Method and system for improving compressed image chroma information

A method comprising:

• receiving a compressed video image comprising a luminance channel (Y), a first chroma channel (V) and a second chroma channel (U);
• accessing, at the decoder, at least a luminance quantization parameter value;
• characterized by
• receiving a first image-region-dependent chroma quantization parameter bias value;
• utilizing, with the decoder, the luminance quantization parameter value and the first image-region-dependent chroma quantization parameter bias value to determine a first chroma quantization parameter value by adding the first image-region-dependent chroma quantization parameter bias value to the luminance quantization parameter value;
• and
• decompressing an image region of the video image using the luminance quantization parameter value and the first chroma quantization parameter value,
• wherein the first chroma quantization parameter value is less than or equal to a predetermined maximum value,
• wherein the first chroma quantization parameter value is no less than one, and
• wherein the first chroma quantization parameter value is determined for the first chroma channel (V).

A method comprising:

• receiving, at the decoder, at least a luminance QP (quantization parameter) value and a first image-region-dependent chroma QP bias value, the first image-region-dependent chroma QP bias value was determined at an encoder and signaled from the encoder to the decoder, wherein the decoder comprises a luminance channel, a first chroma channel and a second chroma channel;
• utilizing, with the decoder, the luminance QP value and the first image-region-dependent chroma QP bias value to determine the first chroma QP value by adding the first image-region-dependent chroma QP bias value to the luminance QP value;
• decompressing an image region of a video image using the luminance QP value and the first chroma QP value, wherein the first chroma QP value is less than a predetermined maximum value and greater than a predetermined minimum value, and
• wherein the first chroma QP value is determined for the first chroma channel.