U.S. patent number RE35,158 [Application Number 07/997,238] was granted by the patent office on 1996-02-20 for apparatus for adaptive inter-frame predictive encoding of video signal.
This patent grant is currently assigned to Victor Company of Japan Limited. Invention is credited to Kenji Sugiyama.
United States Patent |
RE35,158 |
Sugiyama |
February 20, 1996 |
Apparatus for adaptive inter-frame predictive encoding of video
signal
Abstract
An adaptive predictive encoding apparatus for encoding a video
signal by utilizing correlation between frames in both the forward
and reverse directions of the time axis. A prediction signal for
use in deriving prediction error values to be encoded for a frame
is selected by an adaptive prediction section, in units of blocks,
from a plurality of mutually differently derived prediction
signals, in accordance with the degree of correlation of the block
with corresponding ones of a specific preceding independently
encoded frame and a specific succeeding independently encoded
frame. .Iadd.A complementary adaptive decoding apparatus receives
the encoded information and reconstructs the video signal in
accordance with information supplied to the adaptive decoding
apparatus by the encoding signal. .Iaddend.
Inventors: |
Sugiyama; Kenji (Kanagawa,
JP) |
Assignee: |
Victor Company of Japan Limited
(Yokohama, JP)
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Family
ID: |
14484288 |
Appl.
No.: |
07/997,238 |
Filed: |
December 28, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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465747 |
Jan 16, 1990 |
4985768 |
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Reissue of: |
514015 |
Apr 26, 1990 |
04982285 |
Jan 1, 1991 |
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Foreign Application Priority Data
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Apr 27, 1989 [JP] |
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1-108419 |
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Current U.S.
Class: |
348/401.1;
348/415.1 |
Current CPC
Class: |
H04N
19/503 (20141101); H04N 19/61 (20141101); H04N
19/82 (20141101); H04N 19/587 (20141101); H04N
19/90 (20141101) |
Current International
Class: |
G06T
9/00 (20060101); H04N 7/36 (20060101); H04N
7/26 (20060101); H04N 7/50 (20060101); H04N
007/13 () |
Field of
Search: |
;358/136,135,133,105 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"15/30 Mb/s Motion-Compensated Interframe, Interfield and
Intrafield Adaptive Prediction Coding" (Oct. '85); Bulletin of the
Society of Television Engineers (Japan); vol. 39, No. 10. .
"Adaptive Hybrid Transform/Predictive Image Coding" (Mar. '87);
Document D-1115 of the 70th Anniversary National Convention of the
Society of Information and Communication Engineers
(Japan)..
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Primary Examiner: Kostak; Victor R.
Attorney, Agent or Firm: Amster, Rothstein &
Ebenstein
Parent Case Text
The present application is a .Iadd.reissue of application No.
514,015 now U.S. Pat. No. 4,982,285, which is a
.Iaddend.continuation-in-part of a U.S. patent application
(application number 465,747) with filing date Jan. 16, 1990.Iadd.,
now U.S. Pat. No. 4,985,768.Iaddend..
Claims
What is claimed is:
1. An adaptive encoding apparatus for encoding an input video
signal, said video signal comprising a sequence of frames each
comprising successive pixel data the apparatus comprising:
encoder means for encoding successive blocks of a frame of said
video signal, each of said blocks comprising a fixed-size array of
said pixel data values;
means for selecting one in every N of said frames to be transferred
directly to said encoder means as a reference frame, to be encoded
by intra-frame encoding, where N is a fixed integer of value
greater than one; and
adaptive prediction means for executing adaptive prediction
processing, as a dependent frame, of each frame occurring between a
preceding one and a succeeding one of said reference frames in said
frame sequence, by deriving for the data values of each block of a
dependent frame respective prediction error values based upon an
optimum prediction signal selected from a plurality of prediction
signals derived using a plurality of combinations of said preceding
and succeeding reference frames.
2. An adaptive predictive encoding apparatus according to claim 1,
in which said adaptive prediction means comprises:
means for deriving a first prediction signal based on a combination
of pixel data of said preceding and succeeding reference frames, a
second prediction signal derived only from said preceding reference
frame, a third prediction signal derived only from said succeeding,
and a non-prediction signal derived only from said dependent frame;
and
predictive mode selection means for selecting, for each of said
blocks, one out of four prediction modes in which said first,
second and third prediction signals and said non-prediction signal
are respectively used in deriving predictive error values for
respective pixel data of said block, to be sent to said encoder
means and encoded thereby, said selection being based upon
judgement of said errors, said predictive mode selection means
further supplying to said encoding means, to be encoded thereby,
predictive mode data indicating predictive modes which have been
selected for respective ones of the blocks.
3. An adaptive predictive encoding apparatus according to claim 2,
in which said adaptive prediction means further comprises means for
varying, in accordance with respective time axis positions of said
frames in said video signal, respective weighting values assigned
to said preceding and succeeding reference frames for establishing
said combination.
4. An adaptive predictive encoding apparatus according to claim 1,
and further comprising decoding means for decoding said reference
frames after encoding by said encoding means, and for supplying
resultant decoded reference frames to said adaptive prediction
means for use in producing said prediction signals.
5. An adaptive predictive encoding apparatus according to claim 1,
and further comprising an (N-1) frame memory for temporarily
storing each dependent frame of said video signal and outputting
said each dependent frame to said adaptive prediction means after a
fixed delay time, and first and second 1-frame memories for
respectively holding pixel data of said preceding and succeeding
reference frames and supplying pixel data of said preceding and
succeeding reference frames to said adaptive prediction means
during adaptive prediction processing of successive ones of said
dependent frames. .Iadd.
