Apparatus and method for image encoding/decoding using predictability of intra-prediction mode
An apparatus for decoding a video, includes: a mode information extractor to extract mode information on an intra-prediction mode of a current block from encoded data; a prediction mode determiner to determine a candidate intra-prediction mode selected from a plurality of candidate intra-prediction modes as the intra-prediction mode of the current block, when the mode information indicates a first encoding mode; a prediction mode extractor to determine the intra-prediction mode of the current block by using a prediction mode identifier, when the mode information indicates a second encoding mode and includes the prediction mode identifier; and a decoder to decode the encoded data to produce a residual block, and reconstruct the current block by adding the produced residual block to a prediction block predicted based on the intra-prediction mode of the current block determined by either the prediction mode determiner or the prediction mode extractor.
1. An apparatus for decoding a video, the apparatus comprising:
a mode information extractor configured to extract mode information on an intra-prediction mode of a current block from encoded data;
a prediction mode determiner configured to
derive a set of candidate intra-prediction modes including at least three candidate intra-prediction modes, depending on the current block, wherein the derived set of candidate intra-prediction modes includes an intra-prediction mode of at least one neighboring block adjacent to the current block when the intra-prediction mode of the at least one neighboring block is available, and
determine a candidate intra-prediction mode selected from the derived set of candidate intra-prediction modes as the intra-prediction mode of the current block without comparing mode numbers of candidate intra-prediction modes included in the derived set each other, when the mode information indicates a first encoding mode;
a prediction mode extractor configured to determine the intra-prediction mode of the current block by using a prediction mode identification information, when the mode information indicates a second encoding mode and includes the prediction mode identification information; and
a decoder configured to decode the encoded data to produce a residual block, and reconstruct the current block by adding the produced residual block to a prediction block predicted based on the intra-prediction mode of the current block determined by either the prediction mode determiner or the prediction mode extractor.
2. The apparatus of claim 1 , wherein, when the mode information indicates the second encoding mode and includes the prediction mode identification including a representative mode identifier,
wherein the prediction mode extractor is further configured to
set the intra-prediction mode of the current block to the intra-prediction mode having a smaller mode number among the mode numbers of the intra-prediction modes of the left and upper blocks of the current block, when the representative mode identifier indicates a first value, and
set the intra-prediction mode of the current block by using a prediction mode identifier included in the prediction mode identification information, when the representative mode identifier indicates a second value.
3. A method performed by an apparatus for decoding a video, the method comprising:
extracting mode information for predicting a current block from encoded data;
deriving a set of candidate intra-prediction modes including at least three candidate intra-prediction modes, depending on the current block, wherein the derived set of candidate intra-prediction modes includes an intra-prediction mode of at least one neighboring block adjacent to the current block when the intra-prediction mode of the at least one neighboring block is available;
determining a candidate intra-prediction mode selected from the derived set of candidate intra-prediction modes as the intra-prediction mode of the current block without comparing mode numbers of candidate intra-prediction modes included in the derived set each other, when the mode information indicates a first encoding mode;
determining the intra-prediction mode of the current block by using a prediction mode identification information, when the mode information indicates a second encoding mode and includes the prediction mode identification information;
generating a prediction block by predicting the current block based on the determined intra-prediction mode of the current block, and decoding the encoded data to produce a residual block; and
reconstructing the current block by adding the residual block to the prediction block.
4. The method of claim 3 , wherein when the mode information indicates the second encoding mode and includes the prediction mode identification including
a representative mode identifier,
wherein determining the intra-prediction mode of the current block by using the prediction mode identification information further comprises:
setting the intra-prediction mode of the current block to the intra-prediction mode having a smaller mode number among the mode numbers of the intra-prediction modes of the left and upper blocks of the current block, when the representative mode identifier indicates a first value, and
setting the intra-prediction mode of the current block by using a prediction mode identifier included in the prediction mode identification information, when the representative mode identifier indicates a second value.