Note: Descriptions are shown in the official language in which they were submitted.
TIME-VARYING IMAGE SIGNAL CODING/DECODING SYSTEM
.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a time~varying image
signal coding/decoding system, and more particularly to
a time-varying image signal (moving picture signal or
video signal) coding/decoding system using an interframe
differential orthogonal transform coding method combining
the prediction of interframe differentials and orthogonal
transform.
Description of the Prior Art
In a time-varying image signal coding/decoding system
of this kind according to the prior art, the frame memory in
the time-varying image signal decoding unit is periodically
refreshed in order to prevent any error on the transmission
path from deteriorating the picture quality on the receiving
side. Where an interframe differential orthogonal transform
coding method or a orthogonal transform interframe coding
method is used, since the content of the frame memory is
a transform coefficient after orthogonal transform, time-
varying image signals entered into the time-varying image
signal coding unit are su~jected to orthogonal transform,
and quantized signals are transmitted at a rate of, for
instance, one block line per frame as refreshing signals
-- 2
to refresh a whole frame in the frame memory in the time-
varying image decodiny unit at fixed intervals. Incidentally,
where coding takes place in units of a two-dimensional
block of I lines by J pixels each, for example, I lines of
signals are collectively referred to as one block line.
In the conventional time-varying image signal coding/
decoding system mentioned above, all the transform
coefficient components of the signals resulting from the
orthogonal transform coding of time-varying image signals
entered into the time-varying image signal coding unit are
collectively used as refreshing signals. However, picture
~uality deterioration on the receiving side due to any
error on the transmission path usually results from a
partial error in the transform coefficient. The time-
varying image signal coding/decoding system according tothe prior art, which collectively refreshes even the
components needing no refreshing, involves the problem
of wastefulness. Furthermore the conventional time-varying
image signal coding/decoding system often accomplishes
refreshing in units of block lines, and in that case there
is the additional problem of restricting the efficiency
of coding because information for the refreshing purposes
accounts for a high propor-tion in each frame.
The above-mentioned time-varying image signal coding/
decoding system according to the prior art is described in
detail in a paper entitled "International Standardization
of Video Codes for ISDN Videoconfereneing and Videophone
Services" in NTT Review, Vol. 2, No. 3, May 1990
(p.p. 110-117).
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
An object of the present invention is to solve the
aforementioned problems and provide a time-varying image
signal eoding/decoding system capable of improving the
eoding efficiency while maintaining the effeet of refreshing.
Summary of the Invention
In a first time-varying image signal eoding apparatus
aeeording to the invention, orthogonal transform means
orthogonally transforms an inputted time-varying image
signal on a bloek-by-bloek basis, eaeh block consisting of
a plurality of pixesl. Subtracting means subtraets a first
predieted signal from said orthogonally transformed signal
to supply a prediction error signal. First quantizing
means quantizes said prediction error signal to supply
a first quantized signal. Adding means adds said first
quantized signal and said first predieted signal to supply
a loeal deeoded signal. Seeond quantizing means quantizes
said loeal deeoded signal to supply a seeond quantized
signal. First switehing means seleetively eonneets either
; said local decoded signal or said second quantized signal.
A first frame memory delays the signal seleetively connected
by said first switching means by a predetermined nu~ber of
frames, to supply the delayed signal as said first predieted
signal. Second switching means selectively connects either
said first or second quan-tized signal. Switching control
means provides a switching control siynal which gives an
instruction to said f:irst and seeond switching means to
selectively connect said second quantized signal when a
second frame memory built into a time-varying image signal
deeoding apparatus is to be refreshed, or to said first
switehing means and said second switching means to
seleetively eonnect said local deeoded signal and said
first quantized signal, respeetively, if said seeond frame
memory is not to be refreshed. Code transform means
subjeets said first and seeond quantized signals, seleeted
by said second switehing means, and said switehing eontrol
signal, and transmits the transformed signals.
