METHOD OF PREDICTING MOTION AND TEXTURE DATA
The invention relates to a method for generating for at least one block of pixels of a picture of a sequence of interlaced pictures at least one motion predictor and at least one texture predictor from motion data, respectively texture data, associated with the pictures of a sequence of low resolution interlaced pictures.
This application is a Continuation Application of Co-pending U.S. patent application Ser. No. 12/085,987, filed Sep. 23, 2009, herein incorporated by reference.
BACKGROUND OF THE INVENTIONThe invention relates to a method for generating, for pictures of a high resolution interlaced sequence, at least one motion predictor and, where appropriate, at least one texture predictor from motion data and, where appropriate, texture data associated with pictures of a low resolution interlaced sequence.
STATE OF THE ARTHierarchical encoding methods with spatial scalability are known. Scalability represents the ability to stagger information to make it decodable at multiple resolution and/or quality levels. More specifically, a data stream generated by this type of encoding method is divided into several layers, in particular a basic layer and one or more enhancement layers. These methods are used in particular to adapt a single data stream to variable transport conditions (bandwidth, error ratios, etc.), and to the expectations of the customers and the varying capabilities of their receivers (CPU, specifications of the display device, etc.). In the particular case of spatial scalability, the part of the data stream corresponding to low resolution pictures of the sequence can be decoded independently of the part of the data stream corresponding to high resolution pictures. On the other hand, the part of the data stream corresponding to the high resolution pictures of the sequence can be decoded only from the part of the data stream corresponding to the low resolution pictures.
Hierarchical encoding with spatial scalability makes it possible to encode a first data part called basic layer, relative to the low resolution pictures and, from this basic layer, a second data part called enhancement layer, relative to the high resolution pictures. Normally, each macroblock of the high resolution picture is temporally predicted according to a conventional prediction mode (for example, bidirectional prediction mode, direct prediction method, early prediction mode, etc.) or indeed is predicted according to an inter-layer prediction method. In this latter case, motion data (for example, a partitioning of the macroblock into blocks, possibly motion vectors and reference picture indices) and, where appropriate, texture data associated with a block of pixels of the high resolution picture is deduced or inherited from the motion data, respectively texture data, associated with blocks of pixels of a low resolution picture. However, the known methods do not allow such predictors to be generated in the case where the low resolution sequence and the high resolution sequence are interlaced.
SUMMARY OF THE INVENTIONThe object of the invention is to overcome at least one of the drawbacks of the prior art.
The invention relates to a method for generating for at least one block of pixels of a picture of a sequence of high resolution interlaced pictures, called high resolution sequence, at least one motion predictor from motion data associated with the pictures of a sequence of low resolution interlaced pictures, called low resolution sequence, of the same temporal frequency as the high resolution sequence. Each interlaced picture comprises a top field interlaced with a bottom field and is able to be coded in frame mode or in field mode. Each field of an interlaced picture has associated with it a temporal reference. The method makes it possible in particular to generate the at least one motion predictor for the at least one block of pixels of the high resolution picture:
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- from the motion data associated with at least one block of pixels of the top field of a low resolution picture of the same temporal reference as the top field of the high resolution picture if the low resolution picture is coded in field mode; and/or
- from the motion data associated with at least one block of pixels of the bottom field of the low resolution picture of the same temporal reference as the bottom field of the high resolution picture if the low resolution picture is coded in field mode; and/or
- from the motion data associated with at least one block of pixels of a low resolution picture comprising a field with the same temporal reference as the top field or bottom field of the high resolution picture if the low resolution picture is coded in frame mode.
According to a first embodiment, the at least one motion predictor is generated for the at least one block of pixels of the high resolution picture by sub-sampling the motion data associated with the at least one block of pixels of the top field of a low resolution picture of the same temporal reference as the top field of the high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
According to another embodiment, the at least one motion predictor is generated for the at least one block of pixels of the high resolution picture by sub-sampling the motion data associated with the at least one block of pixels of the bottom field of the low resolution picture of the same temporal reference as the bottom field of the high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
According to another embodiment, the at least one motion predictor is generated for the at least one block of pixels of the high resolution picture by sub-sampling the motion data associated with the at least one block of pixels of the low resolution picture comprising a field with the same temporal reference as the top field or bottom field of the high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
The method also makes it possible to generate, for the block of pixels of the high resolution picture, at least one texture predictor:
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- from the texture data associated with at least one block of pixels of the top field of a low resolution picture of the same temporal reference as the top field of the high resolution picture; and/or
- from the texture data associated with at least one block of pixels of the bottom field of a low resolution picture of the same temporal reference as the bottom field of the high resolution picture; and/or
- from the texture data associated with at least one block of pixels of each of the top and bottom fields of the low resolution picture.
Advantageously, the motion data associated with the low resolution pictures comprises motion vectors.
