High precision encoding and decoding of video images

A method for decoding a picture of a wide dynamic range, the method being performed with a video coding system comprising at least a decoder, the method comprising:

• accessing a compressed picture, wherein the compressed picture comprises coded blocks of transformed pixel values using a first set of levels of a set of representational quantization parameter (QP) codes that have been extended into a wider second set of levels using a non-linear mapping function, wherein the set of representational quantization parameter codes comprises at least 32 values, wherein the wider second set of levels depends on a bit-depth of the picture and corresponds to a set of determined quantization parameter (QPd) values, and wherein the wider second set of levels utilizes a mapping of respective representational quantization parameter codes to corresponding determined quantization parameter values;
• for a block of transformed pixel values of the picture, selecting, with the decoder, at least one representational quantization parameter code from the set of representational quantization parameter codes;
• for the block of transformed pixel values of the picture, using the mapping to select at a determined quantization parameter value corresponding to the selected representational quantization parameter code;
• and
• dequantizing, with the decoder, the block of transformed pixel values of the picture using the selected determined quantization parameter value.

An encoder configured to code a picture of a wide dynamic range, the encoder being operable with a video coding system, the encoder being operable to:

• determine a set of representational quantization parameter (QP) codes having at least 32 values, wherein the set of representation quantization parameters codes are within a first set of levels;
• extend the first set of levels of said representational quantization parameter codes into a second set of levels using a non-linear mapping function, wherein the second set of levels is wider than the first set of levels, depends on an image bit depth, and corresponds to a set of determined quantization parameter (QPd) values, and wherein extending the first set of levels of the representation quantization parameter codes comprises a mapping of respective representational quantization parameter codes to corresponding determined quantization parameter values;
• for a block of transformed pixel values of the picture, select a representational quantization parameter code from the set of representational quantization parameter codes;
• for the block of transformed pixel values of the picture, use the mapping to select a determined quantization parameter value for the selected representational quantization parameter code;
• and
• quantize the block of transformed pixel values of the picture, with the encoder, using the selected determined quantization parameter value.

A decoder configured to decode a picture of a wide dynamic range, the decoder being operable with a video coding system, the decoder being operable to:

• access a compressed picture, wherein the compressed picture comprises coded blocks of transformed pixel values using a first set of levels of a set of representational quantization parameter (QP) codes that have been extended into a wider second set of levels using a non-linear mapping function, wherein the set of representational quantization parameter codes comprises at least 32 values, wherein the wider second set of levels depends on a bit-depth of the picture and corresponds to a set of determined quantization parameter (QPd) values, and wherein the wider second set of levels utilizes a mapping of respective representational quantization parameter codes to corresponding determined quantization parameter values;
• for a block of transformed pixel values of the picture, select, with the decoder, at least one representational quantization parameter code from the set of representational quantization parameter codes;
• for the block of transformed pixel values of the picture, use the mapping to select at a determined quantization parameter value corresponding to the selected representational quantization parameter code;
• and
• dequantize, with the decoder, the block of transformed pixel values of the picture using the selected determined quantization parameter value.

A computer program product, stored on a non-transitory computer-readable medium, for decoding pictures of a wide dynamic range, the computer program being operable with a video coding system comprising at least a decoder, the computer program comprising instructions for causing a computer to:

• access a compressed picture, wherein the compressed picture comprises coded blocks of transformed pixel values using a first set of levels of a set of representational quantization parameter (QP) codes that have been extended into a wider second set of levels using a non-linear mapping function, wherein the set of representational quantization parameter codes comprises at least 32 values, wherein the wider second set of levels depends on a bit-depth of the picture and corresponds to a set of determined quantization parameter (QPd) values, and wherein the wider second set of levels utilizes a mapping of respective representational quantization parameter codes to corresponding determined quantization parameter values;
• for a block of transformed pixel values of the picture, select, with the decoder, at least one representational quantization parameter code from the set of representational quantization parameter codes;
• for the block of transformed pixel values of the picture, use the mapping to select a determined quantization parameter value corresponding to the selected representational quantization parameter code;
• and
• dequantize, with the decoder, the block of transformed pixel values of the picture using the selected determined quantization parameter value.

A method to decode a picture with a decoder, the picture comprising coded blocks of transformed pixel values, the method comprising:

• for a block of transformed pixel values of the picture, receiving a representational quantization parameter code from a first set of levels of representational quantization parameter codes, the first set of levels of representational quantization parameter codes having at least 32 values;
• mapping using a non-linear mapping function the received representational quantization parameter code from the first set of levels to a second set of levels for determined quantization parameter values, the second set of levels differing in number of levels from the first set of levels;
• and
• dequantizing the block of transformed pixel values of the picture using the determined quantization parameter.