Method and apparatus for the conversion of color values
First Claim
Patent Images
1. A method for conversion of color values of a color negative with a positive/negative reversal function, comprising the steps of:
- acquiring color values (Rn, Gn, Bn) for three color components by point-by-point and line-by-line, optoelectronic scanning of a color negative and storing the color values;
determining separately a brightest color value as an image luminance value (BLr, BLg, BLb) and a darkest color value as an image depth value (BTr, BTg, BTb) of the color negative from the color values (Rn, Gn, Bn) for each color component;
determining density ranges (Δ
Dr, Δ
Dg, Δ
Db) for each color component by difference formation between the corresponding image luminance values (BLr, BLg, BLb) and the image depth values (BTr, BTg, BTb) of the color negative;
defining a density range (Δ
D′
) by difference formation between a prescribed density value (DL) for image luminance and a prescribed density value (DT) for image depth;
determining a positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} for conversion of the color values (Rn, Gn, Bn) of the color negative into color values (Rp, Gp, Bp) of a corresponding, chromatically correct color positive from the three density ranges (Δ
Dr, Δ
Dg, Δ
Db) of the color negative and the defined density range (Δ
D′
);
calculating functionally corresponding color values (Rp, Gp, Bp) of the color positive for a value range of the color values (Rn, Gn, Bn) of the color negative with the positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} and depositing the color values (Rp, Gp, Bp) in a table memory addressable by the corresponding color values (Rn, Gn, Bn); and
converting the color values (Rn, Gn, Bn) of the color negative with the table memory into the color values (Rp, Gp, Bp) of the corresponding color positive for further processing.
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Abstract
In a method and apparatus for conversion of color values of a color negative according to a positive/negative reversal function [Rp, Gp, Bp=f(Rn, Gn, Bn)] color values (Rn, Gn, Bn) for the three color components are acquired by optoelectronic scanning of a color negative in a color scanner. The image luminance value (BLr, BLg, BLb) and the image depth value (BTr, BTg, BTb) of the color negative as well as the corresponding density ranges (ΔDr, ΔDg, ΔDb) are determined from the color values (Rn, Gn, Bn) in an image analysis unit for each color component. The positive/negative reversal function is determined in a calculating stage from the density ranges (ΔDr, ΔDg, ΔDb) and a defined density range (ΔD′). The positive/negative reversal function is deposited in a table memory as a value table. The color values (Rn, Gn, Bn) of the color negative are then converted into the color values (Rp, Gp, Bp) of the corresponding color positive with the stored value table.
25 Citations
17 Claims
-
1. A method for conversion of color values of a color negative with a positive/negative reversal function, comprising the steps of:
-
acquiring color values (Rn, Gn, Bn) for three color components by point-by-point and line-by-line, optoelectronic scanning of a color negative and storing the color values;
determining separately a brightest color value as an image luminance value (BLr, BLg, BLb) and a darkest color value as an image depth value (BTr, BTg, BTb) of the color negative from the color values (Rn, Gn, Bn) for each color component;
determining density ranges (Δ
Dr, Δ
Dg, Δ
Db) for each color component by difference formation between the corresponding image luminance values (BLr, BLg, BLb) and the image depth values (BTr, BTg, BTb) of the color negative;
defining a density range (Δ
D′
) by difference formation between a prescribed density value (DL) for image luminance and a prescribed density value (DT) for image depth;
determining a positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} for conversion of the color values (Rn, Gn, Bn) of the color negative into color values (Rp, Gp, Bp) of a corresponding, chromatically correct color positive from the three density ranges (Δ
Dr, Δ
Dg, Δ
Db) of the color negative and the defined density range (Δ
D′
);
calculating functionally corresponding color values (Rp, Gp, Bp) of the color positive for a value range of the color values (Rn, Gn, Bn) of the color negative with the positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} and depositing the color values (Rp, Gp, Bp) in a table memory addressable by the corresponding color values (Rn, Gn, Bn); and
converting the color values (Rn, Gn, Bn) of the color negative with the table memory into the color values (Rp, Gp, Bp) of the corresponding color positive for further processing. - View Dependent Claims (2, 3, 4)
determining the frequency distributions (H(R), H(G) and H(B)) of the color values (R, G, and B) as brightness histograms;
determining by characteristic brightness values in a luminance histogram limits of a possible image luminance range in which image luminance values (BLr, BLg and Bb) should lie and limits of a possible image depth range in which image depth values (BTr, BTg and BTb) should lie; and
calculating from a curve of the luminance histogram within an expanded luminance range around the image luminance range the image luminance values (BLr, BLg and BLb) and from a curve of the luminance histogram within an expanded luminance range around the image depth range the image depth values (BTr, BTg and BTb).
