Methods and apparatus for transform selection in video encoding and decoding

Abstract

There are provided methods and apparatus for transform selection in video coding. An apparatus includes a video encoder ( 300 ) for encoding at least a block in a picture by selecting a transform ( 329 ) to apply to a residue of the block from a set of two or more available transforms ( 325, 326, 327 ). The transform is selected based on at least one of an inter prediction mode used to predict at least one reference for the block, one or more values corresponding to a motion vector, a value of a residue of one or more previously encoded blocks, a value of prediction data for the block, one or more transform selections of one or more neighboring reconstructed blocks, and a quantization step applied to transform coefficients for the residue of the block.

1 . An apparatus, comprising:
 a video encoder ( 300 ) for encoding at least a block in a picture by selecting a transform to apply to a residue of the block between contiguous pictures in a video sequence from a set of two or more transforms,   wherein the transform is selected responsive to an inter prediction mode used to predict at least one reference for the block.   
     
     
         2 . The apparatus of  claim 1 , wherein the set of transforms is determined off-line. 
     
     
         3 . The apparatus of  claim 2 , wherein the set of transforms is determined by at least one of:
 (i) using training data, and   (ii) choosing a subset of a family of transforms.   
     
     
         4 . The apparatus of  claim 1 , wherein information describing the selected transform is explicitly signaled only for block sizes greater than a threshold block size. 
     
     
         5 . The apparatus of  claim 1 , wherein a flag describing the selected transform is embedded in coefficients of the transform when block sizes are less than a threshold block size. 
     
     
         6 . In a video encoder, a method, comprising:
 encoding ( 510 ) at least a block in a picture by selecting ( 520 ) a transform to apply to a residue of the block between contiguous pictures in a video sequence from a set of two or more transforms,   wherein the transform is selected responsive to an inter prediction mode used to predict at least one reference for the block.   
     
     
         7 . The method of  claim 6 , wherein the set of transforms is determined by at least one of:
 (i) using training data ( 515 ), and   (ii) choosing a subset of a family of transforms ( 520 ).   
     
     
         8 . The method of  claim 6 , wherein the transforms in the set are any of separable or non-separable, and horizontal and vertical directions of the transforms are capable of being different when the transforms are separable. 
     
     
         9 . The method of  claim 6 , wherein information describing the selected transform is explicitly signaled only for block sizes greater than a threshold block size. 
     
     
         10 . The method of  claim 6 , wherein a flag describing the selected transform is embedded in coefficients of the transform when block sizes are less than a threshold block size. 
     
     
         11 . The apparatus of  claim 6 , wherein information describing the selected transform is explicitly signaled only for block sizes greater than a threshold block size. 
     
     
         12 . The apparatus of  claim 6 , wherein a flag describing the selected transform is embedded in coefficients of the transform when block sizes are less than a threshold block size. 
     
     
         13 . An apparatus, comprising:
 a video decoder ( 400 ) for decoding at least a block in a picture by determining an inverse transform to apply to quantized coefficients of the block between contiguous pictures in a video sequence from a set of two or more inverse transforms,   wherein the inverse transform is determined responsive to an inter prediction mode used to predict at least one reference for the block.   
     
     
         14 . In a video decoder, a method, comprising:
 decoding ( 610 ) at least a block in a picture by determining ( 615 ,  620 ) an inverse transform to apply to quantized coefficients of the block between contiguous pictures in a video sequence from a set of two or more inverse transforms,   wherein the inverse transform is determined responsive to an inter prediction mode used to predict at least one reference for the block.   
     
     
         15 . A storage media having video signal data encoded thereupon, comprising:
 data corresponding to at least one block between contiguous pictures in a video sequence in a picture encoded by selecting a transform to apply to a residue of the block from a set of two or more transforms,   wherein the transform is selected responsive to an inter prediction mode used to predict at least one reference for the block.