Coordinating color produced by two devices--using a hue-controlled machine color space, or surface scaling

• US 5,883,632 A
• Filed: 05/03/1994
• Issued: 03/16/1999
• Est. Priority Date: 05/04/1992
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Dillinger, Paul H.
• Primary Examiner(s): Zimmerman, Mark K.
• Application Number:
  US08/238,137
• Time in Patent Office: 1,778 Days
• Field of Search: 395/131, 345/431, 345/150, 345/186
• US Class Current: 345/589
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/6016 Conversion to subtractive colour signals
• CPC Class Codes: H04N 1/6022 Generating a fourth subtractive colour signal, e.g. under colour removal, black masking
• CPC Class Codes: H04N 1/6052 Matching two or more picture signal generators or two or more picture reproducers
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

Device-space color specifications for two color-presentation devices are interrelated through the intermediary of at least one perceptual color space. This interrelation is performed by either tabulations or real-time software processing, and in such a way that color, and color changes, specified in relation to one device--in a control language of that device--are tracked in both the language and the actual performance of the other device. This mapping through perceptual space can be used to produce the effect of matching the two device gamuts to each other, so that the full gamuts of both are in effect merged. When so used, this new kind of mapping preserves relative positions in color space--and thus the capability of the tracking device to maintain distinctions between colors seen on the source/input device that appear very closely similar. Such discrimination between adjacent colors can be supported essentially throughout the gamut of both devices and in particular even very near the lightness extrema and maximum-saturation point on a hue page. A related technique of merging two- or three-dimensional color elements can be used either to implement the new mapping, or for very different purposes such as converting colors from perceptual into machine space. A new radial-displacement surface scaling also preserves relative color information by avoiding lightning-rod effects at the lightness extrema, and at the maximum-saturation point.

Claims

1. A method for presentation of a color image in a form viewable as a color image, using a color-image presentation device;

said method comprising the steps of;

interpreting first relative-position values of color parameters, within and throughout a first color element of at least two dimensions, as also being the same relative-position values of corresponding color parameters within a second color element of the same number of dimensions, with no intermediate color space other than normalized forms recited herebelow;

said first color element having a portion that is not contained within the second color element, and the second color element having a portion that is not contained within the first color element;

said interpreting step comprising the substeps of;

finding normalized forms of said first color-parameter values, normalized with respect to the two dimensions of the first color element, and

while treating the normalized forms of said first color-parameter values as also normalized relative-position values with respect to two dimensions of the second color element, reversing the normalization with respect to the second color element to determine unnormalized values within the second color element;

using said unnormalized values within the second color element to derive signals for controlling the color-image presentation device; and

then applying the signals to operate the color-image presentation device for presentation of the color image in said viewable form; and

wherein;

said first and second color elements are color surfaces;

the first and second color elements have respective shapes;

the interpreting and using steps comprise using simplified, geometrically more-regular approximations to the respective shapes of the first and second color elements;

said surfaces are hue pages; and

the approximation-using step comprises finding vertex coordinates for straight-line-bounded figures representing respective simplified shapes of the first and second color elements.

2. The method of claim 1, wherein:

the straight-line-bounded figures are triangles.

3. The method of claim 2, wherein the vertex coordinates represent respectively:

a maximum-saturation point;

a maximum-lightness point; and

a minimum-lightness point.

4. The method of claim 1, wherein:

said hue pages are for a common selected hue.

5. A method for presentation of a color image in a form viewable as a color image, using a color-image presentation device;

said method comprising the steps of;

interpreting relative-position values of color parameters, within and throughout a first color element of at least two dimensions, as also being the same relative-position values of corresponding color parameters within a second color element of the same number of dimensions, with no intermediate color space;

said first color element having a portion that is not contained within the second color element, and the second color element having a portion that is not contained within the first color element;

using said relative-position values within the second color element to derive signals for controlling the color-image presentation device; and

then applying the signals to operate the color-image presentation device for presentation of the color image in said viewable form; and

wherein;

the first color element is expressed in terms of a perceptual color space;

the second color element is expressed in terms of a device color space; and

the interpreting step translates perceptual-space values within the first color element into device-space values within the second color element;

the first color element is a highly simplified perceptual-space hue page of an output device;

the second color element is a less-highly simplified machine-space hue page, for the same hue, of the same output device; and

each of said relative-position values within the highly simplified perceptual hue page acts as a pointer into the less-highly simplified machine-space hue page of the same output device.