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3. The method according to claim 1 wherein the image analysis of the color negative occurs with color values (Rn, Gn, Bn) that are acquired by scanning the color negative with a coarser resolution as a course scan compared to a fine scan resolution required for the reproduction of the color negative.
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4. The method according to claim 1 wherein:
-
the color negative is first scanned with a coarser resolution as a course scan compared to a fine scan resolution required for the reproduction of the color negative for the acquisition of the color values (Rn, Gn, Bn);
a value table is calculated for the table memory;
the color negative is scanned with the fine scan resolution required for the reproduction; and
the color values (Rn, Gn, Bn) acquired in the fine scan are converted into the color values (Rp, Gp, Bp) for further processing.
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5. A method for conversion of color values of a color negative with a positive/negative reversal function, comprising the steps of:
-
acquiring color values (Rn, Gn, Bn) for three color components by point-by-point and line-by-line, optoelectronic scanning of a color negative and storing the color values;
determining separately a brightest color value as an image luminance value (BLr, BLg, BLb) and a darkest color value as an image depth value (BTr, BTg, BTb) of the color negative from the color values (Rn, Gn, Bn) for each color component;
determining density ranges (Δ
Dr, Δ
Dg, Δ
Db) for each color component by difference formation between the corresponding image luminance values (BLr, BLg, BLb) and the image depth values (BTr, BTg, BTb) of the color negative;
defining a density range (Δ
D′
) by difference formation between a prescribed density value (DL) for image luminance and a prescribed density value (DT) for image depth;
determining a positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} for conversion of the color values (Rn, Gn, Bn) of the color negative into color values (Rp, Gp, Bp) of a corresponding, chromatically correct color positive from the three density ranges (Δ
Dr, Δ
Dg, Δ
Db) of the color negative and the defined density range (Δ
D′
);
calculating functionally corresponding color values (Rp, Gp, Bp) of the color positive for a value range of the color values (Rn, Gn, Bn) of the color negative with the positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} and depositing the color values (Rp, Gp, Bp) in a table memory addressable by the corresponding color values (Rn, Gn, Bn);
converting the color values (Rn, Gn, Bn) of the color negative with the table memory into the color values (Rp, Gp, Bp) of the corresponding color positive for further processing; and
for determining the positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)}, transmission values (τ
r, τ
g, τ
b) acquired by scanning the color negative are logarithmized into density values (Dr, Dg, Db),the three density ranges (Δ
Dr, Δ
Dg, Δ
Db) of the color negative are matched to the defined density range (Δ
D′
) via linear norming functions {D′
r=fr(Dr), D′
g=fg(Dg), D′
b=fb(Db)}, as a result of which the three color density curves of the color negative material are normed onto a color density curve with a slope (γ
n), a normed color density curve [D′
=f(D)] of the color negative material is converted into a normed inverse color density curve [D″
=f(D′
)] of a positive material with a slope [γ
p=1/γ
n],inverse density values (D″
r, D″
g, D″
b) are calculated from the density values (D′
r, D′
g, D′
b) with the normed inverse color density curve [D″
=f(D′
)] according to a color reversal,the inverse density values (D″
r, D″
g, D″
b) are delogarithmized into transmission values (τ
′
r, τ
′
g, τ
′
b),the defined density range {Δ
D′
} is matched in gradation to a signal range {Δ
S=(τ
″
L−
τ
″
T)} defined by fixed points (τ
″
L, τ
″
T) and the positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} is formed.- View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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7. The method according to claim 5 wherein the determination of the density values (D′
-
r, D′
g, D′
b) sequences according to the following equations;
-
r, D′
-
8. The method according to claim 5 wherein the determination of the density values (D″
-
r, D″
g, D″
b) sequences according to the following equations
-
r, D″
-
9. The method according to claim 5 wherein the delogarithmization sequences according to the following equations:
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10. The method according to claim 5 wherein the gradation matching sequences according to the following equations:
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11. The method according to claim 5 wherein a positive/negative reversal function {τ
- ″
r, τ
″
g, τ
″
b32 f(τ
r, τ
g, τ
b)} is provided according to the following equations;
- ″
-
12. The method according to claim 11 wherein
transmission values (τ -
r, τ
g, τ
b) acquired in the scanning of the color negative are predistorted according to relationships Rn=f(τ
r), Gn=f(τ
g) and Bn=f(τ
b) in order to obtain the color values (Rn, Gn, Bn);
for calculating the positive-negative reversal function, the pre-distortions are in turn reversed according to relationships τ
r[r]=f1(Rn), τ
g=f1(Gn) and τ
b=f1(Bn) before logarithmization of the transmission values (τ
r, τ
g, τ
b); and
the pre-distortions are calculated back into the calculated positive/negative reversal function according to relationships Rp=f(τ
″
r), Gp=f(τ
″
g) and Bp=f(τ
″
b).
