Interpolation of Color Gamut For Display on Target Display

• US 20120229495A1
• Filed: 03/06/2012
• Published: 09/13/2012
• Est. Priority Date: 03/08/2011
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Longhurst, Peter W.
• Granted Patent: US 8,767,004 B2
• Time in Patent Office: Days
• US Class Current: 345/590
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 5/026 Control of mixing and/or overlay of colours in general G09G5/022 and G09G5/024 take precedence
• CPC Class Codes: G09G 5/377 for mixing or overlaying two or more graphic patterns G09G5/02, G09G5/397 take precedence
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85

Abstract

Output image data for display on a target display having a target gamut is generated from first and second input image data. The first and second input image data may be color timed for display on different types of display. Chromaticity values in the output image data may be generated by interpolation using an interpolation parameter derived from the target gamut and gamuts associated with the first and second image data.

Claims

1. A method for generating an output image for display on a target display associated with a target gamut, the method comprising:

obtaining first and second image data depicting the image, the first and second image data respectively associated with first and second gamuts;

determining primary interpolation lines through corresponding pairs of primaries of the first and second gamuts;

generating first and second bracketing gamuts, the first and second bracketing gamuts having primaries on the primary interpolation lines, the first bracketing gamut containing the target gamut and the second bracketing gamut contained within the target gamut;

generating a first interpolation parameter based on the locations of the primaries of the bracketing gamuts along the primary interpolation lines; and

,

generating the output image by interpolating between chrominance values of the first and second image data using the first interpolation parameter.

2. A method according to claim 1 wherein the first bracketing gamut is a smallest gamut having primaries on the primary interpolation lines that entirely contains the target gamut.

3. A method according to claim 2 wherein the second bracketing gamut is a largest gamut having primaries on the primary interpolation lines that is contained within the target gamut.

4. A method according to claim 3 wherein generating the first interpolation parameter comprises determining a first value based on a minimum proportion of a distance along the primary interpolation lines for the primaries of the first bracketing gamut and determining a second value based on a maximum proportion of a distance along the primary interpolation lines for the primaries of the second bracketing gamut and determining the first interpolation parameter based at least in part on the first and second values.

5. A method according to claim 4 wherein determining the first interpolation parameter comprises averaging the first and second values.

6. A method according to claim 5 comprising identifying pixels in the output image data that are outside of the target gamut and adjusting values of such pixels to be in the target gamut.

7. A method according to claim 6 wherein adjusting the values of the pixels comprises clipping values of the pixels to a boundary of the target gamut.

8. A method according to claim 5 comprising transforming the output image data to a RGB format native to the target display for which the target gamut is defined by maximum values for R, G, and B coordinates wherein the adjusting comprises clipping pixel values to the corresponding maximum values for the R, G, and B coordinates.

9. A method according to claim 5 comprising representing the first and second input image data in a format wherein pixel values comprise a luminance value and a pair of chrominance values and wherein the method comprises generating luminance values for the output image data by interpolating between corresponding luminance values of the first and second image data.

10. A method according to claim 1 comprising representing the first and second input image data in a format wherein pixel values comprise a luminance value and a pair of chrominance values and wherein the method comprises generating luminance values for the output image data by interpolating between corresponding luminance values of the first and second image data using a luminance interpolation parameter.

11. A method according to claim 10 comprising performing interpolating between corresponding chrominance values of the first and second image data using a chrominance interpolation parameter different from the luminance interpolation parameter.

12. A method according to claim 11 comprising receiving metadata specifying the first and second gamuts.

13. A method according to claim 11 wherein one or more primaries of the target gamut do not lie on any of the primary interpolation lines.

14. A method according to claim 1 comprising receiving metadata specifying the first and second gamuts.

15. Image processing apparatus comprising:

an interpolator configured to generate chromaticity values for output image data by interpolating between corresponding chromaticity values for first and second input image data according to a first interpolation parameter; and

,

an interpolation parameter calculator configured to determine the first interpolation parameter based on first and second gamuts respectively associated with the first and second image data and on a target gamut associated with a target display.

16. Image processing apparatus according to claim 15 wherein the interpolation parameter calculator is configured to determine the first interpolation parameter by:

determining primary interpolation lines through corresponding pairs of primaries of the first and second gamuts;

generating first and second bracketing gamuts, the first and second bracketing gamuts having primaries on the primary interpolation lines, the first bracketing gamut containing the target gamut and the second bracketing gamut contained within the target gamut; and

generating the first interpolation parameter based on the locations of the primaries of the bracketing gamuts along the primary interpolation lines.

17. Image processing apparatus according to claim 16 comprising one or more inputs for receiving the first and second image data, the apparatus comprising a color space converter configured to convert the first and second image data into a common color space.

18. Apparatus according to claim 17 wherein the common color space comprises a color space in which pixel values comprise a luminance value and a plurality of chrominance values.

19. Apparatus according to claim 18 wherein the first bracketing gamut is a smallest gamut having primaries on the primary interpolation lines that entirely contains the target gamut.

20. Apparatus according to claim 19 wherein the second bracketing gamut is a largest gamut having primaries on the primary interpolation lines that is contained within the target gamut.

21. Apparatus according to claim 20 wherein the interpolation parameter calculator is configured to generate the first interpolation parameter by:

determining a first value based on a minimum proportion of a distance along the primary interpolation lines for the primaries of the first bracketing gamut and determining a second value based on a maximum proportion of a distance along the primary interpolation lines for the primaries of the second bracketing gamut and determining the first interpolation parameter based at least in part on the first and second values.

22. Apparatus according to claim 21 wherein the interpolation parameter calculator is configured to generate the first interpolation parameter by averaging the first and second values.

23. Apparatus according to claim 16 comprising a gamut mapping unit connected to receive the output image data and to map pixel values in the output image data for pixels that are out-of-gamut for the target gamut into the target gamut.