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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a coding method of coding a digital video signal
by subjecting the digital video signal to redundancy reduction coding.
This invention relates also to a coding device for use in carrying out the
method.
Each of the successive pictures is called a frame when the digital video
signal is, for example, a television signal. Redundancy reduction coding
is effective to code the digital video signal into a coded video signal
having a low bit rate. As the redundancy reduction coding, basic
interframe predictive coding is known in the art. The basic interframe
predictive coding makes use of a correlation factor between adjacent ones
of the pictures or frames. In the basic interframe predictive coding, the
redundancy reduction coding is carried out on a difference between
corresponding picture elements of two successive pictures to provide a
result of the basic interframe predictive coding.
Motion-compensated interframe predictive coding is also known in the art as
the redundancy reduction coding. In the motion-compensated interframe
predictive coding, a motion vector is detected which represents a movement
of each picture element between two of pictures. The motion-compensated
interframe predictive coding carries out interframe predictive coding of
the digital video signal by using the motion vector.
Inasmuch as the motion-compensated interframe predictive coding is also
carried out by using a correlation factor between two adjacent pictures
like the basic interframe predictive coding, not only the basic interframe
predictive coding but also the motion-compensated interframe predictive
coding will be referred to as interframe coding.
Intraframe or inframe coding is still also known in the art as the
redundancy reduction coding. The intraframe coding is carried out by using
a correlation factor between the picture elements within each of the
pictures. The intraframe coding is, for example, PCM (pulse code
modulation) coding, intraframe predictive coding, orthogonal
transformation coding, or vector quantization coding.
Such redundancy reduction coding is generally used in transmitting the
digital video signal. However, the redundancy reduction coding is also
used in a video signal processing system which is for use in a recording
medium, such as a compact disk read-only memory (CD-ROM), to record and/or
reproduce the digital video signal.
In the meanwhile, it may be preferable that the compact disk read-only
memory can be operable like a video tape in performing not only a normal
reproduction but also various other functions, such as a reverse
reproduction, a high speed reproduction, scene skipping, an arbitrary
reproduction of an arbitrary scene. However, it is difficult to perform
the reverse reproduction when the digital video signal is subjected to the
interframe coding alone. More specifically, the digital video signal is
divided into a zeroth or leading frame to an end or trailing frame as
leading through trailing compressed video signals subjected to the
interframe coding. The digital video signal is successively recorded on
the recording medium from the leading compressed video signal to the
trailing compressed video signal in a normal order. Merely for convenience
of description, the zeroth through the end frames may be understood to
correspond to zeroth through end scenes, respectively. On carrying out the
reverse reproduction, the digital video signal is reproduced from the
recording medium in a reverse order from the end scene in response to a
request issued by an operator or user to indicate the reverse
reproduction.
In order to perform the reverse reproduction, an improved method is
disclosed in a prior U.S. patent application Ser. No. 189,249 which was
filed May 2, 1988, by Toshio Koga, Junichi Ohki, Mutsumi Ohta, and Hideto
Kunihiro for assignment to the present assignee and c/o NEC Home
Electronics, Ltd. The above-named Mutsumi Ohta is the instant applicant.
The Ohta et al patent application corresponds to a prior Canadian patent
application No. 565,485 which was filed Apr. 29, 1988. In the prior patent
applications, the video signal processing system is called an image
processing system. The digital video signal is called a sequence of image
signals. In the improved method, the digital video signal is coded with
the leading and the trailing frames subjected to the intraframe predictive
coding and with the remaining frames subjected to the interframe
predictive coding. According to the improved method, it is possible to
carry out not only the normal reproduction but also the reverse
reproduction. The improved method is, however, defective in that the
reverse reproduction can not be performed when an interframe/intraframe
adaptive coding is used as the redundancy reduction coding. In the
interframe/intraframe adaptive predictive coding, the digital video signal
is decoded into a decoded signal with a first result of the interframe
coding and a second result of the intraframe coding alternatingly
appearing in the coded signal. More specifically, the interframe coding
and the intraframe coding are adaptively alternatingly carried out in
consideration of an amount of produced information of the first result and
another amount of produced information of the second result.
SUMMARY OF THE INVENTION
It is therefore a general object of this invention to provide a method of
coding a digital video signal, whereby reverse reproduction can be
performed when interframe/intraframe adaptive coding is used in coding the
digital video signal.
Other objects of this invention will become clear as the description
proceeds.
