EP0309224A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Reproduction of coloured images
Assignee: Crosfield Electronics Ltd
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Filing: 1988-09-21
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Granted: —
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Expires: 2008-09-21
Abstract
Abstract A method and apparatus for reproducing a coloured orignal image represented by first signals defining the colour content of pixels of the original image in terms of a first set of colour components (C, M, Y). The coloured original image is reproduced using at least two separations representing respective colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of a second set which is different from the first set. The colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set are ranked in order of similarity to each pixel (C p , M p , Y p ) and a value is selected for the highest ranked colour component (C₂, M₂, Y₂) for which each of the first set of colour component values (C, M, Y) defining said selected colour component (C₂, M₂, Y₂) does not exceed the corresponding pixel values. The pixel values are then adjusted to take account of the select value of the colour component (C₂ , M₂, Y₂) of the second set. The process is then repeated for each of the remaining colour components (C₁, M₁, Y₁) of the second set in the order of ranking.
Inventors
- 👤 Peter William Stansfield
- 👤 Alastair Reed
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 11:11
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/46; H04N1/54
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
210 words
A method of reproducing a coloured original image represented by first signals, defining the colour content of pixels of the original image in terms of a first set of colour components (C, M, Y), in which at least two separations are prepared representing respective colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of a second set different from the first set comprises for each pixel (C p , M p , Y p ) of the original image i) ranking the colour components (C₁, M₁, Y₁ ; C₂, M₂, Y₂) of the second set in order of similarity to the pixel (C p , M p , Y p ); ii) selecting a value for the highest ranked colour component (C₂, M₂, Y₂) for which each of the first set of colour component values (C, M, Y) defining said selected colour component (C₂, M₂, Y₂) does not exceed the corresponding pixel values (C p , M p , Y p ); iii) adjusting the pixel values to take account of the selected value of the colour component (C₂, M₂, Y₂) of the second set; and, iv) repeating steps ii) and iii) for each of the remaining colour components (C₁, M₁, Y₁) of the second set in the order of ranking.
Claim 2
Independent Claim
210 words
A method of reproducing a coloured original image represented by first signals, defining the colour content of pixels of the original image in terms of a first set of colour components (C, M, Y), in which at least two separations are prepared representing respective colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of a second set different from the first set comprises for each pixel (C p , M p , Y p ) of the original image i) ranking the colour components (C₁, M₁, Y₁ ; C₂, M₂, Y₂) of the second set in order of similarity to the pixel (C p , M p , Y p ); ii) selecting a value for the highest ranked colour component (C₂, M₂, Y₂) for which each of the first set of colour component values (C, M, Y) defining said selected colour component (C₂, M₂, Y₂) does not exceed the corresponding pixel values (C p , M p , Y p ); iii) adjusting the pixel values to take account of the selected value of the colour component (C₂, M₂, Y₂) of the second set; and, iv) repeating steps ii) and iii) for each of the remaining colour components (C₁, M₁, Y₁) of the second set in the order of ranking.
Claim 3
Dependent Claim
60 words
A method according to claim 1, further comprising an initial step of storing values defining at least the characteristic elements of curves (C br , M br , Y br ) which respectively represent the colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set in terms of colour component values of the first set (C, M, Y).
Claim 4
Dependent Claim
176 words
A method according to claim 1 or claim 2, in which there are two colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) in the second set, step (ii) comprising determining the proportions (P₁, P₂) of each colour component (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set to extract from the pixel values (C p , M p , Y p ) by constructing a triangle in colour space whose apices are defined by respectively the pixel colour (C p , M p , Y p ) and the closest matches of the two colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set to the pixel colour (C p , M p , Y p ), the proportions (P₁, P₂) being defined by the lengths (X₁, X₂) of the portions of a line (X) joining the apices defined by the colour components (C₁, M₁, Y₁; C₂, M₂, Y₂ ) of the second set divided by a perpendicular (Z) dropped from the other apex (C p , M p , Y p ).
