EP0750419A2
Expired / Lapsed
EP
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Color conversion method and color conversion table generating apparatus
Assignee: Fujifilm Holdings Corp
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Filing: 1996-06-18
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Granted: —
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Expires: 2016-06-18
Abstract
Abstract A plurality of color patches whose colors differ stepwise are colorimetrically analyzed to determining a relationship between color signals (CMY) and stimulus signals (XYZ) (step S11). A method of least squares is applied to the determined relationship to determine a relationship between first hypothetical color signals (CMY1*) and first hypothetical stimulus signals (XYZ1*) (step S12). These relationships are established as a forward conversion table (step S13). Then, a first reverse conversion table is generated from the forward conversion table using the Newton's method (step S14). The relationship between the first hypothetical color signals (CMY1*) and the first hypothetical stimulus signals (XYZ1*) in the first reverse conversion table is replaced with a relationship between second hypothetical color signals (CMY2*) and second hypothetical stimulus signals (XYZ2*) which have a physically matching capability (step S15), thus generating a second reverse conversion table from the first reverse conversion table (step S16). The second reverse conversion table is mapped to produce a reverse conversion table which is used (step S17) to convert stimulus signals (XYZ) into color signals (CMY).
Inventors
- 👤 Akito c/o Fuji Photo Film Co. Ltd. Ohkubo
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 11:35
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/46; H04N1/56; H04N1/60; H04N1/603; H04N1/6033
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
190 words
A method of converting color signals from a first colorimetric system to a second colorimetric system, comprising the steps of: (a) determining a relationship of actual color signals (XYZ) of the first colorimetric system obtained from known actual color signals (CMY) of the second colorimetric system, as a first forward conversion relationship; (b) approximating said first forward conversion relationship with a monotonous function to establish hypothetical color signals (CMY1*, XYZ1*) outside a region made up of said actual color signals (CMY, XYZ); (c) determining a relationship of color signals (XYZ, XYZ1*) of the first colorimetric system obtained from color signals which comprise said actual color signals (CMY) and said hypothetical color signals (CMY1*) of the second colorimetric system, as a second forward conversion relationship; (d) determining a relationship of the color signals (CMY, CMY1*) of the second colorimetric system obtained from the color signals (XYZ, XYZ1*) of the first colorimetric system, as a reverse conversion relationship from said second forward conversion relationship using a method of repetitive calculations; and (e) converting the color signals (XYZ) from the first colorimetric system to the second colorimetric system using said reverse conversion relationship.
Claim 2
Dependent Claim
53 words
A method according to claim 1, wherein said step (a) comprises the steps of colorimetrically analyzing color patches generated based on the known actual color signals (CMY) of the second colorimetric system, and determining said first forward conversion relationship as a relationship between colorimetrically analyzed values (XYZ) and said actual color signals (CMY).
Claim 3
Dependent Claim
28 words
A method according to claim 1, wherein said step (b) comprises the step of establishing the hypothetical color signals (CMY1*, XYZ1*) according to a method of least squares.
Claim 4
Dependent Claim
16 words
A method according to claim 1, wherein said method of repetitive calculations comprises a Newton's method.
Claim 5
Dependent Claim
78 words
A method according to claim 1, further comprising the steps of: replacing the hypothetical color signals (CMY1*, XYZ1*) which make up the reverse conversion relationship with new hypothetical color signals (CMY2*, XYZ2*) calculated according to the method of least squares, using the actual color signals (CMY, XYZ) close to said hypothetical color signals (CMY1*, XYZ1*), for thereby producing a new reverse conversion relationship between said actual color signals (CMY, XYZ) and said new hypothetical color signals (CMY2*, XYZ2*).
Claim 6
Dependent Claim
50 words
A method according to claim 5, further comprising the step of mapping said hypothetical color signals (CMY2*, XYZ2*) making up said new reverse conversion relationship onto a color-reproducible range of an image output apparatus, for thereby producing a reverse conversion relationship made up of the actual color signals (CMY, XYZ).
Claim 7
Dependent Claim
171 words
A color conversion table generating apparatus for use in an image output apparatus for converting color signals from a first colorimetric system to a second colorimetric system and outputting a color image based on color signals of the second colorimetric system, comprising: a colorimeter (20) for colorimetrically analyzing color patches which are outputted from the image output apparatus based on the color signals of the second colorimetric system; hypothetical signal generating means (26) for generating, from the color signals and colorimetrically analyzed values of the color patches, hypothetical color signals and hypothetical colorimetrically analyzed values capable of maintaining a monotonous relationship between the color signals and the colorimetrically analyzed values; forward conversion table generating means (28) for determining a relationship between said color signals and said hypothetical color signals, and said colorimetrically analyzed values and said hypothetical colorimetrically analyzed values, as a forward conversion table; and reverse conversion table generating means (30) for generating a reverse conversion table corresponding to said forward conversion table according to a method of repetitive calculations.
Claim 8
Dependent Claim
75 words
A color conversion table generating apparatus according to claim 7, further comprising second reverse conversion table generating means (34) for replacing the hypothetical color signals and the hypothetical colorimetrically analyzed values which make up the reverse conversion relationship generated by said reverse conversion table generating means (30), with new hypothetical color signals and hypothetical colorimetrically analyzed values which are calculated according to a method of least squares for thereby generating a new reverse conversion table.
Claim 9
Dependent Claim
44 words
A color conversion table generating apparatus according to claim 8, further comprising mapping means (36) for mapping said hypothetical color signals and said hypothetical colorimetrically analyzed values which make up said new reverse conversion table onto a color-reproducible range of said image output apparatus.
References Cited (Backward Citations)
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