-
r, τ
-
13. A method for conversion of color values of a color negative with a positive/negative reversal function, comprising the steps of:
-
acquiring color values for three color components of a color negative;
determining a brightest color value as an image luminance value and a darkest color value as an image depth value of the color negative from the color values for each color component;
determining density ranges for each color component by difference formation between corresponding image luminance values and image depth values of the color negative;
defining a density range by difference formation between a predetermined density value for image luminance and a predetermined density value for image depth;
determining a positive/negative reversal function for conversion of the color values of the color negative into color values of a corresponding, chromatically correct color positive from the density ranges of the color negative and the defined density ranges;
calculating functionally corresponding color values of the color positive for a value range of the color values of the color negative with the positive/negative reversal function and depositing the functionally corresponding color values in a memory addressable by the corresponding color values; and
converting the color values of the color negative with the memory into the color values of the corresponding color positive for further processing.
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14. An apparatus for conversion of color values of a color negative with a positive/negative reversal function comprising:
-
an optoelectronic color scanner for acquiring color values (Rn, Gn, Bn) for three color components by point-by-point and line-by-scanning of a color negative;
an image data memory connected to the color scanner for intermediate storage of the color values (Rn, Gn, Bn);
an image analysis unit connected to the image data memory for separately determining a brightest color value as an image luminance value (BLr, BLg, BLb), and a darkest color value as an image depth value (BTr, BTg, BTb) of the color negative from the color values (Rn, Gn, Bn) for each color component;
a calculating stage connected to the image analysis unit for determining parameters of a positive/negative reversal function {Rp, Gp, Bp=f(Rn, Gn, Bn)} conversion of the color values (Rn, Gn, Bn) of the color negative into corresponding color values (Rp, Gp, Bp) of a corresponding, chromatically correct color positive from the image luminance values (BLr, BLg, BLb), the image depth values (BTr, BTg, BTb), density ranges (Δ
Dr, Δ
Dg, Δ
Db) representing a difference between the image luminance values (BLr, BLg, BLb) and the image depth values (BTr, BTg, BTb), prescribed density values (DL, DT) for image luminance and image depth, and a density range (Δ
D′
) representing a difference between the prescribed density values (DL, DT) for image luminance and image depth, and for calculating functionally corresponding color values (Rp, Gp, Bp) of the color positive from the color values (Rn, Gn, Bn) of the color negative with the positive/negative reversal function; and
a table memory following the calculating stage for depositing the calculated color values (Rp, Gp, Bp) and which is addressable by the corresponding color values (Rn, Gn, Bn). - View Dependent Claims (15, 16)
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17. An apparatus for conversion of color values of a color negative with a positive/negative reversal function comprising:
-
a unit for acquiring color values for three color components of a color negative;
an image analysis unit for determining a brightest color value as an image luminance value, and a darkest color value as an image depth value of the color negative from the color values for each color component;
a calculating stare connected to the image analysis unit for determining parameters of a positive/negative reversal function for conversion of the color values of the color negative into corresponding color values of a corresponding, chromatically correct color positive from the image luminance values, the image depth values, density ranges for each color component by difference formation between the corresponding image luminance values and the image depth values, prescribed density values for image luminance and image depth, and a density range representing a difference between said prescribed density values for image luminance and image depth, and for calculating functionally corresponding color values of the color positive from the color values of the color negative with the positive/negative reversal function; and
a memory following, the calculating stage for depositing the calculated color values and which is addressable by the corresponding color values.
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Specification
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- Resources
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Current AssigneeHeidelberger Druckmaschinen Ag
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Original AssigneeHeidelberger Druckmaschinen Ag
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InventorsBestmann, Günter
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Primary Examiner(s)Coles, Edward
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Assistant Examiner(s)Pokrzywa, Joseph R.
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Application NumberUS09/011,105Time in Patent Office1,538 DaysField of Search358/505, 358/506, 358/518, 358/519, 358/520, 358/521, 358/522, 358/523, 358/524, 358/455, 358/456, 358/457, 358/458, 382/167, 382/168, 382/274, 382/169US Class Current358/518CPC Class CodesH04N 1/6027 Correction or control of co...
