow) is the minimum data value, the input data value (minimum data value) is a predetermined value (C (cyan) corresponding conversion table). In the above example, black data is set not to be generated when the value is equal to or smaller than a predetermined value (for example, 16) smaller than 72).

Therefore, according to the technique disclosed in Patent Document 2, for example, when Y (yellow) is the minimum data value (that is, when cyan is relatively more), a large amount of black data is generated, and vice versa. In addition, when C (cyan) is the minimum data value (that is, when there is relatively more yellow), the black data can be appropriately adjusted according to the color of the minimum data value. It becomes possible. This makes it possible to form a high-quality image with good reproducibility regardless of the main color of the color image.
JP-A-4-281668 JP 2004-66822 A

  However, in the technique disclosed in Patent Document 2, the minimum data value is the basis for determining which conversion table is selected, and the black ink data is generated based on the conversion table selected based on the minimum data value. Is used to generate a minimum data value as an input, and does not directly reflect what the main color (the color of the maximum data value) is.

  That is, for example, when C (cyan) is the minimum data value, what value is M (magenta) or Y (yellow), and whether the main color (maximum data value) is Y (yellow) M ( Magenta) is not reflected in the generation of black ink data.

  When C (cyan) is the minimum data value, the maximum data value is either Y (yellow) or M (magenta). For example, Y (yellow) is not so different from C (cyan) and M ( The data value of (magenta) may be very large, and conversely, Y (yellow) may be very large with respect to C (cyan). At this time, in the latter case (yellow subject) rather than the former case (magenta subject), it is desired to further reduce the amount of ink data so that the ink data does not stand out too much. However, in any case, the black data is generated based on the data value of C (cyan) using the conversion table corresponding to C (cyan) of the minimum data value. Adjustment is difficult.

  As described above, the technique disclosed in Patent Document 2 does not directly consider what the maximum data value is when generating black data, and is based solely on the minimum data value and the corresponding color conversion table. Since black data is generated, depending on what the main color is, the K (black) data value is not necessarily generated properly, and the above effect may not be obtained sufficiently.

  The present invention has been made in view of the above problems, and in a color image forming apparatus, it is possible to generate high-precision black ink data according to the main color of a color image, thereby achieving a high-quality image with good reproducibility. It aims at making it possible to form.

  According to a first aspect of the present invention, there is provided a color image forming apparatus including black data from pre-conversion color data including three colors of cyan, magenta, and yellow representing a color image to be formed in a color image forming apparatus. This is a color data generation method for generating color data after color conversion.

  In the method of the present invention, the maximum color data extraction step for extracting one maximum color data having the maximum data value from the pre-conversion color data, and the maximum color included in the first black data conversion table for generating black data. A conversion characteristic selection step for selecting a black data conversion characteristic associated with the data; a minimum data value extraction step for extracting a minimum data value from the pre-conversion color data; a black value from the minimum data value and the selected black data conversion characteristic; A first black data generating step for generating data.

  In this color data generation method, the black data conversion characteristic for generating black data is selected based on the maximum color data among the three color data before conversion, and the black data selected based on the maximum color data is selected. Black data for the minimum data value is generated using the conversion characteristics. In other words, the black data is generated by the black data conversion characteristic that matches the main color having the largest color data.

  Therefore, according to the color data generation method according to claim 1, since the black data is generated based on the black data conversion characteristic corresponding to the main color of the color image, high-precision black data generation corresponding to the main color is generated. This makes it possible to form a high-quality image with good reproducibility.

  The invention described in claim 2 is the color data generation method according to claim 1, wherein the first black data conversion table has two or three types of black data conversion characteristics associated with any of the three colors. Each of the three colors is associated with one of the black data conversion characteristics.

  If two or three types of black data conversion characteristics are prepared, for example, the black data conversion characteristics associated with the light yellow of the three colors and the black data conversion characteristics associated with the dark cyan are provided. As different, by setting each black data conversion characteristic according to the corresponding color, black data can be appropriately generated regardless of the main color.

  The invention according to claim 3 is the color data generation method according to claim 1 or 2, wherein the black data conversion characteristics and the minimum data value common to the three colors of the second black data conversion table for generating black data are provided. From the second black data generation step for generating black data, the saturation derivation step for deriving the saturation of the color image, and the black data generated in the first black data generation step and the second black data generation step A weight deriving step for deriving a weight for the derived saturation using a weighting table in which the relative weight of the ink data to be set is set according to the saturation, and each black data generated in each black data generation step And a third black data generation step of generating black data reflecting the weight based on the derived weights.

  In this color data generation method, as in the first aspect, the black data is generated using the black data conversion characteristics corresponding to the maximum color data in the first black data conversion table. In the method of claim 1, the result generated using the first black data conversion table is directly used as the black data generation result by the method. In the method of claim 3, the first black data conversion table is used. In addition to generating the black ink data, black data is generated using a second black data conversion table prepared separately from the first black data conversion table and shared by each color. That is, black data is generated for each of the same minimum data values using two black data conversion tables. Then, a weight indicating which one of the two generated black data is to be weighted is derived using a weighting table in which the weight is set according to the saturation. Based on the derived weight, black data reflecting the weight is generated from the two black data.

  Therefore, according to the color data generation method of claim 3, the black data is generated using both the first and second black data conversion tables, and the color image is generated based on both of the generated black data. Since the black data that reflects the weighting according to the saturation of the color is generated, it is possible to generate the black data with higher accuracy according to the main color and the saturation. A high-quality image can be formed.

  As the weighting table, for example, as described in claim 4, it is preferable to use a table set so that the weight of the black data generated in the first black data generation step increases as the saturation of the color image increases. . The higher the saturation is, the more noticeable the ink is. On the contrary, the lower the saturation is, the less noticeable the ink is. If the weight of the black data generated using the black data conversion characteristic is increased, the black data can be appropriately generated according to the main color.

  The invention according to claim 5 is the color data generation method according to claim 3 or 4, wherein the weighting table includes the black data generated in the first black data generation step when the saturation of the color image is zero. When the weight is 0 and the saturation of the color image is greater than or equal to a predetermined saturation threshold, the weight of the black data generated in the second black data generation step is 0.

  According to the color data generation method of the fifth aspect, since more appropriate weighting according to the saturation of the color image is obtained and black data is generated based on the weighting, the black data generation accuracy is further increased. It becomes possible.

  A sixth aspect of the present invention is the color data generation method according to any one of the first to fifth aspects, wherein the first black data conversion table is associated with yellow as a black data conversion characteristic, and the minimum data value is A black data conversion characteristic configured not to generate black data when it is equal to or lower than a predetermined first set value, and a second set value that is associated with cyan or magenta and whose minimum data value is smaller than the first set value. In the following cases, there is a black data conversion characteristic configured so that black data is not generated.

  In other words, even if the minimum data value is the same, if the maximum color data is yellow, black data is less likely to occur than if the maximum color data is cyan or magenta (if the minimum data value is not larger, black data is generated. Not).

  Therefore, according to the color data generation method of the sixth aspect, since the black data is generated based on the black data conversion characteristics corresponding to the main color of the color image, the generation of black data corresponding to the main color is further enhanced. Thus, it is possible to form an image with better reproducibility and higher quality.

  The invention according to claim 7 is the color data generation method according to any one of claims 3 to 5, wherein the first black data conversion table is associated with yellow as a black data conversion characteristic, and the minimum data value is A black data conversion characteristic configured not to generate black data when it is equal to or lower than a predetermined first set value, and a second set value that is associated with cyan or magenta and whose minimum data value is smaller than the first set value. In the following cases, the ink data conversion characteristic is configured such that the ink data is not generated. Further, the black data conversion characteristic of the second black data conversion table is configured so that black data does not occur when the minimum data value is smaller than the first set value and equal to or smaller than the third set value greater than the second set value. Has been.

  According to the color data generation method of the seventh aspect, the usage balance between the first black data conversion table and the second black data conversion table is appropriately set, and the black ink is calculated based on these tables and the saturation (weighting). Since data is generated, the generation accuracy of black data can be further increased.

  The invention according to claim 8 is the color data generation method according to claim 6 or 7, wherein the first black data conversion table has three types of black data conversion characteristics, and each black data conversion characteristic has three colors. The black data conversion characteristic associated with magenta is one-to-one, and the minimum data value is smaller than the first set value and larger than the second set value. In this case, black data is not generated.

  According to the color data generation method of claim 8, since each of the three color data has black data conversion characteristics, the black data with higher accuracy corresponding to the main color (color data of the maximum data value) is obtained. Can be generated.

  According to a ninth aspect of the present invention, in the color image forming apparatus, four post-conversion color data including black ink data is generated from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. This is a color data generation method.

  In the method of the present invention, the black data is extracted from the minimum data value extracting step for extracting the minimum data value from the pre-conversion color data, and the black data conversion characteristics and the minimum data value of the black data conversion table for generating black data. A black data generation step for generating color data, a maximum color data extraction step for extracting one maximum color data having the maximum data value from the pre-conversion color data, and an adjustment rate for black data according to saturation An adjustment characteristic selection step for selecting an adjustment characteristic associated with the maximum color data in the adjustment table, a saturation derivation step for deriving the saturation of the color image, and an adjustment rate from the derived saturation and the selected adjustment characteristic. An adjustment rate deriving step for deriving; and a black ink data adjusting step for adjusting the black ink data generated in the black ink data generating step based on the adjustment rate.

  In this color data generation method, black data is not generated using the first black data conversion table as in the method according to claim 1, but first black data corresponding to the second black data conversion table in claim 3 is used. Black ink data is generated using the conversion table.

  On the other hand, when forming a color image, if the saturation of the color image is low, even if the amount of ink data is increased to some extent, the problem that the color of the ink color is too strong and the image becomes dirty is less likely to occur. The higher the saturation of, there is a possibility that depending on the amount of ink data, the color of the ink color will be too strong and the image will become dirty. In other words, if black data is generated uniformly regardless of the saturation (generated using only the black data conversion table), the image may become dirty or the contrast of the image may not be sufficiently reproduced. There is.

Therefore, in the method of claim 9, an adjustment rate corresponding to the saturation of the color image is derived, and the amount of black data is adjusted using this adjustment rate.
Therefore, according to the color data generation method according to claim 9, although the black data itself generated using the black data conversion table shared by the three colors does not take the main color into consideration, the generated color data is generated. The black data is adjusted according to the maximum color data and the saturation of the color image. Therefore, it is possible to generate black data with high accuracy according to the main color and saturation, and thereby it is possible to form a higher-quality image with better reproducibility.

