Transform coefficient coding

Abstract

Techniques are described for determining a scan order for transform coefficients of a block. The techniques may determine context for encoding or decoding significance syntax elements for the transform coefficients based on the determined scan order. A video encoder may encode the significance syntax elements and a video decoder may decode the significance syntax elements based on the determined contexts.

What is claimed is: 
     
         1 . A method for decoding video data, the method comprising:
 receiving, from a coded bitstream, significance flags of transform coefficients of a block;   determining a scan order for the transform coefficients of the block;   determining contexts for the significance flags of the transform coefficients of the block based on the determined scan order; and   context adaptive binary arithmetic coding (CABAC) decoding the significance flags of the transform coefficients based at least on the determined contexts.   
     
     
         2 . The method of  claim 1 , wherein determining the contexts comprises determining the contexts based on size of the block, positions of the transform coefficients within the block, and the scan order. 
     
     
         3 . The method of  claim 1 , wherein determining the contexts comprises:
 determining the contexts that are the same if the determined scan order is a horizontal scan and if the determined scan order is a vertical scan; and   determining the contexts, which are different than the contexts if the determined scan order is the horizontal scan and if the determined scan order is the vertical scan, if the determined scan order is not the horizontal scan or the vertical scan.   
     
     
         4 . The method of  claim 1 , wherein determining contexts for the significance flags of the transform coefficients of the block based on the determined scan order comprises determining the same contexts if the scan order is horizontal scan order or vertical scan order. 
     
     
         5 . The method of  claim 1 , wherein determining the contexts comprises:
 determining a first set of contexts for the significance flags if the scan order is a first scan order; and   determining a second set of contexts for the significance flags if the scan order is a second scan order.   
     
     
         6 . The method of  claim 5 , wherein the first set of contexts is the same as the second set of contexts if the first scan order is a horizontal scan and the second scan order is a vertical scan. 
     
     
         7 . The method of  claim 5 , wherein the first set of context is different than the second set of contexts if the first scan order is one of a horizontal scan or a vertical scan and the second scan order is not the horizontal scan or the vertical scan. 
     
     
         8 . The method of  claim 1 , wherein determining the contexts comprises determining the contexts for the significance flags of the transform coefficients of the block based on the determined scan order and based on size of the block. 
     
     
         9 . The method of  claim 1 , further comprising:
 determining whether size of the block is a first size or a second size,   wherein, if the size of the block is the first size, determining the contexts comprises determining the contexts that are the same for all scan orders, and   wherein, if the size of the block is the second size, determining the contexts comprises determining the contexts that are different for at least two different scan orders.   
     
     
         10 . The method of  claim 1 , wherein the block comprises an 8×8 block of transform coefficients. 
     
     
         11 . A method for encoding video data, the method comprising:
 determining a scan order for transform coefficients of a block;   determining contexts for significance flags of the transform coefficients of the block based on the determined scan order;   context adaptive binary arithmetic coding (CABAC) encoding the significance flags of the transform coefficients based at least on the determined contexts; and   signaling the encoded significance flags in a coded bitstream.   
     
     
         12 . The method of  claim 11 , wherein determining the contexts comprises determining the contexts based on size of the block, positions of the transform coefficients within the block, and the scan order. 
     
     
         13 . The method of  claim 11 , wherein determining the contexts comprises:
 determining the contexts that are the same if the determined scan order is a horizontal scan and if the determined scan order is a vertical scan; and   determining the contexts, which are different than the contexts if the determined scan order is the horizontal scan and if the determined scan order is the vertical scan, if the determined scan order is not the horizontal scan or the vertical scan.   
     
     
         14 . The method of  claim 11 , wherein determining contexts for the significance flags of the transform coefficients of the block based on the determined scan order comprises determining the same contexts if the scan order is horizontal scan order or vertical scan order. 
     
     
         15 . The method of  claim 11 , wherein determining the contexts comprises:
 determining a first set of contexts for the significance flags if the scan order is a first scan order; and   determining a second set of contexts for the significance flags if the scan order is a second scan order.   
     
     
         16 . The method of  claim 15 , wherein the first set of contexts is the same as the second set of contexts if the first scan order is a horizontal scan and the second scan order is a vertical scan. 
     
     
         17 . The method of  claim 15 , wherein the first set of context is different than the second set of contexts if the first scan order is one of a horizontal scan or a vertical scan and the second scan order is not the horizontal scan or the vertical scan. 
     
     
         18 . The method of  claim 11 , wherein determining the contexts comprises determining the contexts for the significance flags of the transform coefficients of the block based on the determined scan order and based on size of the block. 
     
