Method and apparatus to encode a moving image with fixed computational complexity

• US 20030156644A1
• Filed: 12/20/2002
• Published: 08/21/2003
• Est. Priority Date: 02/21/2002
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Chun, Kang-wook, Song, Byung-cheol
• Granted Patent: US 7,177,359 B2
• Time in Patent Office: Days
• US Class Current: 375/240.13
• CPC Class Codes: H04N 19/112 according to a given display mode, e.g. for interlaced or progressive display mode
• CPC Class Codes: H04N 19/127 Prioritisation of hardware or computational resources
• 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 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/192 the adaptation method, adaptation tool or adaptation type being iterative or recursive
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 5/145 Movement estimation for video coding H04N19/51

Abstract

A method, a computer readable storage, and an apparatus estimate a motion of a moving image and comprising a process of adjusting a number of search points per frame by adaptively updating a threshold value per frame to regularly maintain fixed a computational complexity of a video encoder irrespective of characteristics of the moving image.

Claims

1. A method to encode a moving image to estimate motion vectors of the moving image, the method comprising:

comparing a sum of absolute difference (SAD) of candidate motion vectors with a threshold value that is set based on a number of search points per macro block of a previous frame;

ending searching of the motion vectors of macro blocks when the SAD of each candidate motion vector is smaller than the threshold value;

determining one of the candidate motion vectors having a minimum SAD to be a motion vector; and

updating the threshold value with respect to a next frame according to the number of search points per macro block of a current frame when searching for the motion vector ends.

2. The method of claim 1, wherein the comparing of the SAD further comprises:

comparing the SAD with a minimum SAD when the SAD of each candidate motion vector is larger than the threshold value;

determining the SAD to be the minimum SAD when the SAD is smaller than the minimum SAD;

calculating the SAD of a next candidate motion vector when the SAD is larger than the minimum SAD;

ending searching of the motion vector of a current macro block when the next candidate motion vector is not present;

determining the candidate motion vector having the minimum SAD to be the motion vector; and

updating the threshold value to be applied to the next frame according to the number of search points per macro block of the current frame when searching for the candidate motion vector ends.

3. The method of claim 1, wherein the updating of the threshold value is determined according to the number of search points per macro block of the current frame when the next macro block is not present.

4. The method of claim 1, wherein the threshold value is updated by THn′

Sn/St,

where THn denotes a previous threshold value, Sn denotes an average number of search points per macro block of the previous frame, and St denotes a target number of search points per macro block.

5. A method to encode a moving image, comprising:

comparing a threshold value, which is set according to a number of search points per macro block of a previous frame, with a sum of absolute difference (SAD) of a motion vector of the previous frame and outputting a compared result;

determining whether searching of a macro block ends according to the compared result and outputting a determination result;

estimating a motion estimation (ME) of the moving image based on the determination result;

calculating a computational complexity of the motion estimation (ME) to obtain a difference between the ME computational complexity and a target;

updating a target discrete cosine transform (DCT) complexity based on a difference between the ME computational complexity and the target,;

setting the threshold value based on the updated target DCT complexity, in order to determine whether to skip performing the DCT on video data; and

determining whether to perform a DCT process on the video data of a current frame according to the set threshold value.

6. The method of claim 5, wherein the ME computational complexity is obtained by calculating a number of search points per macro block.

7. The method of claim 5, where the target DCT computational complexity is updated by adding the difference in the ME computational complexity to the target DCT computational complexity.

8. The method of claim 5, wherein in the skipped performing of the DCT process, the threshold value of the current frame is calculated by the following equation:

9. An apparatus to encode a moving image, comprising:

a discrete cosine transform (DCT) unit performing DCT on input video data on a block-by-block basis;

a quantizer quantizing the video data on which the DCT is performed and generating a quantization parameter;

a motion estimation (ME) unit updating a threshold value TH according to an average number of search points per macro block of a previous frame, comparing the threshold value TH with a sum of absolute difference (SAD) per macro block, and estimating a motion vector of a current frame;

a DCT computational complexity calculator calculating computational complexity according to the average number of search points per macro block according to the threshold value TH per frame updated, estimating a difference between the calculated computational complexity and a target ME computational complexity, and updating a target DCT computational complexity based on the estimated ME computational complexity; and

a DCT skipping unit setting a threshold value to determine whether to skip performing DCT on the video data based on the updated target DCT computational complexity, comparing the SAD per macro block generated by the ME unit and the quantization parameter with the threshold value, and determining whether to allow the DCT unit to perform the DCT on the video data.