  A tenth aspect of the present invention is the color data generation method according to the ninth aspect, wherein the adjustment table has two or three types of adjustment characteristics associated with any one of the three colors. Each is associated with one of the adjustment characteristics.

  If two or three types of adjustment characteristics are prepared in this way, for example, the adjustment characteristic associated with light yellow among the three colors is different from the adjustment characteristic associated with dark cyan. By setting each adjustment characteristic according to the corresponding color, black data can be generated appropriately regardless of the main color.

  The invention described in claim 11 is the color data generation method according to claim 9 or 10, wherein the adjustment rate is a direct or indirect ratio of the adjusted black data to the black data generated in the black data generation step. The adjustment characteristic associated with yellow is configured such that the ratio for the same saturation is smaller than the adjustment characteristic associated with cyan or magenta.

  In other words, even if the minimum data value is the same, if the maximum color data is yellow, black data is less likely to occur than if the maximum color data is cyan or magenta (if the minimum data value is not larger, black data is generated. Not).

  Therefore, according to the color data generation method of claim 11, it is possible to generate the black data according to the main color and the saturation with higher accuracy, thereby achieving better reproducibility and higher A quality image can be formed.

  A twelfth aspect of the present invention is the color data generation method according to the eleventh aspect, wherein each adjustment characteristic in the adjustment table is configured such that the adjustment rate decreases as the saturation of the color image increases.

  According to the color data generation method of claim 12, since the higher the saturation, the smaller the black data generated by the method is actually generated, the lower the black data generated in the black data generation step. Therefore, more appropriate black ink data can be generated according to the color.

  A thirteenth aspect of the present invention is the color data generation method according to the eleventh or twelfth aspect, wherein each adjustment characteristic in the adjustment table is configured such that the adjustment rate is 100% when the saturation of the color image is zero. In addition, the adjustment characteristic associated with yellow is configured such that the adjustment rate is 0 when the saturation is equal to or higher than the predetermined first saturation, and the adjustment characteristic associated with cyan or magenta is The adjustment rate is configured to be 0 when the saturation is equal to or higher than the second saturation higher than the first saturation.

  According to the color data generation method of claim 13, since a more appropriate adjustment rate according to the saturation and maximum color data of the color image is obtained and the black data is adjusted based on the adjustment rate, the black data The generation accuracy of can be further increased.

  A fourteenth aspect of the present invention is the color data generation method according to the thirteenth aspect, wherein the adjustment table has three types of adjustment characteristics, and each of the adjustment characteristics is associated with one of the three colors on a one-to-one basis. The adjustment characteristic associated with magenta is configured such that the adjustment rate becomes 0 when the saturation is equal to or higher than the third saturation which is higher than the first saturation and lower than the second saturation.

  According to the color data generation method of claim 14, since each of the three color data has adjustment characteristics, more accurate black data generation according to the main color (color data of the maximum data value) is generated. Is possible.

  The saturation derivation in the saturation derivation step is performed, for example, as described in claim 15 between the maximum color data extracted in the maximum color data extraction step and the minimum data value extracted in the minimum data value extraction step. It can be derived based on the difference.

  The invention described in claim 16 is the color data generation method according to any one of claims 1 to 15, wherein the black data generated by the color data generation method is subtracted from each of the color data before conversion. The method includes a three-color generation step of generating color data of three colors, cyan, magenta, and yellow, that constitute the converted color data.

  According to the color data generation method of claim 16, the amount of black data generated with high accuracy is subtracted from the pre-conversion color data of each color of cyan, magenta, and yellow, and the post-conversion color of each color Since data is generated, the total amount of ink of each color used in image formation can be appropriately regulated.

  According to a seventeenth aspect of the present invention, in a color image forming apparatus, four post-conversion color data including black ink data are generated from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. This is a color data generation method.

  In the method of the present invention, the black data is extracted from the minimum data value extracting step for extracting the minimum data value from the pre-conversion color data, and the black data conversion characteristics and the minimum data value of the black data conversion table for generating black data. A black color data generation step, a maximum color data extraction step for extracting one maximum color data having the maximum data value from the pre-conversion color data, and a black image generated from the black data generated in the black data generation step. Output correction table for correcting according to the characteristics of the image forming means for performing the output correction characteristic selection step for selecting the output correction characteristic associated with the maximum color data, and the black data generated in the black data generation step A black ink data output correcting step for correcting the ink color based on the selected output correction characteristic.

  In this color data generation method, as in the case of claim 9, black data is not generated using the first black data conversion table as in the method of claim 1, but first, the second black data in claim 3 is used. Black data is generated using a black data conversion table corresponding to the conversion table. Here, if the generated value is used for image formation as it is, there is a possibility that the image becomes dirty, or conversely, the contrast of the image cannot be sufficiently reproduced.

  Accordingly, in the method of claim 17, a table having an output correction characteristic associated with the maximum color data is prepared as an output correction table for correcting the generated black data in accordance with the characteristics of the image forming unit. In the output correction table, appropriate black data correction corresponding to the maximum color data is performed.

  Therefore, according to the color data generation method of claim 17, although the black data itself generated using the black data conversion table shared by the three colors does not consider the main color, the generated color data is generated. The black data is corrected according to the maximum color data in a stage where correction according to the characteristics of the image forming means is performed. For this reason, it is possible to generate high-precision black ink data according to the main color, thereby forming a high-quality image with good reproducibility.

  The invention according to claim 18 is the color data generation method according to claim 17, wherein the output correction table has two or three types of output correction characteristics associated with any of the three colors. Each color is associated with one of the output correction characteristics.

  If two or three types of output correction characteristics are prepared, for example, the output correction characteristics associated with light yellow among the three colors are different from the output correction characteristics associated with cyan, which is a dark color. By setting each output correction characteristic in accordance with the corresponding color, black data can be appropriately generated regardless of the main color.

  The invention according to claim 19 is the color data generation method according to claim 18, wherein the output correction characteristic associated with yellow in the output correction table corresponds to the output correction characteristic associated with cyan or magenta. The corrected black data value for the same black data is configured to be small.

  That is, even if the black data to be corrected has the same value, if the maximum color data is yellow, black data is less likely to occur than if the maximum color data is cyan or magenta.

  Therefore, according to the color data generation method of claim 19, it is possible to generate black data according to the main color with higher accuracy, and thereby, an image with higher reproducibility and higher quality can be obtained. It becomes possible to form.

  The invention according to claim 20 is the color data generation method according to claim 19, wherein the output correction table has three types of output correction characteristics, and each output correction characteristic is one-to-one for any of the three colors. The output correction characteristic associated with magenta is greater than the output correction characteristic associated with yellow for which the corrected value for the same black data is greater than the output correction characteristic associated with yellow. It is configured to be smaller than in the case of characteristics.

According to the color data generation method of the twentieth aspect, since there is an output correction characteristic for every three colors, it is possible to generate more accurate black data according to the main color (maximum color data).
In the color data generation method according to any one of claims 17 to 20, as described in claim 21, in the three-color generation step, the black data generated in the black data generation step is generated from each of the color data before conversion. By subtracting, it is preferable to generate three color data of cyan, magenta, and yellow constituting the converted color data.

  According to a twenty-second aspect of the present invention, there is provided color image forming apparatus for converting four-color converted color data including black ink from unconverted color data including three colors of cyan, magenta, and yellow representing a color image to be formed. A color data generating device for generating a first black data conversion table having black data conversion characteristics associated with three colors, and a minimum data extracting unit for extracting minimum data values by comparing pre-conversion color data; The maximum color data extracting means for comparing the pre-conversion color data and extracting the color data having the maximum data value, and the maximum color data extracted by the maximum color data extracting means in the first black data conversion table. First black data calculation means for calculating black data for the minimum data value extracted by the minimum data extraction means using the black data conversion characteristic For example, to produce a calculation result by the first black data calculating means as a black data.

  According to the color data generating apparatus according to claim 22 configured as described above, the color data generating method according to claim 1 can be realized, and the same operations and effects as in claim 1 are provided. In other words, since the black data is generated based on the black data conversion characteristics corresponding to the main color of the color image, it is possible to generate high-precision black data corresponding to the main color, thereby achieving high reproducibility and high quality. A quality image can be formed.

  According to a twenty-third aspect of the present invention, in the color data generating device according to the twenty-second aspect, a second black data conversion table having black data conversion characteristics common to the three colors is used, and the second black data conversion table is used. The second black data calculating means for calculating black data for the minimum data value extracted by the minimum data extracting means, the black data calculated by the first black data calculating means, and the second black data calculating means. Derived by the saturation derivation means using the weighting table in which the relative weight of the ink data is set according to the saturation of the color image, the saturation derivation means for deriving the saturation of the color image, and the weighting table Weight deriving means for deriving weights for the saturation, black data calculated by the first black data calculating means, black data calculated by the second black data calculating means, and weighting And a third black data calculating means for calculating black data reflecting the weight based on the weight derived by the means, wherein the calculation result by the third black data calculating means is generated as black data. Has been.

  According to the color data generating apparatus of claim 23 configured as described above, the color data generating method of claim 3 can be realized, and the same operation and effect as in claim 3 are obtained. That is, black data is generated using both the first and second black data conversion tables, and the black data reflecting the weight according to the saturation of the color image based on the generated black data. Therefore, the black ink data can be generated with higher accuracy according to the main color and the saturation, and it is possible to form a higher quality image with better reproducibility.

  According to a twenty-fourth aspect of the present invention, four color post-conversion color data including black ink are converted from pre-conversion color data consisting of three colors of cyan, magenta, and yellow, which are provided in a color image forming apparatus and represent a color image to be formed. A color data generation device for generating a black data conversion table having black data conversion characteristics common to the three colors, a minimum data extraction means for comparing the color data before conversion and extracting a minimum data value, and a color before conversion Maximum color data extracting means for comparing the data and extracting color data having the maximum data value, and black data for calculating black data for the minimum data value extracted by the minimum data extracting means using the black data conversion table The calculation means, the adjustment table for adjusting the three colors for deriving the black ink adjustment rate according to the saturation, and the saturation of the color image are derived. Deriving the adjustment rate for the saturation derived by the saturation deriving means using the saturation characteristic deriving means and the adjustment characteristic associated with the maximum color data extracted by the maximum color data extracting means in the adjustment table An adjustment rate deriving unit that adjusts the black ink data calculated by the black ink data calculating unit based on the adjustment rate derived by the adjustment rate deriving unit. Is generated as black ink data.

