Methods and Systems for Hue Adjustment

• US 20100195173A1
• Filed: 02/03/2009
• Published: 08/05/2010
• Est. Priority Date: 02/03/2009
• Status: Active Grant

• Current Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Dalrymple, John C.
• Granted Patent: US 8,027,070 B2
• Time in Patent Office: Days
• US Class Current: 358/520
• CPC Class Codes: G06T 1/00 General purpose image data processing
• CPC Class Codes: H04N 1/6075 Corrections to the hue

Abstract

Aspects of the present invention relate to systems and methods for color image hue shifting. Some aspects relate to processes by which reference hue values and corresponding hue shift values are used to modify color hue values in a non-perceptually-uniform color space. Some aspects relate to processes that generate a hue shift table for modifying image hue values.

Claims

1. A method for shifting the hue of an input color represented by numeric input coordinates of an input color space, thereby creating an output color represented by numeric output coordinates of an output color space, said method comprising:

a) receiving a plurality of hue values and corresponding hue shift values at a computing device, wherein said values are defined by at least one coordinate in a non-perceptually-uniform color space (NPU space), said NPU space being indexed by a hue coordinate, HH, together with at least one other coordinate;

b) expressing the hue attribute of said input color as a first NPU color represented in the coordinates of said NPU space;

c) applying said hue shift values to said first NPU color based on said hue values, thereby creating a second NPU color having a shifted hue attribute;

d) creating a first PU color by representing said input color in the coordinates of a PU space, said PU space being a perceptually uniform color space indexed by a hue coordinate, h, together with at least one other coordinate;

e) creating a second PU color by representing said second NPU color in the coordinates of said PU space;

f) creating a third PU color by combining the hue coordinate of said second PU color together with another coordinate of said first PU color; and

g) creating said output color by converting said third PU color to said output color space.

2. A method as described in claim 1 wherein said expressing said hue attribute of said input color as a first NPU color comprises converting said input color to a color space comprising a hue coordinate and a lightness coordinate, and replacing said lightness coordinate with a constant lightness value that is approximately one half of a maximum lightness value of a reference color volume.

3. A method as described in claim 1 wherein said expressing said hue attribute of said input color as a first NPU color comprises converting said input color to a color space comprising a hue coordinate and a chroma coordinate, and replacing said chroma coordinate with a constant chroma value, thereby creating a constrained input color, wherein said constant chroma value is sufficiently low that said constrained input color is located inside a reference color volume.

4. A method as described in claim 1 wherein said expressing said hue attribute of said input color as a first NPU color comprises:

a) converting said input color to a color space comprising a hue coordinate, a chroma coordinate and a lightness coordinate; and

b) replacing said lightness coordinate with a constant lightness value that is approximately one half of a maximum lightness value of a reference color volume and replacing said chroma coordinate with a constant chroma value, thereby creating a constrained input color, wherein said constant chroma value is sufficiently low that said constrained input color is located inside said reference color volume.

5. A method as described in claim 4 further comprising converting said constrained input color to said NPU color space.

6. A method as described in claim 1 wherein said creating a third PU color comprises combining the hue coordinate of said second PU color together with a lightness coordinate and a chroma coordinate of said first PU color.

7. A method as described in claim 1 wherein the coordinate systems of said input color space and said output color space are substantially similar and comprise a luminance coordinate.

8. A method as described in claim 7 further comprising replacing a luminance-related attribute of said output color with a luminance-related attribute of said input color.

9. A method for shifting the hue of an input color represented by numeric input coordinates of an input color space, thereby creating an output color represented by numeric output coordinates of an output color space, said method comprising:

a) receiving a plurality of hue values and hue shift values at a computing device, wherein said hue values and said hue shift values are defined by coordinates in a colorimetry-based color space;

b) applying a hue scale conversion process to said hue values and said hue shift values, thereby creating converted hue values and converted hue shift values;

c) expressing the hue attribute of said input color as a first non-perceptually-uniform (NPU) color represented in the coordinates of an NPU color space;

d) applying said converted hue shift values to said first NPU color based on said converted hue values, thereby creating a second NPU color having a shifted hue attribute;

e) creating a first perceptually uniform (PU) color by representing said input color in the coordinates of a PU color space, the PU space comprising a perceptually uniform color space indexed by a hue coordinate, h, together with at least one other coordinate;

f) creating a second PU color by representing said second NPU color in the coordinates of said PU space;

g) creating a third PU color by combining the hue coordinate of said second PU color together with another coordinate of said first PU color; and

h) creating said output color by converting said third PU color to said output color space.

