TITLE
Decoding and coding method of moving image signal, and
decoding and coding apparatus of moving image signal using the same
FIELD OF THE INVENTION
The present invention relates to a decoding method and coding
method of digital moving image signal, and a decoding apparatus and
coding apparatus using the same methods, for use in television telephone,
television conference, and recording of video signals and communication
of various signals. More particularly, it relates to a decoding method
and coding method of digital moving image signal, and a decoding
apparatus and coding apparatus using the same, being designed so that
effects of decoding errors may not propagate to frames and fields later in
time.
BACKGROUND OF THE INVENTION
In television telephone or television conference, in order to
transmit a moving image efficiently even in a narrow transmission route,
the moving image is digitized, and this signal is further processed by
digital image compression, and is transmitted, and at the receiving side,
the compressed digital moving image signal is decoded, and the moving
image is reproduced.
In a video disc or the like, in order to accumulate more moving
images in one disc, the digital moving image signal is coded and the
image is compressed.
The conventional coding method and decoding method of digital
moving image signal include the ITU-T Recommendation H. 261
recommended in March 1993, and the MPEG by the ISO, and the ITU-T
Recommendation is mainly described in this specification. For the sake
of convenience, the coding method is first described, and then the
decoding method, by referring to Fig. 4 to Fig. 6.
The coding method of H. 261 is realized, as shown in Fig. 4, by a
coding apparatus comprising motion vector detecting means 401, motion
compensation means 402, prediction error calculating means 403, intra-
inter judging means 404, DCT 405, quantizing means 406, variable
length coding means 407, inverse quantizing means 408, inverse DCT
409, reconstruction means 410, frame memory 411, and intra/inter
switch 412.
Each constituent element of H. 261 coding method is described
below. First, the motion vector detecting means 401 detects the motion
vector between a previous reconstruction frame stored in the frame
memory 411, and an entered present frame. The motion vector is
detected, as shown in Fig. 5, in a unit of pixel block called macro block.
The motion vector may be regarded as a spatial displacement amount of
pixel block between the previous reconstruction frame and the present
frame. Next, the motion compensation means 402 displaces the pixel
block of the previous reconstruction frame stored in the frame memory
411 according to the motion vector, and generates a predicted image.
This motion compensation is a process for reducing the prediction error
in the prediction error calculation at a next step.
The prediction error calculating means 403 calculates the
differential value between the macro block of the entered present frame
and the predicted image in the pixel unit, and issues as a prediction
error. Further, both the macro block of the present frame and the
prediction error are entered into the intra/inter judging means 404.
Herein, for example, by comparison between the variance of pixels in the
macro block of the present frame and the variance of the prediction error,
it is judged whether coding is more efficient by directly coding the macro
block of the present frame (intra-coding), or coding is more efficient by
coding the prediction error (inter-coding), and according to the result,
either the macro block of the present frame or the prediction error is
issued. At the same time, the result of judgement is issued as an
intra/inter control signal.
The macro block of the present frame or the prediction error
issued from the intra/inter judging means 404 is transformed into a
frequency region by the DCT 405 and is further transformed into a
quantizing coefficient by the quantizing means 406 to be curtailed in
redundancy, and further the quantizing coefficient is transformed into a
variable length code on the basis of the statistic character by the
variable length coding means 407, and the quantity of information is
curtailed. In the variable length coding means 407, further, the
intra/inter control signal and motion vector are entered, and coded into
variable length codes. The variable length coding means 407
multiplexes all these variable length codes, and issues as a bit stream.
On the other hand, the quantizing coefficient which is the output
of the quantizing means 406 is inversely quantized by the inverse
quantizing means 408, and is inversely transformed from the frequency
region by the inverse DCT 409. When the macro block being presently
coded is intra-coding, the intra/inter switch 412 is turned off, and the
output from the inverse DCT 409 is directly stored in the frame memory
411. To the contrary, when the macro block being presently coded is
inter-coding, the intra/inter switch 412 is turned on, and the output of
the inverse DCT 409 and the output of the motion compensation means
402 are added in the reconstruction means 410, and stored in the frame
memory 411. Thus, the present reconstruction frame is stored in the
frame memory 411, and it is used in prediction of next frame.
