HK1228622B - Method for decoding video using buffer compression for motion vector competition - Google Patents

Description

TECHNICAL FIELD

The present invention relates to a method for image decoding using buffer compression for motion vector competition.

BACKGROUND ART

CROSS-REFERENCE TO RELATED APPLICATIONS: THIS APPLICATION CLAIMS THE BENEFIT OF U.S. PROVISIONAL APP. NO. 61/435,243. FILED JANUARY 21. 2011 .

Existing video coding standards, such as H.264/AVC, generally provide relatively high coding efficiency at the expense of increased computational complexity. As the computational complexity increases, the encoding and/or decoding speeds tend to decrease. Also, the desire for increasingly accurate motion estimation tends to require increasingly larger memory requirements. The increasing memory requirements tend to result in increasingly more expensive and computationally complex circuitry, especially in the case of embedded systems.ONNO P: "CE9: Cross verification about the adaption and modification (3.2.c) of the set of predictors", 4. JCT-VS Meeting; 95. MPEG MEETING; 20-1-2011 - 28-1-2011; DAEGU;(JOINT COLLABORATIVE TEAM ON VIDEO CODING OF ISO/IEC JTC1/SC29/WG11AND ITU-T SG.16);URL: HTTP://WFTP3.ITU.INT/AV-ARCH/JCTVC-SITE/,, no. JCTVC-D117, 15 January 2011 (2011-01-15), XP030008157, ISSN: 0000-0015 describes an experiment, having the principle to change the order of motion vector predictor candidates in a list in such a way that the temporarily collocated motion vector predictor is the first element to be considered in the list. This is to be contrasted to former approaches where it is considered as the last element.

FUJIBAYASHI (NTT DOCOMO) A ET AL: "CE9: 3.2d Simplified motion vector prediction", 95 MPEG MEETING; 24-1-2011 - 28-1-2011; DAEGU; (MOTION PICTURE EXPERT GROUP OR ISO/IEC JTC1/SC29/WG11),, no. m18991, 15 January 2011 (2011-01-15), XP030047560, reports simulation results for an experiment where a selection manner of predictive motion vector candidates is modified. The number of these candidates is changed to be formed from up to three motion vector predictors: a left, a top and a collocated predictor. The process of getting a left and a top predictor is modified where the first available motion vector is searched from the group of neighboring blocks left of the current block. The top predictor is derived in a similar fashion. The third predictor is derived from the collocated block as conventional and the list predicted is then decimated by removing duplicate predictors.

TOURAPIS A M ET AL: "FAST ME in the JM reference software", 16. JVT MEETING; 73. MPEG MEETING; 24-07-2005 - 29-07-2005; POZNAN,PL; (JOINT VIDEO TEAM OF ISO/IEC JTC1/SC29/WG11 AND ITU-T SG.16),, no. JVT-P026r1, 29 July 2005 (2005-07-29), XP030006068,ISSN: 0000-0416 discloses a predictor selection, wherein instead of having to examine all possible checking positions within a given search area, only a smaller set of highly reliable predictors is examined, which is believed that might contain or be close enough to the best possible position. An adaptive predictor set is defined.

BOSSEN F ET AL: "Simplified motion vector coding method", 2. JCT-VC MEETING; 21-7-2010 - 28-7-2010; GENEVA; (JOINT COLLABORATIVETEAM ON VIDEO CODING OF ISO/IEC JTC1/SC29/WG11 AND ITU-T SG.16); URL:HTTP://WFTP3.ITU.INT/AV-ARCH/JCTVC-SITE/,, no. JCTVC-B094, 17 July 2010 (2010-07-17), XP030007674, ISSN: 0000-0046 relates to a method for coding vector motion data. Again, a left predictor is obtained by searching for the first available motion left of the current block. A motion vector is considered available if the vector exists and the reference frame index of the searched block is identical to the reference index of the current block. The search is performed from top to bottom, and only the first available predictor is added to the list of candidates. A top predictor is derived in a similar fashion. A third predictor is derived from the collocated block. If the collocated block has a motion vector, it is scaled according to the current temporal distance between the current frame and the reference frame. The list of predictors is then decimated by removing duplicate predictors.