Preferably, the motion vectors associated with a low resolution picture coded in frame mode or with each of the top and bottom fields of a low resolution picture coded in field mode have the same parity.
The method is advantageously used by a method of encoding high resolution pictures from low resolution pictures and by a method of decoding high resolution pictures from low resolution pictures.
Preferably, the low resolution pictures are encoded according to the MPEG-4 AVC standard.
The invention will be better understood and illustrated by means of exemplary embodiments and advantageous implementations, by no means limiting, given with reference to the appended figures in which:
The invention relates to an inter-layer prediction method which consists in generating motion predictors and, where appropriate, texture predictors for pictures of an ordered sequence of high resolution interlaced pictures, called high resolution sequence, from pictures of an ordered sequence of low resolution interlaced pictures, called low resolution sequence. The sequences are divided into groups of pictures (GOP). Each low and high resolution picture comprises a top field interlaced with a bottom field. In
The invention therefore consists in generating, for pictures of the high resolution sequence or for at least one block of pixels of the latter, at least one motion predictor and, where appropriate, at least one texture predictor. A texture predictor associated with a high resolution picture or with at least one block of pixels of a high resolution picture is a picture or a prediction block which associates with each of its pixels texture data (for example, a luminance value and, where appropriate, chrominance values), which is generated from texture data associated with at least one picture (or field) or at least one block of pixels of a low resolution picture (or at least one block of pixels of a field) according to a method of sub-sampling the texture such as the ESS method applied to the texture (ESS standing for Extended Spatial Scalability) which is described in sections S.8.3.6.4 and S.8.5.14.2 of document ISO/IEC MPEG & ITU-T VCEG, entitled “Joint Scalable Video Model JSVM3 Annex-S”, referenced JVT-P202, J. Reichel, H. Schwarz, M. Wien. This document is referenced JSVM3 below. A motion predictor associated with a high resolution picture or with at least one block of pixels of a high resolution picture is defined as a prediction picture or a prediction block with which is associated motion data (for example, a type of partitioning, possibly reference picture indices making it possible to identify the reference pictures to which the motion vectors point). The motion predictor is generated from motion data associated with at least one picture (or field) or at least one block of pixels of a low resolution picture (or at least one block of pixels of a field) according to a motion sub-sampling method such as the ESS method applied to the motion which is described in section S.8.4.1.6.3 of JSVM3, or such as the modified ESS method, described below, derived from the ESS method applied to the motion. The modified ESS method, referenced MESS in
in the horizontal direction of the picture and
in the vertical direction of the picture, where wi and 2hi are respectively the width and the height of the last intermediate motion predictor generated. Furthermore, for each prediction macroblock, the motion vector inheritance method is modified so as not to generate invalid motion vectors, i.e. vectors that point to fields or frame pictures that are not available in the temporal breakdown process. In this case, if all the motion vectors associated with a prediction macroblock MB_pred are invalid then the inter-layer motion prediction is not authorized for this macroblock. Otherwise (i.e. if at least one of the vectors is valid), the ESS prediction method applied to the motion is used.
The method according to the invention, illustrated by
Texture predictors associated with a high resolution picture of index k in
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- A texture predictor of dimension W by H is generated 20 for the top field of the high resolution picture on the basis of the texture data of the top field of the low resolution picture of index k by applying the ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture;
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- A texture predictor of dimension W by H is generated 21 for the bottom field of the high resolution picture on the basis of the texture data of the bottom field of the low resolution picture of index k by applying the ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture.
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- A frame texture predictor of dimension W by 2H is generated 22 by interlacing the texture predictors associated with the top and bottom fields.
According to an embodiment illustrated in
in the horizontal direction of the picture and
in the vertical direction of the picture.
If the low resolution picture of index k is coded in field mode, motion predictors associated with a high resolution picture of index k in
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- a motion predictor of dimension W by H is generated 30 for the top field of the high resolution picture on the basis of the motion data of the top field of the low resolution picture of index k for the top field of the high resolution picture on the basis of the low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture;
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- A motion predictor of dimension W by H is generated 31 for the bottom field of the high resolution picture on the basis of the motion data of the bottom field of the low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture; and
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- A frame motion predictor of dimension W by 2H is generated 32 on the basis of the motion data of the bottom field of the low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture.
In the other cases, i.e. if the low resolution picture of index k is coded in frame mode, motion predictors associated with a high resolution picture of index k in
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- A motion predictor of dimension W by H is generated 33 for the top field of the high resolution picture on the basis of the motion data of the frame low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture;
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- A motion predictor of dimension W by H is generated 33 for the bottom field of the high resolution picture on the basis of the motion data of the frame low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture; and
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- A frame motion predictor of dimension W by 2H is generated 34 on the basis of the motion data of the frame low resolution picture of index k by applying the modified ESS method with an inter-layer ratio of
in the horizontal direction of the picture and
in the vertical direction of the picture.