6. A method for presentation of a color image in a form viewable as a color image, using a color-image presentation device;

said method comprising;

interpreting relative-position values of color parameters, within and throughout a highly simplified perceptual-space hue page of an output device, as also being the same relative-position values of corresponding color parameters within a less-highly simplified machine-space hue page, of the same output device;

wherein each of said relative-position values within the highly simplified perceptual hue page acts as a pointer into the less-highly simplified machine-space hue page of the same output device; and

then applying pointed-to values in the less-highly simplified machine-space hue page to operate the color-image presentation device for presentation of the color image in said viewable form.

7. A method for processing information to control a color-image-presentation device that presents color images in a form viewable as color images;

said method comprising;

receiving or developing color-image specifications defining a desired image, at least some of said specifications being expressed in terms of a hue page;

finding vertex coordinates for a straight-line-bounded figure representing a simplified shape of the hue page;

characterizing the hue page in terms of the vertex coordinates;

expressing the specifications with reference to the vertex coordinates;

then manipulating the specifications as thus expressed with reference to the vertex coordinates; and

then applying the manipulated specifications to operate the presentation device for presentation of the image in a form viewable as a color image, including control of colors as seen in the image.

8. The method of claim 7, wherein:

the straight-line-bounded figure is a triangle.

9. The method of claim 8, wherein the vertex coordinates represent respectively:

a maximum-saturation point;

a maximum-lightness point; and

a minimum-lightness point.

10. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary and a gamut gray-scale axis, including surface-scaling a color point that is outside the gamut of the device;

said method comprising the steps of;

defining a point within the device gamut and significantly displaced away from the gamut gray-scale axis;

then constructing a line that joins an out-of-gamut color point with said defined point;

then determining the intersection of the constructed line with the gamut boundary;

then scaling the out-of-gamut point to said intersection to determine a surface-scaled color specification corresponding to said out-of-gamut point; and

applying the surface-scaled color specification, for the out-of-gamut point, to control presentation of the corresponding color by the color-presentation device.

11. The method of claim 10:

wherein said image comprises a multiplicity of such out-of-gamut points; and

further comprising the step of repeating the constructing, determining and scaling steps with respect to a multiplicity of other out-of-gamut points.

12. The method of claim 10, further comprising the step of:

using color points, of said image, that are inside the gamut of the device substantially without color-coordinate change.

13. The method of claim 10, wherein the applying step comprises:

storing in a lookup table each of said multiplicity of out-of-gamut color specifications with its corresponding new surface-scaled color specification;

then later receiving or developing a particular out-of-gamut color specification, for a particular portion of the image;

then finding the particular out-of-gamut color specification in the lookup table, and extracting from the lookup table the corresponding particular new surface-scaled color specification; and

then applying the found surface-scaled color specification, for the out-of-gamut point, to control presentation of the corresponding color by the color-presentation device.

14. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary and a gamut gray-scale axis, including surface-scaling a color point that is outside the gamut of the device;

said method comprising the steps of;

defining a point within the device gamut and significantly displaced away from the gamut gray-scale axis;

then constructing a line that joins an out-of-gamut color point with said defined point;

then determining the intersection of the constructed line with the gamut boundary;

then scaling the out-of-gamut point to said intersection to determine a surface-scaled color specification corresponding to said out-of-gamut point; and

applying the surface-scaled color specification, for the out-of-gamut point, to control presentation of the corresponding color by the color-presentation device; and

wherein the defining, constructing, determining, and scaling steps are performed by;

automatically finding the particular out-of-gamut color specification in a lookup table previously constructed to incorporate the defining, constructing, determining and scaling steps; and

extracting from the lookup table the corresponding particular new surface-scaled color specification, without performing anew said defining, constructing, determining and scaling steps at the time of said extracting step.

15. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary, including surface-scaling first and second colors respectively corresponding to first and second color points that are outside the gamut of the device;

said method comprising the steps of;

defining a first point within the device gamut;

then constructing a first line that joins the first out-of-gamut color point with said first defined point;

then determining a first intersection of the first constructed line with the gamut boundary;

then scaling the first out-of-gamut point to said first intersection to determine a first surface-scaled color specification corresponding to said first out-of-gamut point; and

applying the first surface-scaled color specification, for the first out-of-gamut point, to control presentation of the first corresponding color by the color-presentation device;

defining a second point within the same device gamut;

constructing a second line that joins the second out-of-gamut color point with said second defined point;

determining a second intersection of this second constructed line with the gamut boundary;

scaling the second out-of-gamut point to said second intersection to determine a second surface-scaled color specification corresponding to said second out-of-gamut point; and

applying the second surface-scaled color specification, for said second defined point, to control presentation of the corresponding second color by the color-presentation device.