In a first time-varying image signal deeoding apparatus
aeeording to the invention, eode inverse transform means
separates and reproduces said first or seeond quantized
signal and said switehing eontrol signal by subjeeting a
sequenee of eodes, transmitted from the time-varying image
signal eoding apparatus, to code inverse transform.
Adding means adds a seeond preeieted signal to said first
quantized signal reprodueed by said eode inverse transform
means. Third switehing means seleetively eonneets said
seeond quantized signal if the switehing eontrol signal
-- 5
reproduced by said code inverse transform rneans gives an
instruction to refresh, or the addition signal of said
adding means if the instruction is not to refresh. The
second frame memory delays the signal selectively connected
by said third switching means by a predetermined number of
frames to supply the delayed signal as said second predicted
signal. Orthogonal inverse transform means reproduces said
time-varying image signal by subjecting the signal selectively
connected by said third switching means to inverse transform
to said orthogonal transform.
In a second time-varying image signal coding apparatus
according to the invention, subtracting means subtracts
a first predicted signal from an inputted time-varying
image signal to supply a prediction error signal. A
motion detecting:circuit detects a moving vector signal by
subjecting said time-varying image signal to interframe
block matching. First orthogonal transform means
orthogonally transforms said prediction error signal on a
block-by-block basis, each block consisting of a plurality
of pixels. First quantizing means quantizes the result of
said orthogonal transform to supply a first quantized signal.
First adding means adds said first quantized signal and
orthogonally transformed signal to supply a local decoded
. .
signal. Second quantizing means quantizes said local
decoded signal to supply a second quantized signal. First
switching means selectively connects either said local
-- 6
decoded signal or said second quantized signal. A first
frame memory delays the signal selectively connected by
said first switching means by a predetermined number of
frames to supply the delayed signal as a second predicted
signal. A second orthogonal inverse transform circuit
returns said second predicted signal from the transform
region to the space region. A variable delay circuit
gives a delay corresponding to said moving vector signal
to the signal returned to the space region by said first
orthogonal inverse transform circuit to generate said first
predicted signal. A first orthogonal transform circuit
generates said orthogonally transformed signal by subjecting
said first predicted signal to orthogonal transform.
Second switching means selectively connects either said
first or second quantized signal. Switching control means
provides a switching control signal which gives an
instruction to said first and second switching means to
selectively connect said second quantized signal when a
second frame memory built into a time-varying image signal
decoding apparatus is to be refreshed, or to said first
switching means and said second switching means to
selectively connect said local decoded signal and the
quantized signal from said first quantizing means,
respectively, if said second frame memory is not to be
refreshed. Code transform means subjects the quantized
signal selectively connected by said second switching means
to variable leng-tih coding, encodes said moving vector
signal and said switching control signal, and transmits
the coded signals.
In a second time-varying image signal decoding
apparatus according to -the invention, code inverse
transform means separates and reproduces said quantized
signals, said switching control signal and said moving
vector signal by subjecting a sequence of codes, transmitted
from said code transform means, to code inverse transform.
Second adding means adds a third predicted signal to said
first quantized signal which has been reproduced. Third
switching means selectively connects said second quantized
signal if said switching control signal which has been
reproduced gives an instruction to refresh, or the addition
signal of said adding means if the instruction is not to
refresh. The second frame memory delays the signal
selectively connected by said third switching means by
a predetermined number of frames. A third orthogonal
inverse transform circuit returns the output signal of
said frame memory by subjecting it to orthogonal transform.
A variable delay circuit gives a delay corresponding to
said moving vector signal which has been reproduced to
the signal returned to the space region by said orthogonal
inverse transform circuit. A second orthogonal transform
circuit generates said third predicted signal by subjectin~
the signal delayed by said variable delay circuit to
.
orthogonal transform. A third orthogonal inverse transforTn
circuit reproduces said time-varying image signal by
subjecting the signal selectively connected by said third
switching means to inverse transform to said orthogonal
transform.