6. An adaptive decoding apparatus for decoding a video signal
encoded by the apparatus of claim 1, comprising:
decoding means for receiving and decoding the encoded reference
frames, the prediction error values and a prediction mode signal
that identifies which of said plurality of combinations of said
preceding and succeeding reference frames were used during encoding
to obtain said optimum prediction signal;
prediction signal generating means responsive to the decoded
prediction mode signal for reconstructing said optimum prediction
signal;
means for combining said prediction error values and said optimum
prediction signal for each dependent frame to generate display
information corresponding thereto; and
means for outputting the decoded reference frames and the display
information for each dependent frame in proper sequence to produce
a video signal. .Iaddend. .Iadd.7. A decoding system for decoding
video signals that have been encoded in an encoder by arranging
said video signals into spaced-apart reference frames and dependent
frames located therebetween; said reference frames being output
from said encoder in encoded form and used therein to implement one
of a plurality of prediction modes for adaptively predicting the
display information in each of said dependent frames based upon the
degree of correlation between each dependent frame and the
reference frames which immediately precede and follow said
dependent frame; said encoder thereby generating and outputting
therefrom an encoded frame signal for each dependent frame and a
prediction mode signal for identifying the prediction mode used to
generate said frame signal, said decoding system comprising:
decoding means for receiving and decoding each of the encoded
reference frames, and the frame signals and the prediction mode
signals associated with each dependent frame;
processing means responsive to said prediction mode signal for
reconstructing the display information for each dependent frame
from its respective decoded frame signal and the reference frames
which precede and follow said dependent frame; and
means for outputting the decoded reference frames and the
reconstructed display information generated for each of said
dependent frames in proper sequence to produce a video signal.
.Iaddend. .Iadd.8. The decoding system in accordance with claim 7,
wherein said processing means includes
memory means for storing the two decoded reference frames which
respectively precede and follow each dependent frame; and
means responsive to the prediction mode signal for generating and
combining weighted values of said display information from said two
reference frames to reconstruct the predicted display information
for said dependent frame.
.Iaddend. .Iadd.9. The decoding system in accordance with claim 8,
including means for combining said predicted display information
with said decoded frame signal to produce an output representing
the display information for said dependent frame. .Iaddend.
.Iadd.10. The decoding system in accordance with claim 8, wherein
said weighted values are generated by multiplying said display
information in the preceding reference frame by a first weighting
coefficient and said display information in the following reference
frame by a second weighting coefficient. .Iaddend. .Iadd.11. The
decoding system in accordance with claim 10, wherein, in response
to a first prediction mode signal, the first and second weighting
coefficients are non-zero. .Iaddend. .Iadd.12. The decoding system
in accordance with claim 11 wherein the weighting coefficients are
selected such that the reference frame temporally closer to the
dependent frame is given a greater weight than the other reference
frame. .Iaddend. .Iadd.13. The decoding system in accordance with
claim 10, wherein, in response to a second prediction mode signal,
the second weighting coefficient is effectively zero. .Iaddend.
.Iadd.14. The decoding system in accordance with claim 10, wherein,
in response to a third prediction mode signal, the first weighting
coefficient is
effectively zero. .Iaddend. .Iadd.15. The decoding system in
accordance with claim 7, wherein, in response to a fourth
prediction mode signal, the decoded frame signal is output to
represent the display information of said dependent frame.
.Iaddend. .Iadd.16. A method for decoding and generating a video
signal from video signals that have been encoded in an encoder by
arranging said video signals into spaced-apart reference frames and
dependent frames located therebetween, said reference frames being
output from said encoder in encoded form and used therein to
implement one of a plurality of prediction modes for adaptively
predicting the display information in each of said dependent frames
based upon the degree of correlation between each of said dependent
frames and the reference frames which immediately precede and
follow each of said dependent frames, said encoder generating and
outputting therefrom an encoded frame signal for each of said
dependent frames and a prediction mode signal for identifying the
prediction mode used to generate said encoded frame signal, said
method comprising the steps of:
(a) receiving and decoding each of said encoded reference frames,
said encoded frame signals and said prediction mode signal
associated with each dependent frame;
(b) reconstructing the display information for each dependent frame
from the corresponding decoded frame signal and the decoded
reference frames which precede and follow said dependent frame in
accordance with said associated prediction mode signal; and
(c) outputting the decoded reference frames and the reconstructed
display information generated for each of said dependent frames in
proper sequence
to generate a video signal. .Iaddend. .Iadd.17. The method of claim
16 wherein step (b) includes the steps of storing the display
information of the two decoded reference frames which respectively
precede and follow said dependent frame and combining weighted
values of said display information with said decoded frame signal
to reconstruct the display information for said dependent frame.
.Iaddend. .Iadd.18. The method in accordance with claim 17, wherein
said weighted values are generated by multiplying said display
information of the preceding reference frame by a first weighting
coefficient and said display information in the following reference
frame by a second weighting coefficient. .Iaddend. .Iadd.19. The
method in accordance with claim 18, wherein, in response to a first
prediction mode signal, the first and second weighting coefficients
are non-zero. .Iaddend. .Iadd.20. The method in accordance with
claim 19, wherein the weighting coefficients are selected such that
the reference frame temporally closer to the dependent frame is
given a greater weight
than the other reference frame. .Iaddend. .Iadd.21. The method in
accordance with claim 18, wherein, in response to a second
prediction mode signal, the second weighting coefficient is
effectively zero. .Iaddend. .Iadd.22. The method in accordance with
claim 18, wherein, in response to a third prediction mode signal,
the first weighting coefficient is effectively zero. .Iaddend.
.Iadd.23. The method in accordance with claim 16, wherein, in
response to a fourth prediction mode signal, the decoded frame
signal is added to a fixed data value to reconstruct the display
information of said dependent frame. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of Application
The present invention relates to an apparatus for encoding a video
signal to produce an encoded signal for transmission or recording,
with the encoded signal containing substantially lower amounts of
data than the original video signal. In particular, the invention
relates to an apparatus for inter-frame predictive encoding of a
video signal, which is especially applicable to television
conferencing systems or to moving-image video telephone
systems.
2. Prior Art Technology
Various methods have been proposed in the prior art for converting
a digital video signal to a signal containing smaller amounts of
data, for example in order to reduce the bandwidth requirements of
a communications link, or to reduce the storage capacity required
for recording the video signal. Such methods are especially
applicable to television conferencing or moving image video
telephone systems, and utilize the fact that there is generally a
high degree of correlation between successive frames of a video
signal, and hence some degree of redundancy if all of the frames
are transmitted. One basic method, described for example in U.S.