10. A method as described in claim 9 further comprising:

a) expressing a set of initial hue coordinates as hue mapping colors represented in the coordinates of said NPU space;

b) creating PU hue mapping colors by representing said hue mapping colors in the coordinates of said PU space;

c) extracting hue coordinates of said PU hue mapping colors; and

d) relating said extracted hue coordinates to corresponding initial hue coordinates, thereby creating a hue scale conversion lookup table used in said hue scale conversion process.

11. A method as described in claim 9 wherein said expressing the hue attribute of said input color as a first non-perceptually-uniform (NPU) color comprises blending an achromatic color with said hue mapping color in a linear light color space.

12. A method as described in claim 11 wherein said representing said input color in the coordinates of said PU space comprises blending an achromatic color with said hue input color in a linear light color space.

13. A method as described in claim 9 wherein said expressing the hue attribute of said input color as a first non-perceptually-uniform (NPU) color comprises:

a) converting said PU hue mapping colors to a color space comprising a hue coordinate and a lightness coordinate, and

b) replacing said lightness coordinate with a constant lightness value that is approximately one half of a maximum lightness value of a reference color volume.

14. A method as described in claim 9 wherein said expressing the hue attribute of said input color as a first non-perceptually-uniform (NPU) color comprises converting said input color to a color space comprising a hue coordinate and a chroma coordinate, and replacing said chroma coordinate with a constant chroma value, thereby creating a constrained input color, wherein said constant chroma value is sufficiently low that said constrained input color is located inside a reference color volume.

15. A method as described in claim 9 wherein said expressing the hue attribute of said input color as a first non-perceptually-uniform (NPU) color comprises converting said PU hue mapping colors to a color space comprising a hue coordinate, a chroma coordinate and a lightness coordinate, replacing said lightness coordinate with a constant lightness value that is approximately one half of a maximum lightness value of a reference color volume and replacing said chroma coordinate with a constant chroma value thereby creating a constrained input color, wherein said constant chroma value is sufficiently low that said constrained input color is located inside said reference color volume.

16. A method for color processing of colors represented by a plurality of numeric input color coordinates of an input color space, thereby creating a plurality of numeric output coordinates of an output color space, said method comprising:

a) receiving a plurality of hue values and corresponding hue shift values at a computing device, wherein said hue values and said corresponding hue shift values are defined by coordinates in a colorimetry-based color space;

b) applying a hue scale conversion process to said hue values and said hue shift values, thereby creating converted hue values and converted hue shift values;

c) expressing the hue attributes of said input color coordinates as a plurality of first NPU colors represented by first NPU color coordinates of said NPU space;

d) converting said NPU color coordinates to a color space comprising a hue coordinate, a chroma coordinate and a lightness coordinate, thereby creating perceptually-uniform cylindrical color space (PUCCS) coordinates for each of said NPU colors,

e) replacing said lightness coordinates for each of said PUCCS coordinates with a constant lightness value that is approximately one half of a maximum lightness value of a reference color volume;

f) replacing said chroma coordinates for each of said PUCCS coordinates with a constant chroma value, thereby creating constrained input colors,

g) wherein said constant chroma value is sufficiently low that said constrained input colors are located inside a reference color volume;

h) representing said constrained input colors in said NPU color space, thereby creating constrained NPU input colors;

i) applying said converted hue shift values to said constrained NPU input colors based on said converted hue values, thereby creating second NPU color coordinates having a shifted hue attribute;

j) creating first perceptually-uniform (PU) color coordinates by representing said input color coordinates in the coordinates of a PU space, said PU space comprising a perceptually uniform color space indexed by a hue coordinate, h, together with at least one other coordinate;

k) creating second PU color coordinates by representing said second NPU color coordinates in the coordinates of said PU space;

l) creating third PU color coordinates by combining hue attributes of said second PU color coordinates together with other coordinates of said first PU color; and

m) creating said output color coordinates by converting said third PU color coordinates to said output color space.

17. A method as described in claim 16 further comprising:

a) expressing a set of initial hue coordinates as hue mapping colors represented in the coordinates of said NPU space;

b) creating PU hue mapping colors by representing said hue mapping colors in the coordinates of said PU space;

c) extracting hue coordinates of said PU hue mapping colors;

d) relating said extracted hue coordinates to corresponding initial hue coordinates, thereby creating a hue scale conversion lookup table; and

e) wherein said converting comprises the application of said hue scale conversion lookup table.

18. A method as described in claim 16 wherein said expressing the hue attributes of said input color coordinates comprises blending an achromatic color with said input color coordinates in a linear light color space.

19. A method as described in claim 16 wherein said applying a hue scale conversion process comprises blending an achromatic color with said hue mapping colors in a linear light color space.

20. A method as described in claim 16 further comprising replacing luminance-related attributes of said output color coordinates with corresponding luminance-related attributes of said input color coordinates.