Motion vector prediction method

Details Motion vector prediction method Motion vector prediction method

1998-12-01

2002-07-30

Rao, Andy (Department: 2713)

Pulse or digital communications

Bandwidth reduction or expansion

Television or motion video signal

C375S240160

Reexamination Certificate

active

06426976

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motion vector prediction method, and more particularly, to a motion vector prediction method in an error resilient mode.
2. Description of the Related Art
In general, redundancy of a moving picture must be effectively eliminated so as to compress the moving image. The moving picture experts group (MPEG) adopts a motion prediction method. According to the motion prediction method, the current frame is divided into a plurality of macro blocks, and then each macro block (reference block) is compared with each macro block (matching block) of a previous frame within a given area, to calculate the difference therebetween. Then, the macro blocks having the lowest difference are selected to calculate motion vectors representing the difference in positions between the reference and matching blocks. In the motion vector prediction, the difference between a predicted motion vector and actual motion vector of the current block is encoded, in place of encoding the motion vector itself of the current block, thereby improving coding efficiency.
FIG. 1
is a diagram illustrating a conventional motion prediction method and coding sequence adopted in the MPEG-4 and the H.263 standards.
In
FIG. 1
, reference numerals
10
through
18
represent macro blocks each consisting of 16 pixels×16 pixels, reference numerals
10
and
16
are macro blocks each having one motion vector, and reference numerals
12
,
14
and
18
represents macro blocks each
10
having four motion vectors. The macro blocks
12
,
14
and
18
are divided into four subblocks of 8 pixels×8 pixels, based on the MPEG-4 or the H.263 standard, and those four motion vectors are calculated from the four subblocks.
Here, prior to transmission of the difference among each
15
motion vector, motion vector prediction is separately performed in upper subblocks
121
,
122
,
141
and
142
and lower subblocks
123
,
124
,
143
and
144
of the macro blocks
12
and
14
from the macro block
10
in a solid arrow direction. Here, a motion vector is predicted from motion vectors calculated in the upper subblock
142
, the macro blocks
16
and the subblocks
181
through
184
of the macro block
18
with correlation. However, the motion vector prediction is not performed between the motion vectors of the subblock
144
and the macro block
16
, and the motion vector prediction continues toward the lower subblocks
183
and
184
from the macro block
16
.
Thus, if an error occurs, the motion vector can be decoded from the macro block
16
toward the upper subblock
142
in a backward direction. However, if an error occurs in the lower subblock
123
of the macro block
12
, it is not possible to reversely calculate the motion vectors of the subblock
144
and its left subblock
143
from the macro block
16
using a motion vector prediction code.
As a result, it is not possible to decode the blocks following the erroneous block, thereby increasing loss in motion vector value. Although an error concealment is adopted, there is a problem of loss of information.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a motion vector prediction method capable of restoring a motion vector lost after an error occurs, through backward decoding, even when information is lost during transmission due to the error.
Accordingly, to achieve the above object, there is provided a motion vector prediction method capable of decoding backwards, comprising the steps of: (a) calculating motion vectors of macro blocks; and (b) predicting motion vectors of macro blocks each having one motion vector while moving to another macro block from left to right, and motion vectors of macro blocks each having four motion vectors continuously in a predetermined sequence to have correlation in prediction of the four motion vectors.
Preferably, in the step (b) when one macro block has one motion vector, the motion vector prediction of the current block is performed using the motion vector of the macro block on the left of the current block or the previous coded macro block.
Preferably, in the step (b) when one macro block has four motion vectors, the motion vectors are continuously predicted from the motion vectors of the upper-left, lower-left, lower-right and upper-right subblocks in sequence.


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