METHODS AND DEVICES FOR ENCODING AND DECODING AN IMAGE SEQUENCE IMPLEMENTING A PREDICTION BY FORWARD MOTION COMPENSATION, CORRESPONDING STREAM AND COMPUTER PROGRAM

• US 20130034163A1
• Filed: 03/29/2011
• Published: 02/07/2013
• Est. Priority Date: 03/31/2010
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Amonou, Isabelle, Pateux, Stephane, Cammas, Nathalie
• Granted Patent: US 9,756,357 B2
• Time in Patent Office: Days
• US Class Current: 375/240.16
• CPC Class Codes: H04N 19/52 by predictive encoding
• CPC Class Codes: H04N 19/553 Motion estimation dealing with occlusions
• CPC Class Codes: H04N 19/57 Motion estimation characterised by a search window with variable size or shape
• CPC Class Codes: H04N 19/583 Motion compensation with overlapping blocks
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards

Abstract

A method and apparatus for encoding a sequence of images by predicting at least one current image by forward motion compensation from at least one reference image. Prediction implements, for at least one current block of the current image: forward projection of a block of the reference image on the current image, delivering a projected block at least partially overlapping the current block; partitioning the current block delivering a sub-block at least partially overlapped by at least one projected block; and at least one iteration of the following steps for at least one overlapped sub-block: checking that the overlapped sub-block complies with a predetermined allotting criterion; with a positive check, allotting, to the overlapped sub-block, one of the projected motion vectors; and with a negative check, and so long as a predetermined minimum size is not reached for the overlapped sub-block: partitioning of the overlapped sub-block.

Claims

1. A method for encoding a sequence of images, the method comprising:

predicting with a processor at least one current image by forward motion compensation from at least one reference image, wherein predicting implements;

for at least one block of said current image, called a current block, a sub-step of forward projection of at least one block of the reference image on said current image, delivering at least one projected block at least partially overlapping said current block, a motion vector representing shift of the projected block in the current image, standardized to take account of a temporal distance between said reference image and said current image, called a projected motion vector, being associated with each projected block;

partitioning said current block delivering at least one sub-block at least partially overlapped by at least one of said projected blocks, called an overlapped sub-block; and

at least one iteration of the following steps for at least one overlapped sub-block;

checking that the overlapped sub-block complies with a predetermined allotting criterion;

in the event of a positive check, allotting, to said overlapped sub-block, one of the projected motion vectors selected from among the projected motion vector or vectors associated with the projected block or blocks at least partially overlapping said overlapped sub-block; and

in the event of a negative check, and so long as a predetermined minimum size is not reached for said overlapped sub-block;

partitioning of said overlapped sub-block delivering at least one new overlapped sub-block.

2. The method for encoding according to claim 1, wherein said predetermined allotting criterion pertains to the group consisting of the following criteria:

the overlapped sub-block is overlapped at least partially by only one of the projected blocks;

a predetermined number of pixels of the overlapped sub-block is overlapped by one of the projected blocks.

3. The method for encoding according to claim 1, wherein said allotting step selects the projected motion vector associated with the projected block overlapping the most pixels of said overlapped sub-block.

4. The method for encoding according to claim 1, wherein said allotting step implements the following for at least two projected blocks at least partially overlapping said overlapped sub-block with which projected motion vectors called candidate vectors are associated:

a step of backward projection, in said reference image, of said overlapped sub-block along each of said candidate vectors, delivering at least two backward projected sub-blocks;

for each sub-block projected backward along a candidate vector, determining the number of pixels of said reference image overlapped by said backward projected sub-block having a motion vector similar to said candidate vector, delivering an overlap rate per candidate vector;

allotting, to the overlapped sub-block, the candidate vector having the best overlap rate.

5. The method for encoding according to claim 1, wherein the method also comprises the following steps:

predicting said current block by shifting the block of the reference image, associated with the projected motion vector selected during said allotting step, along said selected projected motion vector, delivering a predicted block;

determining at least one residue of texture by comparison of said current block and the predicted block;

encoding said at least one residue of texture.

6. The method for encoding according to claim 1, wherein the method also comprises the following steps:

determining a motion vector associated with said current block;

determining at least one motion vector residue by comparison of said selected projected motion vector and said motion vector associated with said current block;

encoding said at least one motion vector residue.

7. The method for encoding according to claim 1, wherein the method comprises predicting at least one motion vector associated with a block neighboring said current block in said current image, from said projected motion vector selected during said allotting step.

8. The method for encoding according to claim 1, wherein the method comprises a step of insertion, into a stream representing said sequence of images, of at least one flag representing a novel mode of encoding implemented for at least one block or sub-block of the current image, signaling the use of at least one projected motion vector selected for the encoding of said block or sub-block.

10. The method of claim 1, further comprising:

generating a stream representing the sequence of images encoded, wherein the stream comprises at least one flag representing a novel encoding mode implemented for at least one block or sub-block of the current image, signaling use of at least one selected projected motion vector for the encoding of said block or sub-block.