  According to the color data generation device of claim 24 configured as described above, the color data generation method of claim 9 can be realized and has the same operations and effects as those of claim 9. That is, the black data generated using the black data conversion table shared by the three colors is adjusted according to the maximum color data and the saturation of the color image. Therefore, it is possible to generate black data with high accuracy according to the main color and saturation, and thereby it is possible to form a higher-quality image with better reproducibility.

  According to a twenty-fifth aspect of the present invention, there is provided color image forming apparatus for converting four color converted color data including black ink from pre-converted color data consisting of three colors of cyan, magenta and yellow representing a color image to be formed. A color data generation device for generating a black data conversion table having black data conversion characteristics common to the three colors, a minimum data extraction means for comparing the color data before conversion and extracting a minimum data value, and a color before conversion Maximum color data extracting means for comparing the data and extracting color data having the maximum data value, and black data for calculating black data for the minimum data value extracted by the minimum data extracting means using the black data conversion table The three colors for correcting the black data calculated by the calculating means and the black data calculating means according to the characteristics of the image forming means for forming a color image Using the output correction table having the output correction characteristic to be attached and the output correction characteristic associated with the maximum color data extracted by the maximum color data extraction unit in the output correction table, the black data is calculated by the black data calculation unit. Output correction means for correcting the black data, and a value corrected by the output correction means is generated as black data.

  Therefore, according to the color data generating device of the twenty-fifth aspect, the color data generating method of the seventeenth aspect can be realized, and the same operations and effects as the seventeenth aspect are achieved. That is, the black data generated using the black data conversion table shared by the three colors is corrected according to the maximum color data at the stage of performing correction according to the characteristics of the image forming means. For this reason, it is possible to generate high-precision black ink data according to the main color, thereby forming a high-quality image with good reproducibility.

  According to a twenty-sixth aspect of the present invention, a color image is formed on a recording medium based on the color data generating apparatus according to any one of the twenty-second to twenty-fifth aspects and the four color converted color data generated by the color data generating apparatus. And a color image forming apparatus.

  According to the color image forming apparatus configured as described above, four-color color data is generated based on the black data generated with high accuracy by the color data generating apparatus according to any one of claims 22 to 25. Since a color image is formed on the recording medium, a high-quality color image with good reproducibility can be obtained.

  According to a twenty-seventh aspect of the present invention, in a color image forming apparatus, four post-conversion color data including black ink data is generated from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. A color data generation method comprising: a minimum data value extraction step for extracting a minimum data value from color data before conversion; a black data conversion characteristic and a minimum data value of a black data conversion table for generating black data; Derived in the saturation derivation step from the ink data generation step for generating the ink data, the saturation derivation step for deriving the saturation of the color image, and the adjustment table in which the adjustment rate of the ink data according to the saturation is set An adjustment rate deriving step for deriving an adjustment rate corresponding to the saturated saturation, and adjusting the black data generated in the black data generation step based on the derived adjustment rate. Including a black data adjustment step.

  The black data itself generated in the black data generation step is uniformly generated from the black data conversion table and the minimum data value regardless of the saturation of the color image. Therefore, depending on the saturation, the generated black data may not necessarily be appropriate. For example, when the saturation is high, there is a possibility that the expression of black becomes too strong. Further, for example, when the saturation is low, there is a possibility that the expression of black is too weak to sufficiently reproduce the contrast of the image.

  Therefore, in the invention described in claim 27, instead of using the black data generated by the black data generation step as the black data generation result as it is, the generated black data (temporary black data) is used according to the saturation. Adjust. Thus, the saturation of the color image can be reflected in the generation of the black data, so that the black data can be generated with high accuracy according to the saturation.

  According to a twenty-eighth aspect of the present invention, in a color image forming apparatus, four post-conversion color data including black ink data is generated from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. A method for generating color data, which includes a minimum data value extracting step for extracting a minimum data value from pre-conversion color data, and a plurality of colors corresponding to the main color of the first black data conversion table for generating black data Among the selected black data conversion characteristics, a conversion characteristic selection step for selecting black data conversion characteristics corresponding to the main color of the color image, and a first black for generating black data from the minimum data value and the selected black data conversion characteristics Generates black data from the data generation step and the black data conversion characteristics common to the three colors and the minimum data value of the second black data conversion table for generating black data The second black data generation step, the saturation derivation step for deriving the saturation of the color image, the black data generated in the first black data generation step and the black data generated in the second black data generation step. A weighting derivation step for deriving a weighting for the derived saturation using the weighting table in which a specific weighting is set according to the saturation, each black data generated in each black data generation step, and the derived weighting And a third black data generation step for generating black data in which the weight is reflected.

  That is, in addition to the second black data conversion table used in common for the three colors, the first black data conversion table in which a plurality of black data conversion characteristics are prepared according to the main color is provided. Then, the black data is generated using the second black data conversion table (second black data generation step), and the black data is converted using the conversion characteristics corresponding to the main color of the color image in the first black data conversion table. Generate (first black data generation step). Then, black data is generated based on each of the generated black data and a weight corresponding to the saturation (third black data generation step).

Therefore, the saturation of the color image can be reflected in the generation of black data, so that the black data can be generated with high accuracy according to the saturation.
Various characteristics can be set as the plurality of black data conversion characteristics in the first black data conversion table as long as appropriate black data corresponding to the main color can be generated as a result.

  According to a twenty-ninth aspect of the present invention, in a color image forming apparatus, four post-conversion color data including black ink data are generated from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. A color data generation method comprising: a minimum data value extraction step for extracting a minimum data value from color data before conversion; a black data conversion characteristic and a minimum data value of a black data conversion table for generating black data; According to the main color of the black data generation step for generating black data and the output correction table for correcting the black data generated in the black data generation step according to the characteristics of the image forming means for forming the color image An output correction characteristic selection step for selecting an output correction characteristic corresponding to the main color of the color image from among a plurality of prepared output correction characteristics; The black data generated in step; and a black data output correction step of correcting, based on the output correction characteristic selected above.

  That is, as an output correction table for correcting the generated black data according to the characteristics of the image forming means, a table having a plurality of output correction characteristics associated with the main color is prepared. An appropriate characteristic corresponding to the main color is selected from among them, and appropriate black data correction corresponding to the main color is performed.

  Therefore, although the black data itself generated using the black data conversion table shared by the three colors does not consider the main color, the generated black data is corrected according to the characteristics of the image forming means. In the step of performing correction, correction is performed according to the main color. For this reason, it is possible to generate high-precision black ink data according to the main color, thereby forming a high-quality image with good reproducibility.

Preferred embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
(1) Configuration of Color Printing Device FIG. 1 shows a schematic configuration of a color printing device according to this embodiment. As shown in FIG. 1, the color printing apparatus 1 according to this embodiment as a color image forming apparatus has three colors R (red), G (green), and B (blue) input from a personal computer, a scanner, or the like. Image data composed of data is converted into four color image forming color data composed of C (cyan), M (magenta), Y (yellow), and K (black), and based on the color data of the four colors This is for recording a color image on a recording medium such as paper.

  As shown in FIG. 1, the color printing apparatus 1 according to this embodiment includes a pixel data input unit 2 to which R, G, and B pixel data representing a color image is input, and the pixel data input unit 2 inputs the pixel data. An image data processing unit 3 that generates four color data C3 (cyan), M3 (magenta), Y3 (yellow), and K2 (black) for image recording from R, G, and B pixel data, and this image And an image recording unit 4 that records (forms) a color image on a recording medium using the four color inks or toners based on the four color data of C3, M3, Y3, and K2 generated by the data processing unit 3. Yes.

  The image data processing unit 3 uses the preset look-up table (LUT) for the R, G, and B pixel data input via the pixel data input unit 2 to have a complementary color relationship C1. (Cyan), M1 (Magenta), Y1 (Yellow) conversion unit 6 for conversion into data, and C3, M1, and Y1 color data (corresponding to the pre-conversion color data of the present invention) , C2 (cyan), M2 (magenta), Y2 (yellow), and K1 (black) color data (corresponding to the color data after conversion of the present invention) UCR (Under Coarition Rejection) processing unit 7 And the four color data C2, M2, Y2, and K1 generated by the UCR processing unit 7 respectively adjust image characteristics such as a luminance value and a reflection density value according to the image recording characteristics of the image recording unit 4. By And a recording γ correction unit 8 for converting color data C3 (cyan), M3 (magenta), Y3 (yellow), and K2 (black) for printing on a recording medium.

(2) Function of UCR Processing Unit Next, the function of the UCR processing unit 7 constituting the color printing apparatus 1 will be described more specifically with reference to FIGS. FIG. 2 is a functional block diagram showing the operation of the UCR processing unit 7. As shown in FIG. 2, the UCR processing unit 7 compares the inputted three color data C1, M1, and Y1, and selects the first parameter min_K that is the color data having the smallest value. 11 is compared with the input three color data C1, M1, and Y1 to select the second parameter max_K that is the color data having the largest value, and based on the parameters min_K and max_K. Then, the max_K corresponding UCRγ calculating unit 13 for calculating the black data K1 and the black data K1 calculated by the max_K corresponding UCRγ calculating unit 13 from the input three color data C1, M1, and Y1 are subtracted from these C1. , M1 and Y1 are included.

  The max_K corresponding UCRγ calculating unit 13 calculates the black data K by converting the first parameter min_K into the black data K using the max_K corresponding UCRγ table prepared in advance.

  In this max_K correspondence UCRγ table, as shown in FIG. 4, different black data conversion characteristics are set for each of the three colors of CMY. That is, the KCγ table (FIG. 4A) serving as the black data conversion characteristic that is associated with cyan and used when the cyan color data is maximum (max_K), and the magenta color data associated with magenta. The KMγ table (FIG. 4B) as the black data conversion characteristic used at the maximum (max_K) and the black data conversion characteristic associated with yellow and used when the yellow color data is the maximum (max_K) A KCγ table (FIG. 4C) is prepared.

  In FIG. 4, the horizontal axis as input data represents the first parameter min_K to be converted, and the vertical axis as output data represents the black data K1 after conversion. Each data value represents a 256-tone color value, which is the same for each axis in the tables shown in FIGS. 7 and 14 and the horizontal axes in FIGS. . In FIG. 4, b2 is shown in parentheses, but this indicates that the black data is calculated as b2 in the second embodiment to be described later, and the description thereof is omitted here.