Claim 5
Dependent Claim
67 words
A method according to Claim 3, wherein the closest match of each component is achieved by determining the composition of the colour component (C₁, M₁ , Y₁; C₂, M₂, Y₂) which, when extracted from the original pixel colour (C p , M p , Y p ), causes one of the pixel colour components (C p , M p , Y p ) to fall to zero.
Claim 6
Independent Claim
41 words
A method according to any of the preceding claims, wherein the ranking of the colours is achieved by comparing the distances (X₁, X₂) in colour space to the pixel position of each special colour component (C₁, M₁, Y₁; C₂, M₂, Y₂).
Claim 7
Independent Claim
62 words
A method according to any of the preceding claims, further comprising after extracting the second colours (C₁, M₁, Y₁), determining to which second colour (C₁, M₁ or Y₁) the residual pixel colour (C, M, Y) is most similar, and extracting that second colour (C₁, M₁ Y₁) until a pixel colour component (C p , M p , Y p ) is zero.
Claim 8
Dependent Claim
179 words
Apparatus for reproducing a coloured original image represented by first signals defining the colour content of pixels of the original image in terms of a first set of colour components (C, M, Y), the coloured original image being reproduced using at least two separations representing respective colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of a second set different from the first set, the apparatus comprising means (1) for ranking the colour components (C₁ , M₁, Y₁; C₂, M₂, Y₂) of the second set in order of similarity to each pixel (C p , M p , Y p ); means (1) responsive to the values of each pixel to select a value for the ranked colour components in turn for which each of the first set of colour component values (C, M, Y) defining the corresponding ranked colour component does not exceed the corresponding pixel values (C p , M p , Y p ); and means (5) for adjusting the pixel values to take account of the selected value of the colour component of the second set.
Claim 9
Dependent Claim
179 words
Apparatus for reproducing a coloured original image represented by first signals defining the colour content of pixels of the original image in terms of a first set of colour components (C, M, Y), the coloured original image being reproduced using at least two separations representing respective colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of a second set different from the first set, the apparatus comprising means (1) for ranking the colour components (C₁ , M₁, Y₁; C₂, M₂, Y₂) of the second set in order of similarity to each pixel (C p , M p , Y p ); means (1) responsive to the values of each pixel to select a value for the ranked colour components in turn for which each of the first set of colour component values (C, M, Y) defining the corresponding ranked colour component does not exceed the corresponding pixel values (C p , M p , Y p ); and means (5) for adjusting the pixel values to take account of the selected value of the colour component of the second set.
Claim 10
Dependent Claim
58 words
Apparatus according to Claim 7, further comprising means (4) for storing values defining at least the characteristic elements of curves (C br , M br , Y br ) which respectively represent the colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set in terms of colour components values of the first set (C, M, Y).
Claim 11
Dependent Claim
188 words
Apparatus according to Claim 7 or claim 8, in which there are two colour components (C₁, M₁, Y₁ ; C₂, M₂, Y₂) in the second set, wherein the means (1) responsive to the values of each pixel comprises means to determine the proportions (P₁, P₂) of each colour component (C₁ , M₁, Y₁ ; C₂, M₂, Y₂) of the second set to extract from the pixel values (C p , M p , Y p ) by constructing a triangle in colour space whose apices are defined by respectively the pixel colour (C p , M p , Y p ) and the closest matches of the two colour components (C₁, M₁, Y₁; C₂, M₂, Y₂) of the second set to the pixel colour (C p , M p , Y p ), the proportions (P₁, P₂) defined by the lengths (X₁, X₂) of the portions of a line (X) joining the apices defined by the colour components (C₁, M₁, Y₁; C₂ , M₂, Y₂) of the second set divided by a perpendicular (Z) dropped from the other apex (C p , M p , Y p ).
References Cited (Backward Citations)
EP0184289A1
Cited
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