16. The procedure of claim 15, wherein the applying step comprises:

storing in a lookup table each of said multiplicity of out-of-gamut color specifications with its corresponding new surface-scaled color specification;

then later receiving or developing a particular out-of-gamut color specification, for a particular portion of the image;

then finding the particular out-of-gamut color specification in the lookup table, and extracting from the lookup table the corresponding particular new surface-scaled specification; and

then applying the found particular new surface-scaled color specification to control presentation of a color by the color-presentation device.

17. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary, including surface-scaling first and second colors respectively corresponding to first and second color points that are outside the gamut of the device;

said method comprising the steps of;

defining a first point within the device gamut;

then constructing a first line that joins the first out-of-gamut color point with said first defined point;

then determining a first intersection of the first constructed line with the gamut boundary;

then scaling the first out-of-gamut point to said first intersection to determine a first surface-scaled color specification corresponding to said first out-of-gamut point; and

applying the first surface-scaled color specification, for the first out-of-gamut point, to control presentation of the first corresponding color by the color-presentation device;

defining a second point within the same device gamut;

constructing a second line that joins the second out-of-gamut color point with said second defined point;

determining a second intersection of this second constructed line with the gamut boundary;

scaling the second out-of-gamut point to said second intersection to determine a second surface-scaled color specification corresponding to said second out-of-gamut point; and

applying the second surface-scaled color specification, for said second defined point, to control presentation of the corresponding second color by the color-presentation device; and

wherein the defining, constructing, determining, and scaling steps are performed by;

automatically finding the particular out-of-gamut color specification in a lookup table previously constructed to incorporate the defining, constructing, determining and scaling steps; and

extracting from the lookup table the corresponding particular new surface-scaled specification, without performing anew said defining, constructing, determining and scaling steps at the time of said extracting step.

18. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary, including surface-scaling first and other colors respectively corresponding to plural color points that are outside the gamut of the device;

said method comprising the steps of;

defining a first point within the device gamut;

then constructing a first line that joins a first of said out-of-gamut color points with said first defined point;

then determining a first intersection of the first constructed line with the gamut boundary;

then scaling the first out-of-gamut point to said first intersection to determine a first surface-scaled color specification corresponding to said first out-of-gamut point; and

applying the first surface-scaled color specification, for the first out-of-gamut point, to control presentation of the first corresponding color by the color-presentation device;

defining a plurality of other points within the device gamut;

defining plural zones, with respect to the device gamut, that correspond to the points defined within the gamut;

for each particular out-of-gamut color point, determining the zone within which that particular out-of-gamut point falls;

for each particular out-of-gamut color point, selecting the point, defined within the gamut, that corresponds to the zone within which that particular point falls;

scaling that particular point to the intersection of the gamut boundary with a line constructed between that particular out-of-gamut point and the selected defined point; and

applying each thus-surface-scaled color point to control presentation of the corresponding out-of-gamut color by the color-presentation device.

19. The method of claim 18, wherein:

at least some boundaries of said zones are defined by lines constructed from each of the points, defined within the gamut, and extending outward past the gamut boundary.

20. The method of claim 19, wherein:

at least one boundary of said zones is defined by a line constructed to pass through a maximum-saturation element of the gamut.

21. The method of claim 19, wherein:

at least one boundary of said zones is defined by a lightness/darkness axis.

22. The method of claim 19, wherein each zone respectively is defined as an area bounded by:

the gamut boundary; and

one of said outward-extending lines; and

either;

another of said outward-extending lines, or

the lightness/darkness axis.

23. The method of claim 18, wherein:

out-of-gamut points in at least one of the zones are scaled to the gamut boundary by displacement parallel to a predetermined line for that zone.

24. The method of claim 18, wherein:

out-of-gamut points in at least one of the zones are scaled to the gamut boundary by displacement parallel to a zone boundary.

25. The procedure of claim 18, wherein the applying step comprises:

storing in a lookup table each of said multiplicity of out-of-gamut color specifications with its corresponding new surface-scaled color specification;

then later receiving or developing a particular out-of-gamut color specification, for a particular portion of the image;

then finding the particular out-of-gamut color specification in the lookup table, and extracting from the lookup table the corresponding particular new surface-scaled specification; and

then applying the found particular new surface-scaled color specification to control presentation of the corresponding color by the color-presentation device.

