Inverse transformation using pruning for video coding

Patent metadata

Field	Value
Publication number	US-9747255-B2
Application number	US-201213470352-A
Country	US
Kind code	B2
Filing date	May 13, 2012
Priority date	May 13, 2011
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

A method for decoding an encoded video bit stream in a video decoder is provided that includes determining a scan pattern type for a transform block to be decoded, decoding a column position X and a row position Y of a last non-zero coefficient in the transform block from the encoded video bit stream, selecting a column-row inverse transform order when the scan pattern type is a first type, selecting a row-column inverse transform order when the scan pattern type is a second type, and performing one dimensional (1D) inverse discrete cosine transformation (IDCT) computations according to the selected transform order to inversely transform the transform block to generate a residual block.

First claim

What is claimed is:

1. A method for decoding an encoded video bit stream in a video decoder, the method comprising:
decoding a pruned transform flag in the encoded video bit stream, wherein the pruned transform flag indicates that a subset region of a transform block contains all non-zero coefficients of the transform block, wherein the subset region consists of M rows and N columns of the transform block;
inverse scanning only quantized transform coefficients of the subset region decoded from the encoded video bit stream to generate the transform block; and
performing one dimensional (1D) inverse discrete cosine transformation (IDCT) computations on the transform block to generate a residual block, wherein one of a value of M or N of the subset region signaled by the pruned transform flag is used to determine pruning of the 1D IDCT computations, wherein performing the 1D IDCT computations includes:
receiving a transform coefficient and a corresponding IDCT coefficient;
setting a prune flag to indicate pruning when a value of the transform coefficient is zero;
setting the prune flag to indicate no pruning when the value of the transform coefficient is non-zero;
disabling latching of the transform coefficient for multiplication with the IDCT coefficient during a clock cycle and outputting a zero when the prune flag is set to indicate pruning; and
enabling latching of the transform coefficient for multiplication with the IDCT coefficient during a clock cycle and outputting a product of the transform coefficient and the IDCT coefficient when the pruning flag is set to indicate no pruning.

2. The method of claim 1 , wherein M=N=4.

3. The method of claim 1 , wherein performing the 1D IDCT computations comprises:
using a column-row inverse transform order when N>M, wherein 1D IDCT computations are performed on only N columns of the transform block to generate an interim results block; and
using a row-column inverse transform order when M>N, wherein 1D IDCT computations are performed on only M rows of the transform block to generate an interim results block.

4. The method of claim 1 , further comprising:
determining a scan pattern type for the transform block;
decoding a column position X and a row position Y of a last non-zero coefficient in the transform block from the encoded video bit stream;
selecting a column-row inverse transform order when the scan pattern type is a first type; and
selecting a row-column inverse transform order when the scan pattern type is a second type, wherein performing the 1D IDCT computations further includes:
performing the 1D IDCT computations according to the selected transform order to inversely transform the transform block to generate the residual block.

5. The method of claim 4 ,
wherein the first type is a vertical scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of columns of the transform block to generate an interim results block, wherein a number of columns in the subset is derived from the column position; and
performing 1D IDCT computations on all rows of the interim results block to generate the residual block.

6. The method of claim 4 ,
wherein the second type is a horizontal scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of rows of the transform block to generate an interim results block, wherein a number of rows in the subset is derived from the row position; and
performing 1D IDCT computations on all columns of the interim results block to generate the residual block.

7. The method of claim 4 ,
wherein the first type is an up-right scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of columns of the transform block to generate an interim results block, wherein a number of columns in the subset is derived from the column position and the row position; and
performing 1D IDCT computations on all rows of the interim results block to generate the residual block.

8. The method of claim 4 ,
wherein the second type is a down-left scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of rows of the transform block to generate an interim results block, wherein a number of rows in the subset is derived from the row position and the column position; and
performing 1D IDCT computations on all columns of the interim results block to generate the residual block.

9. The method of claim 4 ,
wherein the first type is a zigzag scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of columns of the transform block to generate an interim results block, wherein a number of columns in the subset is derived from the column position and the row position; and
performing 1D IDCT computations on all rows of the interim results block to generate the residual block.

10. The method of claim 4 ,
wherein the second type is a zigzag scan pattern; and
wherein performing the 1D IDCT computations further includes:
performing 1D IDCT computations on only a subset of rows of the transform block to generate an interim results block, wherein a number of rows in the subset is derived from the row position and the column position; and
performing 1D IDCT computations on all columns of the interim results block to generate the residual block.

11. The method of claim 4 , further comprising:
wherein selecting a column-row inverse transform order comprises selecting the column-row inverse transform order when the scan pattern type is a zigzag scan pattern and a scan direction of a diagonal of the transform block in which the last non-zero coefficient is located is up-right; and
wherein selecting a row-column inverse transform order comprises selecting the row-column inverse transform order when the scan pattern type is a zigzag scan pattern and a scan direction of a diagonal of the transform block in which the last non-zero coefficient is located is down-left.

Assignees

• Budagavi Madhukar
• Sze Vivienne
• Texas Instruments Inc

Inventors

• Budagavi Madhukar
• Sze Vivienne

Classifications

• H04N19/61

  in combination with predictive coding · CPC title

• H04N19/42

  characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation (H04N19/635 takes precedence) · CPC title

• H04N19/176

  the region being a block, e.g. a macroblock · CPC title

• H04N19/46

  Embedding additional information in the video signal during the compression process (H04N19/517, H04N19/68, H04N19/70 take precedence) · CPC title

• H04N19/48

  using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data (motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513) · CPC title