Adaptive video encoding using a perceptual model

1. In a computing device that implements a video encoder, a method comprising, with the computing device, for each of plural blocks to be encoded using adaptive inter-picture compression:

classifying the block according to content of the block, wherein the classifying the block includes:

determining a block gradient for the block to be encoded using the adaptive inter-picture compression, including:

downsampling luminance samples for the block; and

determining a pixel gradient for each of plural pixels within the block, the pixel gradient being between one or more samples for the pixel and one or more corresponding samples for surrounding pixels, wherein the pixel gradient is quantified as a sum of differences between the samples for the pixel and the one or more corresponding samples for surrounding pixels, wherein the sum of differences is determined based upon both the luminance samples and chrominance samples for the block, and wherein the downsampling of the luminance samples is performed before the sum of differences is determined; and

evaluating the block gradient to determine a block value; and

adaptively encoding the block using adaptive inter-picture compression and depending at least in part upon the block classification, wherein the adaptive encoding includes using two or more of:

adaptive median filtering depending at least in part on the block classification, selective dropping of a last non-zero transform coefficient depending at least in part on the block classification,

adaptive dead zone re-sizing depending at least in part on the block classification, or

quantization step size adjustment depending at least in part on the block classification.

2. In a computing device that implements a video encoder, a method comprising, with the computing device, for each of plural blocks:

classifying the block according to its content, wherein the classifying the block includes:

determining a block gradient, including determining a pixel gradient for each of plural pixels within the block, wherein the pixel gradient is quantified as a sum of differences between samples from the pixel and corresponding samples from neighboring pixels, and wherein the samples include both luminance and chrominance samples; and

evaluating the block gradient to determine a block value; and

adaptively encoding the block using adaptive inter-picture compression and depending at least in part upon the block classification, wherein the adaptive encoding includes using selective dropping of a last non-zero transform coefficient, wherein the selective dropping of a last non-zero coefficient depends at least in part on the block classification and a number of consecutive zero coefficients preceding the last non-zero coefficient in a zig-zag scan, and wherein the adaptive encoding further includes using one or more of:

adaptive median filtering,

adaptive dead zone re-sizing, or

quantization step size adjustment.

3. The method of claim 2 wherein evaluating the block gradient to determine the block value comprises ordering pixel gradient values numerically and selecting a median value as the block value.

4. The method of claim 2 wherein the adaptive median filtering includes changing filter dimensions depending on the block classification, and wherein the adaptive median filtering is performed on a motion compensation prediction residual as part of the adaptive inter-picture compression of the block.

5. The method of claim 2 wherein the determining the pixel gradient comprises using only pixel data from the plural pixels within the block.

6. The method of claim 2 wherein the block value is determined based on an average of pixel gradients.

7. The method of claim 2 wherein the block value is determined based on a median of pixel gradients.

8. The method of claim 2 wherein the adaptive encoding includes using the quantization step size adjustment, and wherein the quantization step size adjustment includes applying differential quantization depending at least in part on the block classification.

9. The method of claim 2 wherein the adaptive encoding further comprises applying adaptive quantization dependent upon:

a characterization of the block, and

a frequency characterization of a coefficient within a block.

10. The method of claim 2 wherein the adaptive encoding includes using the adaptive dead zone re-sizing, and wherein the adaptive dead zone re-sizing includes switching between plural quantizer dead zone sizes depending at least in part on the block classification.

11. A video decoder, decoding an output of an encoder performing the method of claim 2 .

12. In a computing device that implements a video encoder, a method comprising:

with the computing device that implements the video encoder, for each of plural blocks of video data, classifying the block according to content of the block and adaptively encoding the block based at least in part upon the block classification, wherein the adaptive encoding includes selective dropping of a last non-zero transform coefficient depending at least in part on the block classification, wherein the selective dropping of a last non-zero coefficient further depends at least in part on a number of consecutive zero coefficients preceding the last non-zero coefficient in a zig-zag scan, and wherein the adaptive encoding further includes using one or more of:

adaptive median filtering depending at least in part on the block classification,

adaptive dead zone re-sizing depending at least in part on the block classification, or

quantization step size adjustment depending at least in part on the block classification.

13. The method of claim 12 , wherein the classifying the block includes:

determining a block gradient for the block, including determining a pixel gradient for each of plural pixels of the block, the pixel gradient between one or more samples for the pixel and one or more corresponding samples from surrounding pixels; and

evaluating the block gradient to determine a block value.

