Image encoding/decoding method and apparatus using block transformation

An apparatus for encoding an intra block in the unit of sub-blocks, the apparatus comprising:

• a block rectangle-shaper configured to divide the intra block into a plurality of sub-blocks;
• an intra-predictor configured to
• select an intra prediction mode of the intra block from among a plurality of intra prediction modes, and
• predict the plurality of sub-blocks based on sequentially predicting the plurality of sub-blocks in a predefined order by using neighboring pixels adjacent to each of the plurality of sub-blocks;
• a subtractor configured to generate a residual sub-block by subtracting a predicted sub-block from a first sub-block of the sub-blocks;
• a transformer configured to transform the residual sub-block into a frequency domain;
• a quantizer configured to perform quantization with respect to the transformed residual sub-block;
• and
• an encoder configured to encode information on the selected intra prediction mode of the intra block and the quantized residual sub-block into a bitstream,
• wherein the number of pixels of each sub-block is the square of a natural number,
• wherein each of the plurality of sub-blocks is predicted by using the same intra prediction mode as the selected intra prediction mode of the intra block,
• wherein the intra-predictor is further configured to
• identify one or more pixels in a reconstructed sub-block for predicting a second sub-block which is subsequent to the first sub-block in the predefined order, the one or more pixels in the reconstructed sub-block being located adjacent to the second sub-block, and
• predict the second sub-block based on the same intra prediction mode as the selected intra prediction mode of the intra block, and based on the one or more pixels in the reconstructed sub-block, instead of original pixels in the first sub-block, and
• wherein the reconstructed sub-block is reconstructed by using the residual sub-block and the predicted sub-block,
• wherein the plurality of sub-blocks have a size L×M, respectively,
• where L is a horizontal length, M is a vertical length, L is unequal to M, and L and M are natural numbers,
• wherein the values of L and M are determined in accordance with a prediction direction of the selected intra prediction mode,
• wherein the value of L is greater than the value of M when the prediction direction is vertical or the value of L is smaller than the value of M when the prediction direction is horizontal.

A method of decoding an intra block in the unit of sub-blocks, the method comprising:

• obtaining mode information of the intra block from a bitstream;
• determining an intra prediction mode of the intra block from among a plurality of intra prediction modes, based on the obtained mode information;
• identifying a plurality of sub-blocks of the intra block when the intra block is divided into the plurality of sub-blocks;
• and
• reconstructing the plurality of sub-blocks based on sequentially predicting the plurality of sub-blocks in a predefined order by using neighboring pixels adjacent to each of the plurality of sub-blocks,
• wherein each of the plurality of sub-blocks is predicted by using the same intra prediction mode as the determined intra prediction mode of the intra block,
• wherein the number of pixels of each sub-block is the square of a natural number,
• wherein the reconstructing of the plurality of sub-blocks comprises:
• predicting a first sub-block of the sub-blocks based on the same intra prediction mode as the determined intra prediction mode of the intra block to generate a predicted sub-block;
• reconstructing a residual sub-block of the first sub-block by decoding the bitstream;
• adding the predicted sub-block to the reconstructed residual sub-block to thereby generate a reconstructed sub-block;
• identifying one or more pixels in the reconstructed sub-block for predicting a second sub-block which is subsequent to the first sub-block in the predefined order, the one or more pixels in the reconstructed sub-block being located adjacent to the second sub-block;
• and
• predicting the second sub-block based on the same intra prediction mode as the selected intra prediction mode of the intra block, and based on the one or more pixels in the reconstructed sub-block,
• wherein the plurality of sub-blocks have a size L×M, respectively,
• where L is a horizontal length, M is a vertical length, L is unequal to M, and L and M are natural numbers,
• wherein the values of L and M are determined in accordance with a prediction direction of the selected intra prediction mode,
• wherein the value of L is greater than the value of M when the prediction direction is vertical or the value of L is smaller than the value of M when the prediction direction is horizontal.

An apparatus for decoding an intra block in the unit of sub-blocks, the apparatus comprising:

• a decoder configured to
• obtain mode information of the intra block from a bitstream,
• identify a plurality of sub-blocks of the intra block when the intra block is divided into the plurality of sub-blocks, and
• extract a plurality of residual sub-blocks corresponding to the sub-blocks from the bitstream;
• an inverse quantizer configured to perform an inverse quantization with respect to an extracted residual sub-block to generate an inverse-quantized residual sub-block;
• an inverse transformer configured to perform an inverse transformation with respect to the inverse-quantized residual sub-block to thereby generate a reconstructed residual sub-block;
• an intra predictor configured to sequentially predict the plurality of sub-blocks in a predefined order by using neighboring pixels adjacent to each of the plurality of sub-blocks, according to an intra prediction mode determined for the intra block from the mode information;
• and
• an adder configured to add a predicted sub-block to the reconstructed residual sub-block to thereby generate a reconstructed sub-block,
• wherein each of the plurality of sub-blocks is predicted by using the same intra prediction mode as the determined intra prediction mode of the intra block,
• wherein the number of pixels of each sub-block is the square of a natural number, and
• wherein the intra-predictor is further configured to
• identify one or more pixels in the reconstructed sub-block for predicting a second sub-block which is subsequent to the first sub-block in the predefined order, the one or more pixels in the reconstructed sub-block being located adjacent to the second sub-block, and
• predict the second sub-block based on the same intra prediction mode as the selected intra prediction mode of the intra block, and based on the one or more pixels in the reconstructed sub-block,
• wherein the plurality of sub-blocks have a size L×M, respectively,
• where L is a horizontal length, M is a vertical length, L is unequal to M, and L and M are natural numbers,
• wherein the values of L and M are determined in accordance with a prediction direction of the selected intra prediction mode,
• wherein the value of L is greater than the value of M when the prediction direction is vertical or the value of L is smaller than the value of M when the prediction direction is horizontal.