Patent ID: 9674530
Date: 2017-06-06
CPC Classifications: H04N

Claim:
1. A method, comprising: identifying an intra prediction mode of a current block of a frame in a video stream, the intra prediction mode being one of a plurality of intra prediction modes; predicting, with a processor, the current block to form a residual block using the intra prediction mode, the current block and the residual block having a prediction size; identifying a plurality of transform subblocks for the residual block, each of the plurality of transform subblocks having a transform size smaller than the prediction size; identifying a transform mode for the residual block from a plurality of transform modes based on the intra prediction mode of the current block, each transform mode of the plurality of transform modes associated with a different combination of a one-dimensional transform type for columns of the residual block and a one-dimensional transform type for rows of the residual block, wherein the one-dimensional transform type for columns of the residual block comprises one of a first one-dimensional transform type having a base function that conforms with a pattern of a variance of pixel values resulting from the intra prediction mode, wherein the first one-dimensional transform type is a one-dimensional Asymmetrical Discrete Sine Transform, or a second one-dimensional transform type having a base function that treats pixel values relatively uniformly, and the one-dimensional transform type for rows of the residual block comprises one of the first one-dimensional transform type or the second one-dimensional transform type; identifying each of the transform subblocks as an upper-left transform subblock, an upper row transform subblock, a left-hand column transform subblock or a remainder transform subblock based on a position of the transform subblock within the residual block; for each transform subblock of the plurality of transform subblocks, identifying a one-dimensional subblock transform type for columns of the transform subblock and a one-dimensional subblock transform type for rows of the transform subblock based on the intra prediction mode of the current block, the transform mode for the residual block, and whether the transform subblock is the upper-left transform subblock, the upper row transform subblock, the left-hand transform subblock or the remainder transform subblock, wherein the one-dimensional Asymmetrical Discrete Sine Transform is at least one of the one-dimensional subblock transform type for columns or the one-dimensional subblock transform type for rows of each of the upper-left, upper row and left-hand column subblocks; and transforming each transform subblock of the plurality of transform subblocks to include in an encoded video bitstream using the one-dimensional subblock transform type identified for the columns of the transform subblock and the one-dimensional subblock transform type identified for the rows of the transform subblock.