Image decoding device using differential coding

1 . A video decoding apparatus for reconstructing a current block that is encoded using an intra prediction, the video decoding apparatus comprising at least one processor configured to:

decode, from a bitstream, based on size of the current block, a flag indicating whether differential coding has been applied to a residual block of the current block;

when the flag indicates that the differential coding has been applied to the residual block, decode, from the bitstream, direction information indicating a direction of the differential coding applied to the residual block;

generate the residual block by reconstructing information on residual signals from the bitstream;

generate a modified residual block by modifying the residual signals in the residual block based on the direction information, wherein each target residual signal to be modified in the residual block is modified by being summed with one or more residual signals in the residual block that are arranged in a direction indicated by the direction information from the target residual signal;

inversely quantize the modified residual block into an inverse quantized residual block;

infer an intra prediction mode of the current block from the direction of the differential coding indicated by the direction information decoded from the bitstream, without decoding information on the intra prediction mode of the current block from the bitstream and without using information on an intra prediction mode of a neighboring block adjacent to the current block, and generate a prediction block for the current block by intra predicting the current block based on the inferred intra prediction mode; and

reconstruct the current block by adding the prediction block and the inverse quantized residual block.

2 . The video decoding apparatus of claim 1 , wherein the direction information indicates any one of a horizontal direction or a vertical direction.

3 . The video decoding apparatus of claim 2 , wherein, when the direction information indicates the horizontal direction, the target residual signal is modified by being summed with left residual signals located leftward of the target residual signal on a same row as the target residual signal.

4 . The video decoding apparatus of claim 2 , wherein, when the direction information indicates the vertical direction, the target residual signal is modified by being summed with upper residual signals located upwardly of the target residual signal on a same column as the target residual signal.

5 . The video decoding apparatus of claim 1 , wherein the intra prediction mode of the current block is set to have a prediction direction that coincides with a direction indicated by the direction information.

6 . The video decoding apparatus of claim 1 , wherein an inverse transform for the inverse quantized residual block is skipped.

7 . The video decoding apparatus of claim 1 , wherein the information on the residual signals comprises:

information indicating whether the residual signals exist; and

information indicating whether a transform skip mode is used.

8 . The video decoding apparatus of claim 1 , wherein the at least one processor is further configured to:

deblock-filter a boundary between the reconstructed current block and a reconstructed neighboring block adjacent to the reconstructed current block,

wherein the deblock-filtering is not performed on the boundary between the reconstructed current block and the reconstructed neighboring block when the differential coding is applied to both a residual block of the reconstructed neighboring block and the residual block of the current block.

9 . An apparatus for transmitting a bitstream including encoded data of a current block, the apparatus comprising at least one processor configured to:

generate the bitstream by encoding a current block using an intra prediction; and

transmit the bitstream,

wherein the at least one processor is configured to encode the current block by:

determining, based on size of the current block, whether to apply differential coding to a residual block of the current block;

when the differential coding is applied to the residual block, determining a direction of the differential coding to be applied to the residual block of the current block;

generating a prediction block of the current block by intra-predicting the current block based on an intra prediction mode of the current block which is equal to the direction of the differential coding, without using information on an intra prediction mode of a neighboring block adjacent to the current block;

generating the residual block by subtracting the prediction block from the current block;

generating a modified residual block by modifying residual signals in the residual block based on the direction of the differential coding, wherein each target residual signal to be modified in the residual block is modified by subtracting, from the target residual signal, a neighboring residual signal which is adjacent to the target residual signal in the direction of the differential coding; and

encoding, into the bitstream, the modified residual block and information for indicating the direction of the differential coding, wherein information on the intra prediction mode of the current block is not encoded such that the intra prediction mode of the current block is inferred from the information for indicating the direction of the differential coding by a video decoding apparatus.

10 . A video encoding apparatus for encoding a current block using an intra prediction, the apparatus comprising at least one processor configured to:

determine, based on size of the current block, whether to apply differential coding to a residual block of the current block;

when the differential coding is applied to the residual block, determine a direction of the differential coding to be applied to the residual block of the current block;

generate a prediction block of the current block by intra-predicting the current block based on an intra prediction mode of the current block which is equal to the direction of the differential coding, without using information on an intra prediction mode of a neighboring block adjacent to the current block;

generate the residual block by subtracting the prediction block from the current block;

generate a modified residual block by modifying residual signals in the residual block based on the direction of the differential coding, wherein each target residual signal to be modified in the residual block is modified by subtracting, from the target residual signal, a neighboring residual signal which is adjacent to the target residual signal in the direction of the differential coding; and

encode, into a bitstream, the modified residual block and information for indicating the direction of the differential coding, wherein information on the intra prediction mode of the current block is not encoded such that the intra prediction mode of the current block is inferred from the information for indicating the direction of the differential coding by a video decoding apparatus.