A method to which this invention is applicable is for coding a digital
video signal by subjecting the digital video signal to redundancy
reduction coding. The digital video signal is representative of successive
pictures, each comprising a predetermined number of picture elements.
According to an aspect of this invention, the method comprises the steps
of (a) producing a coding mode signal which indicates, as the redundancy
reduction coding, a selected one of interframe coding and intraframe
coding which are carried out with reference to a first correlation factor
between adjacent ones of the successive pictures and a second correlation
factor between the picture elements within each of the successive
pictures, respectively, (b) selectively coding said digital video signal
into a first coded signal by carrying out the selected one of the
interframe and the intraframe coding in response to the coding mode
signal, the first coded signal carrying a first result of the interframe
coding and a second result of the intraframe coding, (c) making the
selectively coding step carry out the intraframe coding on a particular
element of the picture elements of a current picture to produce a second
coded signal when the coding mode signal indicates that the particular
element should be subjected to the interframe coding and that a
corresponding element of a following picture should be subjected to the
intraframe coding, the following picture following the current picture in
the successive pictures, the corresponding element corresponds to the
particular element, and (d) multiplexing the first, and the second coded
signals and the coding mode signal into a multiplexed signal.
According to another aspect of this invention, the method comprising the
steps of (a) producing a coding mode signal which indicates, as the
redundancy reduction coding, a selected one of interframe coding and
intraframe coding, the interframe coding being carried out by detecting a
motion vector representative of a movement of each picture element between
adjacent ones of the successive pictures and by using said motion vector,
the intraframe coding being carried out by using a correlation between the
picture elements within each of the successive pictures, (b) selectively
coding the digital video signal into a first coded signal by carrying out
the selected one of the interframe and the intraframe coding in response
to the coding mode signal, the first coded signal carrying a first result
of the interframe coding and a second result of the intraframe coding, (c)
making the selectively coding step carry out the intraframe coding on a
specific element of the picture elements of a current picture to produce a
second coded signal when the coding mode signal indicates that the
specific element should be subjected to the interframe coding and
furthermore when the specific element has no relation to the movement
represented by each of the motion vectors which are used in carrying out
the interframe coding on the picture elements of a following frame when
the coding mode signal indicates that the picture elements of the
following frame should be subjected to the interframe coding, the
following picture following the current picture in the successive
pictures, and (d) multiplexing the first and the second coded signals, the
motion vectors, and the coding mode signal into a multiplexed signal.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagram for use in describing a coding method according to a
first embodiment of this invention;
FIG. 2 is another diagram for use in describing the coding method according
to the first embodiment of this invention;
FIG. 3 is still another diagram for use in describing the coding method
according to the first embodiment of this invention;
FIG. 4 is yet another diagram for use in describing the coding method
according to the first embodiment of this invention;
FIG. 5 is a diagram for use in describing a coding method according to a
second embodiment of this invention;
FIG. 6 is another diagram for use in describing the coding method according
to the second embodiment of this invention;
FIG. 7 is still another diagram for use in describing the coding method
according to the second embodiment of this invention;
FIG. 8 is a block diagram of a coding device for use in carrying out the
coding method according to the first embodiment of this invention;
FIG. 9 is a block diagram of a processing circuit for use in the coding
device illustrated in FIG. 8;
FIG. 10 is a block diagram of a coding device for use in carrying out the
coding method according to the second embodiment of this invention;
FIG. 11 is a block diagram of a processing circuit for use in the coding
device illustrated in FIG. 10;
FIG. 12 is a block diagram of another coding device for use in carrying out
the coding method according to the second embodiment of this invention;
FIG. 13 shows, in blocks and together with a recording medium, a decoding
device for decoding a read-out signal read out of the recording medium on
which an output signal of the coding device illustrated in FIG. 8 is
recorded;
FIG. 14 shows, in blocks and together with a recording medium, a decoding
device for decoding a read-out signal read out of the recording medium on
which an output signal of the coding device illustrated in FIG. 10 is
recorded;
FIG. 15 shows, in blocks and together with a recording medium, another
decoding device for decoding a read-out signal read out of the recording
medium on which an output signal of the coding device illustrated in FIG.