Next, the decoding method of H. 261 is realized by an apparatus,
as shown in Fig. 6, comprising variable length code decoding means 601,
inverse quantizing means 602, inverse DCT 603, frame memory 604,
motion compensation means 605, intra/inter switch 606, and
reconstruction means 607.
Each constituent element of the H. 261 decoding method is
described below. First, the variable length code decoding means 601
separates and decodes the variable length code from the entered bit
stream, and issues the quantizing coefficient, intra/inter control signal,
and motion vector in the macro block unit. The quantizing coefficient is
inversely quantized by the inverse quantizing means 602, and is
inversely transformed from the frequency region by the inverse DCT 603.
The motion compensation means 605 displaces the pixel block of the
previous reconstruction frame stored in the frame memory 604, on the
basis of the motion vector, and generates a predicted image.
When the intra/inter control signal instructs intra-coding, the
intra/inter switch 606 is turned off, and the output from the inverse DCT
603 is directly stored in the frame memory 604. On the other hand,
when the intra/inter control signal instructs inter-coding, the intra/inter
switch 606 is turned on, and the output of the inverse DCT 603 and the
output of the motion compensation means 605 are added in the
reconstruction means 607, and stored in the frame memory 604. Thus,
the present reconstruction frame is stored in the frame memory 604, and
it is used in prediction of next frame and is also issued as a decoded
image.
In the coding method and decoding method of H. 261, the inverse
quantizing means, inverse DCT, and motion compensation means
process the same, and therefore the reconstruction frames stored in the
frame memory of the coding method and decoding method always
coincide with each other.
Generally, since the bit stream issued by the coding method of
moving image signal is composed of variable length codes, in case an
error occurs in transmission or accumulation; if it is an error of one bit,
the decoding error occurs in a wide range, and the picture quality of the
reconstruction frame deteriorates. In the conventional decoding
method of moving image signal, the reconstruction frame lowed in
picture quality due to decoding error is used in prediction of next frame,
this picture quality deterioration can propagate to the succeeding frames
later in time.
As one of the prior arts presenting a method of solving this
problem, "Error Resilient Video Coding by Dynamic Replacing of
Reference Pictures" (S. Fukunaka et al.) (1996 IEEE) is known, but
when a decoding error occurs, the previously decoded video signal is
directly used again, the improving effect of picture quality deterioration
was trifling.
SUMMARY OF THE INVENTION
It is hence an object of the invention to present an excellent
decoding method and coding method of digital moving image signal, and
a decoding apparatus and coding apparatus using the same, capable of
preventing propagation of picture quality deterioration in time even if a
decoding error occurs due to bit error in the bit stream, and decoding
with less picture quality deterioration.
Relating to the present processing pixel block, in the coding
method and decoding method of digital moving image signal of the
invention, at least two or more motion vectors are coded or decoded, and
the motion of the decoded frame corresponding to each motion vector is
compensated, and two or more predicted images relating to the present
processing pixel block are generated. In the decoding method of moving
image signal of the invention, depending on the presence or absence of
decoding error contained in the two or more predicted images, the
predicted image to be used reconstruction of the present processing pixel
block is selected.
According to the invention thus constituted, if decoding error
occurs due to bit error in the bit stream, an excellent coding method and
decoding method of digital moving image signal capable of suppressing
propagation of picture quality deterioration in time can be presented.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a drawing showing a constitution of a decoding
apparatus for realizing a decoding method of moving image signal in
first and second embodiments of the invention.
Fig. 2 is a diagram showing an estimating method of macro
block having a decoding error in the decoding method of moving image
signal in the first and second embodiments of the invention.
Fig. 3 is a diagram showing a constitution of a coding
apparatus for realizing a coding method of moving image signal in third
and fourth embodiments of the invention.
