Method for generating reconstructed blocks using a filter for an intra prediction mode
According to the present invention, an image encoding/decoding method comprises the steps of: performing an intra prediction on a current block so as to generate a prediction block; performing filtering on a filtering target pixel in the prediction block on the basis of the intra prediction mode of the current block so as to generate a final prediction block; and generating a reconstructed block on the basis of a reconstructed differential block corresponding to the current block and on the final prediction block. According to the present invention, image encoding/decoding efficiency can be improved.
1. A method for generating a reconstructed block, the method comprising:
generating a prediction block by performing intra prediction on a current block for a DC mode, and
generating the reconstructed block based on the prediction block and a reconstructed residual block corresponding to the current block, wherein
pixel values of filtered prediction pixels of the prediction block are generated using a filter for the DC mode during the intra prediction,
the filtered prediction pixels are one or more pixels located in a vertical pixel line at a leftmost side of the prediction block and one or more pixels located in a horizontal pixel line at an uppermost side of the prediction block, and
the filter has a predetermined fixed filter shape, a filter tap, and a plurality of filter coefficients regardless of the size of the current block.
2. The method of claim 1 , wherein a pixel value of a leftmost and uppermost filtered prediction pixel among the filtered prediction pixels is generated using a 3-tap filter based on a value which is derived by the DC mode, an upper reference pixel adjacent to an upper portion of the leftmost and uppermost filtered prediction pixel, and a left reference pixel adjacent to a left of the filtered prediction pixel, and
each of the upper reference pixel and the left reference pixel is a pixel of reconstructed reference pixels adjacent to the current block.
3. The method of claim 2 , wherein the value which is derived by the DC mode is an average of the reconstructed reference pixels.
4. The method of claim 2 , wherein, in the 3-tap filter, a filter coefficient allocated to a filter tap corresponding to the value which is derived by the DC mode being 2/4, a filter coefficient allocated to a filter tap corresponding to the upper reference pixel being ¼, and a filter coefficient allocated to a filter tap corresponding to the left reference pixel being ¼.
5. The method of claim 1 , wherein the filter is used when the current block is a luma component block, and the filter is not used when the current block is a chroma component block.
6. The method of claim 1 , wherein whether or not to use the filter is determined based on a size of the current block, and the filter is used when the current block has a size of smaller than 32×32.
7. The method of claim 1 , wherein the prediction block is generated using reference pixels which have been reconstructed, the reference pixels include first reference pixels which are adjacent to the vertical pixel line and second reference pixels which are adjacent to the horizontal pixel line, and the filtered prediction pixels are filtered with the first reference pixels and the second reference pixels.
8. An apparatus for generating a reconstructed block, the apparatus comprising:
a prediction block generator to generate a prediction block by performing intra prediction on a current block for a DC mode, and
a reconstructed block generator to generate the reconstructed block based on the prediction block and a reconstructed residual block corresponding to the current block, wherein
pixel values of filtered prediction pixels of the prediction block are generated using a filter for the DC mode during the intra prediction,
the filtered prediction pixels are one or more pixels located in a vertical pixel line at a leftmost side of the prediction block and one or more pixels located in a horizontal pixel line at an uppermost side of the prediction block, and
the filter has a predetermined fixed filter shape, a filter tap, and a plurality of filter coefficients regardless of a size of the current block.
9. The apparatus of claim 8 , wherein the prediction block generating unit generates a pixel value of a leftmost and uppermost filtered prediction pixel among the filtered prediction pixels using a 3-tap filter based on a value which is derived by the DC mode, an upper reference pixel adjacent to an upper portion of the leftmost and uppermost filtered prediction pixel, and a left reference pixel adjacent to a left of the leftmost and uppermost filtered prediction pixel, and
each of the upper reference pixel and the left reference pixel is a pixel of reconstructed reference pixels adjacent to the current block.
10. The apparatus of claim 9 , wherein the value which is derived by the DC mode is an average of the reconstructed reference pixels.
11. The apparatus of claim 9 , wherein, in the 3-tap filter, a filter coefficient allocated to a filter tap corresponding to the value which is derived by the DC mode is 2/4, a filter coefficient allocated to a filter tap corresponding to the upper reference pixel is ¼, and a filter coefficient allocated to a filter tap corresponding to the left reference pixel is ¼.
12. The apparatus of claim 8 , wherein the prediction block generating unit uses the filter when the current block is a luma component block, and does not use the filter when the current block is a chroma component block.
13. The apparatus of claim 8 , wherein the prediction block generating unit determines whether to use the filter based on a size of the current block, and the prediction block generating unit determines to uses the filter when the size of the current block is smaller than 32×32.
14. The apparatus of claim 8 , wherein the prediction block generating unit generates the prediction block using reference pixels which have been reconstructed, and
the reference pixels include first reference pixels which are adjacent to the vertical pixel line and second reference pixels which are adjacent to the horizontal pixel line, and the filtered prediction pixels are filtered with the first reference pixels and the second reference pixels.
15. A non-transitory computer-readable medium storing a bitstream, the bitstream comprising:
prediction mode information indicating a prediction mode for a current block,
wherein the prediction mode information represents that
a prediction block is generated by performing intra prediction on the current block for a DC mode in a case that the DC mode of the intra prediction is indicated as the prediction mode for the current block based on the prediction mode information,
pixel values of filtered prediction pixels of the prediction block are generated using a filter for the DC mode during the intra prediction,
wherein the filtered prediction pixels are one or more pixels located in a vertical pixel line at a leftmost side of the prediction block and one or more pixels located in a horizontal pixel line at an uppermost side of the prediction block, and
wherein the filter has a predetermined fixed filter shape, a filter tap, and a plurality of filter coefficients regardless of a size of the current block.
16. The non-transitory computer-readable medium of claim 15 ,
wherein the filter is used when the current block is a luma component block, and the filter is not used when the current block is a chroma component block.
17. The non-transitory computer-readable medium of claim 15 ,
wherein whether to use the filter is dependent on a size of the current block, and the filter is used when the current block has a size of smaller than 32×32.