Pat. No. 4,651,207, is to periodically omit one or more frames from
being transmitted, and to derive information at the receiving end
for interpolating the omitted frames (based on movement components
in the transmitted frames). Such a method will provide satisfactory
operation only so long as successive frames contain only relatively
small amounts of change between one frame and the next. Another
basic method known in the prior art is to periodically transmit
(i.e. at fixed numbers of frame intervals) frames which are
independently encoded, these being referred to in the following as
independent frames, while, for each frame occurring between
successive independent frames (these being referred to in the
following as dependent frames), only amounts of difference between
that frame and the preceding independent frame as encoded and
transmitted, i.e. inter-frame predictive encoding is executed with
the independent frames being used as reference frames. With a more
practical form of that method, known as adaptive predictive
encoding, such inter-frame predictive encoding is executed only
when it is appropriate, that is to say only when there is no great
difference between successive frames. When such a large difference
is detected, then intra-frame encoding is executed. Example of such
inter-frame encoding are described in the prior art for example in
"15/30 Mb/s Motion-Compensated Inter-frame, Inter-field and
Intrafield Adaptive Prediction Coding" (Oct. 1985) Bulletin of the
Society of Television Engineers (Japan), Vol. 39, No. 10. With that
method, a television signal is encoded at a comparatively high data
rate. Movement-compensation inter-frame prediction, intra-field
prediction, and inter-field (i.e. intra-frame) prediction are
utilized. Another example is described in "Adapative Hybrid
Transform/Predictive Image Coding" (March 1987) Document D-1115 of
the 70th Anniversary National Convention of the Society of
Information and Communication Engineers (Japan). With that method,
switching is executed between inter-frame prediction of each
dependent frame based on a preceding independent frame (which is
the normal encoding method) and prediction that is based on
adjacent blocks of pixels, prediction that is based on the image
background, and no prediction (i.e. direct encoding of the original
video signal). In the case of the "no-prediction" processing,
orthogonal transform intra-frame encoding is executed, while in the
case of background prediction, a special type of prediction is
utilized which is suitable for a video signal to be used in
television conferencing applications. Processing operation is
switched between pixel blocks varying in size from 16.times.16 to
8.times.8 elements, as block units.
With such prior art adaptive predictive encoding methods, when a
dependent frame is to be decoded (at the receiving end of the
system, or after playback from a recording medium) the required
data are obtained by cumulative superposition of past data relating
to that frame, so that all of the related past data are required.
It is necessary to use storage media for decoding which will enable
random access operation, to obtain such data. This sets a limit to
the maximum size of period of repetition of the independent frames
(alternatively stated, the period of resetting of inter-frame
predictive encoding operation), since if that period is excessively
long then decoding storage requirements and operation will be
difficult. However the shorter this resetting period is made, the
greater will be the amounts of data contained in the encoded output
signal and hence the lower will become the encoding efficiency.
Typically, a period of 4 to 8 frames has been proposed for the
prior art methods.
FIGS. 1A and 1B are simple conceptual diagrams to respectively
illustrate the basic features of the aforementioned inter-frame
predictive encoding methods and the method used in the
aforementioned U.S. patent application by the assignee of the
present invention. A succession of frames of a video signal are
indicated as rectangles numbered 1, 2, . . . The shaded rectangles
denote independent frames (i.e. independently encoded frames that
are utilized as reference frames) which occur with a fixed period
of four frame intervals, i.e. inter-frame predictive encoding is
assumed to be reset once in every four frames. As indicated by the
arrows, prediction operation is executed only along the forward
direction of the time axis, so that difference values between a
dependent frame and an independent frame (referred to in the
following as prediction error values) are always obtained by using
a preceding independent frame as a reference frame. Thus,
independent frame No. 1 is used to derive prediction error values
for each of frames 2, 3, and 4, which are encoded and transmitted
as data representing these frames.
Such a prior art prediction method has a basic disadvantage.
Specifically, only the correlation disadvantage. Specifically, only
the correlation between successive frames of the video signal along
the forward direction of the time axis is utilized. However in fact
there is generally also strong correlation between successive
frames in the opposite direction. The operation of the
aforementioned related patent application by the assignee of the
present invention utilizes that fact, as illustrated in FIG. 1B.
Here, each frame occurring between two successive independent
frames is subjected to inter-frame predictive encoding based on
these two independent frames, as indicated by the arrows. For
example, inter-frame predictive encoding of frame 2 is executed
based on the independent frames 1 and 5. This is also true for
frames 3 and 4. More precisely, a first prediction signal for frame
2 is derived based on frame 1 as a reference frame, and a second
prediction signal for frame 2 is derived based on frame 5 as a
reference frame. These two prediction signals are then multiplied
by respective weighting factors and combined to obtain a final
prediction error signal for frame 2, with greater weight being
given to the first prediction signal (since frame 2 will have
greater correlation with frame 1 than frame 5). Prediction signals
for the other dependent frames are similarly derived, and
differences between the prediction signal and a signal of a current
frame are derived as prediction errors, then encoded and
transmitted. Since in this case correlation between a preceding
independent frame and a succeeding independent frame is utilized to
obtain prediction signals for each dependent frame, a substantially
greater degree of accuracy of prediction is attained than is
possible with prior art methods in which only inter-frame
correlation along the forward direction of the time axis is
utilized.
Prior art methods of adaptive inter-frame predictive encoding can
overcome the basic disadvantages described above referring to FIG.
1A, as will be described referring to FIGS. 2A, 2C. In FIGS. 2A and
2C (and also in FIGS. 2B, 2D, described hereinafter) respective
numbered rectangles represent successive frames of a video signal.
The frames indicated by the # symbol represent independently
encoded frames. Of these, frames 1 and 5 are independent frames
which occur with a fixed period of four frame intervals, i.e.
inter-frame predictive encoding is reset once in every four
successive frame intervals in these examples. The white rectangles
denote frames whose image contents are mutually comparatively
similar. The dark rectangles denote frames whose image contents are
mutually comparatively similar, but are considerably different from
the contents of the "white rectangle" frames. In FIG. 2A, frame 1
is an independent frame, and frame 2 is a dependent frame whose
contents are encoded by inter-frame predictive encoding using frame
1 as a reference frame. There is a significant change (e.g.
resulting from a "scene change", or resulting from a new portion of
the background of the image being uncovered, for example due to the
movement of a person or object within the scene that is being
televised) in the video signal contents between frames 2 and 3 of
FIG. 2A, so that it becomes impossible to execute inter-frame
predictive encoding of frame 3 by using frame 2 as a reference
frame. With a prior art method of adaptive inter-frame predictive
encoding, this is detected, and results in frame 3 being
independently encoded. Frame 3 is then used as a reference frame
for inter-frame predictive encoding of frame 4.