10. An apparatus to encode video data, comprising:

a discrete cosine transform (DCT) skipping unit generating a DCT skipping control signal;

a DCT unit performing a DCT process on the video data in an 8×

8 block-by-block unit or processing the video data not to be coded in response to the DCT skipping control signal;

a quantizer quantizing the video data on which the DCT process is performed;

a variable length coding (VLC) unit removing statistical redundancy from the quantized video data;

an inverse quantizer (IQ) inversely quantizing the quantized video data;

an inverse DCT (IDCT) unit performing an IDCT on the inversely quantized video data;

a motion estimation (ME) unit estimating a motion vector (MV) and a sum of absolute difference (SAD) per macro block using the video data of a current frame and the video data of a previous frame, wherein during the estimation of the MV and the SAD, the ME unit updates a threshold value TH according to an average number of search points of the previous frame per macro block, compares the updated threshold value TH and the SAD with respect to the current frame, and determines whether searching for the motion vector is terminated.

11. The apparatus of claim 10, further comprising:

a DCT computational complexity calculator calculating an overall ME computational complexity of the previous frame to estimate a difference between the overall ME computational complexity and a target ME, and updating a target DCT computational complexity based on the difference.

12. The apparatus of claim 10, further comprising:

a frame memory (FM) unit storing the video data, on which the IDCT unit, in frame units, performs the IDCT.

13. The apparatus of claim 10, wherein the DCT skipping unit sets a threshold value T_on+1 according to the updated target DCT computational complexity to skip performing the DCT process on the current frame.

14. The apparatus of claim 13, wherein the DCT skipping unit compares the SAD per block estimated by the ME unit and a quantization parameter (QP) estimated by the quantizer with the set threshold value T_on+1, and sends the DCT unit a compared result as the DCT skipping information.

15. A computer readable storage controlling a computer to estimate a motion of a moving image and comprising a process of:

comparing a sum of absolute difference (SAD) of candidate motion vectors with a threshold value that is set based on a number of search points per macro block of a previous frame;

ending searching of the motion vectors of macro blocks when the SAD of each candidate motion vector is smaller than the threshold value;

determining one of the candidate motion vectors having a minimum SAD to be a motion vector; and

updating the threshold value with respect to a next frame according to the number of search points per macro block of a current frame when searching for the motion vector ends.

16. A computer readable storage controlling a computer to estimate a motion of a moving image and comprising a process of adjusting a number of search points per frame by adaptively updating a threshold value TH per frame to regularly maintain fixed a computational complexity of a video encoder irrespective of characteristics of the moving image.

17. The computer readable storage of claim 16, wherein the comparing of the SAD further comprises:

comparing the SAD with a minimum SAD when the SAD of each candidate motion vector is larger than the threshold value;

determining the SAD to be the minimum SAD when the SAD is smaller than the minimum SAD;

calculating the SAD of a next candidate motion vector when the SAD is larger than the minimum SAD;

ending searching of the motion vector of a current macro block when the next candidate motion vector is not present;

determining the candidate motion vector having the minimum SAD to be the motion vector; and

updating the threshold value to be applied to the next frame according to the number of search points per macro block of the current frame when searching for the candidate motion vector ends.

18. The computer readable storage of claim 16, further comprising:

updating the threshold value TH according to the average number of searching points of each macro block of the current frame; and

estimating a motion of a next frame based on the threshold value TH.

19. The computer readable storage of claim 16, wherein the threshold value TH of an n+1st frame is calculated as follows:

20. The computer readable storage of claim 16, wherein the threshold value TH is inversely proportional to an average number of search points as follows:

21. A computer readable storage controlling a computer to estimate a motion of a moving image and comprising a process of:

comparing a threshold value, which is set according to a number of search points per macro block of a previous frame, with a sum of absolute difference (SAD) of a motion vector of the previous frame and outputting a compared result;

determining whether searching of a macro block ends according to the compared result and outputting a determination result;

estimating a motion estimation (ME) of the moving image based on the determination result;

calculating a computational complexity of the motion estimation (ME) to obtain a difference between the ME computational complexity and a target;

updating a target discrete cosine transform (DCT) complexity based on a difference between the ME computational complexity and the target;

setting the threshold value based on the updated target DCT complexity, in order to determine whether to skip performing the DCT on video data; and

determining whether to perform a DCT process on the video data of a current frame according to the set threshold value.