  When the second parameter max_K selected by the second parameter selection unit 12 is the cyan color data C1, the max_K corresponding UCRγ calculation unit 13 uses a KCγ table associated with cyan as a table used for the calculation of the black data K1. select. Then, using this KCγ table, black data K1 for the first parameter min_K selected by the first parameter selection unit 11 is calculated. Similarly, when the second parameter max_K is magenta color data M1, the KMγ table associated with magenta is selected as the table used for the black data K1, and the first parameter min_K is selected using this KMγ table. Black ink data K1 is calculated. When the second parameter max_K is yellow color data Y1, the KYγ table associated with yellow is selected as the table used for the calculation of the black data K1, and the black data K1 for the first parameter min_K is selected using this KYγ table. Is calculated.

  The three black data conversion characteristics (KCγ table, KMγ table, and KYγ table) constituting the max_K compatible UCRγ table are all output data (black data) as the input data (first parameter min_K) to be converted increases. The data value of K1) is set to be large.

  Then, as shown in FIG. 4C, the KYγ table corresponding to yellow is set so that black data is not generated when the input first parameter min_K is equal to or less than P, where P is a predetermined threshold value. Yes. On the other hand, as shown in FIG. 4A, the KCγ table corresponding to cyan has black data when the input first parameter min_K is equal to or less than Q, where Q is a predetermined threshold value smaller than P. Is set not to occur. Further, as shown in FIG. 4B, the KMγ table corresponding to magenta has a predetermined threshold value smaller than P and larger than Q as L, and when the input first parameter min_K is L or less, The black ink data is set not to be generated.

  By configuring the max_K correspondence UCRγ table in this way, for example, when the main color is a cyan (dark color) color image and cyan (C1) is selected as the second parameter max_K, this is handled. The KCγ table shown in FIG. 4A is selected. In this case, if the first parameter min_K is larger than Q, the black data K1 is generated. On the other hand, when the main color is yellow (light color) and yellow (Y1) is selected as the second parameter max_K, the corresponding KYγ table of FIG. 4C is selected. However, in this case, even if the first parameter min_K is greater than Q, the black data K1 is not generated as long as it is P or less.

  That is, in the UCRγ table corresponding to max_K, when the magenta is the largest among the three color data, the black data is not generated unless the input data min_K is larger, and the yellow is In the maximum case, each black data conversion characteristic is set so that black data is not generated unless the input data min_K is larger than cyan and magenta.

  Therefore, if the second parameter max_K is, for example, cyan (that is, a dark color image) for the same first parameter min_K, the second parameter max_K is, for example, yellow (that is, the light color system). In this case, the black data is 0, or the calculated amount is smaller than in the case of cyan or magenta. In other words, by preparing a table (black data conversion characteristics) that matches the maximum color data among the three color data for each color, the black data that matches the main color with the largest color data is calculated. As a result, the black data can be suppressed in the light color system, and the black data can be increased in the dark color system so that the contrast of the image can be sufficiently reproduced.

  When the black data K1 is calculated by the max_K-corresponding UCRγ calculating unit 13, the calculation result is output as a final black data generation result from the UCR processing unit 7, and the black data removing unit 14 receives C1, M1, Used to correct each color data of Y1. The black data removing unit 14 obtains new color data C2, M2, and Y2 by subtracting and correcting the black data K1 from C1, M1, and Y1, respectively. The four color data C2, M2, Y2, and K1 obtained in this way are output as the color data generation result by the UCR processing unit 7 and input to the recording γ correction unit 8.

  The operation of each unit in the UCR processing unit 7 shown in FIG. 2 is realized by arithmetic processing executed by a microcomputer or a dedicated logic circuit. Further, the max_K correspondence UCRγ table shown in FIG. 4 is stored in advance in a memory such as a ROM or a RAM. The same applies to the tables shown in FIGS. 7, 8, 11 and 14, which will be described later. Therefore, when the UCR processing unit 7 is realized by a calculation process by a microcomputer, the max_K-compatible UCRγ calculation unit 13 calculates black data by referring to the max_K-compatible UCRγ table stored in the memory. Is realized.

Therefore, the procedure of the arithmetic processing when the UCR processing unit 7 is realized by the arithmetic processing by the microcomputer will be described based on the flowchart of FIG.
As shown in FIG. 3, the UCR processing unit 7 first reads color data C1, M1, Y1 of a color image to be formed by the color printing apparatus 1 from the conversion unit 6 (S110). Then, the read color data C1, M1, and Y1 are compared, and the first parameter min_K having the smallest value is selected (S120). The process of S120 is a function of the first parameter selection unit 11. Further, the color data C1, M1, and Y1 are compared, and the second parameter max_K having the largest value is selected (S130). The process of S130 is a function of the second parameter selection unit 12.

  Then, a max_K correspondence UCRγ table (any one of the KCγ table, the KMγ table, and the KYγ table) corresponding to the color data of the second parameter max_K selected in S120 is selected, and any one of the selected tables is used in S110. The black data K1 is calculated using the selected first parameter min_K as an input (S140). The process of S140 is a function of the max_K compatible UCRγ computing unit 13.

  When the black data K1 is calculated in this way, the corrected color data C2, M2, and Y2 are obtained by subtracting the black data K1 from the color data C1, M1, and Y1 input from the conversion unit 6 ( S150). Then, the corrected color data C2, M2, Y2, and black data K1 are output to the recording γ correction unit 8 (S160).

(3) Effects of the First Embodiment According to the color printing apparatus 1 of the present embodiment described above, the black data is calculated and generated based on the black data conversion characteristics corresponding to the main color of the color image. It is possible to generate high-precision black ink data according to the main color. Therefore, regardless of the main color of the color image, the reproducibility does not occur because the black color appears too strong and the image looks dirty, or the black color appears too weak to reproduce the contrast of the image sufficiently. A good and high-quality image can be formed.

  Each black data has different black data conversion characteristics for each of the three color data CMY, and the black data appearance points (minimum input data values for generating black data) increase in the order of C, M, and Y. Since the conversion characteristics are set, it is possible to generate more accurate black data according to the main color.

  Then, the amount of black data generated with such high accuracy is subtracted from the color data of each color of cyan, magenta, and yellow to correct the color data of each color. The total amount of each color ink used in the section 4 can be appropriately regulated.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. In the present embodiment, the first parameter selection unit 11 corresponds to the minimum data extraction unit of the present invention, the second parameter selection unit 12 corresponds to the maximum color data extraction unit of the present invention, and the max_K corresponding UCRγ calculation unit 13 The black data removing unit 14 corresponds to the three-color generating unit of the present invention, and the image recording unit 4 corresponds to the image forming unit of the present invention. 4 corresponds to the first black data conversion table of the present invention, the predetermined threshold value P corresponds to the first setting value of the present invention, and the predetermined threshold value Q corresponds to the second setting of the present invention. The predetermined threshold value L corresponds to a fourth set value of the present invention.

(4) Modification In this embodiment, the max_K-compatible UCRγ table shown in FIGS. 4A to 4C is used, but these tables (black data conversion characteristics) are merely examples, and black The ink data conversion characteristics corresponding to each color of C, M, and Y do not cause the image to appear dirty because the expression of the color is too strong, or the contrast of the image cannot be sufficiently reproduced because the expression of the ink color is too weak. It only has to be set.

  That is, the threshold values P, Q, and L in the table corresponding to each color are not limited to the values shown in FIG. 4, and at least the threshold value P corresponding to yellow is larger than the threshold value Q corresponding to cyan. It only has to be set. The threshold value L corresponding to magenta may be the same value as the threshold value Q corresponding to cyan. In other words, only one table corresponding to cyan and one corresponding to magenta may be shared.

  In the table of FIG. 4, when the input data min_K is close to the maximum 255, the calculated black data K1 is also set to be close to the maximum 255. This is just an example, and the input data min_K is the maximum. The black data K1 calculated even when approaching 255 may be set to be smaller than 255 (for example, about 200 at the maximum).

[Second Embodiment]
In the first embodiment, the black data K1 in the UCR processing unit 7 is calculated using the max_K correspondence UCRγ table (FIG. 4). In the present embodiment, in addition to the max_K correspondence UCRγ table, a separate preparation is provided. Calculation is also performed using the normal mode UCRγ table (FIG. 7), and final black data K1 is generated by reflecting the weight corresponding to the saturation of the color image with respect to the black data calculated in each table.

  That is, the color printing apparatus of the present embodiment is different from the color printing apparatus 1 of the first embodiment in the configuration of the UCR processing unit, and is otherwise the same as that of the first embodiment. Therefore, hereinafter, the configuration and function of the UCR processing unit different from the first embodiment will be described with reference to FIGS.

(1) Configuration and Function of UCR Processing Unit FIG. 5 is a functional block diagram showing the operation of the UCR processing unit 20 of the present embodiment. As shown in FIG. 5, the UCR processing unit 20 includes a first parameter selection unit 11, a second parameter selection unit 12, and a max_K-compatible UCRγ calculation unit 13, similar to the UCR processing unit 7 of the first embodiment. . Since these functions are as described in the first embodiment, description thereof is omitted here. However, in this embodiment, the value calculated by the max_K corresponding UCRγ calculating unit 13 is not directly used as the black data K1, but is input to the K1 calculating unit 24 as the temporary black data b2 (vertical in FIG. 4). (See axis brackets).

  The UCR processing unit 20 of the present embodiment further includes a normal mode UCRγ calculating unit 21 that calculates black data b1 for the first parameter min_K using a normal mode UCRγ table (FIG. 7). The normal mode UCRγ table in FIG. 7 is a table that is shared by three CMY colors regardless of the color of the second parameter max_K, and has black data conversion characteristics for converting the first parameter min_K into black data. In this normal mode UCRγ table, as shown in FIG. 7, when a predetermined threshold value smaller than P and larger than Q is set to T, black data is not generated when the input first parameter min_K is T or less. Is set. Note that the magnitude relationship between T and L may be determined as appropriate.

  In addition, the UCR processing unit 20 of the present embodiment includes a difference calculation unit 22 that calculates a difference c between the second parameter max_K and the first parameter min_K, and a normal mode UCRγ based on the difference c calculated by the difference calculation unit 22. A max_K dependency ratio coefficient calculation unit 23 is provided that calculates a max_K dependency ratio coefficient d indicating the relative weight of the black data b2 calculated by the max_K corresponding UCRγ calculation unit 13 with respect to the black data b1 calculated by the calculation unit 21. ing.

  The difference c calculated by the difference calculation unit 22 is also a value indicating the saturation of the color image composed of C1, M1, and Y1. That is, the smaller the difference c is, the lower the saturation is. If the difference c is 0, the saturation is also 0 (that is, an achromatic color). Conversely, the greater the difference c is, the higher the saturation is.