8 is recorded;
FIG. 16 is a block diagram of a vector & mode processing circuit for use in
each of the decoding device illustrated in FIGS. 14 and 15; and
FIG. 17 is a block diagram of another vector & mode processing circuit for
use in each of the decoding devices illustrated in FIGS. 14 and 15.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, description will now be made as regards a coding
method according to a first embodiment of this invention. Attention will
be directed at first to a basic interframe predictive coding method. It
will be assumed that a (j, k)-th picture element of an i-th frame of a
digital video signal is represented by X(i, j, k), where i is equal to one
of integers 0, . . . , and n. Likewise, j is equal to one of integers 1, .
. . , and p while k is equal to one of integers 1, . . . , and q. Further
supposing that an interframe predictive error signal (namely, an
interframe difference signal) is represented by E(i, j, k), the interframe
predictive error signal E(i, j, k) is represented by Formula (1)
hereunder:
E(i, j, k)=X(i, j, k)-X(i-1, j, k). (1)
In the basic interframe predictive coding method, the interframe predictive
error signal E(i, j, K) is calculated at first. The interframe predictive
error signal E(i, j, k) is subsequently coded into a coded predictive
error signal. In order to carry out a normal reproduction of the picture
element X(i, j, k) by decoding the coded predictive error signal in a
decoder, the picture element X(i, j, k) is obtained by Formula (2)
hereunder which is given by modification of Formula (1):
X(i, j, k)=E(i, j, k)+X(i-1, j, k). (2)
It should be noted here that picture elements x(0, j, k) of the zeroth
frame or picture are given to the decoder in order to carry out the normal
reproduction by using Formula (2). In general, first and second method are
used in order to supply the decoder with the picture elements X(0, j, k)
of the zeroth picture. In the first method, the picture elements X(0, j,
k) of the zeroth picture are coded by intraframe coding described in the
preamble of the instant specification. In the prior patent application
described in the preamble of the instant specification, the picture
elements X(0, j, k) of the zeroth picture are coded by using an intraframe
predictive coding as the intraframe coding. In the second method, the
zeroth picture is preliminarily determined to have a fixed picture.
Description will proceed to a reverse reproduction. In order to carry out
the reverse reproduction of the picture elements X(i, j, k), the picture
elements X(i, j, k) are successively decoded by the decoder from the n-th
frame to the zeroth frame by Formula (3) hereunder which is given by
different modification of Formula (1):
X(i-1, j, k)=-E(i, j, k)+X(i, j, k). (3)
In this case, picture elements X(n, j, k) of the n-th or trailing picture
should be obtained by the decoder. In order to carry out the reverse
reproduction, the picture elements X(n, j, k) of the n-th picture are also
coded by the intraframe coding. In the prior patent application described
in the preamble of the instant specification, the picture elements X(n, j,
k) of the n-th picture are coded by using the intraframe predictive coding
as the intraframe coding.
Thus, the digital video signal is coded in the prior patent application
with the zeroth and the n-th pictures subjected to intraframe predictive
coding and with the remaining pictures subjected to intraframe predictive
coding. However, the reverse reproduction can not be performed according
to the prior patent application when interframe/intraframe adaptive coding
is used as redundancy reduction coding. This incapability of the reverse
reproduction will be described hereunder.
In FIG. 1, it will be assumed that each frame of the digital video signal
is represented by a one-dimensional signal merely for convenience of the
description although each frame cf the digital video signal is a
two-dimensional signal in fact. In FIG. 1, an interframe predictive error
signal of a j-th picture element of an i-th frame is represented by E(i,
j). The interframe predictive error signal E(i, j) is equivalent to a
first result of interframe predictive coding when the j-th picture element
of the i-th frame is subjected to the interframe predictive coding. An
intraframe coded signal of the j-th picture element of the i-th frame is
represented by P(i, j). The intraframe coded signal P(i, j) is equivalent
to a second result of intraframe coding when the j-th picture element of
the i-th frame is subjected to the intraframe coding.
In order to perform the normal reproduction, all of the picture elements of
the zeroth frame are subjected to the intraframe predictive coding to
produce second results P(0, 1), P(0, 2), P(0, 3), and P(0, 4). All of the
picture elements of the first frame are subjected to the basic interframe
predictive coding to produce first results E(1, 1), E(1, 2), E(1, 3), and
E(1, 4).
A first picture element of the second frame is subjected to the basic
intraframe predictive coding to produce a second result P(2, 1). Second
through fourth picture elements of the second frame are subjected to the
basic interframe predictive coding to produce first results E(2, 2), E(2,
3), and E(2, 4).
