Luma-Based Chroma Intra-Prediction for Video Coding

• US 20120328013A1
• Filed: 06/25/2012
• Published: 12/27/2012
• Est. Priority Date: 06/24/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Budagavi, Madhukar, Osamoto, Akira
• Granted Patent: US 9,693,070 B2
• Time in Patent Office: Days
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/105 Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
• CPC Class Codes: H04N 19/167 Position within a video image, e.g. region of interest [ROI]
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/96 Tree coding, e.g. quad-tree coding

Abstract

A method for luma-based chroma intra-prediction in a video encoder or a video decoder is provided that includes down sampling a first reconstructed luma block of a largest coding unit (LCU), computing parameters α and β of a linear model using immediate top neighboring reconstructed luma samples and left neighboring reconstructed luma samples of the first reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the first reconstructed luma block, wherein the linear model is Pred_C[x,y]=α·Rec_L′[x,y]+β, wherein x and y are sample coordinates, Pred_C is predicted chroma samples, and Rec_L′ is samples of the down sampled first reconstructed luma block, and wherein the immediate top neighboring reconstructed luma samples are the only top neighboring reconstructed luma samples used, and computing samples of a first predicted chroma block from corresponding samples of the down sampled first reconstructed luma block using the linear model and the parameters.

Claims

1. A method for luma-based chroma intra-prediction in a video encoder or a video decoder, the method comprising:

down sampling a first reconstructed luma block of a largest coding unit (LCU);

computing parameters α and

β

of a linear model using immediate top neighboring reconstructed luma samples and left neighboring reconstructed luma samples of the first reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the first reconstructed luma block, wherein the linear model is Pred_C[x,y]=α

·

Rec_L′

[x,y]+β

, wherein x and y are sample coordinates, Pred_C is predicted chroma samples, and Rec_L′

is samples of the down sampled first reconstructed luma block, and wherein the immediate top neighboring reconstructed luma samples are the only top neighboring reconstructed luma samples used; and

computing samples of a first predicted chroma block from corresponding samples of the down sampled first reconstructed luma block using the linear model and the parameters.

2. The method of claim 1, wherein the first reconstructed luma block is at a top border of the LCU.

3. The method of claim 2, wherein the immediate top neighboring reconstructed luma samples are received from an top neighboring sample line buffer comprising a last row of reconstructed luma samples from each LCU of a row of LCUs immediately above the LCU.

4. The method of claim 1, wherein the first reconstructed luma block is not at a top border of the LCU.

5. The method of claim 1, wherein the left neighboring reconstructed luma samples are immediately left of immediately left neighboring reconstructed luma samples of the first reconstructed luma block.

6. The method of claim 2, further comprising:

down sampling a second reconstructed luma block of the LCU, wherein the second reconstructed luma block is not at the top border of the LCU;

computing parameters α and

β

of the linear model using immediate top neighboring reconstructed luma samples, top neighboring reconstructed luma samples immediately above the immediate top neighboring reconstructed luma samples, and left neighboring reconstructed luma samples of the second reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the second reconstructed luma block; and

computing samples of a second predicted chroma block from corresponding samples of the down sampled second reconstructed luma block using the linear model and the parameters.

7. A digital system configured to perform luma-based chroma intra-prediction, the digital system comprising:

means for down sampling a first reconstructed luma block of a largest coding unit (LCU);

means for computing parameters α and

β

of a linear model using immediate top neighboring reconstructed luma samples and left neighboring reconstructed luma samples of the first reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the first reconstructed luma block, wherein the linear model is Pred_C[x,y]=α

·

Rec_L′

[x,y]+β

, wherein x and y are sample coordinates, Pred_C is predicted chroma samples, and Rec_L′

is samples of the down sampled first reconstructed luma block, and wherein the immediate top neighboring reconstructed luma samples are the only top neighboring reconstructed luma samples used; and

means for computing samples of a first predicted chroma block from corresponding samples of the down sampled first reconstructed luma block using the linear model and the parameters.

8. The digital system of claim 7, wherein the first reconstructed luma block is at a top border of the LCU.

9. The digital system of claim 7, wherein the first reconstructed luma block is not at a top border of the LCU.

10. The digital system of claim 7, wherein the left neighboring reconstructed luma samples are immediately left of immediately left neighboring reconstructed luma samples of the first reconstructed luma block.

11. The digital system of claim 8, further comprising:

means for down sampling a second reconstructed luma block of the LCU, wherein the second reconstructed luma block is not at the top border of the LCU;

means for computing parameters α and

β

of the linear model using immediate top neighboring reconstructed luma samples, top neighboring reconstructed luma samples immediately above the immediate top neighboring reconstructed luma samples, and left neighboring reconstructed luma samples of the second reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the second reconstructed luma block; and

means for computing samples of a second predicted chroma block from corresponding samples of the down sampled second reconstructed luma block using the linear model and the parameters.

12. The digital system of claim 8, further comprising:

means for storing a last row of reconstructed luma samples from each LCU of a row of LCUs, wherein the means for computing parameters α and

β

receives the immediate top neighboring reconstructed luma samples from the means for storing.

13. A computer readable medium storing software instructions that when executed in a digital system cause the digital system to perform a method for luma-based chroma intra-prediction, the method comprising:

down sampling a first reconstructed luma block of a largest coding unit (LCU);

computing parameters α and

β

of a linear model using immediate top neighboring reconstructed luma samples and left neighboring reconstructed luma samples of the first reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the first reconstructed luma block, wherein the linear model is Pred_C[x,y]=α

·

Rec_L′

[x,y]+β

, wherein x and y are sample coordinates, Pred_C is predicted chroma samples, and Rec_L′

is samples of the down sampled first reconstructed luma block, and wherein the immediate top neighboring reconstructed luma samples are the only top neighboring reconstructed luma samples used; and

computing samples of a first predicted chroma block from corresponding samples of the down sampled first reconstructed luma block using the linear model and the parameters.

14. The computer readable medium of claim 13, wherein the first reconstructed luma block is at a top border of the LCU.

15. The computer readable medium of claim 14, wherein the immediate top neighboring reconstructed luma samples are received from an top neighboring sample line buffer comprising a last row of reconstructed luma samples from each LCU of a row of LCUs immediately above the LCU.

16. The computer readable medium of claim 13, wherein the first reconstructed luma block is not at a top border of the LCU.

17. The computer readable medium of claim 13, wherein the left neighboring reconstructed luma samples are immediately left of immediately left neighboring reconstructed luma samples of the first reconstructed luma block.

18. The computer readable medium of claim 14, the method further comprising:

down sampling a second reconstructed luma block of the LCU, wherein the second reconstructed luma block is not at the top border of the LCU;

computing parameters α and

β

of the linear model using immediate top neighboring reconstructed luma samples, top neighboring reconstructed luma samples immediately above the immediate top neighboring reconstructed luma samples, and left neighboring reconstructed luma samples of the second reconstructed luma block and reconstructed neighboring chroma samples of a chroma block corresponding to the second reconstructed luma block; and

computing samples of a second predicted chroma block from corresponding samples of the down sampled second reconstructed luma block using the linear model and the parameters.