  The max_K dependence ratio coefficient calculating unit 23 calculates a max_K dependence ratio coefficient d for the difference c using the max_K dependence ratio table. FIG. 8 shows a max_K dependency ratio table. In the max_K dependency ratio table, the characteristics of the weight (max_K dependency ratio coefficient d) of the black data b2 with respect to the difference c (saturation) are set. As shown in FIG. 0), the weight of the black data b2 calculated by the max_K corresponding UCRγ calculator 13 is 0, the weight of the black data b1 calculated by the normal mode UCRγ calculator 21 is 100%, and the difference c increases ( As the saturation increases, the weight of the black data b2 increases and the weight of the black data b1 decreases. When the difference c is equal to or greater than the predetermined threshold V, the weight of the black data b2 by the max_K corresponding UCRγ computing unit 13 becomes 100%, and the weight of the black data b1 by the normal mode UCRγ computing unit 21 becomes zero.

  When considering the relationship between saturation and the amount of ink data, if the saturation is low, even if the amount of ink data is increased to a certain extent, the color of the ink color will be too strong and the image will become dirty. Negative effects on sex are unlikely to occur. For this reason, the total amount of CMYK ink can be reduced by increasing the amount of black data to such an extent that the reproducibility of the color image is not adversely affected. On the other hand, as the saturation increases, the reproducibility of the color image may be adversely affected, for example, depending on the amount of ink data, the ink color may become too conspicuous and the image may become dirty. Therefore, it is necessary to suppress the amount of black data as much as possible as the saturation is high.

  Therefore, in the present embodiment, the weight of the black data b1 by the normal mode UCRγ calculating unit 21 is increased as the saturation is lower, and the weight of the black data b2 by the max_K corresponding UCRγ calculating unit 13 is increased as the saturation is higher. The amount of black data is appropriately controlled according to the saturation.

  Note that the max_K dependency ratio coefficient d calculated by the max_K dependency ratio table in FIG. 8 is a value directly indicating the weight of the black data b2 calculated by the max_K corresponding UCRγ calculation unit 13. Indirectly, the weighting of the black data b1 calculated by the normal mode UCRγ calculating unit 21 is also shown at the same time. That is, in this embodiment, when the max_K dependence ratio coefficient d is a certain value x% (the weight of b2 is x%), the weight of b1 is (100−x)%. Based on such relative weighting, the final black data K1 is generated by the K1 calculation unit 24.

  The K1 calculation unit 24 calculates the max_K dependency ratio coefficient d calculated by the max_K dependency ratio coefficient calculation unit 23 based on the black data b1 by the normal mode UCRγ calculation unit 21 and the black data b2 by the max_K corresponding UCRγ calculation unit 13. The reflected black data K1 is calculated. In the present embodiment, a weighted average value corresponding to the max_K dependence ratio coefficient d is calculated for b1 and b2. That is, the black data K1 is calculated by the following equation (1).

K1 = {b1 * (100−d) + b2 * d} / 100 (1)
The black data K1 calculated in this way and the C2, M2, and Y2 corrected by the black data removal unit 14 using the black data K1 are output as color data generation results by the UCR processing unit 20, The data is input to the recording γ correction unit 8.

Next, the procedure of arithmetic processing when the UCR processing unit 20 is realized by arithmetic processing by a microcomputer will be described based on the flowchart of FIG.
As shown in FIG. 6, the UCR processing unit 20 first reads the color data C1, M1, and Y1 of the color image to be formed by the color printing apparatus 1 as in S110 to S130 of the first embodiment ( In step S210, the first parameter min_K and the second parameter max_K are selected from the read color data C1, M1, and Y1, respectively (S220 and S230).

  Then, using the normal mode UCRγ table, the black data b1 with the first parameter min_K as an input is calculated (S240). The process of S240 is a function of the normal mode UCRγ computing unit 21. Further, similarly to S140 of the first embodiment, a max_K-corresponding UCRγ table (any one of a KCγ table, a KMγ table, or a KYγ table) corresponding to the second parameter max_K is selected, and any one of the selected tables is used. Then, black data (b2 in this example) is calculated using the first parameter min_K as an input (S250).

  Furthermore, using the max_K dependency ratio table, a max_K dependency ratio coefficient d is calculated with the difference c between the parameters max_K and min_K as input (S260). The process of S260 is a function of the difference calculation unit 22 and the max_K dependence ratio coefficient calculation unit 23. Then, using the calculated parameters min_K, max_K, and max_K dependence ratio coefficient d, the black data K1 is calculated by the above equation (1) (S270). The process of S270 is a function of the K1 calculation unit 24.

  Thereafter, similarly to S150 to S160 of the first embodiment, the corrected color data C2, M2, and Y2 are obtained by subtracting the black data K1 from the color data C1, M1, and Y1 input from the conversion unit 6. (S280), the corrected color data C2, M2, Y2, and black data K1 are output to the recording gamma correction unit 8 (S290).

(2) Effects of the Second Embodiment According to the color printing apparatus of the present embodiment described above, the black data b1 and b2 are calculated using both the normal mode UCRγ table and the max_K compatible UCRγ table, and the calculation is performed. Since the black data K1 in which the weighting according to the saturation of the color image is reflected is generated on the basis of both the black data b1 and b2, the black data is further converted according to the main color and the saturation of the color image. It is possible to generate with high accuracy, and thereby it is possible to form a higher quality image with better reproducibility.

  Further, since the max_K dependency ratio table is set as shown in FIG. 8, more appropriate weighting according to the saturation of the color image can be calculated by appropriately setting the threshold value V. The generation accuracy can be further increased.

  Further, in the normal mode UCRγ table, the threshold value T, which is the black data appearance point, is smaller than the threshold value P of the KYγ table corresponding to yellow in the max_K compatible UCRγ table, and larger than the KCγ table corresponding to cyan. Is set. Therefore, the normal mode UCRγ table and the max_K compatible UCRγ table are appropriately balanced, and the black data is generated based on these tables and the saturation (weighting), so that the generation accuracy of the black data can be further increased. it can.

  Then, the amount of black data generated with such high accuracy is subtracted from the color data of each color of cyan, magenta, and yellow to correct the color data of each color. The total amount of each color ink used in the section 4 can be appropriately regulated.

  In the present embodiment, the normal mode UCRγ calculation unit 21 corresponds to the second black data calculation unit of the present invention, the difference calculation unit 22 corresponds to the saturation derivation unit of the present invention, and the max_K dependence ratio coefficient calculation unit 23. Corresponds to the weighting derivation means of the present invention, the K1 calculation unit 24 corresponds to the third black data calculation means of the present invention, the normal mode UCRγ table of FIG. 7 corresponds to the second black data conversion table of the present invention, 8 corresponds to the weighting table of the present invention, the predetermined threshold T in FIG. 7 corresponds to the third set value of the present invention, and the predetermined threshold V in FIG. 8 is the saturation threshold of the present invention. It corresponds to.

(3) Modified Example Also in this embodiment, the normal mode UCRγ table shown in FIG. 7 and the max_K dependency ratio table shown in FIG. 8 are merely examples, and the normal mode UCRγ table is the same as the setting contents of the max_K-compatible UCRγ table. What is necessary is just to set suitably in consideration of a balance etc. Also for this normal mode UCRγ table, b1 calculated even when the input data min_K approaches the maximum 255 may be set to be smaller than 255 (for example, about 200 at the maximum).

  Also in the max_K dependence ratio table, when the difference c is 0, the max_K dependence ratio coefficient d does not necessarily have to be completely zero, and the difference c at which the max_K dependence ratio coefficient d becomes 100% is obtained from V in FIG. May be set to a large value or a small value.

  Further, in obtaining the saturation, in this embodiment, the difference c between the second parameter max_K and the first parameter min_K is calculated and treated as the saturation, but the method for obtaining the saturation is limited to this. However, the saturation may be obtained using other methods. The same applies to the third embodiment described later.

  Further, the black data K1 is calculated using the above formula (1) based on the weighting (max_K dependence ratio coefficient d) according to the saturation. However, this formula (1) is only an example, and b1, b2 As long as the black data K1 in which the weighting corresponding to the saturation is reflected can be calculated, the specific calculation method is not particularly limited.

  Further, in the present embodiment, in order to generate black data that more reliably reflects the main color, a black data conversion characteristic (FIG. 4) for each color used when each CMY color has a maximum data value is prepared. The black data b2 is generated using this, but it is not always necessary to prepare a conversion characteristic corresponding to the maximum data value as shown in FIG. 4, and as long as the main color is reflected in the black data generation result, The conversion characteristics can be prepared.

  As the black data conversion characteristic corresponding to the main color, for example, the min_K compatible UCRγ table of FIG. 15 can be used. As shown in FIG. 15, this min_K UCRγ table has black data conversion characteristics for each color. Among these, the KCγ table shown in (a) is a black data conversion characteristic selected when the minimum data value is C1 (cyan), and the KMγ table shown in (b) is when the minimum data value is M1 (magenta). The black data conversion characteristics selected, the KYγ table shown in (c), is the black data conversion characteristics selected when the minimum data value is Y1 (yellow).

  The KCγ table selected when C1 is the minimum data value is set not to generate black data when the color data C1 as input data is equal to or less than J1, and is selected when M1 is the minimum data value. The KMγ table is set so as not to generate black data when the color data M1 as input data is equal to or less than J2 smaller than J1, and the KYγ table selected when Y1 is the minimum data value is used as input data. When the color data Y1 is equal to or smaller than J3 smaller than J2, black ink data is set not to be generated.

  That is, when the minimum data value is Y1, for example, it is expected that the main color is a dark color system of M or C. Therefore, even if the input data Y1 is small using the conversion characteristics of FIG. Ink data is generated. On the contrary, when the minimum data value is C1, for example, it is expected that the main color is a light color system of Y. Therefore, the generation of black data is suppressed using the conversion characteristics of FIG. The data expression point becomes higher).

  As described above, even if the black data conversion characteristics illustrated in FIG. 15 are used, since both the main color and the saturation of the color image can be reflected in the generation of the black data, highly accurate black data can be generated. It becomes.

  The black data conversion characteristics shown in FIG. 15 are merely examples, and various conversion characteristics (tables) can be set as long as appropriate black data corresponding to the main color can be generated. Further, when the black data conversion characteristic of FIG. 15 is used, the process of S230 is not necessary in the process of FIG.

