Methods and devices for encoding and decoding transform domain filters
Methods and devices for encoding and decoding data using transform domain filtering are described. The encoder determines a set of transform domain filter coefficients to be applied to a transform domain prediction. The filtering may, in some cases, also apply to transform domain reconstructions. Rate-distortion optimization may be used to determine the optimal filter coefficients on a frame-basis, coding-unit-basis, or other basis. Multiple filters may be developed and communicated from the encoder to the decoder for different combinations of transform block size, coding mode, prediction mode, and texture type. In other cases, the filtering is applied in the pixel-domain to a pixel-domain prediction or a pixel-domain reconstruction of a block of samples.
1. A method of reconstructing a block of samples from a bitstream of encoded data in a decoder, the method comprising:
reconstructing a spectrally transformed prediction block of samples associated with the block of samples;
reading filter-type flags from the bitstream, wherein the filter-type flags identify one or more filter types;
for each of the filter types identified, decoding a set of filter coefficients from the bitstream; and
calculating a filtered transform domain reconstruction by applying, to at least a portion of the transformed prediction block, one of the sets of filter coefficients based on its filter type matching characteristics associated with the block of samples.
2. The method claimed in claim 1 , wherein calculating includes determining the characteristics of the block of samples and selecting the one of the sets of filter coefficients based on its filter type matching the characteristics.
3. The method claimed in claim 1 , wherein the filter types are based on at least one of transform size, coding mode, prediction mode, and texture type.
4. The method claimed in claim 1 , wherein the characteristics include motion vector characteristics, and wherein the filter types include two or more filter types applicable to respective groups of inter-coded blocks, and wherein each respective group of inter-coded blocks is associated with a respective group of motion vector characteristics.
5. The method claimed in claim 1 , wherein the characteristics include directional prediction modes, and wherein the filter types include two or more filter types applicable to respective groups of intra-coded blocks, and wherein each respective group of intra-coded blocks is associated with a group of directional prediction modes.
6. The method claimed in claim 1 , wherein the set of filter coefficients defines a filter, wherein the set of filter coefficients includes a coefficient for each coefficient group in the filter, and wherein at least one coefficient group includes two or more coefficient positions.
7. The method claimed in claim 1 , wherein calculating the filtered transform domain reconstruction comprises calculating a filtered prediction by scaling at least a portion of the transformed prediction block by the filter coefficients and dequantizing a block of quantized transform domain coefficients, and wherein the filtered transform domain reconstruction comprises the sum of the filtered prediction and the dequantized block of transform domain coefficients.
8. The method claimed in claim 1 , wherein calculating the filtered transform domain reconstruction comprises:
dequantizing a block of quantized transform domain coefficients;
calculating a transform domain reconstruction block as the transformed prediction block plus the dequantized block of transform domain coefficients; and
scaling the transform domain reconstruction block using the filter coefficients.
9. A non-transitory computer-readable medium storing computer-executable instructions which, when executed by a processor, configure the processor to perform the method claimed in claim 1 .
10. A method of reconstructing a block of samples from a bitstream of encoded data in a decoder, the method comprising:
reconstructing a prediction block of samples associated with the block of samples;
reading filter-type flags from the bitstream, wherein the filter-type flags identify one or more filter types;
for each of the filter types identified, decoding a set of filter coefficients from the bitstream; and
calculating a filtered pixel-domain reconstruction by applying, to at least a portion of the prediction block, one of the sets of filter coefficients based on its filter type matching characteristic associated with the block of samples.
11. A non-transitory computer-readable medium storing computer-executable instructions which, when executed by a processor, configure the processor to perform the method claimed in claim 10 .
12. A decoder, comprising:
a processor;
a memory; and
a decoding application stored in memory and containing instructions for configuring the processor to
reconstruct a spectrally transformed prediction block of samples associated with the block of samples;
read filter-type flags from the bitstream, wherein the filter-type flags identify one or more filter types;
for each of the filter types identified, decode a set of filter coefficients from the bitstream; and
calculate a filtered transform domain reconstruction by applying, to at least a portion of the transformed prediction block, one of the sets of filter coefficients based on its filter type matching characteristics associated with the block of samples.
13. The decoder claimed in claim 12 , wherein the processor is configured to calculate the filtered transform domain reconstruction by determining the characteristics of the block of samples and selecting the one of the sets of filter coefficients based on its filter type matching the characteristics.
14. The decoder claimed in claim 12 , wherein the filter types are based on at least one of transform size, coding mode, prediction mode, and texture type.
15. The decoder claimed in claim 12 , wherein the characteristics include motion vector characteristics, and wherein the filter types include two or more filter types applicable to respective groups of inter-coded blocks, and wherein each respective group of inter-coded blocks is associated with a respective group of motion vector characteristics.
16. The decoder claimed in claim 12 , wherein the characteristics include directional prediction modes, and wherein the filter types include two or more filter types applicable to respective groups of intra-coded blocks, and wherein each respective group of intra-coded blocks is associated with a group of directional prediction modes.
17. The decoder claimed in claim 12 , wherein the set of filter coefficients defines a filter, wherein the set of filter coefficients includes a coefficient for each coefficient group in the filter, and wherein at least one coefficient group includes two or more coefficient positions.
18. The decoder claimed in claim 12 , wherein the processor is configured to calculate the filtered transform domain reconstruction by calculating a filtered prediction by scaling at least a portion of the transformed prediction block by the filter coefficients and dequantizing a block of quantized transform domain coefficients, and wherein the filtered transform domain reconstruction comprises the sum of the filtered prediction and the dequantized block of transform domain coefficients.
19. The decoder claimed in claim 12 , wherein the processor is configured to calculate the filtered transform domain reconstruction by:
dequantizing a block of quantized transform domain coefficients;
calculating a transform domain reconstruction block as the transformed prediction block plus the dequantized block of transform domain coefficients; and
scaling the transform domain reconstruction block using the filter coefficients.