Bit depth variable for high precision data in weighted prediction syntax and semantics
Particular embodiments provide a variable, BitDepth, that may be set at a value based on a number of bits used to represent pixels in pictures of a video. The variable may be used in syntax elements in HEVC, such as the HEVC range extension, but other coding standards may be used. By using the variable, different resolutions for the video may be accommodated during the encoding and decoding process. For example, the number of pixels in the pictures may be represented by 8 bits, 10 bits, 12 bits, or another number of bits depending on the resolution. Using the BitDepth variable in the syntax provides flexibility in the motion estimation and motion compensation process. For example, syntax elements used in the weighted prediction process may take into account different numbers of bits used to represent the pictures.
1. A method for decoding a bitstream, the method comprising:
identifying one or more weight flags signaled in the bitstream that indicates presence of weighting factors for at least one of a luma component and/or a chroma component;
determining a first weighting factor for performing weighted prediction for a current unit of a current picture the first weighting factor for weighting pixels of a first reference unit of a first reference picture when performing motion compensation for the current unit;
determining a second weighting factor for weighting pixels of a second reference unit of a second reference picture when performing motion compensation for the current unit,
wherein when weighting factors for a luma component is present:
determining from a signaled delta_luma_weight_l0 syntax element a difference of the first weighting factor and the second weighting factor applied to a luma prediction value for list 0 prediction using a variable RefPicList0[i] for a first luma component, and
deriving a variable LumaWeightL0 associated with the luma component weighting factors, wherein when the one or more weight flags indicates presence of the weighting factor for a luma component, LumaWeightL0 is derived to be equal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of −(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive,
wherein luma_log2_weight_denom is a base 2 logarithm of a denominator for all luma weighting factors, and BitDepthy is a bit depth for the luma component of the respective reference picture; and
wherein when weighting factors for a chroma component is present:
determining from a delta_chroma_weight_l0[i][j] syntax element a difference of the first weighting factor and the second weighting factor applied to a chroma prediction value for list 0 prediction using a variable RefPicList0[i] with j equal to 0 for Cb or j equal to 1 for Cr for a second component; and
deriving a variable ChromaWeightL0 associated with the chroma component weighting factor, wherein when the one or more weight flags indicates presence of the weighting factor for a chroma component, ChromaWeightL0 is derived to be equal to ((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))−+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)), ((1<<BitDepthc−1)−1), inclusive,
wherein delta_chroma_log2_weight_denom is a difference of a base 2 logarithm of a denominator for all chroma weighting factors, and BitDepthc is a bit depth for the chroma component of the respective reference picture;
wherein the delta_chroma_weight_l0[i][j] syntax element is within the range set by the ChromaWeightL0, and
wherein the second component comprises a chroma component of the first reference unit or the second reference unit;
wherein a determination of at least one value present in a pred_weight_table is dependent on a variable ChromaArrayType;
wherein said delta_luma_weight_l0 syntax element is included in said pred_weight_table.
2. One or more computer-readable memory or storage devices storing encoded data as part of a bitstream, the encoded data being organized to facilitate decoding by a video decoder performing operations, the video decoder being implemented using memory and one or more processing units, the operations comprising:
identifying one or more weight flags signaled in the bitstream that indicates presence of weighting factors for at least one of a luma component and/or a chroma component;
determining a first weighting factor for performing weighted prediction for a current unit of a current picture the first weighting factor for weighting pixels of a first reference unit of a first reference picture when performing motion compensation for the current unit;
determining a second weighting factor for weighting pixels of a second reference unit of a second reference picture when performing motion compensation for the current unit,
wherein when weighting factors for a luma component is present:
determining from a signaled delta_luma_weight_l0 syntax element a difference of the first weighting factor and the second weighting factor applied to a luma prediction value for list 0 prediction using a variable RefPicList0[i] for a first luma component, and
deriving a variable LumaWeightL0 associated with the luma component weighting factors, wherein when the one or more weight flags indicates presence of the weighting factor for a luma component, LumaWeightL0 is derived to be equal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of −(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive,
wherein luma_log2_weight_denom is a base 2 logarithm of a denominator for all luma weighting factors, and BitDepthy is a bit depth for the luma component of the respective reference picture; and
wherein when weighting factors for a chroma component is present:
determining from a delta_chroma_weight_l0[i][j] syntax element a difference of the first weighting factor and the second weighting factor applied to a chroma prediction value for list 0 prediction using a variable RefPicList0[i] with j equal to 0 for Cb or j equal to 1 for Cr for a second component; and
deriving a variable ChromaWeightL0 associated with the chroma component weighting factor, wherein when the one or more weight flags indicates presence of the weighting factor for a chroma component, ChromaWeightL0 is derived to be equal to ((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)), ((1<<BitDepthc−1)−1), inclusive,
wherein delta_chroma_log2_weight_denom is a difference of a base 2 logarithm of a denominator for all chroma weighting factors, and BitDepthc is a bit depth for the chroma component of the respective reference picture;
wherein the delta_chroma_weight_l0[i][j] syntax element is within the range set by the ChromaWeightL0, and
wherein the second component comprises a chroma component of the first reference unit or the second reference unit;
wherein a determination of at least one value present in a pred_weight_table is dependent on a variable ChromaArrayType;
wherein said delta_luma_weight_l0 syntax element is included in said pred_weight_table.
3. A computing device comprising:
a video encoder configured to provide a bitstream and perform operations comprising:
providing one or more weight flags signaled in the bitstream that indicates presence of weighting factors for at least one of a luma component and/or a chroma component;
wherein a first weighting factor for performing weighted prediction for a current unit of a current picture the first weighting factor for weighting pixels of a first reference unit of a first reference picture when performing motion compensation for the current unit;
wherein a second weighting factor for weighting pixels of a second reference unit of a second reference picture when performing motion compensation for the current unit, wherein when weighting factors for a luma component is present:
providing from a signaled delta_luma_weight_l0 syntax element a difference of the first weighting factor and the second weighting factor applied to a luma prediction value for list 0 prediction using a variable RefPicList0[i] for a first luma component, and
wherein a variable LumaWeightL0 associated with the luma component weighting factors, wherein when the one or more weight flags indicates presence of the weighting factor for a luma component, LumaWeightL0 is derived to be equal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of −(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive, wherein luma_log2_weight_denom is a base 2 logarithm of a denominator for all luma weighting factors, and BitDepthy is a bit depth for the luma component of the respective reference picture; and
wherein when weighting factors for a chroma component is present:
providing from a delta_chroma_weight_l0[i][j] syntax element a difference of the first weighting factor and the second weighting factor applied to a chroma prediction value for list 0 prediction using a variable RefPicList0[i] with j equal to 0 for Cb or j equal to 1 for Cr for a second component; and
wherein a variable ChromaWeightL0 associated with the chroma component weighting factor, wherein when the one or more weight flags indicates presence of the weighting factor for a chroma component, ChromaWeightL0 is derived to be equal to ((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)), ((1<<BitDepthc−1)−1), inclusive,
wherein delta_chroma_log2_weight_denom is a difference of a base 2 logarithm of a denominator for all chroma weighting factors, and BitDepthc is a bit depth for the chroma component of the respective reference picture;
wherein the delta_chroma_weight_l0[i][j] syntax element is within the range set by the ChromaWeightL0, and
wherein the second component comprises a chroma component of the first reference unit or the second reference unit;
wherein a determination of at least one value present in a pred_weight_table is dependent on a variable ChromaArrayType;
wherein said delta_luma_weight_l0 syntax element is included in said pred_weight_table.