SUMMARY OF INVENTION

The present invention provides the method of the independent claims.

One embodiment of the present invention discloses a method for decoding video comprising: (a)identifying a first set of motion vectors from at least one neighboring block in a current frame; (b)identifying a second set of motion vectors from at least one block in a previous frame: (c)creating a list by using the first set and the second set of motion vectors; (d)removing a duplicate motion vectors from the list and thereafter selecting a motion vector in the list.

Another embodiment of the present invention discloses a method for decoding video comprising: (a)creating a list of motion vectors by using a first set of motion vectors from at least one neighboring block in a current frame and a second set of motion vectors from at least one block in a previous frame; (b)removing a duplicate motion vectors from the list and thereafter selecting a motion vector transmitted from the list.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

• FIG. 1 illustrates an encoder and decoder.
• FIG. 2 illustrates a vector decoding process.
• FIG. 3 illustrates a partial pair of two frames.
• FIG. 4 illustrates a motion vector competition process.
• FIG. 5 illustrates a particular motion vector competition process.
• FIG. 6 illustrates a decoder with motion vector competition.

DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, a video system typically includes a video source such as an encoder or storage for encoded video, and a decoder. In the video decoder, one of the aspects that facilitates higher compression performance for high resolution video is larger block structures with flexible mechanisms of sub-partitioning.

For example, the TMuC (JCT-VC, "Test Model under Consideration", document JCTVC-A205 of JCT-VC, (2010), incorporated by reference herein) defines coding units (CUs) which define sub-partitioning of an image into rectangular regions. The coding unit contains one or more prediction units (PUs) and transform units (TUs). The partition geometry of these elements may be encoded using a tree segmentation structure. At the level of the PU, either intra-picture or inter-picture prediction may be selected. Intra-picture prediction may be performed from samples of already decoded adjacent PUs, where the different modes may include (1) DC (flat average), (2) horizontal, (3) vertical, (4) one of up to 28 angular directions (number depending on block size), (5) plane (amplitude surface) prediction, and (6) bilinear prediction. The signaling of the mode is derived from the modes of adjacent PUs. Inter-picture prediction is performed from regions(s) of already decoded pictures stored in the reference picture buffer. This permits selection among multiple reference pictures, as well as bi-prediction (including weighted averaging) from two reference pictures or two positions in the same reference picture. The reference area is selected by specifying a motion vector displacement and a reference picture index, which may generally be referred to herein as a motion vector. For efficient encoding or decoding, derivation of motion vectors from those of adjacent PUs may be made by a median computation or as motion vector competition (described below). The motion vector difference between the predicted motion vectors and the actual motion vectors may also be transmitted by the encoder or received by the decoder. Motion compensation may be performed with a motion vector precision up to quarter-sample or one-eights sample precision. Referring to FIG. 2, motion compensation for the current prediction unit or block uses a motion vector coding process that generally includes receiving a motion vector prediction control parameter in the bit stream (Step 100). The motion vector prediction control parameter may be an index value used to select from among a group of available motion vectors. A motion vector prediction (Step 110) may be generated based upon the motion vector prediction control parameter received in Step 100. The decoder may also receive a motion vector difference (Step 120) in the bit stream. The motion vector difference received in Step 120 and the predicted motion vector in Step 110 are used to generate a motion vector for the current prediction unit or block (Step 130). In general, the bit stream provided to the decoder includes, among other data, a control parameter for the motion vector, and the difference between the prediction generated by the motion vector competition tool and the desired motion vector. A motion vector competition tools generally refers to the process of Step 100 and Step 110 in FIG. 2.