Thus, each time that a scene change or other very considerable
change occurs in the video signal, which does not coincide with the
start of a (periodically occurring) independent frame, independent
encoding of an additional frame must be executed instead of
inter-frame predictive encoding, thereby resulting in a
corresponding increase in the amount of encoded data which must be
transmitted or recorded.
In the example of FIG. 2C, with a prior art method of adaptive
inter-frame predictive encoding, it is assumed that only one frame
(frame 3) is considerably different from the preceding and
succeeding frames 1, 2 and 4, 5. This is detected, and frame 3 is
then independently encoded instead of being subjected to
inter-frame predictive encoding. However since frame 4 is now very
different in content from frame 3, it is not possible to apply
inter-frame predictive encoding to frame 4, so that it is also
necessary to independently encode that frame also. Hence, each time
that a single frame occurs which is markedly different from
preceding and succeeding frames, it is necessary to independently
encode an additional two frames, thereby increasing the amount of
encoded data that must be transmitted. Such occurrences of isolated
conspicuously different frames such as frame 3 in FIG. 2C can
occur, for example, each time that a photographic flash is
generated within the images that constitute the video signal.
These factors result in the actual amount of data that must be
encoded and transmitted, in actual practice, being much larger than
that for the ideal case in which only the periodically occuring
independent frames (i.e. frames 1, 5, etc.) are independently
encoded, and in which all other frames are transmitted after
inter-frame predictive encoding based on these independent
frames.
Another basic disadvantage of such a prior art method of adaptive
inter-frame predictive encoding occurs when the enclosed output
data are to be recorded (e.g. by a video tape recorder) and
subsequently played back and decoded to recover the original video
signal. Specifically, when reverse playback operation of the
recorded encoded data is to be executed, in which playback is
executed with data being obtained in the reverse sequence along the
time axis with respect to normal playback operation, it would be
very difficult to apply such a prior art method, due to the fact
that predictive encoding is always based upon a preceding frame.
That is to say, prediction values are not contained the playback
signal (in the case of reverse playback operation) in the correct
sequence for use in decoding the playback data.
The aforementioned related patent application by the assignee of
the present invention overcomes this problem of difficulty of use
with reverse playback operation, since each dependent frame is
predictively encoded based on both a preceding and a succeeding
independent frame. However since the described apparatus is not of
adaptive type, i.e. inter-frame predictive encoding is always
executed for the dependent frames irrespective of whether or not
large image content changes occur between successive ones of the
dependent frames, it has the disadvantage of a deterioration of the
resultant final display image in the event of frequent occurrences
of scene changes, uncovering of the background, or other
significant changes in the image content.
With a prior art method of adaptive inter-frame predictive encoding
as described above, when scene changes occur, or movement of people
or objects within the image conveyed by the video signal occurs,
whereby new portions of the background of the image are uncovered,
then large amounts of additional encoded data are generated, as a
result of an increased number of frames being independently encoded
rather than subjected to inter-frame predictive encoding. Various
methods have been proposed for executing control such as to
suppress the amount of such additional data. However this results
in loss of image quality.
SUMMARY OF THE INVENTION
It is an objective of the present invention to overcome the
disadvantages of the prior art as set out above, by providing an
adaptive predictive encoding apparatus whereby an optimum
prediction signal for use in deriving prediction error values for a
dependent frame is selected, for each of successive blocks of the
frame, from a plurality of prediction signals derived by
respectively different combinations of signals obtained from a pair
of preceding and succeeding independent claims. This selection is
based upon the magnitude of the prediction error values that are
produced, for the respective data values constituting a block, by
these different prediction signals. If there is insufficient
correlation between the block and the corresponding blocks of these
preceding and succeeding frames, then the block is encoded
independently of these other frames, by intra-frame encoding
alone.
More specifically, the present invention provides an adaptive
encoding apparatus for encoding an input video signal comprising a
sequence of frames each comprising successive data values, the
apparatus comprising:
encoder means for encoding successive blocks of a frame of the
video signal, each of the blocks comprising a fixed-size array of
the data values;
means for selecting one of every N of the frames to be transferred
directly to the encoder means as an independent frame, to be
encoded by intra-frame encoding, where N is a fixed integer of
value greater than one; and
adaptive prediction means for executing adaptive prediction
processing, as a dependent frame, of each frame occurring between a
preceding one and a succeeding one of the independent frames in the
frame sequence, by deriving for the data values of each block of a
dependent frame respective prediction error values based upon an
optimum prediction signal selected from a plurality of prediction
signals derived using a plurality of combinations of the preceding
and succeeding independent frames.
The adaptive prediction means of such an adaptive prediction
encoding apparatus preferably comprises:
means for deriving a first prediction signal based on a combination
of data values of the preceding and succeeding independent frames,
a second prediction signal derived only from the preceding
independent frame, a third prediction signal derived only from the
succeeding, and a non-prediction signal derived only from the
dependent frame; and
predictive mode selection means for selecting, for each of the
blocks, one out of four prediction modes in which the first, second
and third prediction signals and the non-prediction signal to are
respectively used in deriving predictive error values for
respective data values of the block, to be sent to the encoder
means and encoded thereby, the selection being based upon judgement
of the error values, the predictive mode selection means further
supplying to the encoding means, to be encoded thereby, predictive
mode data indicating predictive modes which have been selected for
respective ones of the blocks.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are conceptual diagrams for describing inter-frame
predictive operation using one direction and both directions of the
time axis, respectively;
FIGS. 2A, 2C are conceptual diagrams for describing a prior art
method of adaptive inter-frame predictive encoding, and FIGS. 2B,
2D are for describing a method of adaptive inter-frame predictive
encoding according to the present invention;
FIG. 3 is a general block diagram of an embodiment of an encoding
apparatus for adaptive inter-frame predictive encoding according to
the present invention;
FIG. 4 is a block diagram of an adpative prediction section of the
apparatus of FIG. 3; and
FIG. 5 is a timing diagram for assistance in describing the
operations of the apparatus of FIG. 5.
.Iadd.FIG. 6 is a block diagram of a decoding apparatus for
decoding signals in accordance with the present invention.