For the third frame, first, second, and fourth picture elements are
subjected to the basic interframe predictive coding to produce first
results E(3, 1), E(3, 2), and E(3, 4). A third picture element of the
third frame is subjected to the intraframe predictive coding to produce a
second result P(3, 3). For the fourth frame, first through fourth picture
elements are subjected to the basic interframe predictive coding to
produce first results E(4, 1), E(4, 2), E(4, 3), and E(4, 4).
It will be assumed merely for brevity of the description that the fourth
frame is the trailing frame. In order to perform the reverse reproduction,
all of the Picture elements of the fourth frame are subjected to the
intraframe coding to produce second results P(4, 1), P(4, 2), P(4, 3), and
P(4, 4).
Turning to FIG. 2, the first and the second results E and P are represented
for use in carrying out the normal reproduction.
Turning back to FIG. 1, it is impossible to decode the first picture
element of the first frame and the third picture element of the second
frame when the reverse reproduction is carried out in accordance with
Formula (3). This is because the first results E(2, 1) and E(3, 3) are not
produced.
In order to resolve this problem, the first picture element of the first
frame and the third picture element of the second frame are subjected to
the intraframe coding to produce second results P(1, 1) and P(2, 3) in
accordance with this invention. In FIG. 1, a symbol * is attached to the
right upper portion of each of the second results P(1, 1), P(2, 3), P(4,
1), P(4, 2), P(4, 3), and P(4, 4) which are used in carrying out the
reverse reproduction and are not used in carrying out the normal
reproduction.
Turning to FIG. 3, the first and the second results E and P are represented
for use in carrying out the reverse reproduction. Turning to FIG. 4, the
first and the second results E and P are represented for use in carrying
out not only the normal reproduction but also the reverse reproduction.
Turning back to FIG. 1 again, a method according to the first embodiment of
this invention will be described more in detail. The method is for coding
a digital video signal by subjecting the digital video signal to
redundancy reduction coding. The digital video signal is representative of
successive pictures, each of which comprises a predetermined number of
picture elements.
It will be assumed for a short while that the interframe/intraframe
adaptive coding is used in coding the digital video signal. According to
the embodiment being described, the method comprises a producing step
wherein a coding mode signal is produced which indicates, as the
redundancy reduction coding, a selected one of the basic interframe
predictive coding and the intraframe coding.
In a selectively coding step, the digital video signal is selectively coded
into a first coded signal by carrying out the selected one of the basic
interframe predictive coding and the intraframe coding in response to the
coding mode signal. The first coded signal carries a first result E of the
basic interframe predictive coding and a second result P of the intraframe
coding.
The selectively coding step is made to carry out the intraframe predictive
coding on a particular element (for example, the first picture element of
the first frame) of the picture elements of a current picture (that is,
the first frame) to produce a second coded signal P(1, 1) when the coding
mode signal indicates that the particular element should be subjected to
the basic interframe predictive coding and that a corresponding element
(that is, the first picture element of the second frame) of a following
picture (that is, the second frame) should be subjected to the intraframe
coding. The following picture follows the current picture in the
successive pictures. The corresponding element corresponds to the
particular element.
In due course, a second frame or picture becomes the current picture. At
this stage of coding, the particular element corresponds to the third
picture element of the second frame while the corresponding picture of the
following picture corresponds to the third picture element of the third
frame. In this event, the selectively coding step produces the second
coded signal P(2, 3).
The first and the second coded signals and the coding mode signal are
multiplexed into a multiplexed signal.
Description will be made as regards a feature of the method. It will be
assumed that S(i, j) represents the coding mode signal of the j-th picture
element of the i-th frame. When the coding mode signal S(i, j) represents
the intraframe coding, the first result E(i, j) of the basic interframe
predictive coding is not produced. Inasmuch as the first result E(i, j) is
not produced, it is impossible to carry out the reverse reproduction of
the j-th picture element of the (i-1)-th frame. In order to realize the
reverse reproduction of the j-th picture element of the (i-1)-th frame,
the intraframe coding is carried out on the j-th picture element of the
(i-1)-th frame to produce the second result P(i-1, j). That is, not only
the basic interframe predictive coding but also the intraframe coding are
carried out on the j-th picture element of the (i-1)-th frame.