Referring to FIG. 3, for the motion vector competition process a list of candidate motion vectors may be created. In general, the potential motion vectors may include, for example, a motion vector MVB from above the current block A, a motion vector MVC to the left of the current block A, and a motion vector MVD to the above left of the current block A. The potential motion vectors may, for example, include one or more of all of the adjacent blocks. The list of candidate motion vectors may also include one or more motion vectors from one or more previously encoded frames. For example, one of the previous motion vectors may be the co-located block A' of the previous frame with the current block A. It is noted that often the video coding and decoding is not performed in the same temporal order in which it is displayed.

Referring to FIG. 4, a particular implementation of a motion vector competition process utilizes a list of motion vector(s) of neighboring block(s) in the current frame (Step 400) and a list of motion vector(s) from block(s) in a previously transmitted frame (Step 410). The two lists of motion vectors created in Steps 400 and 410 are merged (Step 420) to create a single list. Duplicate values (duplicated motion vectors) in the list are removed (Step 430). According to another embodiment, Step 430 may be omitted. The motion vector competition control parameter (Step 440) is received, which is typically an index. The motion vector competition control parameter, or equivalently the motion vector control parameter, received in Step 440 is used to select (Step 450) an appropriate motion vector in the list obtained in Step 430 at the location indicated. The selected motion vector in Step 450 is provided as the motion vector prediction (Step 460). Thus, in a block by block manner, the motion vector competition tool predicts the motion vector for the current block. In general, the motion vector or any data which may be used to determine the motion vector may be transmitted.

As an illustrative example, referring to FIG. 5, a motion vector competition control parameter (MVCCP) is received in the bit stream, such as for example 3. The motion vector competition control parameter indicates where in the list of candidate motion vectors the desired motion vector is. If a set of motion vectors MVB, MVC, MVD, MVA' is created then the motion vector control parameter would indicates that the third motion vector MVD should be selected for the current block A as the motion vector prediction 460. For example, MVCCP 1 may be MVB, MVCCP 2 may be MVC, MVCCP 3 may be MVD, and MVCCP 4 may be MVA'.

In particular to creating the list of motion vectors from blocks in previously transmitted frames (Step 410), several techniques have been previously used. For example, one such technique includes for a block in the current frame that spans the pixel locations (x,y) to (x+N, y+M), the motion vector from the previous frame used for the pixel prediction located at (x,y) is selected to be included in the list. For example, x,y may indicate the top-left position of the block, N may indicate the horizontal size of the block, and M may indicate the vertical size of the block. For example, another such technique includes for a block in the current frame that spans the pixel locations (x,y) to (x+N, y+M), the motion vector from the previous frame used for the pixel prediction located at (x+N/2, y+M/2) may be selected to be included in the list. The operator "/" indicates the integer division with truncation of the result toward zero. While such techniques may select desirable motion vectors, the resulting list of motion vectors may tend to be large, resulting in significant memory requirements.

A modified technique for the current block in the current frame that spans the pixel locations (x,y) to (x+N, y+M) is to select and to store in the memory buffer the motion vector from the previous frame used for the pixel prediction located at ((x>>Z)<<Z, (y>>Z)<<Z) where Z is an integer. Preferably Z is 4. It is noted that (x>>Z)<<Z is generally equivalent to "the floor of (x/(2^Z))"^∗(2^Z). A floor function maps a real number to the largest previous integer value. For example, the floor(x)=[X] is the largest integer not greater than x. This technique is effective for a block size of 4 x 4 or, alternatively, 16x16.

Another modified technique for the current block in the current frame that spans pixels locations (x,y) to (x+N, y+M) is to select and to store in the memory buffer the motion vector from the previous frame used for the pixel prediction located at (((x>>Z)<<Z)+Y, ((y>>Z)<<Z)+Y), where Y and Z are integers. Preferably Z is 4 and Y is 8. Also, Y may be 1<<(Z-1), which is generally equivalent to (2^Z)/2. It is noted that ((x>>Z)<<Z)+Y is generally equivalent to "the floor of(x/(2^Z))"^∗(2^Z)+Y. This technique is effective for a block size of 4 x 4 or, alternatively, 16 x 16.

