Producing an extended color gamut luminance-chrominance digital image from a captured image

1. A method for producing an extended color gamut luminance-chrominance digital image from sensor color exposure values for a captured digital image comprising:

a) using a color image sensor to provide sensor color exposure values for an original scene;

b) determining intermediate extended gamut scene RGB image values for the captured digital image from the sensor color exposure values by representing the scene colors in terms of a first set of extended gamut RGB primaries;

c) determining intermediate extended gamut rendered RGB image values by applying a rendering transformation to the intermediate extended gamut scene RGB image values, wherein the extended gamut rendered RGB image values are a representation of the colors of a rendered image in terms of the first set of extended gamut RGB primaries;

d) determining extended range output RGB image values from the intermediate extended gamut rendered RGB image values by transforming from the first set of extended gamut RGB primaries to a second set of RGB primaries associated with an output image display device to produce extended range output RGB image values, wherein the extended range output RGB image values include values outside the range that can be displayed on the output image display device; and

e) producing an extended color gamut luminance-chrominance digital image by transforming the extended range output RGB image values to a luminance-chrominance representation.

2. The method of claim 1 wherein the captured digital image is captured by a digital camera.

3. The method of claim 1 wherein the captured digital image is captured by scanning a film with a film scanner.

4. The method of claim 1 wherein the captured digital image is captured by scanning a print with a print scanner.

5. The method of claim 1 where the first set of extended gamut RGB primaries are selected to have an associated chromaticity gamut sufficiently large to encompass the gamut of real world surface colors.

6. The method of claim 1 wherein the first set of extended gamut RGB primaries are selected so as to substantially minimize hue shifts that are induced when a rendering transformation comprised of a channel-independent tone scale function is applied to the intermediate extended gamut scene RCJB image values.

7. The method of claim 1 wherein the extended range output RGB image values retain negative output RGB image values.

8. The method of claim 1 wherein the extended range output RGB image values retain output RGB image values larger than those associated with the output image display device whitepoint.

9. The method of claim 1 wherein step e) includes the steps:

i) determining nonlinear extended range output RGB image values by applying a channel-independent nonlinear transformation to the extended range output RGB image values; and

ii) applying a luminance-chrominance matrix transformation to the nonlinear extended range output RGB image values.

10. The method of claim 1 further including the step of including the extended color gamut luminance-chrorninance digital image in an image file.

11. The method of claim 10 further including the step of compressing the extended color gamut luminance-chrominance digital image to reduce the size of the image file.

12. The method of claim 10 further including the step of reading the extended color gamut luminance-chrominance digital image from the image file.

13. The method of claim 12 further including the step of determining a limited gamut output RGB digital image from the extended color gamut luminance-chrominance digital image.

14. The method of claim 13 wherein the limited gamut output RGB digital image is determined by applying an inverse luminance-chrominance matrix transformation to the extended color gamut luminance-chrominance digital image to compute nonlinear extended range output RGB image values, and then clipping the nonlinear extended range output RGB image values to the gamut of an output image display device.

15. The method of claim 14 where the nonlinear extended range output RGB image values are clipped to the gamut of the output image display device by clipping any negative nonlinear extended range output RGB image values and any nonlinear extended range output RGB image values larger than those associated with a whitepoint of the output image display device.

16. The method of claim 1 wherein the second set of RGB primaries are the sRGB primaries.

17. The method of claim 16 wherein the values outside the range that can be displayed on the output image display device correspond to extended sRGB values where at least one of the R, G or B values is a negative number.

18. The method of claim 16 further including the step of compressing the luminance and chrominance values.

19. The method of claim 18 wherein the compression is JPEG compression.

20. The method of claim 1 wherein step b) is provided by a matrix transformation.

21. The method of claim 1 wherein step d) is provided by a matrix transformation.

22. The method of claim 1 wherein steps b) and d) are provided by matrix transformations, and the rendering transformation in step c) is provided by a channel-independent tone scale function.

23. The method of claim 1 wherein a plurality of the steps are combined and provided by a three-dimensional look-up table.

24. A digital camera for providing an extended color gamut luminance-chrominance digital image from an image captured by the digital camera, comprising:

a) a color image sensor for capturing the image of an original color scene and providing an original color signal;

b) an image processor for processing the original color signal to produce an extended color gamut luminance-chrominance digital image, wherein the image processor converts the original color signal to intermediate extended gamut scene RGB color signals corresponding to a first set of extended gamut RGB primaries, applies a rendering transformation to the intermediate extended gamut scene RGB color signals to produce intermediate extended gamut rendered RGB color signals, transforms the intermediate extended gamut rendered RGB color signals to produce extended range output RGB color signals corresponding to a second set of RGB primaries associated with an output image display device, and uses the extended range output RGB color signals to provide the extended color gamut luminance-chrominance digital image, said digital image including at least one color value outside the range that can be displayed on the output image display device; and

c) a digital storage device for storing the extended color gamut lurninance-chrominance digital image.

25. The digital camera of claim 24 wherein the second set of RGB primaries is the set of sRGB primaries.

26. The digital camera of claim 25 wherein the values outside the range that can be displayed on the output image display device correspond to sRGB values where at least one of the R, G or B values is a negative number.

27. The digital camera of claim 24 further including a means for compressing the luminance and chrominance values.

28. The digital camera ot claim 27 wherein the compression means uses JPEG compression.