Referring to FIG. 5, description will proceed to a coding method according
to a second embodiment of this invention. Attention will be directed to a
motion compensated interframe predictive coding method. It will be assumed
that a motion vector of the picture element X(i, j, k) is represented by
V(i, j, k) and that the motion vector V(i, j, k) is represented by:
V(i, j, k) =(vx(i, j, k), vy(i, j, k)), where vx(i, j, k) and vy(i, j, k)
represent horizontal and vertical components of the motion vector V(i, j,
k), respectively. An interframe predictive error signal E(i, j, k) is
represented by Formula (4) hereunder:
E(i, j, k)=X(i, j, k)-X(i-1, j-vx(i, j, k), k-vy(i, j, k)) (4)
In the motion-compensated interframe predictive coding method, the
interframe predictive error signal E(i, j, k) and the motion vector V(i,
j, k) are coded into a coded predictive error signal and a coded vector,
respectively. In order to carry out a normal reproduction of the picture
element X(i, j, k) by decoding the coded predictive error signal and the
coded vector in a decoder, the picture element X(i, j, k) is obtained by
Formula (5) hereunder which is given by modification of Formula (4):
X(i, j, k)=E(i, j, k)+X(i-1, j-vx(i, j, k), k-vy(i, j, k)) (5)
In order to realize the normal reproduction by using Formula (5), the
picture elements X(0, j, k) of the zeroth frame are given to the decoder.
For this purpose, the picture elements X(0, j, k) of the zeroth picture
are coded by using the intraframe coding.
Description will proceed to a reverse reproduction. In order to carry out
the reverse reproduction of the picture elements X(i, j, k), the picture
elements X(i, j, k) are successively decoded from the n-th frame to the
zeroth frame by Formula (6) hereunder which is given by different
modification of Formula (4):
X(i-1, j-vx(i, j, k), k-vy(i, j, k))=-E(i, j, k)+X(i, j, k). (6)
In order to carry out the reverse reproduction by using Formula (6), the
picture elements X(n, j, k) of the n-th or trailing frame are given to the
decoder. For this purpose, the picture elements X(n, j, k) of the n-th
picture are coded by using intraframe coding.
However, the reverse reproduction can not be performed only by decoding the
picture elements X(n, j, k) of the n-th picture by using the intraframe
predictive coding. This incapability of the reverse reproduction will be
described hereunder.
In FIG. 5, each frame of the digital video signal is represented by a
one-dimensional signal like in FIG. 1. In FIG. 5, a motion vector of a
j-th picture element of an i-th frame is represented by V(i, j) while an
interframe predictive error signal (namely, the first result of the
motion-compensated interframe predictive coding) of the j-th picture
element of the i-th frame is represented by E(i, j). An intraframe coded
signal (namely, the second result of the intraframe predictive coding) of
the j-th picture element of the i-th frame is represented by P(i, j).
In order to perform the normal reproduction, all of the picture elements of
the zeroth frame are subjected to the intraframe coding to produce the
second results P(0, 1), P(0, 2), P(0, 3), and P(0, 4). All of the picture
elements of the first frame are subjected to the motion-compensated
interframe predictive coding to produce the first results E(1, 1), E(1,
2), E(1, 3), and E(1, 4) and the motion vectors V(1, 1), V(1, 2), V(1, 3)
and V(1, 4).
First through third picture elements of the second frame are subjected to
the motion-compensated interframe predictive coding to produce the first
results E(2, 1), E(2, 2), and E(2, 3) and the motion vectors V(2, 1), V(2,
2), and V(2, 3). A fourth picture element of the second frame is subjected
to the intraframe coding to produce the second result P(2, 4).
For the third and the fourth frames, all of the picture elements are
subjected to the motion-compensated interframe predictive coding to
produce the first result E(3, 1), E(3, 2), E(3, 3), E(3, 4), E(4, 1), E(4,
2), E(4, 3), and E(4, 4) and the motion vectors V(3, 1), V(3, 2), V(3, 3),
V(3, 4), V(4, 1), V(4, 2), V(4, 3), and V(4, 4).
In order to perform the reverse reproduction, all of the picture elements
of the trailing frame, namely, the fourth frame, are subjected to the
intraframe coding to produce the second results P(4, 1), P(4, 2), P(4, 3),
and P(4, 4).
