Methods for motion estimation with adaptive motion accuracy

• US RE44,012 E1
• Filed: 11/04/2011
• Issued: 02/19/2013
• Est. Priority Date: 07/27/1999
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ribas-Corbera, Jordi, Shen, Jiandong
• Primary Examiner(s): Rao, Andy
• Application Number:
  US13/289,902
• Time in Patent Office: 473 Days
• Field of Search: 37524001-24029
• US Class Current: 375/240.17
• CPC Class Codes: N/A

Abstract

Methods for motion estimation with adaptive motion accuracy of the present invention include several techniques for computing motion vectors of high pixel accuracy with a minor increase in computation. One technique uses fast-search strategies in sub-pixel space that smartly searches for the best motion vectors. An alternate technique estimates high-accurate motion vectors using different interpolation filters at different stages in order to reduce computational complexity. Yet another technique uses rate-distortion criteria that adapts according to the different motion accuracies to determine both the best motion vectors and the best motion accuracies. Still another technique uses a VLC table that is interpreted differently at different coding units, according to the associated motion vector accuracy.

Claims

1. A fast-search adaptive motion accuracy search method for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said method comprising the steps of:

(a) searching a first set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₁ to find a best motion vector V₂ using a first criteria;

(b) searching a second set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₂ to find a best motion vector V₃ using a second criteria;

(c) searching a third set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₃ to find said best motion vector of said macroblock using a third criteria; and

(d) wherein at least one of said first criteria, said second criteria, and said third criteria is a rate-distortion criteria.

2. The method of claim 1, said step of searching a first set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₁ to find a best motion vector V₂ further comprising the step of searching a first set of eight motion vector candidates in a grid of ½

-pixel resolution of square radius 1 centered on V₁ to find a best motion vector V₂.

3. The method of claim 1, said step of searching a second set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₂ to find a best motion vector V₃ further comprising the step of searching a second set of eight motion vector candidates in a grid of ⅙

-pixel resolution of square radius 1 centered on V₂ to find a best motion vector V₃.

4. The method of claim 1 further comprising the steps of using V₂ as the motion vector for the macroblock if V₂ has the smallest rate-distortion cost and skipping step (c) of claim 1.

5. The method of claim 1, said step of searching a third set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₃ to find said best motion vector of said macroblock further comprising the step of searching a third set of eight motion vector candidates in a grid of ⅙

-pixel resolution of square radius 1 centered on V₃ to find said best motion vector of said macroblock.

6. The method of claim 1, said step of searching a third set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₃ to find said best motion vector of said macroblock further comprising the step of skipping motion vector candidates of said third set of motion vector candidates that have already been tested.

7. The method of claim 1 further wherein said step of searching said first set of motion vector candidates further comprises the step of searching said first set of motion vector candidates using a first filter to do a first interpolation, said step of searching said second set of motion vector candidates further comprises the step of searching said second set of motion vector candidates using a second filter to do a second interpolation, and said step of searching said third set of motion vector candidates further comprises the step of searching said third set of motion vector candidates using a third filter to do a third interpolation.

8. The method of claim 1, said step of searching a second set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₂ to find a best motion vector V₃ further comprising the steps of:

(a) searching three candidates of ⅓

-pel accuracy V₂ and a ½

-pel location with the next lowest rate-distortion cost if V₂ is at the center;

(b) searching four vector candidates of ⅓

-pel accuracy that are closest to V₂ if V₂ is a corner vector; and

(c) determining which of two corners has lower rate-distortion cost and searching four vector candidates of ⅓

-pel accuracy that are closest to a line between said corner with lower rate-distortion cost, if V₂ is between two corners vectors.

24. The method of claim 1, wherein said first criteria, said second criteria, and said third criteria are all rate-distortion criteria.

9. An adaptive motion accuracy search method for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said method comprising the steps of:

(a) searching a first set of motion vector candidates in a grid centered on V₁ using a first criteria to find a best motion vector V₂ using a first filter to do a first interpolation;

(b) searching a second set of motion vector candidates in a grid centered on V₂ using a second criteria to find a best motion vector V₃ using a second filter to do a second interpolation; and

(c) searching a third set of motion vector candidates in a grid centered on V₃ using a third criteria to find said best motion vector of said macroblock using a third filter to do a third interpolation;

(d) wherein at least one of said first criteria, said second criteria, and said third criteria is a rate-distortion criteria.

10. The method of claim 9 wherein said step of searching using a first filter to do a first interpolation further comprises using a simple filter to do a coarse interpolation.

11. The method of claim 9 wherein said step of searching using a first filter to do a first interpolation further comprises using a simple filter to do a coarse interpolation and said step of searching using a second filter to do a second interpolation further comprises using a complex filter to do a fine interpolation.

12. The method of claim 11 wherein said step of searching using a third filter to do a third interpolation further comprises using a complex filter to do a fine interpolation.

13. The method of claim 9 wherein said step of searching using a first filter to do a first interpolation further comprises using a bilinear filter to interpolate the reference frame by 2×

2.

14. The method of claim 9 wherein said step of searching using a first filter to do a first interpolation further comprises using a bilinear filter to interpolate the reference frame by 2×

2 and said step of searching using a second filter to do a second interpolation further comprises using a cubic filter to do a fine interpolation.