In a third time-varying image signal coding apparatus
according to the invention, subtracting means subtracts a
first predicted signal from an inputted time-varying image
signal to supply a prediction error signal. Orthogonal
transform means orthogonally transforms said prediction
error signal on a block-by-block basis, each block
consisting of a plurality of pixels. First quantizing
means quantizes the result of said orthogonal transform
to supply a first quantized signal. First adding means
adds said first quantized signal and a second predicted
signal to supply a local decoded signal. Second quantizing
means quantizes said local decoded signal to supply a
second quantized signal. First switching means selectively
connects either said local decoded signal or said second
quantized signal. A first frame memory delays the signal
selectively connected by said first switching means by a
; predetermined number of frames to supply the delayed signal
as a second predicted signal. First orthogonal inverse
transform means subjects said second predicted signal to
inverse transform to said orthogonal transform to supply
the resultant signal as said first predicted signal.
" ' : '
'
.' ~'
Second switching means selec-tively connects either said
first or second quantized siynal. Switching control means
provides a switching control signal which gives an
instruction -to said first and second switching means to
selectively connect said second quantizing means when a
second frame memory built into a time-varying image signal
decoding apparatus is to be refreshed, or to said first
switching means and said second switching means to
selectively connect said local decoded signal and the
quantized signal from said first quantizing means,
respectively, if said second frame memory is not to be
refreshed. Code transform means subjects either the first
or second quantized signal, selectively connected by said
second switching means, and said switching control signal,
and transmits the transformed signals.
In a third time-~arying image signal decoding apparatus
acco~ding to the invention, code inverse transform means
separates and reproduces said quantized signals and said
switching control signal by subjecting a sequence of codes,
transmitted from said code transform means, to code inverse
transform. Second adding means adds a third predicted
signal to said first quantized signal which has been
reproduced. Third switching means selectively connects
said second quantized signal if said switching control
signal which has been reproduced gives an instruction to
refresh, or the addition signal of said adding means if
.
- 10 -
the lnstruction is not to refresh. The second frame memory
delays the signal selectively connected by said third
switching means by a predetermined number of frames to
supply the delayed signal as said third predicted siynal.
A second orthogonal inverse transform circuit reproduces
said time-varying image signal by subjecting the signal
selectively connected by said third switching means to
inverse transform to said orthogonal transform.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other objects, features and
advantages of the present invention will become more
apparent from the following detailed description when
taken in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a signal timing chart illustrating an
example of the aforementioned periodic~refreshing in a
time-varying image signal coding/decoding system according
to the prior art;
FIG. 2 illustrates the configuration of a fixst
preferred embodiment of the invention;
FIG. 3 is a structurql diagram illustrating an example
of the block formation of transform coefficients in the
first preferred embodiment;
FIG. 4 is a signal timing chart for describing the
periodic refreshing in the first embodiment;
. . , . ~ - .
,
. .' -' . .
:., '
FIG. 5 is a block diagram illustrating an exarnple of
the configuration of the quantizing circuit 7 in the
first embodiment;
FIG. 6 illustrates the configuration of a second
preferred embodiment of the invention, an example in
which motion compensation is introduced into interframe
differential orthogonal transform coding;
FIG. 7 illustrates the configuration of a third
preferred embodiment of the invention; and
FIG. 8 is a block diagram illustrating a four-th
preferred embodiment of the invention, adopting a demand
refresh system using a group-divided block structure as
shown in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Configurations of the Embodiments
A first preferred embodiment of the present invention
consists of a time-varying image signal coding appara-tus,
a time-varying image signal decoding apparatus and a
transmission path connecting these two apparatuses. The
time-varying image signal coding apparatus further comprises
an orthogonal transform circuit 1 connected to a time-
varying image signal input end; a subtractor 2 one of whose
input ends is connected to the output end of the orthogonal
transform circuit l; a first quantizing circuit 3 whose
input end is connected to the output end of the subtractor 2;
.. . . . .
: ' ' ' .
