Coding unit size adaptive palette mode for video compression system

1. A method comprising:

determining a size of a coding unit (CU);

determining whether the size of the CU is less than a threshold size;

upon determining that the size of the CU is less than the threshold size, generating a reconstructed block by applying a prediction method to the CU, and

upon determining that the size of the CU is not less than the threshold size, generating a reconstructed block including:

deriving a prediction block of the CU by using a palette of a non-adjacent CU relative to the CU as a palette predictor to predict a palette table of the CU and applying predicting coding to the palette table to derive the prediction block.

2. The method of claim 1 , wherein generating the reconstructed block by applying the prediction method to the CU comprises:

applying the prediction method to the CU to derive a prediction block;

applying a residual decoding method to a residual block; and

generating the reconstructed block by combining the prediction block and the residual block,

wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC).

3. The method of claim 1 , wherein generating the reconstructed block further includes:

applying a Screen Content Coding Extensions of High Efficiency Video Coding (HEVC SCC) palette mode to the CU, decoding the CU, and generating the reconstructed block.

4. The method of claim 1 , wherein generating the reconstructed block further includes:

decoding palette-based residual information of the CU;

deriving a palette-based residual block based on the decoded palette-based residual information;

refining the prediction block based on the decoded palette-based residual information; and

combining the prediction block and the palette-based residual block to construct the reconstructed block.

5. The method of claim 4 , wherein deriving the prediction block of the CU further includes:

applying a subset of tools of the prediction method including a subset of predictions angles to the CU to derive the prediction block wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC).

6. The method of claim 1 , wherein refining the prediction block based on the decoded palette-based residual information comprises:

decoding the palette-based residual block;

classifying pixels of the palette-based residual block into major color pixels and prediction pixels, the major color pixels having palette indices associated with major color pixel values of the decoded palette-based residual block;

assigning a respective predetermined color index to each of the prediction pixels; and

generating a palette index map based on the major color pixels and prediction pixels.

7. The method of claim 6 , further comprising:

signaling whether a pixel in the palette-based residual block is a major color pixel or a prediction pixel by:

decoding the palette index map and identifying an index having the predetermined color index as a prediction pixel; or

identifying a pixel encoded by a prediction run as a prediction pixel,

wherein combining the prediction block and the palette-based residual block to construct the reconstructed block comprises:

using the major color pixel values of the major color pixels in the reconstructed block; and

transferring pixel values of the prediction block for the prediction pixels in the reconstructed block.

8. A computer-readable storage medium storing computer-readable instructions executable by one or more processors, that when executed by the one or more processors, cause the one or more processors to perform operations comprising:

determining a size of a coding unit (CU);

determining whether the size of the CU is less than a threshold size; and

upon determining that the size of the CU is less than the threshold size, generating a reconstructed block by applying a prediction method to the CU, and

upon determining that the size of the CU is not less than the threshold size, generating a reconstructed block including:

deriving a prediction block of the CU by using a palette of a non-adjacent CU relative to the CU as a palette predictor to predict a palette table of the CU and applying predicting coding to the palette table to derive the prediction block.

9. The computer-readable storage medium of claim 8 , wherein decoding the CU by applying the prediction method comprises:

applying the prediction method to the CU to derive a prediction block;

applying a residual decoding method to a residual block; and

generating a reconstructed block by combining the prediction block and the residual block,

wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC).

10. The computer-readable storage medium of claim 8 , wherein generating the reconstructed block further includes:

applying a Screen Content Coding Extensions of High Efficiency Video Coding (HEVC SCC) palette mode to the CU, decoding the CU, and generating the reconstructed block.

11. The computer-readable storage medium of claim 8 , wherein generating the reconstructed block further includes:

decoding palette-based residual information of the CU;

deriving a palette-based residual block based on the decoded palette-based residual information;

refining the prediction block based on the decoded palette-based residual information; and

combining the prediction block and the palette-based residual block to construct a reconstructed block.