[Third Embodiment]
In the first embodiment, the black data K1 in the UCR processing unit 7 is calculated using the max_K-corresponding UCRγ table (FIG. 4). In the present embodiment, the max_K-corresponding UCRγ table is not used. Black ink data is calculated using the normal mode UCRγ table (FIG. 7) described in the second embodiment. Then, final black data K1 is generated by adjusting the calculated black data according to the saturation of the color image and according to the main color (second parameter max_K).

  That is, the color printing apparatus of the present embodiment is also the same as the first or second embodiment except for the configuration of the UCR processing unit as compared with the color printing apparatus 1 of the first and second embodiments. . Therefore, hereinafter, the configuration and function of the UCR processing unit different from the first and second embodiments will be described with reference to FIGS. 9 to 11.

(1) Configuration and Function of UCR Processing Unit FIG. 9 is a functional block diagram showing the operation of the UCR processing unit 30 of the present embodiment. As illustrated in FIG. 9, the UCR processing unit 30 includes a first parameter selection unit 11 and a second parameter selection unit 12 as in the UCR processing unit 7 of the first embodiment. Further, as in the second embodiment, a normal mode UCRγ calculating unit 21 and a difference calculating unit 22 are provided. Since these functions are as described in the first and second embodiments, the description thereof is omitted here.

  The UCR processing unit 30 of the present embodiment further includes a black data adjustment coefficient calculation unit 31 that calculates a black data adjustment coefficient e for the difference c using a max_K black data adjustment table (FIG. 11).

  In the max_K black data adjustment table of FIG. 11, different adjustment characteristics are set for each of the three colors of CMY. That is, an adjustment characteristic associated with cyan and used when cyan color data is maximum (max_K); an adjustment characteristic associated with magenta and used when magenta color data is maximum (max_K); Adjustment characteristics associated with yellow and used when yellow color data is maximum (max_K) are set.

  This max_K corresponding black data adjustment table is for determining how much of the black data b1 calculated by the normal mode UCRγ computing unit 21 is to be output as the final black data K1. The adjustment coefficient e indirectly indicates the ratio of K1 to b1. That is, as the black data adjustment coefficient e increases, the ratio of K1 to b1 decreases.

  In each adjustment characteristic, when the difference c is 0 (that is, the saturation of the color image is 0), the black data adjustment coefficient e is 0 (that is, b1 is generated as it is as the final black data K1). As c increases, that is, as the saturation of the color image increases, the black data adjustment coefficient e increases (that is, the generated black data K1 decreases), and when the difference c exceeds a predetermined threshold value. The black data adjustment coefficient e is set to 100% and the final black data K1 is set to zero. That is, the higher the saturation is, the lower the amount of black data generated is set.

  Among the adjustment characteristics for each color of CMY, the adjustment characteristic associated with cyan is set so that the black data adjustment coefficient e becomes 100% and black data K1 is not generated when the difference c is equal to or greater than the predetermined threshold value X. On the other hand, in the adjustment characteristic associated with yellow, when the difference c is equal to or greater than a predetermined threshold W smaller than the threshold X, the black data adjustment coefficient e becomes 100% and the black data K1 is not generated. Is set to The adjustment characteristic associated with magenta is set so that the black data adjustment coefficient e is 100% when the difference c is equal to or larger than a predetermined threshold Z that is smaller than the threshold X and larger than the threshold W. That is, even if the saturation is the same, the amount of ink data is reduced as the main color is lighter.

  The K1 calculation unit 32 applies black ink to the black data b1 calculated by the normal mode UCRγ calculation unit 21 based on the black data adjustment coefficient e calculated by the black data adjustment coefficient calculation unit 31 according to the following equation (2). Data K1 is calculated.

K1 = {b1 * (100-e)} / 100 (2)
The black data K1 calculated in this way and the C2, M2, and Y2 corrected by the black data removal unit 14 using the black data K1 are output as color data generation results by the UCR processing unit 30, The data is input to the recording γ correction unit 8.

Next, the procedure of arithmetic processing when the UCR processing unit 30 is realized by arithmetic processing by a microcomputer will be described based on the flowchart of FIG.
As shown in FIG. 10, the UCR processing unit 30 first reads the color data C1, M1, and Y1 of the color image to be formed by the color printing apparatus 1 as in S210 to S240 of the second embodiment ( S310), the first parameter min_K and the second parameter max_K are respectively selected from the read color data C1, M1, and Y1 (S320, S330), and the first parameter min_K is input using the normal mode UCRγ table. Data b1 is calculated (S340).

  Further, an adjustment characteristic associated with the color data of the second parameter max_K is selected from the max_K black data adjustment table, and the difference c between the parameters max_K and min_K is input using the selected adjustment characteristic. The black data adjustment coefficient e is calculated (S350). The processing of S350 is a function of the difference calculation unit 22 and the black data adjustment coefficient calculation unit 31. Then, using the calculated first parameter min_K and the black data adjustment coefficient e, the black data K1 is calculated by the above equation (2) (S360). The process of S360 is a function of the K1 calculation unit 32.

  Thereafter, similarly to S150 to S160 of the first embodiment, the corrected color data C2, M2, and Y2 are obtained by subtracting the black data K1 from the color data C1, M1, and Y1 input from the conversion unit 6. (S370), the corrected color data C2, M2, Y2, and black data K1 are output to the recording γ correction unit 8 (S380).

(2) Effects of the Third Embodiment According to the color printing apparatus of the present embodiment described above, the black data b1 itself calculated using the normal mode UCRγ table does not consider the main color, The calculated black data b1 is adjusted according to the second parameter max_K (main color) and the saturation of the color image, and the adjusted black data K1 is output.

  That is, the higher the saturation, the smaller the value actually generated as the black data K1 in the calculated black data b1. Further, the generation amount of the black ink K1 is suppressed in the case of the light color main body than in the case of the dark color main body.

  Therefore, it is possible to generate black data with higher accuracy according to the main color and saturation, and thereby it is possible to form a higher quality image with better reproducibility. In addition, since the adjustment characteristics are individually set for each color of CMY, it is possible to generate black data with higher accuracy according to the main color.

  Then, the amount of black data generated with such high accuracy is subtracted from the color data of each color of cyan, magenta, and yellow to correct the color data of each color. The total amount of each color ink used in the section 4 can be appropriately regulated.

  In the present embodiment, the normal mode UCRγ computing unit 21 corresponds to the black data calculating unit of the present invention (claim 24), the black data adjustment coefficient calculating unit 31 corresponds to the adjustment rate deriving unit of the present invention, and K1 The calculation unit 32 corresponds to the black data adjustment means of the present invention, the max_K black data adjustment table corresponds to the adjustment table of the present invention, and the black data adjustment coefficient e corresponds to the adjustment rate of the present invention. In FIG. 11, the threshold value W corresponds to the first saturation of the present invention, the threshold value Z corresponds to the third saturation of the present invention, and the threshold value X corresponds to the second saturation of the present invention.

(3) Modification In this embodiment, the black data adjustment table corresponding to max_K shown in FIG. 11 is merely an example, and when the difference c is 0, the black data adjustment coefficient e may not necessarily be completely zero. , C, M, and Y, the difference c at which the black data adjustment coefficient e becomes 100% may be set to a value larger or smaller than W, Z, and X in FIG. At least the threshold value W corresponding to yellow may be set smaller than the threshold value X corresponding to cyan. The threshold value Z corresponding to magenta may be the same value as the threshold value X corresponding to cyan.

  In this embodiment, the black data adjustment coefficient e indirectly indicates the ratio of K1 to b1, but conversely, an adjustment coefficient that directly indicates the ratio of K1 to b1 is set. (That is, K1 increases as the adjustment coefficient increases).

  In this embodiment, as the black data adjustment table in which the black data adjustment rate according to the saturation is set, the max_K compatible black data adjustment table in which different adjustment characteristics are set for each of the three colors of CMY is used. Apart from such a method, the black data may be adjusted using one black data adjustment table (one adjustment characteristic) that is commonly used for the three colors of CMY. An example of adjustment characteristics in this case is shown in FIG.

  FIG. 16 illustrates two types of adjustment characteristics. Among the adjustment characteristics A, when the saturation is 0 (the difference c is 0), the black data adjustment coefficient e is 0 (that is, b1 is generated as it is as the final black data K1), and the difference c is large. As the saturation of the color image increases, the black data adjustment coefficient e increases (that is, the generated black data K1 decreases). When the difference c exceeds a predetermined threshold, the black data adjustment is performed. The final black data K1 is set to 0 when the coefficient e is 100%.

  The adjustment characteristic B is based on a predetermined saturation threshold, and if the saturation is equal to or less than the saturation threshold, the ink data adjustment coefficient e is set to 0, and if the saturation exceeds the saturation threshold, The data adjustment coefficient e is set to 100%. That is, b1 is set to K1 when the saturation is low, and K1 is set to 0 when the saturation is high.

  As described above, when one adjustment characteristic common to the three colors is used, the process of S330 is not necessary in the process of FIG. In the process of S350, the black data adjustment coefficient e is simply calculated from one adjustment characteristic prepared in advance.

Note that the two types of adjustment characteristics shown in FIG. 16 are merely examples, and various specific characteristics can be considered as long as the amount of black data generated can be appropriately adjusted according to the saturation.
As described above, the use of one black data adjustment table (one adjustment characteristic) commonly used for the three colors of CMY can also provide an effect that the black data can be generated with high accuracy according to the saturation.

[Fourth Embodiment]
In the third embodiment, the UCR processing unit 30 generates the black data K1 by adjusting the black data b1 calculated using the normal mode UCRγ table using the black data adjustment coefficient e. In the embodiment, the UCR processing unit outputs the black data calculated using the normal mode UCRγ table as it is as K1 to the recording γ correction unit. Then, in the recording γ correction unit, the black data K1 is corrected. In the recording γ correction unit 8 of each of the first to third embodiments, γ correction corresponding to the characteristics of the image recording unit 4 with respect to the black data K1 is performed. In this embodiment, the black data K1 by the recording γ correction unit is used. This correction is performed using correction characteristics that differ depending on the main color.

  That is, the color printing apparatus according to the present embodiment is different from the color printing apparatuses according to the first to third embodiments in the configuration of the UCR processing unit and the recording γ correction unit, and other than that, the first or second embodiment. Is the same. Therefore, hereinafter, configurations and functions of the UCR processing unit and the recording γ correction unit different from those in the first to third embodiments will be described with reference to FIGS. 12 to 14.