FIG. 7 is a schematic diagram of the adaptive prediction section of
the decoding apparatus of FIG. 6. .Iaddend.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIGS. 2B and 2D illustrate the manner in which the frame sequences
of FIGS. 2A and 2C respectively described hereinabove) are handled
by the method of adaptive inter-frame predictive encoding of the
present invention, as compared with a prior art method of adaptive
inter-frame predictive encoding in the case of FIG. 2B, in which
there is a scene change between frames 2 and 3, so that the
preceding independent frame 1 cannot be used for inter-frame
predictive encoding of frames 3 and 4, use is made of the
correlation between succeeding independent frame 5 and the
dependent frames 3 and 4. That is to say, only the succeeding
independent frame 5 is used for inter-frame predictive processing
of the dependent frames 3 and 4. This makes it unnecessary to
independently encode frame No. 3, as is required with a prior art
method of adaptive inter-frame predictive encoding which uses only
the forward direction of the time axis. Thus, the average amount of
encoded data that are generated will be reduced, since it is no
longer necessary to independently encode a dependent frame (or a
large part of a dependent frame) each time that a scene change or
other very substantial change in the contents of a frame
occurs.
In the case of FIG. 2D, where only frame No. 3 is very different
from the preceding and succeeding frames, it is necessary with a
prior art method of adaptive inter-frame predictive encoding to
independently encode both of frames 3 and 4, as described
hereinabove. However with the present invention, use is made of the
fact that frame 3 is an isolated occurrence, by using the
succeeding independent frame No. 5 for inter-frame predictive
encoding of frame No. 3. In this way, it becomes unnecessary to
independently encode all of (or a large part of) a dependent frame
which succeeds an isolated significantly different dependent frame,
as is required for frame 4 in the case of a prior art method of
adaptive inter-frame predictive encoding, as described above for
FIG. 2C.
The basic operation of an adaptive predictive encoding apparatus
according to the present invention is as follows. The encoder
processes each frame of an input video signal in units of blocks
(where each block will for example consist of an 8.times.8 array of
pixels of the frame), and the apparatus determines for each block
of a frame which of the following correlation conditions exists
between that block and the correspondingly positioned blocks of the
preceding independent frame and the succeeding independent
frame:
(Option 1) Optimum prediction will be achieved by processing using
a combination of the corresponding blocks (i.e. correspondingly
positioned within the frame) of both the preceding and succeeding
independent frames.
(Option 2) Optimum prediction will be achieved by processing using
only the corresponding block of the preceding independent
frame.
(Option 3) Optimum prediction will be achieved by processing using
only the corresponding block of the succeeding independent
frame.
(Option 4) Optimum operation will be achieved by directly encoding
that block (only intra-frame encoding executed).
The decision as to which of the above four options is optimal is
based upon a total of respective squared values of difference
between each data value representing a pixel of the block and the
corresponding data values of the corresponding blocks in the
preceding and succeeding frames. Processing of the block is then
executed, that is to say either a set of inter-frame prediction
error values with respect to the pixels of the corresponding block
of the preceding and/or succeeding independent frames, or the data
values for the pixels of the block in question, slightly modified
as described hereinafter, are then encoded for transmission or
recording. In addition, prediction mode data which indicates which
of the above four options has been selected for that block is
encoded with the yideo data, and transmitted or recorded. At the
receiving end, or upon playback of the recorded encoded data,
decoding is executed, utilizing the prediction mode data to control
the decoding operation.
FIG. 3 is a general block diagram of an embodiment of an
inter-frame adaptive predictive encoding apparatus according to the
present invention. A frame memory 1a receives a (moving picture)
digital video signal from an input terminal 1 as successive data
values, consisting of luminance (Y) values for respective pixels,
as well as chrominance (R-Y) and (B-Y), i.e. color difference,
values. Successive frames of the video signal are stored in the
frame memory 1a. Successive blocks of a frame that is currently
held in the frame memory 1a are read out in a predetermined
sequence, each of the blocks consisting for example of an 8.times.8
element array of luminance (Y) or chrominance, i.e. color
difference (B-Y) or (R-Y) values. Each block of luminance data
values directly corresponds to a physical (display) size of
8.times.8 pixels. However in general each 8.times.8 block of
chrominance values will correspond to a larger physical area that
8.times.8 pixels. For example as set out by the CCITT of the
International Telecommunication Union, Document .pi.339, Mar. 1988
document "Description of Ref. Model 5 (RM5)", in which a common
source input format for coding of color television signals is
specified, each 8.times.8 block of color difference values will
correspond (in display size) to a 16.times.16 macro block of
luminance values consisting of four 8.times.8 blocks.
It should be understood that the description of adaptive prediction
operation given herein applies to both processing of luminance and
color difference values.
The values of each block are successively read out in a
predetermined sequence. The output data from the frame memory 1a is
supplied to a movable contact of a changeover switch 2. The "a"
fixed contact of the changeover switch 2 is connected to the "a"
fixed contact of a changeover switch 5, while the "b" fixed contact
of the changeover switch 2 is connected to the input of a (N-1)
frame memory 3. The (N-1) frame memory 3 is a memory having a
capacity for storing up to (N-1) successively inputted frames,
where N is a fixed integer, and is used to produce a delay of N
frame intervals, i.e. a frame which is written into that memory
during one frame interval is subsequently read out from the memory
in the fourth frame interval to occur thereafter. The output of the
(N-1) frame memory 3 is supplied to an adaptive prediction section
4, while the output of the adaptive prediction section 4 is
supplied to the "b" fixed contact of the changeover switch 5. The
movable contact of the changeover switch 5 is connected to the
input of a orthogonal transform section 6, whose output is supplied
to a quantizer 7. The output from the quantizer 7 is supplied to an
variable-length encoder section 8 and also to a dequantizer 10. The
output from the variable-length encoder section 8 is applied to an
output terminal 9. The output from the dequantizer 10 is supplied
to an inverse orthogonal transform section 11, whose output is
supplied to a (succeeding) frame memory 12. The output from the 12
is supplied to a (preceding) frame memory 13 and also to a second
input of the adaptive prediction section 4. The output of the
(preceding) frame memory 13 is applied to a third input of the
adaptive prediction section 4. An output from the adaptive
prediction section 4, consisting of the aforementioned prediction
mode data, is supplied to a second input of the variable-length
encoder section 8.
A synchronizing signal separator circuit 4 receives the input video
signal and separates the sync signal components thereof to derive
synchronizing signals which are supplied to a control signal
generating circuit 15. The control signal generating circuit 15
thereby generates variuous control and timing signals for
controlling switching operation of the changeover switches 2 and 5,
and memory read and write operations of the frame memory 1a, (N-1)
frame memory 3, (succeeding) frame memory 12 and (preceding) frame
memory 13.