     
         19 . The method of  claim 11 , wherein the block comprises an 8×8 block of transform coefficients. 
     
     
         20 . An apparatus for coding video data, the apparatus comprising a video coder configured to:
 determine a scan order for transform coefficients of a block;   determine contexts for significance flags of the transform coefficients of the block based on the determined scan order; and   context adaptive binary arithmetic coding (CABAC) code the significance flags of the transform coefficients based at least on the determined contexts.   
     
     
         21 . The apparatus of  claim 20 , wherein the video coder comprises a video decoder, and wherein the video decoder is configured to:
 receive, from a coded bitstream, the significance flags of the transform coefficients of the block; and   CABAC decode the significance flags of the transform coefficients based on the determined contexts.   
     
     
         22 . The apparatus of  claim 20 , wherein the video coder comprises a video encoder, and wherein the video encoder is configured to:
 CABAC encode the significance flags of the transform coefficients based on the determined contexts; and   signal, in a coded bitstream, the significance flags of the transform coefficients.   
     
     
         23 . The apparatus of  claim 20 , wherein, to determine the contexts, the video coder is configured to determine the contexts based on size of the block, positions of the transform coefficients within the block, and the scan order. 
     
     
         24 . The apparatus of  claim 20 , wherein, to determine the contexts, the video coder is configured to:
 determine the contexts that are the same if the determined scan order is a horizontal scan and if the determined scan order is a vertical scan; and   determine the contexts, which are different than the contexts if the determined scan order is the horizontal scan and if the determined scan order is the vertical scan, if the determined scan order is not the horizontal scan or the vertical scan.   
     
     
         25 . The apparatus of  claim 20 , wherein, to determine contexts for the significance flags of the transform coefficients of the block based on the determined scan order, the video coder is configured to determine the same contexts if the scan order is horizontal scan order or vertical scan order. 
     
     
         26 . The apparatus of  claim 20 , wherein, to determine the contexts, the video coder is configured to:
 determine a first set of contexts for the significance flags if the scan order is a first scan order; and   determine a second set of contexts for the significance flags if the scan order is a second scan order.   
     
     
         27 . The apparatus of  claim 26 , wherein the first set of contexts is the same as the second set of contexts if the first scan order is a horizontal scan and the second scan order is a vertical scan. 
     
     
         28 . The apparatus of  claim 26 , wherein the first set of context is different than the second set of contexts if the first scan order is one of a horizontal scan or a vertical scan and the second scan order is not the horizontal scan or the vertical scan. 
     
     
         29 . The apparatus of  claim 20 , wherein, to determine the contexts, the video coder is configured to determine the contexts for the significance flags of the transform coefficients of the block based on the determined scan order and based on size of the block. 
     
     
         30 . The apparatus of  claim 20 , wherein the video coder is configured to:
 determine whether size of the block is a first size or a second size,   wherein, if the size of the block is the first size, the video coder is configured to determine the contexts that are the same for all scan orders, and   wherein, if the size of the block is the second size, the video coder is configured to determine the contexts that are different for at least two different scan orders.   
     
     
         31 . The apparatus of  claim 20 , wherein the block comprises an 8×8 block of transform coefficients. 
     
     
         32 . The apparatus of  claim 20 , wherein the apparatus comprises one of:
 a microprocessor;   an integrated circuit (IC); and   a wireless communication device that includes the video coder.   
     
     
         33 . An apparatus for coding video data, the apparatus comprising:
 means for determining a scan order for transform coefficients of a block;   means for determining contexts for significance flags of the transform coefficients of the block based on the determined scan order; and   means for context adaptive binary arithmetic coding (CABAC) the significance flags of the transform coefficients based at least on the determined contexts.   
     
     
         34 . The apparatus of  claim 33 , wherein the means for determining the contexts comprises means for determining the contexts based on size of the block, positions of the transform coefficients within the block, and the scan order. 
     
     
         35 . A computer-readable storage medium having instructions stored thereon that when executed cause one or more processors of an apparatus for coding video data to:
 determine a scan order for transform coefficients of a block;   determine contexts for significance flags of the transform coefficients of the block based on the determined scan order; and   context adaptive binary arithmetic coding (CABAC) code the significance flags of the transform coefficients based at least on the determined contexts.   
     
     
         36 . The computer-readable storage medium of  claim 35 , wherein the instructions that cause the one or more processors to determine the contexts comprise instructions that cause the one or more processors to determine the contexts based on size of the block, positions of the transform coefficients within the block, and the scan order.