Fig. 4 is a diagram showing a constitution of a coding
apparatus for realizing a coding method of moving image signal of prior
art.
Fig. 5 is a diagram showing a detecting method of motion
vector.
Fig. 6 is a diagram showing a constitution of a decoding
apparatus for realizing a decoding method of moving image signal of
prior art.
Reference Numerals
101 Variable length code decoding means
102 Inverse quantizing means
103 Inverse DCT
104 Frame memory A
105 Motion compensation means A
106 Intra/inter switch
107 Reconstruction means
108 Frame memory changeover switch
109 Frame memory B
110 Motion compensation means B
111 Predicted image selecting means
112 Decoding error map A
113 Decoding error map B
114 Decoding error map changeover switch
301 Motion vector detecting means A
302 Motion compensation means A
303 Prediction error calculating means
304 Intra/inter judging means
305 DCT
306 Quantizing means
307 Variable length code decoding means
308 Inverse quantizing means
309 Inverse DCT
310 Reconstruction means
311 Frame memory A
312 Intra/inter switch
313 Motion vector detecting means B
314 Motion compensation means B
315 Predicted image combining means
316 Frame memory B
317 Frame memory changeover switch
401 Motion vector detecting means
402 Motion compensation means
403 Prediction error calculating means
404 Intra/inter judging means
405 DCT
406 Quantizing means
407 Variable length code decoding means
408 Inverse quantizing means
409 Inverse DCT
410 Reconstruction means
411 Frame memory
412 Intra/inter switch
601 Variable length code decoding means
602 Inverse quantizing means
603 Inverse DCT
604 Frame memory
605 Motion compensation means
606 Intra/inter switch
607 Reconstruction means
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention are described below
while referring to Fig. 1 to Fig. 3.
(First embodiment)
A first embodiment of the invention relates to a decoding method
of moving image signal designed to select a predicted image to be used in
reconstruction of present processing pixel block, depending on presence
or absence of decoding error contained in two or more predicted images.
The decoding method of moving image signal in the first
embodiment of the invention is realized, as shown in Fig. 1, by a
decoding apparatus comprising variable length code decoding means 101,
inverse quantizing means 102, inverse DCT 103, frame memory A 104,
motion compensation means A 105, intra/inter switch 106,
reconstruction means 107, frame memory changeover switch 108, frame
memory B 109, motion compensation means B 110, predicted image
selecting means 111, decoding error map A 112, decoding error map B
113, and decoding error map changeover switch 114.
The operation of the decoding method of moving image signal in
the first embodiment of the invention is described below. First, the
decoding error map changeover switch 114 is set at the decoding error
map B 113 side, and the frame memory changeover switch 108 is set at
the frame memory B 109 side.
The variable length code decoding means 101 separates and
decodes a variable length code from the entered bit stream, and issues
quantizing coefficient, intra/inter control signal, motion vector A, and
motion vector B in macro block unit, and also writes presence or absence
of decoding error in the decoding error map B 113. The decoding error
map is a memory for storing the decoded state about all macro blocks in
one frame, by expressing, for example, a correctly decoded macro block
as 1 and a macro block having decoding error as 0. In the decoding
error map A 112, the decoded state one frame before in time from the
present processing macro block is stored, and in the decoding error map
B 113, the decoded state two frames before in time from the present
processing macro block is stored.
In the variable length code decoding means 101, various means
for detecting decoding error of macro block may be considered, and, for
example, it may be realized as follows. When decoding a moving image
signal, if there is a bit error in the entered bit stream, all macro blocks
from the bit having the error until a next synchronizing code (start code)
appears cannot be decoded correctly. Generally, unless bit error
detecting means is provided, macro blocks that cannot be decoded
correctly due to bit error cannot be identified. However, while decoding
the bit stream from the wrong bit until appearance of next synchronizing
code, (1) a variable length code not specified preliminarily may appear,
(2) a value exceeding an allowable range may be decoded, and other
contradictions may occur at high probability.