Description will be made more in detail as regards the motion-compensated
interframe coding of the first picture element of the second frame. The
motion-compensated interframe predictive coding is carried out by
detecting the motion vector V(2, 1) and by using the motion vector V(2,
1). The motion vector V(2, 1) represents a movement from the second
picture element of the first frame to the first picture element of the
second frame in FIG. 5. In other words, motion-compensated interframe
coding of the first picture element of the second frame is carried out
with reference to the second picture element of the first frame. The
motion-compensated interframe coding of each of the second and the third
picture elements of the third frame is carried out with reference to the
third picture element of the second frame. Likewise, the
motion-compensated interframe predictive coding of the first picture
element of the first frame is carried out with reference to the first
picture element of the zeroth frame.
Turning to FIG. 6, the first and the second results E and P and the motion
vectors V are represented for use in carrying out the normal reproduction.
Turning back to FIG. 5, when the reverse reproduction is carried out in
accordance with Formula (6), it is impossible to decode the first picture
element of the first frame and the first picture element of the second
frame for the reason which will be described hereunder. Attention will be
directed to the first picture element of the first frame. The first
picture element of the first frame has no relation to the movement
represented by each of the motion vectors V(2, 1), V(2, 2), V(2, 3), and
V(2, 4) which are used in carrying out the motion-compensated predictive
coding on the picture elements cf the second frame which follows the first
frame. That is, the motion-compensated interframe predictive coding of the
picture elements of the second frame is carried out without reference to
the first picture element of the first frame.
Likewise, the first picture element of the second frame has no relation to
the movement represented by each of the motion vectors V(3, 1), V(3, 2),
V(3, 3), and V(3, 4) which are used in carrying out the motion-compensated
predictive coding on the picture elements of the third frame.
This is the reason why the first picture element of the first frame and the
first picture element of the second frame can not be decoded when the
reverse reproduction is carried out.
In order to resolve this problem, the first picture element of the first
frame and the first picture element of the second frame are subjected to
the intraframe coding to produce the second results P(1, 1) and P(2, 1) in
accordance with this invention. In FIG. 5, a symbol * is again attached to
the right upper portion of each of the second results P(1, 1), P(2, 1),
P(4, 1), P(4, 2), P(4, 3), and P(4, 4) which are used in carrying out the
reverse reproduction and which are not used in carrying out the normal
reproduction.
Turning to FIG. 7, the first and the second results E and P and the motion
vectors V are represented for use in carrying out the reverse
reproduction.
Turning back to FIG. 5 again, a method according to the second embodiment
of this invention will be described in detail. The method comprises a
producing step wherein production is made about a coding mode signal which
indicates a selected one of the motion-compensated interframe predictive
coding and the intraframe coding when the motion-compensated
interframe/intraframe adaptive coding is used in the digital video signal.
The motion-compensated interframe predictive coding is carried out by
detecting a motion vector representative of a movement of each picture
element between adjacent ones of successive pictures of the digital video
signal. The intraframe coding is carried out by using a correlation
between the picture elements within each of the successive pictures.
In a selectively coding step, the digital video signal is selectively coded
into a first coded signal by carrying out the selected one of the
motion-compensated interframe predictive coding and the intraframe coding
in response to the coding mode signal. The first coded signal carries a
first result E of the motion compensated interframe predictive coding and
a second result P of the intraframe coding.
The selectively coding step is made to carry out the intraframe coding on a
specific element (for example, the first picture element of the first
frame) of the picture elements of a current picture (that is, the first
frame) to produce a second coded signal P(1, 1) when the coding mode
signal indicates that the specific element should be subjected to the
motion-compensated interframe predictive coding and furthermore when the
specific element has no relation to the movement represented by each of
the motion vectors V(2, 1), V(2, 2), and V(2, 3). The motion vectors V(2,
1), V(2, 2), and V(2, 3) are used in carrying out the motion-compensated
interframe predictive coding on the picture elements of a following frame
(that is, the second frame) when the coding mode signal indicates that the
picture elements of the following frame should be subjected to the
motion-compensated interframe predictive coding. The following picture
follows the current picture in the successive pictures.
When the second frame becomes the current picture, the specific element
corresponds to the first picture element of the second frame. In this
event, the selectively coding step produces the second result P(2, 1).
The first and the second coded signals, the motion vectors, and the coding
mode signal are multiplexed into a multiplexed signal.