(1) Configuration and Function of UCR Processing Unit FIG. 12 is a functional block diagram showing operations of the UCR processing unit 40 and the recording γ correction unit 42 of this embodiment. First, the UCR processing unit 40 will be described. As shown in FIG. 12, the UCR processing unit 40 is similar to the UCR processing unit 30 of the third embodiment. The UCR processing unit 40 includes a first parameter selection unit 11, a second parameter selection unit 12, a normal mode UCRγ calculation unit 21, and a black data removal unit. Part 14 is provided. Since these functions are as described in the first to third embodiments, the description thereof is omitted here.

With such a configuration, the UCR processing unit 40 outputs the black data calculated by the normal mode UCRγ calculating unit 21 to the recording γ correcting unit 42 as it is.
(2) Configuration and Function of Recording γ Correction Unit The recording γ correction unit 42 of this embodiment is prepared as a recording γ table for color data of three colors C2, M2, and Y2, as shown in FIG. The C2, M2, and Y2 colors are corrected using the Cγ table, Mγ table, and Yγ table. Hereinafter, the correction using the recording γ table is also referred to as “output correction”. This output correction is performed to adjust the color data C3, M3, and Y3 for printing on the recording medium by adjusting the image characteristics such as the luminance value and the reflection density value according to the image recording characteristics of the image recording unit 4 ( Conversion). The recording γ correction unit 42 further corrects the output of K1 based on the max_K correspondence Kγ table (FIG. 14), which is a table for correcting the output of black (K1).

  In the max_K correspondence Kγ table of FIG. 14, different output correction characteristics are set for each of the three colors of CMY. That is, an output correction characteristic associated with cyan and used when cyan color data is maximum (max_K), and an output correction characteristic associated with magenta and used when magenta color data is maximum (max_K). Are set to output correction characteristics that are associated with yellow and used when the color data of yellow is maximum (max_K).

  The max_K correspondence Kγ table is used to determine how much of the black data K1 generated by the UCR processing unit 40 is to be output to the image recording unit 4. Each output correction characteristic is appropriately set according to the image recording characteristic of the image recording unit 4, but in addition to this, according to the second parameter max_K (that is, depending on what the main color is). ), Output correction characteristics matching the color data of the second parameter max_K are set.

  Specifically, the output correction characteristic associated with yellow is set so that the value of the black data K2 after output correction for the same black data K1 is smaller than the output correction characteristic associated with cyan. (Except when K1 = 0,255). Note that the output correction characteristic associated with magenta is set so that the black data K2 after the output correction for the same black data K1 is larger than that corresponding to yellow and smaller than that corresponding to cyan. That is, as the main color is lighter, the amount of black data K2 is reduced.

  Next, the procedure of the arithmetic processing when the UCR processing unit 40 and the recording γ correction unit 42 are realized by arithmetic processing by a microcomputer will be described based on the flowchart of FIG.

  As shown in FIG. 13, first, the UCR processing unit 40 reads the color data C1, M1, and Y1 of the color image to be formed by the color printing apparatus 1 in the same manner as S210 to S240 of the second embodiment ( S410), the first parameter min_K and the second parameter max_K are respectively selected from the read color data C1, M1, and Y1 (S420 and S430), and the first parameter min_K is input using the normal mode UCRγ table. Data K1 is calculated (S440).

  Further, similarly to S150 to S160 of the first embodiment, the color data C2, M2, and Y2 are obtained by subtracting the black data K1 from the color data C1, M1, and Y1 input from the conversion unit 6 (S450). ), The color data C2, M2, Y2, and black data K1 are output to the recording gamma correction unit 42 (S460).

  Then, the recording γ correction unit 42 performs output correction using the recording γ table for the input C2, M2, Y2, and K1. Among these, the output correction for the black data K1 is performed using the max_K correspondence Kγ table as described above. That is, from the max_K correspondence Kγ table, the output correction characteristic associated with the color data of the second parameter max_K is selected, and the black data K2 with the black data K1 as input is calculated using the selected output correction characteristic. (Output correction) is performed (S470).

  Thereafter, the output-corrected black data K2 is output to the image recording unit 4 together with the three color data C3, M3, and Y3 that are also output-corrected (S480). Note that the processing of S470 and S480 is a function of the recording γ correction unit 42.

(3) Effects of the Fourth Embodiment According to the present embodiment described above, the black data K1 obtained using the normal mode UCRγ table is converted into the characteristics of the recording γ correction unit 42, that is, the image recording unit 4. Since the output correction is performed in accordance with the color data of the second parameter max_K (main color) at the stage of performing the corresponding output correction, it is possible to generate high-precision black data according to the main color, thereby achieving reproducibility. Therefore, it is possible to form a high-quality image with good.

In addition, since the max_K correspondence Kγ table has different output correction characteristics for each CMY color, it is possible to generate more accurate black data according to the main color.
Then, the amount of black data generated with such high accuracy is subtracted from the color data of each color of cyan, magenta, and yellow, and the color data of each color is output and corrected. The total amount of each color ink used in the recording unit 4 can be appropriately regulated.

  In the present embodiment, the normal mode UCRγ computing unit 21 corresponds to the black data calculating unit of the present invention (claim 25), the recording γ correcting unit 42 corresponds to the output correcting unit of the present invention, and the max_K correspondence Kγ table. Corresponds to the output correction table of the present invention. In the present embodiment, the black data K2 corrected by the recording γ correction unit 42 corresponds to the black data constituting the converted color data of the present invention.

(4) Modification Also in this embodiment, the max_K correspondence Kγ table shown in FIG. 14 is merely an example. For example, even if the input data K1 is 255 at the maximum, the output data K2 is set to be smaller than 255. Also good. Further, at least the output correction characteristic corresponding to yellow may be set so that the value of the black data K2 after the output correction for the same black data K1 is smaller than the output correction characteristic corresponding to cyan. . However, it is not always necessary to set the output correction characteristic for yellow over the entire range 0 to 255 of the input data K1, so that the output correction characteristic for yellow is smaller than the output correction characteristic for cyan, as long as the object of the present invention is achieved. The output correction characteristic corresponding to each color can be set as appropriate.

  Further, in the present embodiment, the black data K1 generated by the UCR processing unit 40 is corrected using the max_K correspondence Kγ table shown in FIG. 14 to correct the black data according to the main color. However, the output correction characteristic corresponding to max_K as shown in FIG. 14 is an example, and various output correction characteristics can be used as long as appropriate output correction according to the main color is possible. For example, output correction characteristics corresponding to the minimum data value are prepared for each color (or two types for C, M, and Y), and K1 is selected by selecting an output correction characteristic corresponding to the color of the minimum data value. The output may be corrected to K2.

1 is a block diagram illustrating a schematic configuration of a color printing apparatus according to an embodiment. It is a functional block diagram showing operation | movement of the UCR process part of 1st Embodiment. It is a flowchart showing operation | movement of the UCR process part of 1st Embodiment. It is explanatory drawing showing a max_K corresponding | compatible UCR (gamma) table. It is a functional block diagram showing operation | movement of the UCR process part of 2nd Embodiment. It is a flowchart showing operation | movement of the UCR process part of 2nd Embodiment. It is explanatory drawing showing a normal mode UCRγ table. It is explanatory drawing showing a max_K dependence ratio table. It is a functional block diagram showing operation | movement of the UCR process part of 3rd Embodiment. It is a flowchart showing operation | movement of the UCR process part of 3rd Embodiment. It is explanatory drawing showing a max_K corresponding | compatible black data adjustment table. It is a functional block diagram showing operation | movement of the UCR process part and recording gamma correction part of 4th Embodiment. It is a flowchart showing operation | movement of the UCR process part and recording gamma correction part of 4th Embodiment. It is explanatory drawing showing a K (gamma) table corresponding to max_K. It is explanatory drawing showing a min_K corresponding | compatible UCR (gamma) table. It is explanatory drawing showing a black data adjustment table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Color printing apparatus, 2 ... Pixel data input part, 3 ... Image data processing part, 4 ... Image recording part, 6 ... Conversion part, 7, 20, 30, 40 ... UCR processing part, 8, 42 ... Recording gamma correction , 11 ... first parameter selection unit, 12 ... second parameter selection unit, 13 ... K-compatible UCRγ calculation unit, 14 ... black data removal unit, 21 ... normal mode UCRγ calculation unit, 22 ... difference calculation unit, 23 ... K Dependency ratio coefficient calculation unit, 24, 32 ... K1 calculation unit, 31 ... Black data adjustment coefficient calculation unit

Claims (29)