By making use of the character of (1) or (2), it may be possible to
estimate that there is a decoding error in N macro blocks tracing back
from the macro block having such decoding contradiction, and all macro
blocks after the macro block generating decoding contradiction until
appearance of synchronizing code. An example of N=4 is shown in Fig.
2. In the example in Fig. 2, since decoding contradiction took place
when decoding the (n+5)-th macro block, it is estimated that there is a
decoding error in all macro blocks from the (n+l)-th macro block, four
macro blocks before, till the (n+7)-th macro block just before the
synchronizing signal.
Consequently, the quantizing coefficient issued from the variable
length code decoding means 101 is inversely quantized by the inverse
quantizing means 102, and is inversely transformed from the frequency
region by the inverse DCT 103.
On the other hand, in the frame memory A 104, the
reconstruction image of one frame before in time from the present
processing macro block is stored, and in the frame memory B 109, the
reconstruction image of two frames before in time from the present
processing macro block is stored. The motion vector A is a motion
vector corresponding the frame memory A 104, and the motion vector B
is a motion vector corresponding to the frame memory B 109. That is,
the motion compensation means A 105 generates a predicted image A by
displacing the pixel block of the reconstruction frame of one frame before
stored in the frame memory A 104, according to the motion vector A.
Similarly, the motion compensation means B 110 generates a predicted
image B by displacing the pixel block of the reconstruction frame of two
frames before stored in the frame memory B 109, according to the motion
vector B.
The predicted image selecting means 111 first identifies the
position of the pixel block to be compensated of motion, by using the
value of the entered motion vector A. Comparing the position of this
pixel block and the position of the error information stored in the
decoding error map A 112, presence or absence of decoding error
contained in the predicted image A is judged. Similarly, predicted
image selecting means 111 judges presence or absence of decoding error
contained in the predicted image B, from the contents of the value of the
entered motion vector B and decoding error map B 113. When judging
that a decoding error is contained in the predicted image A, the predicted
image selecting means 111 issues only the predicted image B, or, to the
contrary, when judging that a decoding error is contained in the
predicted image B, it issues only the predicted image A. If it is judged
that error is not contained in either predicted image A or predicted
image B, the average of the predicted image A and predicted image B is
calculated and issued in the pixel unit.
If it is judged that error is contained in both predicted image A
and predicted image B, the average of the predicted image A and
predicted image B may be calculated and issued in the pixel unit, the
predicted image A may be issued, or the predicted image B may be issued,
as determined preliminarily.
When the intra/inter control signal issued from the variable
length code decoding means 101 instructs intra-coding, the intra/inter
switch 106 is turned off, and the output from the inverse DCT 103 is
directly stored in the frame memory B 109. On the other hand, when
the intra/inter control signal instructs inter-coding, the intra/inter
switch 106 is turned on, and the output of the inverse DCT 103 and the
output of the predicted image selecting means 111 are added in the
reconstruction means 107, and stored in the frame memory B 109.
Thus, the present reconstruction frame is stored in the frame memory B
109, and it is issued as decoded image.
After completion of decoding process of the present frame, the
decoding error map changeover switch 114 is changed over to the
decoding error map A 112 side, and the frame memory changeover
switch 108 is changed over to the frame memory A 104 side. By this
changeover, in decoding of next frame, the decoded state of two frames
before in time is stored in the decoding error map A 112, and the decoded
state of one frame before in time is stored in the decoding error map B
113. Likewise, the reconstruction image of two frames before in time is
stored in the frame memory A 104, and the reconstruction image of one
frame before in time is stored in the frame memory B 109.
In the first embodiment of the invention, since the decoding
method of moving image signal is thus constituted, by using only the
predicted image not containing decoding error in reconstruction of the
present processing pixel block, the picture quality deterioration due to
decoding error is prevented from propagating into the frames subsequent
in time.
In the decoding method of moving image signal of the invention,
the decoding error map and frame memory are provided by two pieces
each, but by using three pieces or more, the decoded state and
reconstruction image of three frames or more before in time may be
stored. Incidentally, the means for estimating the macro block having
decoding error by decoding contradiction, and the means for judging
decoding error contained in the predicted image by using the decoding
error map are only example, and they may be composed of other means.
