Methods and systems for video transcoding in DCT domain with low complexity

• US 20030081676A1
• Filed: 05/06/2002
• Published: 05/01/2003
• Est. Priority Date: 10/30/2001
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Luo, Jia-Jyh, Lin, Chia-Wen, Tsai, Hsu-Kai
• Granted Patent: US 7,236,529 B2
• Time in Patent Office: Days
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream

Abstract

Methods and systems for transcoding a video sequence in a discrete cosine transform (DCT) domain, wherein a transcoder receives a video bit-stream including frames and each of the frames including blocks. The video bit-stream includes an intra-frame and an inter-frame that has been encoded by motion compensation based on the intra-frame or another inter-frame. A DCT-domain motion compensation module in the transcoder re-calculates first DCT coefficients for a target block in the inter-frame. For this re-calculation of the first DCT coefficients, the motion compensation module inputs second DCT coefficients of neighboring blocks in the inter-frame, and calculates partial DCT coefficients, using significant ones of the second DCT coefficients of the neighboring blocks.

Claims

1. A video transcoding system for transcoding a video sequence in a discrete cosine transform (DCT) domain, the video sequence including frames and each of the frames including blocks, the system comprising:

an input unit configured to receive a video bit-stream including an intra-frame and an inter-frame, the inter-frame having been encoded by motion compensation based on the intra-frame or another inter-frame;

a DCT-domain motion compensation unit configured to re-calculate first DCT coefficients for a target block in the inter-frame included in the video bit-stream received by the input unit; and

an output unit configured to transmit a transcoded video bit-stream including the first DCT coefficients re-calculated by the motion compensation unit,

and wherein the motion compensation unit calculates partial DCT coefficients as the re-calculation of the first DCT coefficients for the target block, using significant ones of second DCT coefficients of neighboring blocks in the inter-frame.

2. The system of claim 1, wherein the motion compensation unit calculates the partial DCT coefficients based on a dependency among the target block and the neighboring blocks.

3. The system of claim 1, wherein the motion compensation unit further specifies the significant ones of the second DCT coefficients in each of the neighboring blocks such that a ratio of a first calculation result of the significant ones of the second DCT coefficients to a second calculation result of all of the second DCT coefficients is greater than a predetermined threshold.

4. The system of claim 3, wherein the motion compensation unit calculates an energy of the significant ones of the second DCT coefficients as the first calculation result and an energy of all of the second DCT coefficients as the second calculation result.

5. The system of claim 3, wherein the motion compensation unit calculates a sum of absolute value of the significant ones of the second DCT coefficients as the first calculation result and a sum of absolute value of all of the second DCT coefficients as the second calculation result.

6. The system of claim 3, wherein the motion compensation unit counts a number of non-zero coefficients among the significant ones of the second DCT coefficients as the first calculation result and a number of non-zero coefficients among all of the second DCT coefficients as the second calculation result.

7. The system of claim 1, wherein the motion compensation unit further estimates a number of the partial DCT coefficients for the target block based on a number of the significant ones of the second DCT coefficients in each of the neighboring blocks.

8. The system of claim 7, wherein the motion compensation unit estimates the number of the partial DCT coefficients using an overlapping area of the target block with each of the neighboring blocks.

9. The system of claim 7, wherein the motion compensation unit calculates the partial DCT coefficients according to the number estimated for the target block in order to skip a part of the re-calculation of the first DCT coefficients beyond the number of the partial DCT coefficients.

10. The system of claim 1, wherein each block contains N×

N DCT coefficients, where N is a positive integer, and the partial DCT coefficients is n×

n DCT coefficients, where n is a positive integer not greater than N.

11. The system of claim 1, wherein each block contains M×

N DCT coefficients, where M and N are positive integers that are different from each other, and the partial DCT coefficients is m×

n DCT coefficients, where m is a positive integer not greater than M and n is a positive integer not greater than N.

12. A method for transcoding a video sequence in a discrete cosine transform (DCT) domain, the video sequence including frames and each of the frames including blocks, the method comprising:

receiving a video bit-stream including an intra-frame and an inter-frame, the inter-frame having been encoded depending on the intra-frame or another inter-frame;

computing first DCT coefficients for a target block in the inter-frame included in the video bit-stream, by inputting second DCT coefficients of neighboring blocks in the inter-frame and by calculating partial DCT coefficients for the target block using significant ones of the second DCT coefficients of the neighboring blocks; and

outputting a transcoded video bit-stream including the partial DCT coefficients as the first DCT coefficients.

13. A method for extracting partial discrete cosine transform (DCT) coefficients for a target block in an inter-frame of a video sequence, the inter-frame being encoded depending on an intra-frame of the video sequence or another inter-frame of the video sequence, the method comprising:

inputting first DCT coefficients of neighboring blocks of the target block;

acquiring a first number of significant ones of the first DCT coefficients for each of the neighboring blocks and a second number of partial DCT coefficients of the target block;

computing, based on the first and second numbers, the partial DCT coefficients from the significant ones of the first DCT coefficients of the neighboring blocks; and

generating second DCT coefficients of the target block by including the partial DCT coefficients and remaining coefficients, the remaining coefficients being set as zero.

14. The method of claim 13, wherein the first number for one of the neighboring blocks is different from the first number for another of the neighboring blocks, and the step of computing uses a number of the significant ones of the first DCT coefficients of one of the neighboring blocks and another number of the significant ones of the first DCT coefficients of another of the neighboring blocks.

15. The method of claim 13, wherein the computing ignores remaining ones of the first DCT coefficients of the neighboring blocks over the first number, and stops computing when a number of the partial DCT coefficients reaches the second number.

16. A method for estimating a number of significant discrete cosine transform (DCT) coefficients of a target block in an inter-frame of a video sequence, the inter-frame being encoded depending on an intra-frame of the video sequence or another inter-frame of the video sequence, the method comprising:

inputting DCT coefficients of neighboring blocks of the target block;

determining respective numbers of significant DCT coefficients of the neighboring blocks based on the input DCT coefficients; and

estimating, prior to calculating DCT coefficients of the target block, the number of significant DCT coefficients of the target block based on the determined respective numbers of significant DCT coefficients of the neighboring blocks.

17. The method of claim 16, wherein the determining includes calculating a first energy of all of the DCT coefficients of each of the neighboring blocks and a second energy of a certain number of the DCT coefficients of said each of the neighboring blocks, and selecting the certain number as each of the respective numbers according to a ratio of the second energy to the first energy.

18. The method of claim 16, wherein the estimating includes determining respective overlapping areas of the target block with the neighboring blocks, and calculating the number for the target block from the respective numbers for the neighboring blocks weighted by the respective overlapping areas.

19. The method of claim 16, wherein each block contains N×

N DCT coefficients, where N is a positive integer, and the number of significant DCT coefficients is determined as n×

n, where n is a positive integer not greater than N.

20. The method of claim 16, wherein each block contains M×

N DCT coefficients, where M and N are positive integers that are different from each other, and the number of significant DCT coefficients is determined as m×

n, where m is a positive integer not greater than M and n is a positive integer not greater than N.