Description will be made as regards a method for detecting the specific
element by the use of Formula (6). Supposing in Formula (6) that:
a=j-vx(i, j, k), b=k-vy(i, j, k), (7)
Formula (6) is modified into Formula (8) hereunder:
X(i=1, a, b)=-E(i, a+vx(i, j, k), b+vy(i, j, k))+X(i, a+vx(i, j, k),
b+vy(i, j, k)). (8)
When first and second integers are given as a and b, respectively, judgment
is made whether or not third and fourth integers are obtained as j and k,
respectively, by using Formula (7). When a result of the judgement
indicates that it is impossible to obtain the third and the fourth
integers, it will be understood that the motion-compensated interframe
predictive coding is carried out on the picture elements of the i-th frame
with no reference to a picture element X(i-1, a, b). That is, the picture
element X(i-1, a, b) is the specific element. Therefore, the intraframe
coding is carried out on the picture element X(i-1, a, b).
Referring to FIG. 8, description will proceed to a coding device for use in
carrying out the method according to the first embodiment of this
invention. That is, the coding device is capable of carrying out the
interframe/intraframe adaptive coding described above.
The coding device is for coding the digital video signal by subjecting the
digital video signal to redundancy reduction coding. The decoding device
comprises a basic interframe predictive coder 41 and an intraframe coder
42. Responsive to the digital video signal, the basic interframe
predictive coder 41 carries out, as the redundancy reduction coding, the
basic interframe predictive coding to produce an interframe predictive
error signal E as a first result of the basic interframe predictive
coding. Responsive to the digital video signal, the intraframe coder 42
carries out, as the redundancy reduction coding, the intraframe coding of,
for example, intraframe predictive coding to produce an intraframe coded
signal P as a second result of the intraframe coding.
Responsive to the first and the second result E and P, a mode signal
producing circuit 43 produces a coding mode signal S which represents for
each picture element a selected one of the basic interframe predictive
coding and the intraframe coding in consideration of a first amount of
produced information of the first result E and a second amount of produced
information of the second result P. More specifically, the mode signal
producing circuit 43 compares the first and the second amounts and
produces a compared result signal. When the compared result signal
represents that the first amount is smaller than the second amount, the
mode signal producing circuit 43 produces the coding mode signal S which
has a logic "0" level to represent the basic interframe predictive coding.
When the compared result signal represents that the first amount is not
smaller than the second amount, the mode signal producing circuit 43
produces the coding mode signal S which has a logic "1" level to represent
the intraframe coding. Inasmuch as the mode signal producing circuit 43 is
known in the art, details will no more be described.
When the coding mode signal S is used for the coders 41 and 42 in coding of
a succeeding part of the digital video signal, the coding signal is
supplied to the coders 41 and 42.
Responsive to the first result E, a first delay circuit 45 delays the first
result E to produce a first delayed signal by providing a delay which is
equal to a period of each frame or picture. Likewise, a second delay
circuits 46 delays the second result P to produce a second delayed signal
by providing the delay equal to the period of each frame. A third delay
circuit 47 delays the coding mode signal S to produce a delayed mode
signal by providing the delay equal to the period of each frame.
Responsive to the coding mode signal S, a processing circuit 48 processes
the coding mode signal S into a processed mode signal S' which has a logic
"1" level to represent the intraframe coding for picture elements which
are necessary on carrying out the reverse reproduction and the normal
reproduction. The above-mentioned particular elements are included in the
picture elements.
Responsive to the first delayed signal and the delayed mode signal, a first
selector 49 selects the first delayed signal as a first selected signal
only when the delayed mode signal has a logic "0" level to represent the
basic interframe predictive coding. Responsive to the second delayed
signal and the processed mode signal, a second selector 50 selects the
second delayed signal as a second selected signal only when the processed
mode signal S' has a logic "1" level to represent the intraframe coding.
A multiplexer 51 multiplexes the first and the second selected signals and
the delayed mode signal into the multiplexed signal.
Referring to FIG. 9, the processing circuit 48 comprises a fourth delay
circuit 52 and an OR gate 53. The fourth delay circuit 52 delays the
coding mode signal S to produce another delayed mode signal by providing
the delay equal to a period of each frame or picture. The other delayed
mode signal is equivalent to the delayed mode signal produced by the third
delay circuit 47 illustrated in FIG. 8. Responsive to the coding mode
signal S and the other delayed signal, the OR gate 53 produces an OR'ed
signal as the processed mode signal S'.
Reviewing FIGS. 8 and 9, the mode signal producing circuit 43 serves as a
producing arrangement for producing the coding mode signal S which
indicates a selected one of the basic interframe predictive coding and the
intraframe coding. A combination of the interframe and the intraframe
coders 41 and 42, the first through the third frame de | | |