(Second embodiment)
A second embodiment of the invention relates to a decoding
method of moving image signal, in which if decoding error is not
contained in plural predicted images out of two or more predicted images,
the predicted image produced from the latest decoded frame in time out
of the predicted images free from decoding error is used in reconstruction
of the present processing pixel block.
The decoding method of moving image signal of the second
embodiment of the invention is realized by the same decoding apparatus
as in the first embodiment shown in Fig. 1. The operation of the
decoding method of the moving image signal of the second embodiment of
the invention is described below. The operation other than that of the
predicted image selecting means 111 is not particularly different from
that in the first embodiment.
In the predicted image selecting means 111, if it is judged that
there is no error contained in either predicted image A or predicted
image B, it is constituted to issue the newer one of the predicted image A
or predicted image B. That is, if it is judged that error is not contained
in either predicted image A or predicted image B, it is constituted to
issue always only the predicted image produced from the reconstruction
image of one frame before.
In the decoding method of the moving image signal realized in
the decoding apparatus shown in Fig. 1, the decoding error map and
frame memory are provided by two pieces each, but by using three pieces
or more, the decoded state and reconstruction image of three frames or
more before in time may be stored. If there are three predicted images,
supposing, for example, there is an error in the latest predicted image A,
out of predicted image A, predicted image B, and predicted image C, and
no error in the predicted image B and predicted image C, it is constituted
to issue the latest predicted image B out of the predicted image B and
predicted image C. It is the same if there are four or more images. If
all predicted images are wrong, one predetermined predicted image may
be issued.
In the second embodiment of the invention, since the decoding
method of the moving image signal is thus constituted, the correlation of
the present processing pixel block to be reconstructed and the predicted
image is heightened due to similarity of moving images in time, so that
the code quantity necessary for reconstruction of present processing
block is decreased.
(Third embodiment)
A third embodiment of the invention is a coding method of
moving image signal for inter-coding the present processing pixel block
when the correlation is high between two or more predicted images
compensated of motion by two or more motion vectors, and intra-coding
the present processing pixel block when the correlation is low between
two or more predicted images.
The coding method of the moving image signal of third
embodiment of the invention is realized, as shown in Fig. 3, by the
coding apparatus comprising motion vector detecting means A 301,
motion compensation means A 302, prediction error calculating means
303, intra/inter judging means 304, DCT 305, quantizing means 306,
variable length code decoding means 307, inverse quantizing means 308,
inverse DCT 309, reconstruction means 310, frame memory A 311,
intra/inter switch 312, motion vector detecting means B 313, motion
compensation means B 314, predicted image combining means 315,
frame memory B 316, and frame memory changeover switch 317.
The operation of the coding method of moving image signal of the
third embodiment of the invention is described below. First, the frame
memory changeover switch 317 is supposed to be set at the frame
memory B 316 side.
To begin with, the motion vector detecting means A 301 detects
the motion vector A by the reconstruction frame stored in the frame
memory A 311 and the entered present frame. Similarly, the motion
vector detecting means B 313 detects the motion vector B by the
reconstruction frame stored in the frame memory B 316 and the entered
present frame. Herein, in the frame memory A 311, the reconstruction
image of one frame before in time from the present processing macro
block is stored, and in the frame memory B 316, the reconstruction
image of two frames before in time from the present processing macro
block is stored.
The motion compensation means A 302 generates a predicted
image A by displacing the pixel block of the reconstruction frame of one
frame before stored in the frame memory A 311, according to the motion
vector A. Similarly, the motion compensation means B 314 generates a
predicted image B by displacing the pixel block of the reconstruction
frame of two frames before stored in the frame memory B 316, according
to the motion vector B. The predicted image combining means 315
calculates and issues the average of the entered predicted image A and
predicted image B in the pixel unit. The prediction error calculating
means 303 calculates the difference of the macro block of the entered
present frame and the output of the predicted image combining means
315 in the pixel unit, and issues as prediction error.
