Transform and quantization architecture for video coding and decoding

• US 9,378,185 B2
• Filed: 09/30/2011
• Issued: 06/28/2016
• Est. Priority Date: 09/30/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sadafale, Mangesh, Budagavi, Madhukar
• Primary Examiner(s): Rao, Andy
• Assistant Examiner(s): WALKER, JARED T
• Application Number:
  US13/250,822
• Publication Number:
  US 20120082212A1
• Time in Patent Office: 1,733 Days
• Field of Search: 37524001-24027
• US Class Current: 1/1
• CPC Class Codes: G06F 17/147 Discrete orthonormal transforms, e.g. discrete cosine transform, discrete sine transform, and variations therefrom, e.g. modified discrete cosine transform, integer transforms approximating the discrete cosine transform G06F17/145 takes precedence
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/122 Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/156 Availability of hardware or computational resources, e.g. encoding based on power-saving criteria
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/174 the region being a slice, e.g. a line of blocks or a group of blocks
• CPC Class Codes: H04N 19/42 characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation H04N19/635 takes precedence
• CPC Class Codes: H04N 19/51 Motion estimation or motion compensation
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A method of encoding a video stream in a video encoder is provided that includes computing an offset into a transform matrix based on a transform block size, wherein a size of the transform matrix is larger than the transform block size, and wherein the transform matrix is one selected from a group consisting of a DCT transform matrix and an IDCT transform matrix, and transforming a residual block to generate a DCT coefficient block, wherein the offset is used to select elements of rows and columns of a DCT submatrix of the transform block size from the transform matrix.

Claims

1. A method of encoding a video stream, comprising:

providing a transform matrix having a size M×

M;

providing a residual block having a size P×

P;

computing an offset into the transform matrix based on the size of the residual block when P is less than M;

transforming the residual block to generate a DCT coefficient block using elements of the transform matrix selected by the offset;

providing a quantization step size for the DCT coefficient block; and

quantizing each non-zero coefficient in the DCT coefficient block using the quantization step size.

2. The method of claim 1, transforming the residual block to generate

the DCT coefficient block using elements of the transform matrix selected by the offset

comprising:

selecting the n^th elements of the n^th rows of the transform matrix.

3. The method of claim 1, transforming the residual block to generate

the DCT coefficient block using elements of the transform matrix selected by the offset

comprising:

selecting the n^th elements of the n^th rows of the transform matrix, including a

zeroth element in a zeroth row, to perform the transforming.

4. The method of claim 1, the elements of the transform matrix limited to

a range represented by a signed seven bit value.

5. The method of claim 1, comprising:

deriving the quantization step size for the DCT coefficient block based on at least

one of a quantization vector and a quantization parameter.

6. The method of claim 1, comprising:

deriving the quantization step size for the DCT coefficient block; and

quantizing each non-zero coefficient in the DCT coefficient block using the quantization

step size; and

entropy coding data representing the quantized DCT coefficients.

7. The method of claim 1, comprising:

capturing an image using a camera;

partially encoding the image to yield an 8×

8 residual block;

quantizing the DCT coefficient block;

entropy coding the quantized DCT coefficient block; and

transmitting encoded data using an RF transmitter.

8. The method of claim 1, comprising:

providing a 32×

32 transform matrix; and

providing a 16×

16 residual block.

9. The method of claim 1, comprising:

providing a 32×

32 transform matrix; and

providing an 8×

8 residual block.

10. A method of encoding data comprising:

capturing an image;

partially encoding the image to yield an 8×

8 residual block;

providing a 32×

32 transform matrix;

transforming the residual block using a matrix comprising values M[l,j]

from the transform matrix where i and j are 0, 4, 8, 12, 16, 20, 24, and 28, to yield a DCT coefficient block;

providing a quantization step size for the DCT coefficient block;

quantizing each non-zero coefficient in the DCT coefficient block using the quantization step size;

entropy coding the quantized DCT coefficient block; and

transmitting the entropy encoded quantized DCT coefficient block.

11. A method of decoding a video stream, comprising:

providing an inverse transform matrix having a size M×

M;

providing an encoded quantized DCT coefficient block having a size P×

P;

inverse quantizing at least one non-zero coefficient in the quantized DCT coefficient

block to provide a DCT coefficient block;

computing an offset into the inverse transform matrix based on the size of the DCT

coefficient block when P is less than M; and

transforming the DCT coefficient block to generate a residual block using

elements of the inverse transform matrix selected by the offset.

12. The method of claim 11, transforming the DCT coefficient block to

generate a residual block using elements of the inverse transform matrix selected by the offset comprising:

selecting the nth elements of the nth rows of the inverse transform matrix.

13. The method of claim 11, transforming the DCT coefficient block to

generate a residual block using elements of the inverse transform matrix

selected by the offset comprising:

selecting the nth elements of the n′

h rows of the inverse transform matrix, including the zeroth element in the zeroth row, to perform the transforming.

14. The method of claim 11, the elements of the inverse transform matrix limited to a range represented by a signed seven bit value.

15. The method of claim 11, comprising:

entropy decoding a bitstream to provide a decoded bitstream including an encoded quantized DCT coefficient block;

inverse quantizing at least one coefficient in the quantized DCT coefficient block to provide the DCT coefficient block.

16. The method of claim 11, comprising:

receiving an encoded bitstream;

entropy decoding the encoded bitstream to provide a quantized DCT coefficient block having a size P×

P;

inverse quantization decoding at least one coefficient of the quantized DCT coefficient block to provide a DCT coefficient block;

transforming the DCT coefficient block to generate a residual block using elements of the inverse transform matrix selected by the offset;

using the residual block to generate a reconstructed image; and

displaying the reconstructed image.

17. The method of claim 11, comprising:

providing a 32×

32 inverse transform matrix; and

providing a 16×

16 DCT coefficient block.

18. The method of claim 11, comprising:

providing a 32×

32 inverse transform matrix; and

providing an 8×

8 DCT coefficient block residual.