12. The computer-readable storage medium of claim 11 , wherein deriving the prediction block of the CU further includes:

applying a subset of tools of the prediction method including a subset of predictions angles to the CU to derive the prediction block wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC).

13. The computer-readable storage medium of claim 8 , wherein refining the prediction block based on the decoded palette-based residual information comprises:

decoding the palette-based residual block;

classifying pixels of the palette-based residual block into major color pixels and prediction pixels, the major color pixels having palette indices associated with major color pixel values of the decoded palette-based residual block;

assigning a respective predetermined color index to each of the prediction pixels; and

generating a palette index map based on the major color pixels and prediction pixels.

14. The computer-readable storage medium of claim 13 , wherein the operations further comprise:

signaling whether a pixel in the palette-based residual block is a major color pixel or a prediction pixel by:

decoding the palette index map and identifying an index having the predetermined color index as a prediction pixel; or

identifying a pixel encoded by a prediction run as a prediction pixel,

wherein combining the prediction block and the palette-based residual block to construct the reconstructed block comprises:

using the major color pixel values of the major color pixels in the reconstructed block; and

transferring pixel values of the prediction block for the prediction pixels in the reconstructed block.

15. A system comprising:

one or more processors; and

memory communicatively coupled to the one or more processors, the memory storing computer-executable modules executable by the one or more processors that, when executed by the one or more processors, perform associated operations, the computer-executable modules including:

a coding unit (CU) size determination module configured to determine a size of a CU and to determine whether the size of the CU is less than a threshold size;

a prediction method module configured to generate a reconstructed block by applying a prediction method to the CU in response to the CU size determination module determining that the size of the CU is less than the threshold size; and

a palette-based method module configured to generate a reconstructed block by applying a palette-based method in response to the CU size determination module determining that the size of the CU is not less than the threshold size, the palette-based method module including:

a palette-based residual refinement module configured to apply a palette-based residual refinement method to the CU to generate the reconstructed block, the palette-based residual refinement module comprising:

a prediction module configured to use a palette of a non-adjacent CU relative to the CU as a palette predictor to predict a palette table of the CU and apply predicting coding to the palette table to derive the prediction block of the CU.

16. The system of claim 15 , wherein the prediction method module is further configured to:

apply the prediction method to the CU to derive a prediction block;

apply a residual decoding method to a residual block; and

generate a reconstructed block by combining the prediction block and the residual block,

wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC).

17. The system of claim 15 , wherein the palette-based method module further includes:

a palette mode module configured to apply a Screen Content Coding Extensions of High Efficiency Video Coding (HEVC SCC) palette mode to the CU, decode the CU, and generate the reconstructed block.

18. The system of claim 15 , wherein the the prediction module is further apply a subset of tools of the prediction method including a subset of predictions angles to the CU to derive the prediction block wherein the prediction method includes an inter-prediction method and an intra-prediction method including a position dependent intra prediction combination (PDPC), and

wherein the palette-based residual refinement module further comprises:

a residual module configured to decode palette-based residual information of the CU and to derive a palette-based residual block based on the decoded palette-based residual information;

refining module is configured to refine the prediction block based on the decoded palette-based residual information by:

decoding the palette-based residual block,

classifying pixels of the palette-based residual block into major color pixels and prediction pixels, the major color pixels having palette indices associated with major color pixel values of the decoded palette-based residual block,

assigning a respective predetermined color index to each of the prediction pixels, and

generating a palette index map based on the major color pixels and prediction pixels; and

a reconstruction module configured to combine the prediction block and the palette-based residual block to construct a reconstructed block.

19. The system of claim 18 , wherein the reconstruction module is further configured to:

signal whether a pixel in the palette-based residual block is a major color pixel or a prediction pixel by:

decoding the palette index map and identifying an index having the predetermined color index as a prediction pixel; or

identifying a pixel encoded by a prediction run as a prediction pixel;

use the major color pixel values of the major color pixels in the reconstructed block; and

transfer pixel values of the prediction block for the prediction pixels in the reconstructed block.