In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A maximum color data extraction step of extracting one maximum color data having a maximum data value from the pre-conversion color data;
A conversion characteristic selection step for selecting a black data conversion characteristic associated with the maximum color data, which the first black data conversion table for generating black data has,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
A first black data generation step for generating black data from the minimum data value and the selected black data conversion characteristic;
A color data generation method comprising: The color data generation method according to claim 1,
The first black data conversion table has two or three types of black data conversion characteristics associated with one of the three colors, and each of the three colors has one of the black data conversion characteristics. A color data generation method characterized by being associated with. The color data generation method according to claim 1 or 2,
A second black data generation step for generating black data from the black data conversion characteristics common to the three colors of the second black data conversion table for generating black data and the minimum data value;
A saturation derivation step for deriving the saturation of the color image;
The derivation is performed using a weighting table in which relative weights of the black data generated in the first black data generation step and the black data generated in the second black data generation step are set according to the saturation. A weighting derivation step for deriving the weighting for the saturated saturation;
A third black data generation step for generating black data reflecting the weighting based on the black data generated in each black data generation step and the derived weight;
A color data generation method comprising: The color data generation method according to claim 3,
The color data generation method, wherein the weighting table is set such that the higher the saturation of the color image, the greater the weight of the black data generated in the first black data generation step. The color data generation method according to claim 3 or 4,
In the weighting table, when the saturation of the color image is 0, the weight of the black data generated in the first black data generation step is 0, and the saturation of the color image is greater than or equal to a predetermined saturation threshold The color data generation method is characterized in that the weight of the black data generated in the second black data generation step is set to zero. The color data generation method according to any one of claims 1 to 5,
The first black data conversion table is associated with yellow as the black data conversion characteristic, and black data is configured such that black data is not generated when the minimum data value is equal to or less than a predetermined first set value. A black ink data conversion characteristic that is associated with cyan or magenta and configured so that black data is not generated when the minimum data value is equal to or smaller than a second set value that is smaller than the first set value; A color data generation method characterized by comprising: The color data generation method according to any one of claims 3 to 5,
The first black data conversion table is associated with yellow as the black data conversion characteristic, and black data is configured such that black data is not generated when the minimum data value is equal to or less than a predetermined first set value. A black ink data conversion characteristic that is associated with cyan or magenta and configured so that black data is not generated when the minimum data value is equal to or smaller than a second set value that is smaller than the first set value; Have
The black data conversion characteristic of the second black data conversion table indicates that black data is not generated when the minimum data value is smaller than the first set value and not greater than the third set value greater than the second set value. The color data generation method characterized by being comprised. The color data generation method according to claim 6 or 7, wherein
The first black data conversion table has three types of black data conversion characteristics, and each black data conversion characteristic is associated with one of the three colors on a one-to-one basis. The data conversion characteristic is configured so that black data is not generated when the minimum data value is smaller than the first set value and not greater than a fourth set value greater than the second set value. Color data generation method. In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink data from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
From the black data conversion characteristic of the black data conversion table for generating black data and the minimum data value, a black data generation step for generating black data;
A maximum color data extraction step of extracting one maximum color data having a maximum data value from the pre-conversion color data;
An adjustment characteristic selection step for selecting an adjustment characteristic associated with the maximum color data, which is included in an adjustment table for deriving an adjustment ratio of black data according to saturation,
A saturation derivation step for deriving the saturation of the color image;
An adjustment rate deriving step for deriving the adjustment rate from the derived saturation and the selected adjustment characteristic;
A black ink data adjustment step for adjusting the black ink data generated in the black ink data generation step based on the derived adjustment rate;
A color data generation method comprising: The color data generation method according to claim 9, comprising:
The adjustment table has two or three types of the adjustment characteristics associated with any one of the three colors, and each of the three colors is associated with any one of the adjustment characteristics. Characteristic color data generation method. The color data generation method according to claim 9 or 10,
The adjustment rate directly or indirectly indicates a ratio of the adjusted black data to the black data generated in the black data generation step, and the adjustment characteristic associated with yellow is cyan or magenta. The color data generation method, wherein the ratio with respect to the same saturation is reduced with respect to the adjustment characteristic associated with the color characteristic. The color data generation method according to claim 11, comprising:
Each of the adjustment characteristics in the adjustment table is configured such that the adjustment rate decreases as the saturation of the color image increases. The color data generation method according to claim 11 or 12,
Each adjustment characteristic in the adjustment table is configured so that the adjustment rate is 100% when the saturation of the color image is 0, and the adjustment characteristic associated with yellow has a predetermined saturation. In the case of the first saturation or higher, the adjustment rate is configured to be 0, and the adjustment characteristic associated with cyan or magenta is equal to or higher than the second saturation where the saturation is higher than the first saturation. In the case of the color data generation method, the adjustment rate is configured to be zero. The color data generation method according to claim 13, comprising:
The adjustment table has three types of adjustment characteristics, and each adjustment characteristic is associated with one of the three colors on a one-to-one basis. The adjustment characteristic associated with magenta has the saturation described above. The color data generation method, wherein the adjustment rate is configured to be 0 when the saturation is higher than the first saturation and is equal to or higher than the third saturation which is lower than the second saturation. The color data generation method according to any one of claims 9 to 14,
In the saturation derivation step, the saturation is derived based on a difference between the maximum color data extracted in the maximum color data extraction step and the minimum data value extracted in the minimum data value extraction step. Color data generation method. The color data generation method according to claim 1,
By subtracting the black data generated by the color data generation method from each of the pre-conversion color data, three colors for generating three color data of cyan, magenta, and yellow constituting the post-conversion color data are generated. A color data generation method comprising a generation step. In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
From the black data conversion characteristic of the black data conversion table for generating black data and the minimum data value, a black data generation step for generating black data;
A maximum color data extraction step of extracting one maximum color data having a maximum data value from the pre-conversion color data;
Select an output correction characteristic associated with the maximum color data in an output correction table for correcting the black data generated in the black data generation step according to the characteristics of the image forming means for forming the color image Output correction characteristic selection step to be performed,
A black ink data output correction step for correcting the black ink data generated in the black data generation step based on the selected output correction characteristics;
A color data generation method comprising: The color data generation method according to claim 17, wherein
The output correction table has two or three types of the output correction characteristics associated with any one of the three colors, and each of the three colors is associated with any one of the output correction characteristics. A method for generating color data. The color data generation method according to claim 18, wherein
The output correction characteristic associated with yellow in the output correction table is configured such that the corrected black data value for the same black data is smaller than the output correction characteristic associated with cyan or magenta. A method of generating color data. The color data generation method according to claim 19, wherein
The output correction table has three types of output correction characteristics, and each output correction characteristic is associated with one of the three colors on a one-to-one basis, and the output correction characteristics associated with magenta are the same. The color is characterized in that the corrected value for the black data is larger than the output correction characteristic associated with yellow and smaller than the output correction characteristic associated with cyan. Data generation method. The color data generation method according to any one of claims 17 to 20,
Three colors are generated by subtracting the black data generated in the black data generation step from each of the pre-conversion color data to generate three color data of cyan, magenta, and yellow constituting the post-conversion color data. A color data generation method comprising a generation step. A color data generating apparatus that is provided in a color image forming apparatus and generates post-conversion color data of four colors including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. And
A first black data conversion table having black data conversion characteristics associated with each of the three colors;
Minimum data extraction means for comparing the pre-conversion color data and extracting a minimum data value;
Maximum color data extracting means for comparing the pre-conversion color data and extracting color data having a maximum data value;
Using the black data conversion characteristic associated with the maximum color data extracted by the maximum color data extraction means in the first black data conversion table, the minimum data value extracted by the minimum data extraction means First black data calculating means for calculating black data;
A color data generation device comprising: a first black data calculation unit configured to generate a calculation result of the first black data calculation unit as black data. The color data generation device according to claim 22, wherein
A second black data conversion table having black data conversion characteristics common to the three colors;
Second black data calculation means for calculating black data for the minimum data value extracted by the minimum data extraction means using the second black data conversion table;
A weighting table in which the relative weighting of the black data calculated by the first black data calculating unit and the black data calculated by the second black data calculating unit is set according to the saturation of the color image;
Saturation derivation means for deriving the saturation of the color image;
Weighting derivation means for deriving the weighting for the saturation derived by the saturation derivation means using the weighting table;
On the basis of the black data calculated by the first black data calculating means, the black data calculated by the second black data calculating means, and the weight derived by the weight deriving means, the black data reflecting the weight A third black ink data calculating means for calculating
A color data generation device, characterized in that the calculation result by the third black data calculation means is generated as black data. A color data generating apparatus that is provided in a color image forming apparatus and generates post-conversion color data of four colors including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. And
A black data conversion table having black data conversion characteristics common to the three colors;
Minimum data extraction means for comparing the pre-conversion color data and extracting a minimum data value;
Maximum color data extracting means for comparing the pre-conversion color data and extracting color data having a maximum data value;
Using the black data conversion table, black data calculation means for calculating black data for the minimum data value extracted by the minimum data extraction means;
An adjustment table having an adjustment characteristic with which each of the three colors is associated, in order to derive an adjustment ratio of black data according to saturation;
Saturation derivation means for deriving the saturation of the color image;
Adjustment for deriving the adjustment rate with respect to the saturation derived by the saturation deriving unit using the adjustment characteristic associated with the maximum color data extracted by the maximum color data extracting unit in the adjustment table Rate derivation means;
Black ink data adjusting means for adjusting the black data calculated by the black data calculating means based on the adjustment rate derived by the adjustment rate deriving means;
A color data generation device, characterized in that the value adjusted by the black data adjustment means is generated as black data. A color data generating apparatus that is provided in a color image forming apparatus and generates post-conversion color data of four colors including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed. And
A black data conversion table having black data conversion characteristics common to the three colors;
Minimum data extraction means for comparing the pre-conversion color data and extracting a minimum data value;
Maximum color data extracting means for comparing the pre-conversion color data and extracting color data having a maximum data value;
Using the black data conversion table, black data calculation means for calculating black data for the minimum data value extracted by the minimum data extraction means;
An output correction table having output correction characteristics associated with the three colors, for correcting the black data calculated by the black data calculation means in accordance with characteristics of the image forming means for forming the color image; ,
Output correction means for correcting the black data calculated by the black data calculation means using the output correction characteristics associated with the maximum color data extracted by the maximum color data extraction means in the output correction table. When,
A color data generation device, characterized in that the value corrected by the output correction means is generated as black ink data. A color data generation device according to any one of claims 22 to 25;
Image forming means for forming a color image on a recording medium based on the converted color data of the four colors generated by the color data generating device;
A color image forming apparatus comprising: In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
From the black data conversion characteristic of the black data conversion table for generating black data and the minimum data value, a black data generation step for generating black data;
A saturation derivation step for deriving the saturation of the color image;
An adjustment rate deriving step for deriving the adjustment rate corresponding to the saturation derived in the saturation deriving step from the adjustment table in which the adjustment rate of the black ink according to the saturation is set;
A black ink data adjustment step for adjusting the black ink data generated in the black ink data generation step based on the derived adjustment rate;
A color data generation method comprising: In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
A conversion characteristic for selecting a black data conversion characteristic corresponding to the main color of the color image from among a plurality of black data conversion characteristics prepared according to the main color, which the first black data conversion table for generating black data has A selection step;
A first black data generation step for generating black data from the minimum data value and the selected black data conversion characteristic;
A second black data generation step for generating black data from the black data conversion characteristics common to the three colors of the second black data conversion table for generating black data and the minimum data value;
A saturation derivation step for deriving the saturation of the color image;
The derivation is performed using a weighting table in which relative weights of the black data generated in the first black data generation step and the black data generated in the second black data generation step are set according to the saturation. A weighting derivation step for deriving the weighting for the saturated saturation;
A third black data generation step for generating black data reflecting the weighting based on the black data generated in each black data generation step and the derived weight;
A color data generation method comprising: In a color image forming apparatus, a color data generation method for generating four color post-conversion color data including black ink from pre-conversion color data consisting of three colors of cyan, magenta, and yellow representing a color image to be formed,
A minimum data value extracting step of extracting a minimum data value from the pre-conversion color data;
From the black data conversion characteristic of the black data conversion table for generating black data and the minimum data value, a black data generation step for generating black data;
The output correction table for correcting the black data generated in the black data generation step according to the characteristics of the image forming means for forming the color image has a plurality of output correction characteristics prepared according to the main color. Among them, an output correction characteristic selection step for selecting an output correction characteristic according to the main color of the color image;
A black ink data output correction step for correcting the black ink data generated in the black data generation step based on the selected output correction characteristics;
A color data generation method comprising:

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