Method and apparatus for the conversion of color values
First Claim
1. A method for conversion of color values of a first color space into color values of a second color space as a printing color space characteristic of a printing process in apparatus and systems for color image processing, comprising the steps of:
- approximately analytically calculating corresponding color separation values of the printing color space for the respective printing process from color values of the first color space and forming an approximated printing table, taking printing colors of the printing color space for the printing process employed, colorimetric properties of a printing material used in the printing process, and printing process parameters into consideration;
by use of the approximated printing table, calculating corresponding color separation values from characteristic color values of a color test table of a data source;
producing a proof of the color test table with said calculated corresponding color separation values and colorimetrically measuring the proof, taking the printing process parameters for the later printing process into consideration;
calculating color difference values as correction color values by determining differences between actual color values acquired by said colorimetric measurement of said proof and said characteristic color values of said color test table as rated color values;
creating corrected color values by combining said difference color values as correction color values with said characteristic color values of the color test table; and
inputting said corrected color values to said approximated printing table so that table values of the printing table are corrected and the printing table can then be used for a substantially more exact conversion of the color values of the first color space into the color separation values of the second color space for the respective printing process.
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Accused Products
Abstract
A method and an apparatus for the conversion of color values of a first color space into color separation values of a printing color space characteristic of a printing process in apparatus and systems for color image processing. For the purpose of exact adaptation of the color separation values C, M, Y, K! of the printing color space to the respective printing process, the functionally allocated color separation values C, M, Y, K! are first approximately analytically calculated from the color values L*, a*, b*! of the first color space as a printing table C, M, Y, K=f(L*, a*, b*)!, taking the printing colors of the respective printing color space of the later printing process, the colorimetric properties of the printing material employed later, and the printing process parameters into consideration. Subsequently, the calculated printing table C, M, Y, K=f(L*, a*, b*)! is corrected by a color value calibration correction values dL*, da*, db*! are calculated by comparison of the color values L*(v), a*(v), b*(v)! of the first color space characteristic of the colors of a test table to the colorimetrically measured color values L*(m), a*(m), b*(m)! of the corresponding colors of the test table produced as a proof, and the table values of the printing table C, M, Y, K=f(L*, a*, b)! are corrected by the correction values dL*, da*, db*!.
90 Citations
33 Claims
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1. A method for conversion of color values of a first color space into color values of a second color space as a printing color space characteristic of a printing process in apparatus and systems for color image processing, comprising the steps of:
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approximately analytically calculating corresponding color separation values of the printing color space for the respective printing process from color values of the first color space and forming an approximated printing table, taking printing colors of the printing color space for the printing process employed, colorimetric properties of a printing material used in the printing process, and printing process parameters into consideration; by use of the approximated printing table, calculating corresponding color separation values from characteristic color values of a color test table of a data source; producing a proof of the color test table with said calculated corresponding color separation values and colorimetrically measuring the proof, taking the printing process parameters for the later printing process into consideration; calculating color difference values as correction color values by determining differences between actual color values acquired by said colorimetric measurement of said proof and said characteristic color values of said color test table as rated color values; creating corrected color values by combining said difference color values as correction color values with said characteristic color values of the color test table; and inputting said corrected color values to said approximated printing table so that table values of the printing table are corrected and the printing table can then be used for a substantially more exact conversion of the color values of the first color space into the color separation values of the second color space for the respective printing process. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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15. The method according to claim 1 wherein the color test table is a color table with colorimetrically defined color fields.
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16. The method according to claim 15 wherein the colors of the color fields of the test table are selected visually equidistant in the color space.
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17. The method according to claim 2 wherein actual color values L*j(m), a*j(m), b*j(m)! of colors of the color test table, are measured with a spectral photometer.
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18. The method according to claim 2 wherein actual color values L*j(m), a*j(m), b*j(m)! of colors of the color test table are measured with a colorimeter.
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19. The method according to claim 2 wherein actual color values L*j(m), a*j(m), b*j(m)! of colors of the color test table are measured with a calibrated input device.
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20. The method according to claim 2 wherein the correction color values dL*, da*, db*! are stored and are added with proper operational sign to stored color values L*j(v), a*j(v), b*j(v)! during ongoing color conversion in order to obtain the corrected color values L*KOR, a*KOR, b*KOR !.
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21. The method according to claim 2 wherein the correction color values dL*, da*, db*! are added with proper operational sign to the stored color values L*j(v), a*j(v), b*j(v)! before ongoing color conversion in order to obtain the corrected color values L*KOR, a*KOR, b*KOR !.
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22. The method according claim 2 wherein the corrected printing table C, M, Y, K=f(L*, a*, b*)! is calculated on the basis of the corrected color values L*KOR, a*KOR, b*KOR !.
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23. The method according to claim 2 wherein the color values of the printing table C, M, Y, K=f(L*, a*, b*)! are stored as a three-dimensional look-up table.
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24. An apparatus for conversion of color values of a first color space into color separation values of a second color space as a printing color space in apparatus and systems for color image processing, comprising:
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a data source for storing rated color values of colors of a color test table; a table memory for depositing an approximately calculated printing table; a measuring instrument for the colorimetric identification of actual color values of colors of a proof of the color test table; a comparison unit whose inputs are connected to outputs of the data source and of the measuring instrument for comparing the rated color values of the colors of the color test table to the measured actual color values of the colors of the proof of the color test table; and a correction value unit whose inputs are connected to the outputs of the data source and of the comparison unit and whose output is connected to an input of the table memory for acquiring color correction values from color difference values acquired by comparison of the rated color values to the actual color values and for generating corrected color values for the color conversion. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32)
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33. A method for conversion of color values of a first color space into color values of a second color space as a printing color space characteristic of a printing process in apparatus and systems for color image processing, comprising the steps of:
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approximately analytically calculating corresponding color separation values of the printing color space for the respective printing process from color values of the first color space and forming an approximated printing table; by use of the approximated printing table, calculating corresponding color separation values from characteristic color values of a color test table of a data source; producing a proof of the color test table with said calculated corresponding color separation values and colorimetrically measuring the proof; calculating color difference values as correction color values by determining differences between actual color values acquired by said colorimetric measurement of said proof and said characteristic color values of said color test table as rated color values; creating corrected color values by combining said difference color values as correction color values with said characteristic color values of the color test table; and inputting said corrected color values to said approximated printing table so that table values of the printing table are corrected and the printing table can then be used for a substantially more exact conversion of the color values of the first color space into the color separation values of the second color space for the respective printing process.
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Specification