Context coding for transform skip mode

Abstract

Devices, systems and methods for coefficient coding in transform skip mode are described. An exemplary method for video processing includes determining, for encoding one or more video blocks in a video region of a visual media data into a bitstream representation of the visual media data, a maximum allowed dimension up to which a current video block of the one or more video blocks is allowed to be encoded using a transform skip mode such that a residual of a prediction error between the current video block and a reference video block is represented in the bitstream representation without applying a transform; and including a syntax element indicative of the maximum allowed dimension in the bitstream representation.

What is claimed is: 
     
         1 . A method of processing video data, comprising:
 using, for a conversion between a current video block in a video region of a video data and a bitstream of the video data, a transform skip mode for the current video block, wherein in the transform skip mode, a transform is skipped on a prediction residual between the current video block and a reference video block;   selecting a context of a sign flag for a current coefficient of the current video block according to one or more sign flags of one or more neighboring coefficients in the current video block; and   performing the conversion based on the selecting.   
     
     
         2 . The method of  claim 1 , wherein the one or more neighboring coefficients in the current video block include at least one of a left neighbor coefficient or an above neighbor coefficient. 
     
     
         3 . The method of  claim 2 , wherein the one or more neighboring coefficients in the current video block include: a left neighbor coefficient and an above neighbor coefficient. 
     
     
         4 . The method of  claim 1 , wherein the context of the sign flag for the current coefficient is based on the one or more sign flags of the one or more neighboring coefficients in accordance with a following rule:
 if sign flags of a pair of the one or more neighboring coefficients are both negative, the rule specifies selecting a first context.   
     
     
         5 . The method of  claim 1 , wherein the context of the sign flag for the current coefficient is based on the one or more sign flags of the one or more neighboring coefficients in accordance with a following rule:
 if one sign flag of a pair of the one or more neighboring coefficients is negative and another sign flag of a pair of the one or more neighboring coefficients is positive, the rule specifies selecting a second context.   
     
     
         6 . The method of  claim 1 , wherein the context of the sign flag for the current coefficient is based on the one or more sign flags of the one or more neighboring coefficients in accordance with a following rule:
 if sign flags of a pair of the one or more neighboring coefficients are both positive, the rule specifies selecting a third context.   
     
     
         7 . The method of  claim 1 , wherein a relationship between the context of the sign flag of the current coefficient and one or more sign flags of the one or more neighboring coefficients is expressed as:
 C=(L+A), where C is a context identifier of the context of the sign flag of the current coefficient, L is a sign flag of a left neighbor coefficient of the current coefficient, and A is a sign flag of an above neighbor coefficient of the current coefficient.   
     
     
         8 . The method of  claim 1 , wherein the context of the sign flag for the current coefficient is further based on the position of the current coefficient. 
     
     
         9 . The method of  claim 1 , wherein a first syntax element indicating whether the transform skip mode is applied to the current video block is conditionally included in the bitstream. 
     
     
         10 . The method of  claim 9 , wherein whether the first syntax element is included in the bitstream is based on a block dimension of the current video block. 
     
     
         11 . The method of  claim 9 , wherein whether the first syntax element is included in the bitstream is based on a coding tree structure of the current video block. 
     
     
         12 . The method of  claim 11 , wherein in response to the current video block is in a single tree structure, the first syntax element is included in the bitstream. 
     
     
         13 . The method of  claim 11 , wherein in response to the current video block is in a dual tree luma structure, the first syntax element is included in the bitstream. 
     
     
         14 . The method of  claim 11 , wherein in response to the current video block is not in a dual tree chroma structure, the first syntax element is included in the bitstream. 
     
     
         15 . The method of  claim 1 , wherein a second syntax element indicating a maximum allowed block size used for the transform skip mode is included in the bitstream. 
     
     
         16 . The method of  claim 1 , wherein the conversion includes encoding the current video block into the bitstream. 
     
     
         17 . The method of  claim 1 , wherein the conversion includes decoding the current video block from the bitstream. 
     
     
         18 . An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
 use, for a conversion between a current video block in a video region of a video data and a bitstream of the video data, a transform skip mode for the current video block, wherein in the transform skip mode, a transform is skipped on a prediction residual between the current video block and a reference video block;   select a context of a sign flag for a current coefficient of the current video block according to one or more sign flags of one or more neighboring coefficients in the current video block; and   perform the conversion based on the selecting.   
     
     
         19 . A non-transitory computer-readable storage medium storing instructions that cause a processor to:
 use, for a conversion between a current video block in a video region of a video data and a bitstream of the video data, a transform skip mode for the current video block, wherein in the transform skip mode, a transform is skipped on a prediction residual between the current video block and a reference video block;   select a context of a sign flag for a current coefficient of the current video block according to one or more sign flags of one or more neighboring coefficients in the current video block; and   perform the conversion based on the selecting.   
     
     
         20 . A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:
 using a transform skip mode for a current video block in a video region of a video data, wherein in the transform skip mode, a transform is skipped on a prediction residual between the current video block and a reference video block;   selecting a context of a sign flag for a current coefficient of the current video block according to one or more sign flags of one or more neighboring coefficients in the current video block; and   generating the bitstream of the video data based on the selecting.