Transform and Quantization Architecture for Video Coding and Decoding

• US 20120082212A1
• Filed: 09/30/2011
• Published: 04/05/2012
• Est. Priority Date: 09/30/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Sadafale, Mangesh, Budagavi, Madhukar
• Granted Patent: US 9,378,185 B2
• Time in Patent Office: Days
• US Class Current: 375/240.2
• 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 in a video encoder, the method comprising:

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.

2. The method of claim 1, further comprising:

deriving a quantization step size for the DCT coefficient block based on a quantization vector and a quantization parameter; and

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

3. The method of claim 1, further comprising:

computing an additional offset into the transform matrix when the transform block size is not square; and

transforming a residual block further comprises using the offset and the additional offset to select the elements of rows and columns of the DCT submatrix.

4. The method of claim 1, wherein elements of the transform matrix are 7-bit signed fixed point values.

5. The method of claim 1, wherein transforming a residual block further comprises:

decomposing the residual block and the DCT submatrix using at least one level of even-odd decomposition.

6. The method of claim 1, wherein transforming a residual block further comprises performing matrix multiplications between the DCT submatrix and the residual block using a matrix multiplication engine.

7. The method of claim 6, further comprising:

applying a directional transform to another residual block to generate a transform coefficient block, wherein matrix multiplications between at least one directional transform matrix and the another residual block are performed using the matrix multiplication engine.

8. A method of decoding an encoded bitstream in a video decoder, the method comprising:

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 DCT coefficient block to reconstruct a residual block, wherein the offset is used to select elements of rows and columns of an IDCT submatrix of the transform block size from the transform matrix.

9. The method of claim 8, further comprising:

deriving a inverse quantization step size for the DCT coefficient block based on an inverse quantization vector and a quantization parameter; and

dequantizing each coefficient in the DCT coefficient block using the inverse quantization step size.

10. The method of claim 8, further comprising:

computing an additional offset into the transform matrix when the transform block size is not square; and

transforming a DCT coefficient block further comprises using the offset and the additional offset to select the elements of rows and columns of the IDCT submatrix.

11. The method of claim 8, wherein elements of the transform matrix are 7-bit signed fixed point values.

12. The method of claim 8, wherein transforming a DCT coefficient block further comprises:

decomposing the DCT coefficient block and the IDCT submatrix using at least one level of even-odd decomposition.

13. The method of claim 8, wherein transforming a DCT coefficient block further comprises performing matrix multiplications between the IDCT submatrix and the DCT coefficient block using a matrix multiplication engine.

14. The method of claim 13, further comprising:

applying an inverse directional transform to a transform coefficient block to reconstruct another residual block, wherein matrix multiplications between at least one inverse directional transform matrix and the transform coefficient block are performed using the matrix multiplication engine.

15. A digital system comprising:

an offset calculator configured to compute 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

a transform engine configured to transform 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.

16. The digital system of claim 15, wherein the digital system further comprises:

a quantization component configured to derive a quantization step size for the DCT coefficient block based on a quantization vector stored in the memory and a quantization parameter and to quantize each coefficient in the DCT coefficient block using the quantization step size.

17. The digital system of claim 15, wherein the transform engine is further configured to decompose the residual block and the DCT submatrix using at least one level of even-odd decomposition.

18. The digital system of claim 15, wherein the transform engine comprises a matrix multiplication engine and the transform engine is further configured to perform matrix multiplications between the DCT submatrix and the residual block using the matrix multiplication engine.

19. The digital system of claim 15, wherein the transform engine is further configured to perform matrix multiplications for application of a directional transform to a residual block using the matrix multiplication engine.

20. A method for transformation in a transform component of a digital system, the method comprising:

decomposing an input vector using even-odd decomposition to generate a first vector consisting of even elements of the input vector and a second vector consisting of odd elements of the input vector;

using butterfly decomposition to apply an odd part of a transform to the second vector wherein the transform is one selected from a group consisting of a DCT transform and an IDCT transform; and

using matrix multiplication to apply an even part of the transform to the first vector.