Two-step quantization and coding method and apparatus

Patent metadata

Field	Value
Publication number	US-9510019-B2
Application number	US-201213570492-A
Country	US
Kind code	B2
Filing date	Aug 9, 2012
Priority date	Aug 9, 2012
Publication date	Nov 29, 2016
Grant date	Nov 29, 2016

Abstract

Encoding and decoding a video image having a plurality of frames using a two-step quantization and coding process are disclosed. A block of a frame are encoded by identifying pixels having certain spatial characteristics, forming a second block from the block while replacing the identified pixels with a single pixel value, such as an average of the remaining original pixels. The second block is encoded, such as by transformation and quantization, and placed into a bitstream. The second block is decoded and subtracted from the original block to generate a difference block. The difference block is encoded, such as by quantization, and is placed in the bitstream. At a decoder, both blocks are decoded and combined to reconstruct the original block.

First claim

What is claimed is:

1. A method of encoding a frame in a video stream, the frame having a plurality of blocks, the method comprising:
identifying a first block of the plurality of blocks;
generating a second block from the first block by copying pixels from the first block to the second block while replacing each pixel value within the second block that is outside of a defined value range with a pixel value within the defined value range such that the second block has a lower entropy than the first block;
encoding the second block using a first encoding technique, wherein the first encoding technique includes:
transforming the second block; and
quantizing the second block using a first quantizer value after transforming the second block;

decoding the encoded second block using a processor;
generating a third data block based on a difference between the decoded second block and the first data block; and
encoding the third data block using a second encoding technique different from the first encoding technique, including quantizing the third block using a second quantizer value different than the first quantizer value.

2. The method of claim 1 , further comprising:
generating an encoded video bitstream including the encoded second data block and the encoded third data block.

3. The method of claim 1 wherein encoding the third block using the second encoding technique comprises:
quantizing the third block without transforming the third block.

4. The method of claim 3 wherein encoding the second block comprises entropy encoding the second block after quantizing the second block and encoding the third block comprises encoding the third block after quantizing the third block.

5. The method of claim 1 wherein replacing each pixel value comprises:
identifying one or more pixels within the second block having pixel values outside of the defined value range;
determining the pixel value that is within the defined value range; and
replacing the one or more pixels having pixel values outside of the defined value range with the pixel value.

6. The method of claim 5 wherein determining the pixel value comprises:
calculating an average of pixel values of the pixels copied from the first block copied to the second block.

7. The method of claim 1 wherein generating the third data block comprises:
performing a pixel-by-pixel subtraction of pixel values of the decoded second block from pixel values of the first block.

8. The apparatus of claim 1 , wherein decoding the encoded second block includes inverse transforming the second encoded block.

9. A method for decoding a frame of an encoded video bitstream including a plurality of encoded blocks and the frame having a plurality of blocks, the method comprising:
receiving a first encoded block and a second encoded block of the plurality of encoded blocks, the first encoded block corresponding to a first block having a plurality of pixels with first pixel values that is encoded, and the second encoded block corresponding to a second block having a plurality of pixels with the first pixel values except that those of the first pixel values outside of a defined value range are replaced with a pixel value within the defined value range;
decoding the first encoded block using a first decoding technique to generate a first decoded block, wherein decoding the first encoded block includes:
dequantizing the first block using a first quantizer value; and
inverse transforming the first encoded block after dequantizing the first encoded block;

decoding the second encoded block using a second decoding technique different from the first decoding technique to generate a second decoded block, the second decoded block having a lower entropy than the first decoded block, wherein decoding the second encoded block includes:
dequantizing the second block with a second quantizer value different than the first quantizer value; and
inverse transforming the second encoded block after dequantizing the direct encoded block; and

combining the first decoded block with the second decoded block to form a block of the plurality of blocks using a processor.

10. The method of claim 9 wherein decoding the first encoded block using the first decoding technique comprises:
entropy decoding the first encoded block before dequantizing the first encoded block.

11. The method of claim 10 wherein decoding the second encoded block using the second decoding technique comprises:
dequantizing the second encoded block without inverse transforming the second encoded block.

12. The method of claim 9 wherein decoding the second encoded block using the second decoding technique comprises:
dequantizing the second encoded block without inverse transforming the second encoded block.

13. The method of claim 9 wherein combining the first decoded block with the second decoded block comprises:
performing a pixel-by-pixel addition of pixel values of the first decoded block and pixel values of the second decoded block.

14. An apparatus for encoding a frame in a video stream, the frame having a plurality of blocks, the apparatus comprising:
a memory; and
a processor configured to execute instructions stored in the memory to:
identify a first block of the plurality of blocks;
generate a second block from the first block by copying pixels from the first block to the second block while replacing each pixel value within the second block that is above a defined value with a single pixel value below the defined value such that the second block has a lower entropy than the first block;
encode the second block using a first encoding technique, wherein the first encoding technique includes:
transforming the second block; and
quantizing the second block using a first quantizer value after transforming the second block; and

decode the encoded second block;
generate a third data block based on a difference between the decoded second block and the first data block; and
encode the third data block using a second encoding technique different from the first encoding technique wherein the first encoding technique includes quantizing the third block using a second quantizer value different than the first quantizer value.

15. The apparatus of claim 14 wherein the processor is configured to:
generate an encoded video bitstream including the encoded second block and the encoded third block, the encoded video bitstream including a coding mode indicating the first coding technique and the second encoding technique.

16. The apparatus of claim 14 wherein the processor is configured to encode the second block by:
entropy encoding the second block after quantizing the second block; and wherein the processor is configured to encoding the third block by:
entropy encoding the third block after quantizing the third block.

17. The apparatus of claim 16 wherein the processor is configured to transform the second block by applying a DCT transform of the second block.

18. The apparatus of claim 14 wherein the defined value is based on at least some of the pixel values of the first block.

Assignees

• Gu Qunshan
• Xu Yaowu
• Google Inc

Inventors

• Gu Qunshan
• Xu Yaowu

Classifications

• H04N19/85 Primary

  using pre-processing or post-processing specially adapted for video compression · CPC title

• H04N19/182

  the unit being a pixel · CPC title

• H04N19/12

  Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264 · CPC title

• H04N19/30

  using hierarchical techniques, e.g. scalability (H04N19/63 takes precedence) · CPC title

• H04N19/176

  the region being a block, e.g. a macroblock · CPC title