Block artifact suppression in video coding
A method for encoding a video sequence in a video encoder is provided that includes adapting a quantization parameter of a block of pixels in a picture of the video sequence based on a transform block size of the block of pixels to determine a final quantization parameter, and quantizing transform coefficients of the block of pixels using the final quantization parameter.
1. A method comprising:
computing, by a video encoder, an activity measure for a first block of pixels in an image;
determining, by the video encoder, a first quantization parameter based on the activity measure;
determining, by the video encoder, a first delta value for the first block of pixels, wherein a 32×32 transform block size is used for the first block of pixels;
determining, by the video encoder, a second delta value for a second block of pixels in the image, wherein an 8×8 transform block size is used for the second block of pixels, and wherein the first delta value is larger than the second delta value;
reducing, by the video encoder, the first quantization parameter using the determined first delta value for the block of pixels to produce a second quantization parameter; and
quantizing, by the video encoder, transform coefficients of the first block of pixels using the second quantization parameter.
2. The method of claim 1 , wherein:
the activity measure is representative of an amount of texture for the first block of pixels.
3. The method of claim 1 , wherein:
the activity measure is a first activity measure; and
the method further comprises:
computing a second activity measure for the second block of pixels, wherein the second activity measure is higher than the first activity measure;
determining a third quantization parameter based on the second activity measure,
wherein the third quantization parameter is higher than the first quantization parameter.
4. The method of claim 1 , wherein:
the first delta value for the first block of pixels is larger than a third delta value for 4×4 transform block size.
5. The method of claim 1 , wherein:
the first delta value for the first block of pixels is a predetermined value assigned to the 32×32 largest transform block size.
6. The method of claim 5 , wherein:
the predetermined value is based on a representative set of video sequences.
7. The method of claim 1 , further comprising:
clipping, by the video encoder, the second quantization parameter to produce a third quantization parameter.
8. The method of claim 7 , wherein clipping the second quantization parameter comprises:
in response to the second quantization parameter being greater than a sum of a distance value and a previous quantization parameter of a previous block of pixels, setting the third quantization parameter equal to the sum of the distance value and the previous quantization parameter.
9. The method of claim 7 , wherein clipping the second quantization parameter comprises:
in response to the second quantization parameter being less than a difference between a distance value and a previous quantization parameter of a previous block of pixels, setting the third quantization parameter equal to the difference of the distance value and the previous quantization parameter.
10. A video encoder comprising one or more processors:
the one or more processors configured to:
compute an activity measure for a block of pixels in an image;
determine a first quantization parameter based on the activity measure;
determine a first delta value for the block of pixels if a 32×32 transform block size is used for the block of pixels;
determine a second delta value for the block of pixels if an 8×8 transform block size is used for the block of pixels, wherein the first delta value is larger than the second delta value;
reduce the first quantization parameter using the determined first or second delta value for the block of pixels to produce a second quantization parameter; and
quantize transform coefficients of the block of pixels using the second quantization parameter.
11. The video encoder of claim 10 , wherein:
the activity measure is representative of an amount of texture for the block of pixels.
12. The video encoder of claim 10 , wherein:
the activity measure is a first activity measure;
the block of pixels is a first block of pixels in the image; and
the one or more processors are further configured to:
compute a second activity measure for a second block of pixels in the image, wherein the second activity measure is higher than the first activity measure;
determine a third quantization parameter based on the second activity measure,
wherein the third quantization parameter is higher than the first quantization parameter.
13. The video encoder of claim 10 , wherein:
the first delta value for the block of pixels is larger than a third delta value for a smaller transform block size.
14. The video encoder of claim 10 , wherein:
the first delta value for the block of pixels is a predetermined value assigned to the 32×32 largest transform block size.
15. The video encoder of claim 14 , wherein:
the predetermined value is based on a representative set of video sequences.
16. The video encoder of claim 10 , wherein the one or more processors are further configured to:
clip the second quantization parameter to produce a third quantization parameter.
17. The video encoder of claim 16 , wherein to clip the second quantization parameter, the one or more processors are further configured to:
in response to the second quantization parameter being greater than a sum of a distance value and a previous quantization parameter of a previous block of pixels, the one or more processors are configured to set the third quantization parameter equal to the sum of the distance value and the previous quantization parameter.
18. The video encoder of claim 16 , wherein to clip the second quantization parameter, the one or more processors are further configured to:
in response to the second quantization parameter being less than a difference between a distance value and a previous quantization parameter of a previous block of pixels, the one or more processors are configured to set the third quantization parameter equal to the difference of the distance value and the previous quantization parameter.
19. A method comprising:
determining, by a video encoder, a first quantization parameter for a first coding unit in an image;
determining, by the video encoder, a first delta value of zero for the first coding unit based on a size of a first transform unit in the first coding unit;
adding, by the video encoder, the first quantization parameter and the first delta value of zero to generate a second quantization parameter for the first coding unit;
quantizing, by the video encoder, transform coefficients in the first coding unit using the second quantization parameter;
determining, by the video encoder, a third quantization parameter for a second coding unit in the image;
determining, by the video encoder, a second delta value for the second coding unit based on a 32×32 size of a second transform unit in the second coding unit, wherein the 32×32 size of the second transform unit is larger than the size of the first transform unit;
reducing, by the video encoder, the third quantization parameter by the second delta value to generate a fourth quantization parameter for the second coding unit; and
quantizing, by the video encoder, transform coefficients in the second coding unit using the fourth quantization parameter.
20. The method of claim 19 , wherein the size of the first transform unit is an 8×8 size.