15. The method of claim 14 wherein said step of searching using a third filter to do a third interpolation further comprises using a cubic filter to do a fine interpolation.

25. The method of claim 9, wherein said first criteria, said second criteria, and said third criteria are all rate-distortion criteria.

16. An adaptive motion accuracy search method for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said method comprising the steps of:

(a) searching at a first motion accuracy for a first best motion vector of said macroblock;

(b) encoding said first best motion vector and said first motion accuracy;

(c) searching for at least one second best motion vector of said macroblock at an at least one second motion accuracy;

(d) encoding said at least one second best motion vector and said at least one second motion accuracy; and

(e) selecting the best motion vector of said first and at least one second best motion vectors using rate-distortion criteria.

17. The method of claim 16 wherein said step of selecting the best motion vector using rate-distortion criteria further comprises the step of said rate-distortion criteria adapting according to the different motion accuracies to determine both the best motion vectors and the best motion accuracies.

18. The method of claim 16, said step of searching for at least one second best motion vector at an at least one second motion accuracy further comprising the step of searching for at least one second best motion vector of said macroblock at an at least one second motion accuracy that is finer than said first motion accuracy.

19. The method of claim 16 wherein said step of selecting the best motion vector using rate-distortion criteria further comprises the step of using rate-distortion criteria of the type “

distortion+L*Bits”

to select the best motion vector.

20. An adaptive motion accuracy search method for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said method comprising the steps of:

(a) searching at a motion accuracy for a best motion vector of said macroblock using rate-distortion criteria;

(b) encoding said motion accuracy using a code from a VLC table that is interpreted differently at different coding units according to the associated motion vector accuracy; and

(c) encoding said best motion vector in the respective accuracy space.

21. A system for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said system comprising:

(a) a first encoder for searching a first set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₁ using a first criteria to find a best motion vector V₂;

(b) a second encoder for searching a second set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₂ using a second criteria to find a best motion vector V₃; and

(c) a third encoder for searching a third set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₃ using a third criteria to find said best motion vector of said macroblock;

(d) wherein at least one of said first criteria, said second criteria, and said third criteria is a rate-distortion criteria.

22. The system of claim 21 wherein said first, second, and third encoders are a single encoder.

26. The system of claim 21, wherein said first criteria, said second criteria, and said third criteria are all rate-distortion criteria.

23. A fast-search adaptive motion accuracy search method for estimating motion vectors in motion-compensated video coding by finding a best motion vector for a macroblock, said method comprising the steps of:

(a) searching a first set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₁ to find a best motion vector V₂;

(b) searching a second set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₂ to find a best motion vector V₃;

(c) searching a third set of motion vector candidates in a grid of sub-pixel resolution of a predetermined square radius centered on V₃ to find said best motion vector of said macroblock, and

(d) using V₂ as the motion vector for the macroblock if V₂ has the smallest rate-distortion cost and skipping step (c).

27. A motion compensated video coding apparatus comprising:

a motion compensation means for compensating a motion, block by block, using the motion vector, that represents an amount of movement from a corresponding position of a reference frame to an objective current block, for each of the blocks divided from a frame of an input image, with two or more fractional accuracy levels expressed by 1/N pel (N is an arbitrary integer); and

an encoding means for encoding the fractional accuracy level and the motion vector, wherein

encoding the fractional accuracy level is performed separately from encoding the motion vector,

encoding the motion vector for each block is performed block by block,

the motion compensation is performed by interpolation with a first filter which is selected among a plurality of different interpolation filters corresponding to a first fractional accuracy level of the two or more fractional accuracy levels,

the motion compensation is performed by interpolation with a second filter that requires more complicated calculation than that for the first filter and is selected among the plurality of different interpolation filters corresponding to a second fractional accuracy level that is more accurate than the first fractional accuracy level of the two or more fractional accuracy levels, and

the fractional accuracy level can be set frame by frame and is fixed for every motion vector within a frame but can be different from the fractional accuracy level used for a different frame.

28. A motion compensated video decoding apparatus comprising:

a decoding means for decoding a motion vector that represents an amount of movement from a corresponding position of a reference frame in an objective current block for each of the blocks included in the coded data obtained by encoding an image frame block by block;

a decoding means for decoding a fractional accuracy level of a motion vector with two or more fractional accuracy levels expressed by 1/N pel (N is an arbitrary integer); and

a motion compensation means for compensating a motion using the decoded fractional accuracy level and the decoded motion vectors, wherein

decoding the fractional accuracy level is performed separately from decoding the motion vector,

decoding the motion vector for each block is performed block by block,

the motion compensation is performed by interpolation with a first filter which is selected from among a plurality of different interpolation filters corresponding to a first fractional accuracy level of the two or more fractional accuracy levels,

the motion compensation is performed by interpolation with a second filter that requires more complicated calculation than that for the first filter and is selected among the plurality of different interpolation filters corresponding to a second fraction accuracy level that is more accurate than the first fractional accuracy level of the two or more fraction accuracy levels, and

the fractional accuracy level can be set frame by frame and is fixed for every motion vector within a frame but can be different from the fractional accuracy level used for a different frame.