Method for entropy coding and decoding having improved coding efficiency and apparatus for providing the same

A video coding method comprising:

• generating a residual by extracting a prediction image from a frame;
• generating a transform coefficient by spatially transforming the residual;
• quantizing the transform coefficient;
• performing context-based adaptive variable length coding on the data symbol of the quantized transform coefficient;
• performing context-based adaptive arithmetic coding on the data symbol of the quantized transform coefficient;
• receiving information regarding a reference block where a coding efficiency of the context-based adaptive arithmetic coding is higher than that of the context-based adaptive variable length coding;
• forming a slice which includes the reference block and performing the context-based adaptive arithmetic coding on blocks coded after the reference block;
• generating a bit stream that comprises information regarding the reference block;
• and
• transmitting the bit stream.

An entropy decoding method comprising:

• interpreting a bit stream comprising coded values of a plurality of blocks in a slice and extracting information regarding a reference block where context-based adaptive arithmetic coding begins;
• performing context-based adaptive variable length decoding on a bit stream of a block to be restored if the block to be restored is decoded earlier than the reference block;
• and
• performing context-based adaptive arithmetic decoding on the bit stream of the block to be restored.

A video decoding method comprising:

• interpreting a bit stream comprising coded values of a plurality of blocks in a slice and extracting information regarding a reference block where context-based adaptive arithmetic coding begins;
• performing context-based adaptive variable length decoding on a bit stream of a block to be restored if the block to be restored is decoded earlier than the reference block;
• performing context-based adaptive arithmetic decoding on the bit stream of the block to be restored;
• inverse-quantizing the decoded value;
• inverse-spatially transforming the inverse-quantized value and restoring a residual signal;
• and
• adding a restored prediction image to the residual signal and restoring a video frame.

A video encoder comprising:

• means for generating a residual by extracting a prediction image from a frame;
• means for generating a transform coefficient by spatial transforming the residual;
• means for quantizing the transform coefficient;
• means for performing context-based adaptive variable length coding on a data symbol of the quantized transform coefficient;
• means for performing context-based adaptive arithmetic coding on a data symbol of the quantized transform coefficient;
• means for receiving information regarding a reference block where a coding efficiency of the context-based adaptive arithmetic coding is higher than that of the context-based adaptive variable length coding;
• means for forming a slice which includes the reference block, and for performing the context-based adaptive arithmetic coding on blocks coded after the reference block;
• means for generating a bit stream that comprises information regarding the reference block;
• and
• means for transmitting the bit stream.

A video decoder comprising:

• means for interpreting a bit stream comprising coded values of a plurality of blocks in a slice and for extracting information regarding a reference block where context-based adaptive arithmetic coding begins;
• means for performing context-based adaptive variable length decoding on a bit stream of a block to be restored if the block to be restored is decoded earlier than the reference block;
• means for performing context-based adaptive arithmetic decoding on the bit stream of the block to be restored;
• means for inverse-quantizing the decoded value;
• means for inverse-spatially transforming the inverse-quantized value and for restoring a residual signal;
• and
• means for adding a restored prediction image to the residual signal and for restoring a video frame.

A video encoder comprising:

• a divider which generates a residual by extracting a prediction image from a frame;
• a spatial transformer which generates a transform coefficient by spatial transforming the residual;
• a quantizer which quantizes the transform coefficient;
• a context-based adaptive variable length coding unit which performs context-based adaptive variable length coding on a data symbol of the quantized transform coefficient;
• a context-based adaptive arithmetic coding unit which performs context-based adaptive arithmetic coding on a data symbol of the quantized transform coefficient;
• a comparator which determines a reference block where a coding efficiency of the context-based adaptive arithmetic coding is higher than that of the context-based adaptive variable length coding, and a bit stream generator which collects information regarding the reference block from the comparator, inserts the information regarding the reference block into the header of a slice, generates a bit stream that comprises the information regarding the reference block, and transmits the stream.

A video decoder comprising:

• a bit stream interpreter which interprets a bit stream comprising the coded values of a plurality of blocks in a slice and extracts information regarding a reference block;
• a context-based adaptive variable length decoding part which performs context-based adaptive variable length decoding on a bit stream of a block to be restored if the block to be restored is decoded earlier than the reference block;
• a context-based adaptive arithmetic decoding part which performs context-based adaptive arithmetic decoding on the bit stream of the block to be restored;
• an inverse quantizer which inverse-quantizes the decoded value;
• an inverse spatial transformer which inverse-spatially transforms the inverse-quantized value and restores a residual signal;
• and
• an adder which adds a restored prediction image to the residual signal and restores a video frame.