Further, the macro block of the present frame, this prediction
error, and the predicted image A and predicted image B are entered into
the intra/inter judging means 304. Herein, as the processing at first
stage, for example, by comparing the variance of pixels in the macro
block of the present frame and the variance of the prediction error, it is
judged whether the macro block of the present frame is processed by
intra-coding or inter-coding. If the inter-coding is judged as a result of
processing at the first stage, the correlation between the predicted image
A and predicted image B is evaluated as the processing at second stage,
and it is judged whether the macro block of the present frame is
processed by intra-coding or inter-coding.
Evaluation of correlation of predicted image A and predicted
image B and intra/inter judgement at the second stage are executed, for
example, as follows. First, the absolute differential sum of predicted
image A and predicted image B is calculated in the pixel unit. If the
absolute differential sum is larger than a predetermined threshold, the
correlation is small, and the macro block of the present frame is judged
to be processed by intra-coding. To the contrary, if the absolute
differential sum is larger than the predetermined threshold, the
correlation is large, and the macro block of the present frame is judged to
be processed by inter-coding.
According to the result of judgement by the intra/inter judging
means 304 consisting of the processing in the first stage and second
stage, either the macro block of the present frame or the pertinent
prediction error is issued. At the same time, the result of judgement is
also issued as intra/inter control signal. The macro block of the present
frame or the pertinent prediction error issued from the intra/inter
judging means 304 is put into the variable length coding means 307
through the DCT 305 and quantizing means 306. In the variable length
coding means 307, the intra/inter control signal, and motion vector A and
motion vector B are also entered, and are coded into variable length
codes. The variable length coding means307 multiplexes all these
variable length codes, and issues as a bit stream.
On the other hand, the quantizing coefficient which is the output
of the quantizing means 306 is put into the reconstruction means 310
through the inverse quantizing means 308 and inverse DCT 309. When
the macro block being presently coded is intra-coding, the intra/inter
switch 312 is turned off, and the output from the inverse DCT 309 is
directly stored in the frame memory B 316. To the contrary, when the
macro block being presently coded is inter-coding, the intra/inter switch
312 is turned on, and the output of the inverse DCT 309 and the output
of the predicted image combining means 315 are added in the
reconstruction means 310, and stored in the frame memory B 316.
Thus, the present reconstruction frame is stored in the frame memory B
316.
After completion of coding process of the present frame, the
frame memory changeover switch 317 is changed over to the frame
memory A 311 side. By this changeover, in coding of next frame, the
reconstruction image of two frames before in time is stored in the frame
memory A 311, and the reconstruction image of one frame before in time
is stored in the frame memory B 316.
In the third embodiment of the invention, since the coding
method of moving image signal is thus constituted, if a predicted image
different from the coding side is selected in the decoding method of
moving image signal, inter-coding is effected only when the correlation
between predicted images is high, so that mis-matching of the predicted
images may be kept to a minimum limit.
In the coding method of moving image signal of the third
embodiment, two frame memories are provided, but by using three or
more, the reconstruction image of three frames or more before in time
may be stored. Incidentally, the means for evaluating the correlation of
the predicted image A and predicted image B is only an example, and it
may be composed of other means.
(Fourth embodiment)
A fourth embodiment of the invention relates to a coding method
of moving image signal for using the predicted image produced from the
latest decoded frame in time out of two or more predicted images
compensated of motion by two or more motion vectors in coding of the
present processing pixel block.
The coding method of moving image signal of the fourth
embodiment of the invention is realized by the same coding apparatus as
in the third embodiment shown in Fig. 3. The operation of the coding
method of the moving image signal of the fourth embodiment of the
invention is described below. The operation other than that of the
predicted image combining means 315 is not particularly different from
that in the third embodiment.
The predicted image combining means 315 is constituted so as to
issue only the newer one of the predicted image A or predicted image B.