Yet another modified technique for the current block in the current frame that spans pixel location (x,y) to (x+N, y+M) is to select and to store in the memory buffer the motion vector from the previous frame used for the pixel prediction located at (((x+N/2)>>Z)<<Z)+Y, (((y+M/2)>>Z)<<Z)+Y, where Y and Z are integers. Preferably Z is 4 and Y is 8. Also, Y may be 1<<(Z-1) which is generally equivalent to (2^Z)/2. It is noted that (((x>>Z)<<Z)+Y is generally equivalent to "the floor (x/(2^Z))"^∗(2^Z)+Y. This technique is effective for a block size of 4 x 4 or, alternatively, 16 x 16.

A further modified technique for the current block in the current frame that spans pixel location (x,y) to (x+N, y+M) is to select and to store in the memory buffer the motion vector from the previous frame used for the pixel prediction located at ((((x+N/2)>>Z)<<Z)+Y, (((y+M/2)>>Z)<<Z)+Y), where Y and Z are integers. Preferably Z is 4 and Y is 4. Also, Y may be 1<<(Z-2) which is generally equivalent to (2^Z)/4. It is noted that (((x>>Z)<<Z)+Y is generally equivalent to "the floor (x/(2^Z))"^∗(2^Z)+Y. This technique is effective for a block size of 4 x 4 or, alternatively, 16 x 16.

In yet another modified technique for the current block in the current frame that spans pixel locations (x,y) to (x+N,y+M) is where the motion vector from the previous frame for the co-located block is coded by interpolation prediction, and the system may select among multiple motion vectors belonging to the co-located block. In this embodiment, a first motion vector for the current block is determined using a first motion vector in the previous frame used for the pixel prediction located at ((((x+N/2)>>Z)<<Z)+Y, (((y+M/2)>>Z)<<Z)+Y), where Y and Z are integers. Additionally, a second motion vector for the current block is determined using a second motion vector in the previous frame used for the pixel prediction located at ((((x+N/2)>>Z)<<Z)+Y, (((y+M/2)>>Z)<<Z)+Y), where Y and Z are integers. Preferably Z is 4 and Y is 4. Also, Y may be 1<<(Z-2) which is generally equivalent to (2^Z)/4. It is noted that (((x>>Z)<<Z)+Y is generally equivalent to "the floor (x/(2^Z))"^∗(2^Z)+Y. This technique is effective for a block size of 4 x 4 or, alternatively, 16 x 16.

Modified techniques may be used to select and to store in the memory buffer the motion vector from a previous frame which no longer requires the storage of every motion vector used in the prediction of previous frames. In a preferred embodiment, the motion vectors that are not used by the modified techniques are removed from memory after all steps required to decode and reconstruct the current frame are completed. In an alternative embodiment, the motion vectors that are not used by the modified techniques are removed from memory after being used for prediction but before all steps required to decode and reconstruct the current frame are completed. In a specific example, the motion vectors that are not used by the modified techniques are removed from memory before a de-blocking operation is performed, and the de-blocking operation uses only the motion vectors that are not used by the modified techniques for processing.

Referring to FIG. 6, a motion vector competition technique may likewise include a decoder that receives a bit stream from which a motion vector competition is applied. This data may include any suitable data previously described. In some embodiments, the motion vector competition technique that includes a buffer compression may be used, without necessarily including the additional features described in relation to FIG. 4 and FIG. 5.

By using a flooring function for the selection of candidate vectors from the previous frame the number of candidate vectors from the previous frame is reduced. In this manner, the system may effectively reduce the number of vectors without likely eliminating the most appropriate motion vector from the available selection. Moreover, by reducing the list of candidate vectors in an effective manner, the memory buffer may be reduced, which reduces the complexity of the system, especially suitable for embedded systems.