14. The method of claim 13 wherein the block classification is based at least in part on the block value, the block classification comprising one of smooth, texture, and edge.

15. The method of claim 13 wherein the block value is determined based on an average of pixel gradients.

16. The method of claim 13 wherein the block value is determined based on a median of pixel gradients.

17. The method of claim 12 wherein the adaptive median filtering includes changing filter dimensions depending on the block classification, and wherein the adaptive median filtering is performed on a motion compensation prediction residual as part of the adaptive encoding.

18. The method of claim 12 wherein the adaptive encoding includes using the quantization step size adjustment, and wherein the quantization step size adjustment includes applying differential quantization depending at least in part on the block classification.

19. The method of claim 12 wherein the adaptive encoding further comprises applying adaptive quantization dependent upon:

a characterization of the block, and

a frequency characterization of a coefficient within a block.

20. The method of claim 12 wherein the adaptive encoding includes using the adaptive dead zone re-sizing, and wherein the adaptive dead zone re-sizing includes switching between plural quantizer dead zone sizes depending at least in part on the block classification.

21. A computing device that implements a video encoder, the computing device comprising a processor, memory and storage that stores computer-executable instructions for causing the processor to perform a method comprising, for each of plural blocks of video data:

classifying the block according to content of the block and adaptively encoding the block based at least in part upon the block classification, wherein the adaptive encoding includes selective dropping of a last non-zero transform coefficient depending at least in part on the block classification, wherein the selective dropping of a last non-zero coefficient further depends at least in part on a number of consecutive zero coefficients preceding the last non-zero coefficient in a zig-zag scan, and wherein the adaptive encoding further includes using one or more of:

adaptive median filtering depending at least in part on the block classification,

adaptive dead zone re-sizing depending at least in part on the block classification, or

quantization step size adjustment depending at least in part on the block classification.

22. A computing device that implements a video encoder, the computing device comprising a processor, memory and storage that stores computer-executable instructions for causing the processor to perform a method comprising, for each of plural non-encoded blocks to be encoded using adaptive inter-picture compression:

classifying the block according to content of the block, wherein the classifying the block includes:

determining a block gradient for the block to be encoded using the adaptive inter-picture compression, including:

downsampling luminance samples for the block; and

determining a pixel gradient for each of plural pixels within the block, the pixel gradient being between one or more samples for the pixel and one or more corresponding samples for surrounding pixels, wherein the pixel gradient is quantified as a sum of differences between the one or more samples for the pixel and the one or more corresponding samples for surrounding pixels, wherein the sum of differences is determined based upon both the luminance samples and chrominance samples for the block, and wherein the downsampling of the luminance samples is performed before the sum of differences is determined; and

evaluating the block gradient to determine a block value; and

adaptively encoding the block using the adaptive inter-picture compression and depending at least in part upon the block classification, wherein the adaptive encoding includes using two or more of:

adaptive median filtering depending at least in part on the block classification,

selective dropping of a last non-zero transform coefficient depending at least in part on the block classification,

adaptive dead zone re-sizing depending at least in part on the block classification, or

quantization step size adjustment depending at least in part on the block classification.

23. In a computing device that implements a video encoder, a method comprising, with the computing device, for each of plural non-encoded blocks to be encoded using adaptive inter-picture compression:

classifying the block according to its content, wherein the classifying the block includes:

determining a block gradient, including determining a pixel gradient for each of plural pixels within the block, the pixel gradient between one or more samples for the pixel and one or more corresponding samples from surrounding pixels; and

evaluating the block gradient to determine a block value, wherein the evaluating comprises ordering pixel gradient values numerically and selecting a median value as the block value; and

adaptively encoding the block using the adaptive inter-picture compression and depending at least in part upon the block classification, wherein the adaptive encoding includes using selective dropping of a last non-zero coefficient, wherein the selective dropping of a last non-zero coefficient depends at least in part on a number of consecutive zero coefficients preceding the last non-zero coefficient in a zig-zag scan, and wherein the adaptive encoding further includes using one or more of:

adaptive median filtering,

adaptive dead zone re-sizing, or

quantization step size adjustment.

24. The computing device of claim 23 wherein the block value is determined based on an average of pixel gradients.

25. The computing device of claim 23 wherein the block value is determined based on a median of pixel gradients.

26. The computing device of claim 23 wherein the adaptive encoding further comprises applying adaptive quantization dependent upon:

a characterization of the block, and

a frequency characterization of a coefficient within a block.