A weighting value generating circuit 16 receives a timing signal
from the control signal generating circuit 15, and generates
successive pairs of weighting values W and (1-W) which vary in
value on successive frames as described hereinafter. These pairs of
weighting values are supplied to the adaptive prediction section
4.
The switching operation of the changeover switch 5 is linked to
that of the changeover switch 2, and when both of these are set to
the respective "a" terminals, the signal of an independent frame is
directly inputted to the orthogonal transform section 6, to be
directly transformed and encoded.
The output signal from the changeover switch 5 thus consists of
successive data values of successive blocks of an independent
frame, during each interval in which data values of an independent
frame are being read out from the frame memory 1a, with switches 2
and 5 set to their "a" positions. When the switches are set to
their "b" positions, then the output signal from the changeover
switch 5 consists of either successive prediction error values for
a block of a dependent frame, or data values (which may have been
modified by intra-frame processing) of a block of a dependent
frame.
In order to maximize the efficiency of encoding, the Y (luminance)
and (R-Y), (B-Y) (chrominance) values of the output signal from the
changeover switch 5 are converted by the orthogonal transform
section 6 to coefficient component values by an orthogonal
transform operation, such as the discrete cosine transform (DCT),
in units of blocks. The resultant output signal from the orthogonal
transform section 6 is then quantized using steps of appropriate
size, by the quantizer 7. Since the distribution of the resultant
quantized signal is close to zero amplitude, encoding efficiency is
further increased by encoding the quantized signal by a
variable-length encoding technique, such as Huffman encoding. In
addition, the aforementioned prediction mode data values supplied
from the adaptive prediction section 4 to the variable-length
encoder section 8 are also encoded by the variable-length encoding
technique. The resultant variable-length data are supplied to an
output terminal 9, to be transmitted to a corresponding decoding
apparatus, or to be recorded and subsequently played back and
supplied to a corresponding decoding apparatus.
FIG. 4 is a general block diagram of the adaptive prediction
section 4 of FIG. 3. The data read out from the (preceding) frame
memory 13 are applied, as a preceding frame signal, to an input
terminal 40 and hence to one input of a subtractor 20. The output
from the (succeeding) frame memory 12 is applied, as a succeeding
frame signal, to an input terminal 40 and hence to one input of a
subtractor 22. 33 denotes a coefficient multiplier which multiplies
each data value from input terminal 40 by the aforementioned
weighting value W and supplies the resultant values to one input of
an adder 34, 35 denotes a coefficient multiplier which multiplies
each data value from input terminal 40 by the aforementioned
weighting value (1-W) and supplies the resultant values to the
other input of the adder 34. The output from the adder 34 is
applied to one input of a prediction signal subtractor 21. The
contents of the frame that is currently being read out from the
(N-1) frame memory 3 (that frame being referred to in the following
as the current frame) is applied as a current frame signal to an
input terminal 42 and hence to one input of a subtractor 23. The
current frame signal is also supplied to the respective other
inputs of the subtractor 20, prediction signal subtractor 21 and
subtractor 22. A fixed data value is applied to the other input of
the subtractor 23.
The value of the DC component of the signal of the current frame is
derived by a DC level detection circuit 38, and applied to one
input of a subtractor 39. The current frame signal is applied to
the other input of the subtractor 39, to have the DC component
subtracted therefrom. This subtraction of the DC component is
necessary in order to prevent excessively high output values from
being produced from a squaring circuit 27, described
hereinafter.
The respective outputs from the subtractors 21, 20, and 22 (these
outputs being referred to in the following as the first, second,
and third prediction signals), and the output from subtractor 23
(referred to in the following as a non-prediction signal) are
applied as to corresponding inputs of a delay section 43, which
subjects each of these signals to a delay which is equal to the
period of one block (i.e. corresponding to 64 pixels, in this
example). The delayed outputs from the 1-block delay circuit 43 are
applied to respective fixed contacts of a prediction mode selector
switch 45, whose movable contact is coupled to an output terminal
46.
The first, second and third prediction signals from the subtractors
21, 20 and 22, and the non-prediction signal from subtractor 39 are
also respectively applied to inputs of squaring circuits 25, 24, 26
and 27. Each of these thereby produces the square of each
(prediction error) data value that is inputted thereto, and these
squared error values produced from circuits 24 to 27 are
respectively supplied to inputs of additive accumulator circuits 28
to 31, each of which functions to obtain the sum of the squared
error values of respective pixels of one block at a time. This is
to say, when the total of the squared error values for one block
has been computed by one of these accumulator circuits, the result
is outputted therefrom, the contents are reset to zero, and
computation of the squared error value total for the next block
begins.
The output from the cumulative adder 28 is supplied directly to a
first input terminal of a minimum value selector circuit 32. The
output from the cumulative adder 29 is supplied via a subtractor
36, in which a predetermined fixed compensation value is subtracted
therefrom, to a second input terminal of the minimum value selector
circuit 32. The output from the cumulative adder 30 is supplied
directly to a third input terminal of the minimum value selector
circuit 32. The output from the cumulative adder 31 is supplied via
an adder 37, in which a predetermined fixed compensation value is
added thereto, to a fourth input terminal of the minimum value
selector circuit 32.
Each time that the respective accumulated total error-squared
values for one block have been derived by the cumulative adder 28
to cumulative adder 31 respectively and supplied to the minimum
value selector circuit 32, the minimum value selector circuit 32
judges which of these is lowest in value and produces an output
data signal indicative of that value. That output data signal
serves as prediction mode data, i.e. is used to determine which
mode of operation will provide optimum encoding accuracy, to
thereby determine which of Option 1 to Option 4 described
hereinabove is applicable to the block for which judgement of the
accumulated total error-squared values has been made. That
prediction mode information is then applied to control the setting
of the prediction mode selector switch 45, to determine which of
the delayed outputs from the 1-block delay circuit 43 will be
selected to be transferred to output terminal 46, and hence to the
"b" terminal of the changeover switch 5 of FIG. 1.