9. A device for encoding a sequence of images, the device comprising:

means for predicting at least one current image by forward motion compensation from at least one reference image, said prediction means comprising, for at least one block of said current image, called a current block;

means for forward projection of at least one block of the reference image on said current image, delivering at least one projected block at least partially overlapping said current block, a motion vector representing shifting of the projected block in the current image, standardized to take account of a temporal distance between the reference image and the current image, called a projected motion vector, being associated with each projected block,

means for partitioning said current block, delivering at least one sub-block at least partially overlapped by at least one of said projected blocks, called an overlapped sub-block, and

the following means, activated at least once for at least one overlapped sub-block in the form of an iteration;

means for checking that the overlapped sub-block complies with a predetermined allotting criterion;

means for allotting, to said overlapped sub-block, one of said projected motion vectors selected from among the projected motion vector or vectors associated with the projected block or blocks at least partially overlapping the overlapped sub-block, activated in the event of a positive check; and

means for partitioning said overlapped sub-block delivering at least one new overlapped sub-block, activated in the event of a negative check, and so long as a predetermined minimum size is not reached for said overlapped sub-block.

11. A method for decoding a stream representing a sequence of images, the method comprising:

predicting with a processor at least one image to be rebuilt by forward motion compensation from at least one reference image, wherein predicting implements;

for at least one block of said image to be rebuilt, called a block to be rebuilt, a sub-step of forward projection of at least one block of the reference image on said image to be rebuilt, delivering at least one projected block at least partially overlapping said block to be rebuilt, a motion vector representing shift of the block projected in the image to be rebuilt, standardized to take account of a temporal distance between said reference image and said image to be rebuilt, called a projected motion vector, being associated with each projected block,

partitioning (53) of said block to be rebuilt, delivering at least one sub-block at least partially overlapped by at least one of said projected blocks, called an overlapped sub-block; and

at least one iteration of the following steps for at least one overlapped sub-block;

checking that the overlapped sub-block complies with a predetermined allotting criterion;

in the event of a positive check;

allotting, to said overlapped sub-block, one of said projected motion vectors selected from among the projected motion vector or vectors associated with said projected block or blocks at least partially overlapping said overlapped sub-block; and

in the event of a negative check, and so long as a predetermined minimum size is not reached for said overlapped sub-block;

partitioning of said overlapped sub-block delivering at least one new overlapped sub-block.

12. The method for decoding according to claim 11, wherein the method also implements the following steps:

predicting said block to be reconstructed, by shifting the block of the reference image associated with the projected motion vector selected during said allotting step along said selected projected motion vector, delivering a predicted block;

decoding at least one residue of texture extracted from said stream representing a sequence of images, obtained during the encoding of said sequence of image; and

rebuilding said block to be rebuilt from said at least one residue of texture and from the predicted block.

13. The method for decoding according to claim 11, wherein the method also implements the following steps:

determining a motion vector associated with said block to be rebuilt;

decoding at least one residue of a motion vector extracted from said stream representing a sequence of images, obtained during the encoding of said sequence of images; and

rebuilding said block to be rebuilt from said at least one residue of the motion vector and from said motion vector associated with said block to be rebuilt.

14. A device for decoding a stream representing a sequence of images, the device comprising:

means for predicting at least one image to be rebuilt by forward motion compensation from at least one reference image, said prediction means comprising, for at least one block of said image to be rebuilt, called a block to be rebuilt;

means for forward projection of at least one block of the reference image on said image to be rebuilt, delivering at least one projected block at least partially overlapping said block to be rebuilt, a motion vector representing shift of the block projected in the image to be rebuilt, standardized to take account of a temporal distance between said reference image and said image to be rebuilt, called a projected motion vector, being associated with each projected block,

means for partitioning said block to be rebuilt delivering at least one sub-block at least partially overlapped by at least one of said projected blocks, called an overlapped sub-block, and

the following means, activated at least once for at least one overlapped sub-block in the form of an iteration;

means for checking that said overlapped sub-block complies with a predetermined allotting criterion;

means for allotting, to said overlapped sub-block, one of said projected motion vectors selected from among the projected motion vector or vectors associated with the projected block or blocks at least partially overlapping said overlapped sub-block, activated in the event of a positive check; and

means for partitioning said overlapped sub-block delivering at least one new overlapped sub-block, activated in the event of a negative check, and so long as a predetermined minimum size is not reached for said overlapped sub-block.

15. A non-transitory computer-readable medium comprising a computer program comprising instructions for implementing a method for encoding a sequence of images, when this program is executed by a processor, wherein the instructions comprise:

instructions configured to cause the processor to predict at least one current image by forward motion compensation from at least one reference image, wherein the processor implements;

for at least one block of said current image, called a current block, a sub-step of forward projection of at least one block of the reference image on said current image, delivering at least one projected block at least partially overlapping said current block, a motion vector representing shift of the projected block in the current image, standardized to take account of a temporal distance between said reference image and said current image, called a projected motion vector, being associated with each projected block;

partitioning said current block delivering at least one sub-block at least partially overlapped by at least one of said projected blocks, called an overlapped sub-block; and

at least one iteration of the following steps for at least one overlapped sub-block;

checking that the overlapped sub-block complies with a predetermined allotting criterion;

in the event of a positive check, allotting, to said overlapped sub-block, one of the projected motion vectors selected from among the projected motion vector or vectors associated with the projected block or blocks at least partially overlapping said overlapped sub-block; and

in the event of a negative check, and so long as a predetermined minimum size is not reached for said overlapped sub-block;

partitioning of said overlapped sub-block delivering at least one new overlapped sub-block.