That is, it is constituted to issue always only the predicted image
produced from the reconstruction image of one frame before. If three or
more frame memories are used and the reconstruction image of three
frames or more before in time is stored, only the latest predicted image
may be issued.
In the fourth embodiment of the invention, since the coding
method of the moving image signal is thus constituted, the prediction
error about the present processing pixel block is smaller owing to the
similarity of moving images in times, and the generated code quantity is
smaller.
Thus, according to the invention, since the present processing
pixel block is reconstructed by selecting the predicted image free from
decoding error, the picture quality deterioration due to decoding error
does not propagate in time, so that deterioration of reproduced picture
quality due to bit error occurring in transmission or accumulation of bit
stream may be kept to a minimum limit.
WE CLAIM:
1. A decoding method of moving image signal, being a decoding
method of moving image signal for decoding at least two or more
motion vectors relating to the present processing pixel block,
compensating the motion of the decoded frame corresponding to
each one of said two or more motion vectors, and generaing two or
more predicted images relating to the present processing pixel
block,
wherein the predicted image used in reconstruction of the
present processing pixel block is selected depending on presence
or absence of decoding error contained in said two or more
predicted images.
2. A decoding method of moving image signal as claimed in claim
1, wherein if there are plural predicted images free from
decoding error in said two or more predicted images,
the predicted image produced from the latest decoded frame in
time out of said plural predicted images free from decoding error
is used in reconstruction of the present processing pixel block.
3. A decoding apparatus of moving image signal comprising:
A
variable length code decoding means (101) for decoding at
least two or more motion vectors relating to the present
processing pixel block,
motion compensation means (105,110) for compensating the
motion of coded frame corresponding to each one of said two or
more motion vectors, and generating two or more predicted images
relating to the present processing pixel block,
bit error detector for detecting a bit error from the output
of said variable length code decoding means,
memory means (112,113) for storing the bit error detecting
result of said bit error detector and
predicted image selecting means (111) for recognizing
presence or absence of decoding error contained in said two or
more predicted images, and selecting the predicted image to be
used in reconstruction of the present processing pixel block.
4. A decoding apparatus of moving image signal as claimed in
claim 3, wherein the bit error detector detects bit error in the
pixel block when the variable length code of the pixel block
decoded by the variable length code decoding means (101) is
contradictory to a specified standard.
5. A decoding apparatus of moving image signal as claimed in
claim 3, wherein the memory means (112,113) stores bit errors in
plural frames by plotting the pixel blocks in which bit error is
detected in each frame in a map form.
6. A decoding apparatus of moving image signal as claimed in
claim 5, wherein the memory means comprises plural decoding error
map memories (112,113) storing each frame consecutive in time,
and also has changeover means (114) and therefore said plural
decoding error map memories are changed over by said changeover
means (114) and issued.
ABSTRACT
The invention relates to a decoding method and coding method of
moving image signal, and a decoding apparatus and coding apparatus
using the same, for coding or decoding at least two or more motion
vectors, relating to the present processing pixel block, compensating the
motion of the coded frame corresponding to each motion vector,
generating two or more predicted images relating to the present
processing image block, and selecting the predicted image for use in
reconstruction of the present processing pixel block depending on
presence or absence of decoding error contained in these two or more
predicted images. Accordingly, if a decoding error occurs due to bit
error in the bit stream, propagation of picture quality deterioration in
time can be suppressed, so that excellent decoding of digital moving
image signal is realized.

The invention relates to a decoding method and coding method of
moving image signal, and a decoding apparatus and coding apparatus
using the same, for coding or decoding at least two or more motion
vectors, relating to the present processing pixel block, compensating the
motion of the coded frame corresponding to each motion vector,
generating two or more predicted images relating to the present
processing image block, and selecting the predicted image for use in
reconstruction of the present processing pixel block depending on
presence or absence of decoding error contained in these two or more
predicted images. Accordingly, if a decoding error occurs due to bit
error in the bit stream, propagation of picture quality deterioration in
time can be suppressed, so that excellent decoding of digital moving
image signal is realized.