More specifically, the setting of the prediction mode selector
switch 45 is controlled by the prediction mode data output from the
minimum value selector circuit 32 such that the delayed prediction
error output from the prediction signal subtractor 21 is selected,
if that output has resulted in the smallest value of accumulated
squared error value for the block in question (representing the
case of Option 1 above being selected). This will be referred to as
mode 1. Similarly, the delayed output from the subtractor 20 will
be selected by the prediction mode selector switch 45 for the case
of Option 2 above being selected (this being referred to the
following as mode 2), the delayed output from the subtractor 22
will be selected by the prediction mode selector switch 45 for the
case of Option 3 above being selected (this being referred to in
the following as mode 3), and the delayed output from the
subtractor 23 will be selected by the prediction mode selector
switch 45 for the case of Option 4 above being selected (this being
the case in which no inter-frame prediction is executed for the
block in question, and referred in the following as mode 4).
The values of the weighting values W and (1-W) vary for successive
ones of the dependent frames in a linear manner, i.e. Option 1
represents 2-dimensional linear prediction operation, with W being
a maximum for the first dependent frame following an independent
frame and reaching a minimum value for a dependent frame which
immediately precedes an independent frame.
Specifically, the weighting value W is defined as:
[where 0>W>1, mc denotes the number of the current frame in
the sequence of frames, mp denotes the number of the preceding
independent frame of that current frame].
The value X of a data value (corresponding to one pixel) of the
output signal from the adder 34, that signal being referred to in
the following as a prediction signal, is obtained as:
[where Vms is the corresponding value of the succeeding independent
frame signal from input terminal 40 and Vmp is the corresponding
value of the preceding independent frame signal from input terminal
41].
Each value X of the prediction signal produced from the adder 34 is
subtracted from a corresponding value of the current frame signal,
in the prediction signal subtractor 21, and the result is supplied
as a preceding/succeeding frame prediction error value to the
squaring circuit 25.
Each value of the preceding frame signal is subtracted from a
corresponding value of the current frame signal, in the subtractor
20, and the result is supplied as a preceding frame prediction
error value to the squaring circuits 24.
Similarly, each value of the succeeding frame signal subtracted
from a corresponding value of the current frame signal, in the
subtractor 22, and the result is supplied as a succeeding frame
prediction error value to the squaring circuit 26.
The fixed value that is subtracted from the current frame signal by
the subtractor 23 can be established in various ways, for example
as being equal to 50% of the maximum white level of the video
signal, when a luminance (Y) value is being processed, and equal to
zero when a color difference (B-Y) or (R-Y) value is being
processed. Alternatively, the DC component of a spatially adjacent
block within the same frame could be utilized instead of that fixed
value. Whichever type of value is utilized, inter-frame prediction
is not executed for a block, in the case of mode 4 being selected,
and only intra-frame processing is executed for the block.
FIG. 5 is a simple timing diagram for illustrating the basic timing
relationships of this embodiment. F1 to F11 denote 11 successive
frames of the input video signal, with corresponding frame
intervals (specifically, intervals in which the respective frames
are read out from the frame memory 1a) designated as T1 to T11.
Each independent frame is designated by a #symbol, i.e. frames F1,
F5 and F9. It is assumed that one out of every 4 frames is an
independent frame, i.e. that periodic resetting of inter-frame
prediction operation occurs with a period of 4 frames. The timings
of processing operations for frames F2 to F5 will be described.
(a) In frame interval T1
The successive blocks of independent frame F1 are transferred
through the switches 2 and 5, to be directly encoded, then are
processed in the dequantizer 10 and inverse orthogonal transform
section 11 to recover the original frame data, and then are written
into the (succeeding) frame memory 12.
(b) In frame intervals T2, T3 and T4
Frames F2, F3, and F4 are successively written into the (N-1) frame
memory 3.
(c) In frame interval T5
The successive blocks of independent frame F5 are transferred
through the switches 2 and 5, to be directly encoded, then are
processed in the dequantizer 10 and inverse orthogonal transform
section 11 to recover the original frame data, and then are written
into the (succeeding) frame memory 12 to replace the previous
contents of that memory, after writing the contents of the
(succeeding) frame memory 12 into the (preceding) frame memory 13
to replace the previous contents thereof.
(d) Frame Interval T6
During T6, frame F6 is written into the frame memory 3, at the same
time frame F2 is read out from memory 3, and corresponding
prediction signals for frame F2 are outputted from the adaptive
prediction section 4 and inputted to delay unit 43 together with
the output from subtractor 23. At the end of T6, the prediction
mode output signal from the minimum value selector 32 sets switch
45 to an appropriate selection position, based on the minimum
accumulated error-squared value that is inputted to the minimum
value selector 32. The mode output signal is also transferred to
the encoder 8 to be encoded and outputted.
(e) Frame Interval T7
Frame F7 is written into the frame memory 3, at the same time,
frame F3 is read out from memory 3, and processed in the same way
as for frame F2, and the prediction mode data for frame F3 is sent
to the encoder 8.
The selected prediction signal for frame F3 (or the output from
subtractor 23) is transferred from switch 45 to the orthogonal
transform section 6, to be processed, encoded and outputted.
It can be understood that the circuit of FIG. 4 serves to execute
adaptive selection, on a block-by-block basis, of the optimum mode
for encoding each block of each dependent frame of the video
signal. That is to say, the variable-length encoder section 8
adaptively selects one of the following modes to be used in
encoding each block of a dependent frame:
(a) Mode 1, in which 2-dimensional linear inter-frame prediction is
executed. This is selected when there is sufficient (linearly
weighted) correlation between the block and the corresponding
blocks of the preceding and succeeding independent frames. This
would be selected for a block in frame 2 of FIG. 2D, for
example.
(b) Mode 2, in which inter-frame prediction is executed using only
the preceding independent frame. This is selected when there is
insufficient correlation with the corresponding block of the
succeeding independent frame. This would be selected for a block of
frame 2 in FIG. 2B, for example.
(c) Mode 3, in which inter-frame prediction is executed using only
the succeeding independent frame. This is selected when there is
sufficient correlation with the corresponding block of the
preceding independent frame. This would be selected for a block of
frame 3 or frame 4 in FIG. 2B, for example.
(d) Mode 4, in which inter-frame prediction is not executed. This
is selected when there is insufficient correlation between the
current block and the corresponding blocks of each of the preceding
and succeeding frames. This would be selected, for example, for a
block in frame 3 of FIG. 2D. It has been assumed, for simplicity of
description, that this applies to all of the blocks of frame 3 of
FIG. 2D, so that inter-frame prediction is not applied to any
blocks of that frame.