26. A method of presenting color images using a color-presentation device that has a gamut and a gamut boundary, including surface-scaling first and other colors respectively corresponding to plural color points that are outside the gamut of the device;

said method comprising the steps of;

defining a first point within the device gamut;

then constructing a first line that joins a first of said out-of-gamut color points with said first defined point;

then determining a first intersection of the first constructed line with the gamut boundary;

then scaling the first out-of-gamut point to said first intersection to determine a first surface-scaled color specification corresponding to said first out-of-gamut point; and

applying the first surface-scaled color specification, for the first out-of-gamut point, to control presentation of the first corresponding color by the color-presentation device;

defining a plurality of other points within the device gamut;

defining plural zones, with respect to the device gamut, that correspond to the points defined within the gamut;

for each particular out-of-gamut color point, determining the zone within which that particular out-of-gamut point falls;

for each particular out-of-gamut color point, selecting the point, defined within the gamut, that corresponds to the zone within which that particular point falls;

scaling that particular point to the intersection of the gamut boundary with a line constructed between that particular out-of-gamut point and the selected defined point; and

applying each thus-surface-scaled color point to control presentation of the corresponding out-of-gamut color by the color-presentation device wherein the defining, constructing, determining, and scaling steps are performed by;

automatically finding the particular out-of-gamut color specification in a lookup table previously constructed to incorporate the defining, constructing, determining and scaling steps; and

extracting from the lookup table the corresponding particular new surface-scaled specification, without performing anew any of said defining, constructing, determining and scaling steps at the time of said extracting step.

27. A method for presentation of a color image in a form viewable as a color image, using an output color-image presentation device that has a color gamut, and based upon initial color specifications developed for use in an input color-presentation device that has a different color gamut;

said initial specifications being expressed in terms related to control of the input device; and

said method comprising;

based upon the initial specifications expressed in terms related to control of the input device, establishing for the corresponding color in perceptual terms, presented by the input device;

the hue of said corresponding color, and

two other coordinates of said corresponding color;

under the control of said established hue, determining working coordinates of a saturated color for use in defining a simplified hue-page model at that hue;

said determining being performed by reference to a tabulation of saturated-color working coordinates as a function of hue;

forming ratios of said two other coordinates with said saturated-color working coordinates to find a relative position, within the simplified hue-page model at said established hue, of said corresponding color; and

applying the found relative position to operate the output device for presentation of a color image in a form viewable as a color image.

28. The method of claim 27, wherein:

said tabulation also contains gray-scale extrema as a function of hue; and

said ratio-forming step further comprises using said gray-scale extrema in forming said ratios.

29. The method of claim 27, wherein:

said saturated-color working-coordinate determining step comprises interpolation between saturated-color coordinates of two adjacent tabulated hues that straddle said established hue.

30. The method of claim 27, wherein:

the working-coordinate determining step determines coordinates of a saturated color which the output device can produce at that hue; and

the applying step comprises the step of using said found relative position to find a relative position within a less-simplified hue-page model applicable to a relatively wide range of hue, to obtain machine-space parameters other than hue.

31. The method of claim 30, wherein the applying step further comprises the steps of:

combining said machine-space parameters other than hue with said determined hue to derive new color specifications for control of the output device for the particular desired image; and

applying the new color specifications to operate the output device for presentation of said image in a form viewable as a color image.

32. The method of claim 30, wherein:

said relative-position using step comprises using, as said less-simplified hue-page model, a single hue page representative of all hues.

33. The method of claim 32, wherein:

said single hue page is a magenta hue page.

34. The method of claim 32, wherein:

said single hue page has on the order of fifty-five data points.

35. The method of claim 30, wherein:

said relative-position using step comprises selecting, under control of said established hue and for use as said less-simplified hue-page model, one of a group of about six to twelve hue pages that are representative of all hues.

36. The method of claim 30, wherein:

both the simplified and the less-simplified hue-page models are normalized with respect to parameter pairs representing gray-scale position and saturation.

37. The method of claim 27, wherein:

the working-coordinate determining step comprises determining coordinates of a saturated color which the input device can produce at the established hue;

the applying step comprises the step of using said found relative position to find a relative position within a comparably simplified hue-page model defined by coordinates of a saturated color which the output device can produce at a substantially like hue, to obtain machine-space parameters other than hue.

38. The method of claim 37, wherein:

both simplified hue-page models are normalized with respect to parameter pairs representing gray-scale position and saturation.