US5835244A — Method and apparatus for the conversion of color …

Claim 1

Independent Claim 280 words

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.

Claim 2

Independent Claim 280 words

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.

Claim 3

Dependent Claim 25 words

The method according to claim 1 wherein the first color space is L, a, b and the second color space is C, M, Y, K.

Claim 4

Dependent Claim 17 words

The method according to claim 1 wherein the first color space is an equidistantly graduated color space.

Claim 5

Dependent Claim 15 words

The method according to claim 3 wherein the equidistantly graduated color space conforms to sensation.

Claim 6

Dependent Claim 17 words

The method according to claim 3 wherein the equidistantly graduated color space is a CIELAB color space.

Claim 7

Dependent Claim 243 words

The method according to claim 2 wherein for the approximate analytical calculation of the printing table C, M, Y, K=f(L*, a*, b*)!, the color values L*, a*, b*! of the first color space are transformed into the standardized color values X, Y, Z! of a CIE 1931 XYZ color space, taking a type of light into consideration; the standardized color values X, Y, Z! are chromatically adapted to the reference white of the respective printing material based on a chromatic adaptation transformation; the effective area coverage values c, m, y! are calculated from the chromatically adapted standardized color values X', Y', Z'! with assistance of Neugebauer equations for three-color printing, said area coverage values being a criterion for raster dot sizes of the three printing colors on the printing material; the functionally corresponding area coverage values k! for a printing color "black" are calculated from the effective area coverage values c, m, y! of the three chromatic printing colors; corrected, effective area coverage values c", m", y"! are calculated from the effective area coverage values c, m, y! of the three chromatic printing colors with assistance of Neugebauer equations for four-color printing upon prescription of the area coverage values k! of the printing color "black"; and the corrected, effective area coverage values c", m", y"! as well as the value k! are converted into the color separation values C, M, Y, K! of the printing table, taking dot growth during printing into consideration.

Claim 8

Dependent Claim 27 words

The method according to claim 6 wherein the chromatic adaptation transformation of the standardized color values X, Y, Z! is implemented according to a "von Kries" transformation.

Claim 9

Dependent Claim 39 words

The method according to claim 6 wherein the area coverage values k! for the printing color "black" are calculated from a respective minimum value of the effective area coverage values c", m", y"! of the three chromatic printing colors.

Claim 10

Dependent Claim 93 words

The method according to claim 6 wherein the calculation and correction of the effective area coverage values is implemented with the assistance of the Neugebauer equations for three-color printing and four-color printing, being iteratively implemented according to an approximation method leaving the color values that arose due to the superimposed printing of raster dots out of consideration; the error of the approximation solution is corrected with a correction value acquired by a series expansion; and the iteration is broken off as soon as the correction value has reached a prescribable, lower limit value.

Claim 11

Dependent Claim 90 words

The method according to claim 8 wherein after the chromatic adaptation transformation, a check is carried out to see whether the chromatically adapted standardized color values X', Y', Z'! lie in the respective printing color space; and if the chromatically adapted standardized color values X', Y', Z'! do not lie in the printing color space, an image of the non-printable color values is implemented onto the surface of the printing color space upon preservation of the hue as well as with uniform reduction of luminance L*! and hue a*, b*!.

Claim 12

Dependent Claim 76 words

The method according to claim 8 wherein after the correction of the effective area coverage values c, m, y, k!, a check is carried out to see whether the sum of the area coverage values is greater than a prescribable limit value; and if this is the case, the area coverage values k! are incremented in small steps and a recalculation of the area coverage values is undertaken according to the Neugebauer equations for four-color printing.

Claim 13

Dependent Claim 214 words

The method according to claim 2 wherein for the correction of the approximately calculated printing table C, M, Y, K=f(L*, a*, b*)!, said color test table is provided with a plurality of colors j! and the color values L*j (v), a*j (v), b*j (v)! of color fields thereof are identified as said rated values; the rated color values L*j(v), a*j(v), b*j(v)! of the color test table are converted into the color separation values C, M, Y, K! based on the approximately calculated printing table C, M, Y, K=f(L*, a*, b*)!; the color test table is proof-printed on the later printing material with assistance of the color separation values C, M, Y, K!; the actual color values L*j(m), a*j(m), b*j(m)! of the corresponding colors of the color test table present as the proof are colorimetrically measured; the rated color values L*j (v), a*j (v), b*j (v)! and the corresponding actual color values L*j(m), a*j(m), *j(m)! are compared to one another; and the corresponding correction color values dL*, da*, db*! for the color values L*, a*, b*! of the printing table C, M, Y, K=f(L*, a*, b*)! are calculated according to a compensation method from the color difference values as correction color values acquired by comparison of the rated color values and the actual color values.