Since the independent frame signal values that are used i deriving
the prediction error values are obtained by recovering the original
video signal by decoding operation (in the dequantizer 10 and
inverse orthogonal transform section 11), in the same way that
decoding is executed in a corresponding decoder apparatus .[.(not
shown in the drawings).]. .Iadd.shown in FIG. 6.Iaddend., the
various quantization errors etc. that are present in the final
decoded data will also be present in the data that are used in
denying the prediction error values. This ensures a greater
accuracy of prediction than would be the case if the independent
frames of the input video signal data were to be written directly
into the memories 12 and then 13.
With this embodiment, evaluation for determining the prediction
mode is based upon error-squared values of prediction error values
that are obtained directly from the input video signal. Greater
accuracy of evaluation would be obtained by using the video signal
data of the dependent frames after all of the encoding processing
(including transform processing, and quantization) has been
executed. However this would require additional circuits for
executing the inverse of such encoding, i.e. for the inverse
transform processing etc., increasing the circuit scale
substantially and making the apparatus more difficult to realize in
practical form.
As stated above, the DC component of the current frame signal is
subtracted from the current frame signal in the subtractor 39, to
thereby prevent an excessively high output value being produced by
the cumulative adder 31. However if not compensated for, this will
tend to produce an excessively high probability that mode 4 will be
selected by the minimum value selector circuit 32, i.e. the output
from the cumulative adder 31 will tend to have too low a value. For
that reason, a compensating offset value B is added to the output
from the cumulative adder 31 in the adder 37.
On the other hand, in cases where there are only small differences
between the respective values of prediction error that are being
produced from the prediction signal subtractor 21, subtractor 20
and subtractor 22, it is preferable to prevent unnecessary
switching between the modes 1, 2 and 3. For that reason, a slight
amount of bias is given towards the selection of mode 1
(2-dimensional linear prediction) by the minimum value selector
circuit 32. This is done by subtracting an offset value A from the
output of the cumulative adder 29, in the subtractor 36. This has
the advantage of increasing the rate of selection of mode 1, and so
enabling a reduction in the amount of encoded data that are
produced by encoding the prediction mode data from the minimum
value selector circuit 32, if entropy encoding using for example
the Huffman code is employed in the variable-length encoder section
8.
.[.The.]. .Iadd.As shown in FIG. 6, the .Iaddend.decoding apparatus
for decoding the encoded data .Iadd.on line 48 .Iaddend.that are
transmitted from such an adaptive predictive encoded apparatus can
be implemented very simply, by using the mode prediction data that
are contained in the encoded output data. After the inverse of the
variable-length encoding executed by the variable-length encoder
section 8 has been performed, .Iadd.in variable length decoder
50.Iaddend., followed by dequantizing .Iadd.in dequantizer 51
.Iaddend.and inverse transform processing .Iadd.in inverse
orthogonal transform section 52.Iaddend., each independent frame is
transferred successively to a first (.Iadd.succeeding) frame memory
54 .Iaddend.and then .Iadd.to .Iaddend.a second frame memory for
use in processing (.Iadd.preceding.Iaddend.) frame memory .Iadd.55
.Iaddend.for use in processing the dependent frames, corresponding
to the memories 12 and 13 of FIG. .[.1 .Iadd.3.Iaddend., and are
outputted .Iadd.on line 70 .Iaddend.without further processing.
.Iadd.The operation of switches 61 and 62 correspond to the
operation of switches 2 and 5 in the encoder of FIG. 3. During
processing of the independent frames, their contacts are in the
respective positions "b" shown in FIG. 6 and during processing of
the dependent frames, their contacts are switched to their
respective "a" positions. .Iaddend.Each block of a dependent frame
is processed .Iadd.by performing the inverse of the operations
performed by the adaptive prediction section 4 of FIG. 3 during the
encoding process in adaptive prediction section 53 of the decoder,
shown schematically in FIG. 7, .Iaddend.depending upon the
.Iadd.position of the movable contact of switch 64 which is
controlled by the .Iaddend.associated decoded prediction mode data
for that block, as follows:
(1) If the prediction mode data .Iadd.on line 57 .Iaddend.indicates
that the block has been encoded in mode 1, then the pixel data
values of the corresponding blocks of the corresponding preceding
and succeeding independent frame (read out .Iadd.on lines 58 and 59
.Iaddend.from the aforementioned two frame memories .Iadd.54 and
55.Iaddend.) are respectively multiplied by the weighting values W
and (1-W), the results added .Iadd.in adder 63.Iaddend., and the
resultant value added .Iadd.in adder 65 .Iaddend.to the current
frame signal .Iadd.supplied on line 56 to generate the output of
the decoder on line 60.Iaddend..
(2) If the prediction mode data .Iadd.on line 57 .Iaddend.indicates
that the block has been encoded in mode 2, then the pixel data
values of the corresponding blocks of the corresponding preceding
independent frame .Iadd.on line 58 .Iaddend.are added .Iadd.in
adder 65 .Iaddend.to the current frame signal .Iadd.on line 56 to
generate the output of the decoder on line 60.Iaddend..
(3) If the prediction mode data .Iadd.on line 57 .Iaddend.indicates
that the block has been encoded in mode 3, then the pixel data
values of the corresponding blocks of the corresponding succeeding
independent frame .Iadd.supplied on line 59 .Iaddend.are added
.Iadd.in adder 65 .Iaddend.to the current frame signal .Iadd.on
line 56 to generate the output of the decoder on line
60.Iaddend..
(It will be apparent that a single circuit can be used to implement
all of the functions (1), (2) and (3) above, by appropriately
setting the weighting value W to either 1 or 0 for functions (2)
and (3)).
(4) If the prediction mode data .Iadd.on line 57 .Iaddend.indicates
that the block has been encoded in mode 4, then the fixed value
.Iadd.on line 66 .Iaddend.(subtracted in the subtractor 23 of FIG.
2 of the encoder apparatus) is added .Iadd.in adder 65 .Iaddend.to
the current frame signal .Iadd.on line 56 to generate the output of
the decoder on line 60.Iaddend..
It will be apparent that the decoder apparatus .Iadd.shown in FIGS.
6 and 7 .Iaddend.for receiving an encoded output signal produced by
an adaptive predictive encoder apparatus according to the present
invention can have a simple configuration, and can for example by
implemented by slightly modifying an encoder apparatus that is
described in the aforementioned related U.S. application by the
assignee of the present invention.
* * * * *