Techniques for advanced chroma processing

A method for processing image data comprising pixels having a luma component value, a first chroma component value and a second chroma component value, comprising:

• determining min and max chroma limit values based on the luma component values of input image data according to relationships among the luma and chroma components;
• transform the first chroma component values by performing a processing operation in a first direction to produce first resultant values of the first chroma component;
• clipping the first resultant values of the first chroma component that are beyond the min and max chroma limit values to produce second resultant values of the first chroma component;
• transform the second resultant values of the first chroma component by performing the processing operation in a second direction to produce third resultant values of the first chroma component;
• and
• clipping the third resultant values of the first chroma component that are beyond the min and max chroma limit values to produce fourth resultant values of the first chroma component.

A processing method for image data having a luma component, a first chroma component and a second chroma component, comprising:

• performing a processing operation on the luma component of the image data;
• determining first min and max limit values for the respective chroma component based on the processed luma component according to relationships among the luma and chroma components;
• clipping those values of a first chroma component that are beyond the first min and max limit values;
• and
• transforming the values of the first chroma component following the clipping by performing the processing operation;
• determining second min and max limit values for the respective chroma component based on the processed luma component and the processed first chroma component according to relationships among the luma and chroma components;
• clipping those values of a second chroma component that are beyond the second min and max limit values;
• and
• transforming the values of the second chroma component following the clipping of the second chroma component by performing the processing operation.

A video coder, comprising:

• a luminance and a pair of chrominance coders to code respective components of image data where coding includes quantization;
• a limit estimator, configured to determine min and max limit values for first and second chroma components based on coded luma data from the luminance coder and according to relationships among the luma and chroma components;
• and
• a pair of clipping units, each clipping unit configured to clip coded output from a respective chroma coder based on the respective min and max limit values from the limit estimator.

A non-transitory computer readable media comprising instructions that, when executed by a processor, cause:

• determining, from image data comprising pixels having a luma component value, a first chroma component value and a second chroma component value, min and max chroma limit values based on the luma component values of input image data according to relationships among the luma and chroma components;
• transform the first chroma component values by performing a processing operation in a first direction to produce first resultant values of the first chroma component;
• clipping the first resultant values of the first chroma component that are beyond the min and max chroma limit values to produce second resultant values of the first chroma component;
• transform the second resultant values of the first chroma component by performing the processing operation in a second direction to produce third resultant values of the first chroma component;
• and
• clipping the third resultant values of the first chroma component that are beyond the min and max chroma limit values to produce fourth resultant values of the first chroma component.