In this case, the motion predictors associated with the bottom field and top field of the high resolution picture are identical.
If the method is used by a coding method all motion predictors (respectively texture predictors) may be generated in order to select the most appropriate one according to a given criteria, e.g. a rate distortion criteria. If said method is used by a decoding method then a single motion predictor (respectively a single texture predictor) is generated, the type of predictor being specified in the bitstream.
Of course, the invention is not limited to the abovementioned exemplary embodiments. In particular, those skilled in the art can apply any variant to the embodiments described and combine them to benefit from their different advantages. For example, the method according to the invention can be applied to a part of the high resolution picture. In practice, it is possible to generate motion and/or texture predictors for blocks of pixels (for example, macroblocks measuring 16 by 16 pixels) of the high resolution picture from motion and/or texture data associated with blocks of pixels of the low resolution pictures. Similarly, the invention has been described in the case where the top field of an interlaced picture is displayed first (“top field first” case) and can be extended directly to the case where the bottom field is displayed first (“bottom field first” case) by reversing the top and bottom fields. Moreover, the invention can also be extended to the case of several high resolution sequences (i.e. several enhancement layers). Furthermore, the invention is advantageously used by a method of encoding or decoding a sequence of pictures or video. Preferably, the sequence of low resolution pictures is encoded according to the MPEG4 AVC encoding standard defined in document ISO/IEC 14496-10 (“Information technology—Coding of audio-visual objects—Part 10: Advanced Video Coding”).
Claims
1. Method, as part of a scalable encoding or decoding method, for generating for at least one block of pixels of a picture of a high resolution sequence of high resolution interlaced pictures at least one motion predictor from motion data associated with the pictures of a low resolution sequence of low resolution interlaced pictures each interlaced picture comprising a top field interlaced with a bottom field and able to be coded in frame mode or in field mode, each field of an interlaced picture having associated with it a temporal reference, wherein the method comprises
- generating said at least one motion predictor from the motion data associated with at least one block of pixels of the top field of a low resolution picture of the same temporal reference as the top field of said high resolution picture when said low resolution picture is coded in field mode;
- generating said at least one motion predictor from the motion data associated with at least one block of pixels of the bottom field of said low resolution picture of the same temporal reference as the bottom field of said high resolution picture when said low resolution picture is coded in field mode; and
- generating said at least one motion predictor from the motion data associated with at least one block of pixels of a low resolution picture comprising a field with the same temporal reference as the top field or bottom field of the high resolution picture when said low resolution picture is coded in frame mode.
2. Method according to claim 1, wherein generating said at least one motion predictor for said at least one block of pixels of said high resolution picture comprises subsampling said motion data associated with said at least one block of pixels of said top field of a low resolution picture of the same temporal reference as the top field of said high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
3. Method according to claim 1, wherein generating said at least one motion predictor for said at least one block of pixels of said high resolution picture comprises subsampling said motion data associated with said at least one block of pixels of said bottom field of said low resolution picture of the same temporal reference as the bottom field of said high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
4. Method according to claim 1, wherein generating said at least one motion predictor for said at least one block of pixels of said high resolution picture comprises subsampling said motion data associated with said at least one block of pixels of said low resolution picture comprising a field with the same temporal reference as the top field or bottom field of the high resolution picture with a horizontal inter-layer ratio in the horizontal direction of the picture and a vertical inter-layer ratio in the vertical direction of the picture.
5. Method according to claim 1, wherein the method further comprises, for said block of pixels of said high resolution picture:
- generating at least one texture predictor from the texture data associated with at least one block of pixels of the top field of a low resolution picture of the same temporal reference as the top field of said high resolution picture; and/or
- generating at least one texture predictor from the texture data associated with at least one block of pixels of the bottom field of a low resolution picture of the same temporal reference as the bottom field of said high resolution picture; and/or
- generating at least one texture predictor from the texture data associated with at least one block of pixels of each of said top and bottom fields of said low resolution picture.
6. Method according to claim 1, wherein the motion data associated with the low resolution pictures comprises motion vectors.
7. Method according to claim 6, wherein the motion vectors associated with a low resolution picture coded in frame mode or with each of the top and bottom fields of a low resolution picture coded in field mode have the same parity.
8. Method according to claim 7 wherein the low resolution pictures are encoded according to the MPEG-4 AVC standard.
Type: Application
Filed: Aug 28, 2014
Publication Date: Dec 18, 2014
Inventors: Jérôme VIERON (Bedee), Vincent BOTTREAU (Chateaubourg), Patrick LOPEZ (Livre Sur Changeon)
Application Number: 14/471,479
International Classification: H04N 19/30 (20060101); H04N 19/51 (20060101);