In particular to creating the list of motion vectors from blocks in previously transmitted frames (Step 410), typically the motion vector is only added to the list if it is available. Thus, for a current block, the system only uses the motion vector from a previous frame if the co-located block uses a motion vector. While functional, such an approach does not take into account the full nature of the video stream of encoded frames.

A modified technique for the current block in the current frame that spans the pixel locations (x,y) to (x+N, y+M) is to only to select and to store in the memory buffer a motion vector if the pixel at location ((x>>Z)<<Z, (y>>Z)<<Z) in the previous frame is coded using an inter-prediction technique. Z is preferably an integer. In general, this means that the location in a previous frame can not be coded with an intra-prediction technique.

Another modified technique for the current block in the current frame that spans pixels locations (x,y) to (x+N, y+M) is to only to select and to store in the memory buffer a motion vector if the pixel at location (((x>>Z)<<Z)+Y, ((y>>Z)<<Z)+Y) in the previous frame is coded using an inter-prediction technique. Preferably Y and Z are integers. In general, this means that the location in a previous frame can not be coded with an intra-prediction technique.

Yet another modified technique for the current block in the current frame that spans pixel location (x,y) to (x+N, y+M) is to only to select and to store in the memory buffer a motion vector if the pixel at location ((((x+N/2)>>Z)<<Z)+Y, (((y+M/2)>>Z)<<Z)+Y) in the previous frame is coded using an inter-prediction technique. Preferably Y and Z are integers. In general, this means that the location in a previous frame can not be coded with an intra-prediction technique.

In a preferred implementation a combination of the flooring function is combined with the limitation of an inter-prediction technique. For example, the system may only select a motion vector from a previous frame if the co-located block is coded using an inter-prediction technique. Furthermore, preferably if the system points to an intra-coded block in the previous frame, then the motion vector may be assumed to be 0 at that location.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims (2)

1. A method for decoding video comprising:

   creating a first list of motion vectors from neighboring blocks of a current block in a current frame (400), wherein the neighboring blocks include an above block of the current block, a left block of the current block, and an above left block of the current block;

   creating a second list comprising a motion vector of a block in a previously transmitted frame (410) by:

   deriving coordinates of a position of the block in the previously transmitted frame by performing a flooring function,

   wherein the flooring function operates an arithmetic right shift operation on a pixel position in the current frame based on a top-left position of the current block followed by an arithmetic left shift operation, and

   wherein a magnitude of the arithmetic right shift operation and a magnitude of the arithmetic left shift operation each have a value of 4;

   generating a third list of candidate motion vectors including the first list and the second list;

   receiving a control parameter (440) indicating a location in the third list;

   selecting a candidate motion vector in the third list, indicated by the control parameter, as a motion vector predictor for the current block (400),

   wherein the current block is a 4 x 4 block.
2. A decoder for decoding video, wherein the decoder comprises means for performing a decoding process comprising:

   creating a first list of motion vectors from neighboring blocks of a current block in a current frame (400), wherein the neighboring blocks include an above block of the current block, a left block of the current block, and an above left block of the current block;

   creating a second list comprising a motion vector of a block in a previously transmitted frame (410) by:

   deriving coordinates of a position of the block in the previously transmitted frame by performing a flooring function,

   wherein the flooring function operates an arithmetic right shift operation on a pixel position in the current frame based on a top-left position of the current block followed by an arithmetic left shift operation, and

   wherein a magnitude of the arithmetic right shift operation and a magnitude of the arithmetic left shift operation each have a value of 4;

   generating a third list of candidate motion vectors including the first list and the second list;

   receiving a control parameter (440) indicating a location in the third list;

   selecting a candidate motion vector in the third list, indicated by the control parameter, as a motion vector predictor for the current block (400),

   wherein the current block is a 4 x 4 block.