Claim 14

Dependent Claim 125 words

The method according to claim 2 wherein the correction color values dL*, da*, db*! are calculated from the rated color values L*j(v), a*j(v), b*j(v)! and the colorimetrically measured actual color values L*j(m), a*j(m), b*j(m)! of the color test table with colorimetric distance evaluation based on a distance function f(j)! according to the following equation: dL*=Σj f(j)×(L*j(m)-L*j(v))!/Σj f(j)! da*=Σj f(j)×(a*j(m)-a*j(v))!/Σj f(j)! db*=Σj f(j)×(b*j(m)-b*j(v))!/Σj f(j)! and the corrected color values L* KOR , a* KOR , b* KOR ! are calculated from the color values L*, a*, b*! and from the correction color values dL*, da*, db*! by addition according to the following equation: L*.sub.KOR =L*+dL* a*.sub.KOR =a*+da* b*.sub.KOR =b*+db* whereby: dL*, da*, db*=correction color values L*j(v),a*j(v),b*j*(v)=measured values of test table L*j(m),a*j(m),b*j(m)=measured values of proof f(j)=distance function.

Claim 15

Dependent Claim 27 words

The method according to claim 12 wherein a function of a fourth order having a form f(j)=1/ (L*-L*j(m)).sup.2 +(a*-a*j(m)).sup.2 +(b*j(m)).sup.2 !.sup.2 is employed as said distance function.

Claim 16

Dependent Claim 20 words

The method according to claim 1 wherein the color test table is a color table with colorimetrically defined color fields.

Claim 17

Dependent Claim 25 words

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.

Claim 18

Dependent Claim 26 words

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.

Claim 19

Dependent Claim 25 words

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.

Claim 20

Dependent Claim 27 words

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.

Claim 21

Dependent Claim 51 words

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 !.

Claim 22

Dependent Claim 49 words

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 !.

Claim 23

Dependent Claim 35 words

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 !.

Claim 24

Dependent Claim 27 words

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.

Claim 25

Independent Claim 195 words

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: 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.

Claim 26

Independent Claim 195 words

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: 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.

Claim 27

Dependent Claim 23 words

An apparatus according to claim 24 wherein the table memory is corrected by the generated corrected color values input to the table memory.

Claim 28

Dependent Claim 25 words

An apparatus according to claim 24 wherein the first color space is L, a, b and the second color space is C, M, Y, K.

Claim 29

Dependent Claim 31 words

The apparatus according to claim 26 wherein the correction value unit comprises a second table memory for depositing the corrected color values L* KOR , a* KOR , b* KOR !.

Claim 30

Dependent Claim 14 words

The apparatus according to claim 24 wherein the correction value unit comprises an interpolator.

Claim 31

Dependent Claim 15 words

The apparatus according to claim 24 wherein a calorimeter is employed as said measuring instrument.

Claim 32

Dependent Claim 15 words

The apparatus according to claim 24 wherein a spectrophotometer is employed as said measuring instrument.

Claim 33

Dependent Claim 17 words

The apparatus according to claim 24 wherein a calibrated input device is employed as said measuring instrument.

Claim 34

Dependent Claim 16 words

The apparatus according to claim 24 wherein a color scanner is employed as said measuring instrument.

Claim 35

Independent Claim 238 words

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; 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.

Claim 36

Independent Claim 238 words

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; 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.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2001-11-09	2002-05-11	2002-11-10	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2005-11-09	2006-05-11	2006-11-10	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2009-11-09	2010-05-11	2010-11-10	$7700.00	Window Closed / Lapsed

Method and apparatus for the conversion of color values

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