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 for encoding at least a block in a picture by determining at least one transform to apply to residuals of the block in a video sequence from a set of two or more transforms,   wherein the transform determined depends on size of said block, and at least one flag is indicative of the transform determined, from among several transforms that can be determined for use on different regions of said block and another flag indicates use of adaptive transforms,   and wherein a choice of transform is made for each region in said block and separate choices of horizontal and vertical transforms are used for each region.   
     
     
         2 . The apparatus of  claim 1 , wherein transform choice is indicated in at least one syntax element. 
     
     
         3 . The apparatus of  claim 1 , wherein the set of transforms is further 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 . A method, comprising:
 encoding at least a block in a picture by determining at least one transform to apply to residuals of the block in a video sequence from a set of two or more transforms,   wherein the transform determined depends on size of said block, and at least one flag is indicative of the transform determined, from among several transforms that can be determined for use on different regions of said block and another flag indicates use of adaptive transforms, and wherein a choice of transform is made for each region in said block and separate choices of horizontal and vertical transforms are used for each region.   
     
     
         7 . The method of  claim 6 , wherein transform choice is indicated in at least one syntax element. 
     
     
         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 method of  claim 6 , wherein information describing the selected transform is explicitly signaled only for block sizes greater than a threshold block size. 
     
     
         12 . 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. 
     
     
         13 . An apparatus, comprising:
 a video decoder for decoding at least a block in a picture by determining at least one inverse transform to apply to inverse quantized coefficients of the block corresponding to residuals of the block in a video sequence from a set of two or more inverse transforms,   wherein the inverse transform determined depends on size of said block, and at least one flag is indicative of the inverse transform determined, from among several inverse transforms that can be determined for use on different regions of said block and another flag indicates use of adaptive transforms,   and wherein a choice of inverse transform is made for each region in said block and separate choices of horizontal and vertical transforms are used for each region.   
     
     
         14 . The apparatus of  claim 13 , wherein transform choice further depends on at least one syntax element. 
     
     
         15 . The apparatus of  claim 13 , wherein said determination is made before decoding of the block. 
     
     
         16 . A method, comprising:
 decoding at least a block in a picture by determining at least one inverse transform to apply to inverse quantized coefficients of the block corresponding to residuals of the block in a video sequence from a set of two or more inverse transforms,   wherein the inverse transform determined depends on size of said block, and at least one flag is indicative of the inverse transform determined, from among several inverse transforms that can be determined for use on different regions of said block and another flag indicates use of adaptive transforms,   and wherein a choice of inverse transform is made for each region in said block and separate choices of horizontal and vertical transforms are used for each region.   
     
     
         17 . The non-transitory computer readable storage media of  claim 15 , wherein transform choice is indicated in at least one syntax element. 
     
     
         18 . The method of  claim 16 , wherein said transforms comprise independent horizontal and vertical transforms. 
     
     
         19 . The method of  claim 16 , wherein said determination is made implicitly. 
     
     
         20 . A non-transitory computer readable storage media having program data encoded thereupon, causing a processor to execute the method of  claim 16 .