- 12 -
a first frame memory 8 whose output end is connected to the
other of the input ends of the subtractor 2; an adder 6 of
whose two input ends one is connected to the output end of
the first quantizing circuit 3 and the other to that of
the frame memory 8; a second quantizing circuit 7 whose
input end is connected to the output end of the adcer 6;
a first switch SW2 for selectively connecting either the
output end of the adder 6 or that of the second quantizing
circuit 7 to the input end of the first frame memory 8; a
code transform circuit 4 whose output end is connected to
~ the transmission path; a second switch SWl for selectively
; connecting either the output end of the first quantizing
circuit 3 or that of the second quantizing circuit 7 to
the code transform circuit 4; and a control circuit 12
whose control output end is connected to the first and
second switches SW2 and S~l, and the control input ends
~ of the second quantizing circuit 7 and of the code
:: transform circuit 4.
~: The time-varying image signal decoding apparatus
comprises a code inverse transform circuit 14 whose input
.
: end is connected to the transmission path; a s-cond frame
memory 16; an adder 15 of whose two input ends one is
connected to -the output end of the frame memory 16 and
the other to that of the code inverse transform circuit 14;
an orthogonal inverse transform circuit 17 whose output end
is connected to a time-varying image signal output end; and
,
. ~; - , , :
,,, ~
,
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a third switch SW3, whose control input end is connected
to the control output end of the code inverse transform
circult 14, for selectively connecting either the output
end of the ~dder 15 or that of the code inverse transform
circui-t 14 to the input end of the second frame memory 16
and that of the orthogonal inverse transform circuit 17.
A second preferred embodiment of the present invention
consists of a time-varying image signal coding apparatus,
a time-varying image si.gnal decoding apparatus and a
transmission path connecting these two apparatuses. The
time-varying image signal coding apparatus further comprises
a subtractor 2 one of whose input ends is connected to a
time-varying image signal input end; a motion detecting
circuit 5 whose input end is connected to the time-varying
image signal input end; a first orthogonal transform
circuit 1 whose input end is connected to the output end
of the subtractor 2; a first quantizing circuit 3 whose
: input end is connected to the output end of the orthogonal
transform circuit l; a first adder 6 one of whose input
ends is connected to the output end of the first quantizing
circuit 3; a second quantizing circuit 7 one of whose input
end is connected to the output end of the first adder 6;
a first frame memory 8; a first switch SW2 for selectively
connecting either the output end of the first adder 6 or
that of the second quantizing circuit 7 to the input end
of the first frame memory 8; a first orthogonal inverse
,
transform circuit 9 whose inpu-t end is connested to the
output end of the first frame memory 8; a variable delay
circuit 10, of whose input ends one is connected to the
output end of the orthogonal inverse transform circuit 9
and the other to tha-t of the motion detecting circuit 5
and whose output end is connected to the other input end
of the subtractor 2; a second orthogonal transform
circuit 11 whose input and output ends are connected to
the output end of the variable delay circuit 10 and to
the other input end of the first adder 6, respectively;
a code transform circuit 4A whose first input end and
output end are connected to the output end of the motion
detecting circuit 5 and to the transmission path,
respectively; a second switch SW1 for selectively connecting
either the output end of the first quantizing circuit 3
or that of the second quantizing circuit 7 to a second
input end of the code transform circuit 4A; and a control
circuit 12 whose output end is connected to the second
switch SWl, and the control input ends of the code
transform circuit 4A and of the second quantizing circuit 7.
The time-varying image signal decoding apparatus
comprises a code inverse transform circuit 14A whose input
end is connected to the transmission pzth; a variable delay
circuit 18, one of whose input ends is connected to a first
output end of the orthogonal inverse transform circuit 14A;
a third orthogonal transform circuit 19 whose input end
~ :L5 -
is connected to the output end of the variable delay
circuit 18; a second adder 15 of whose input ends one is
connected to the output end of the code inverse transform
circuit 14~ and the other to -tha-t of the third orthogonal
transform circuit 19; a second frame memory 16; a second
orthogonal inverse transform circuit 17 whose input and
output ends are connected to the output end of the frame
memory 16 and the other input end of the variable delav
circuit 18, respectively; a third orthogonal inverse
transform circuit 20 whose output end is connected to a
time-varying image signal output end; and a third switch
SW3, whose control input end is connected to the control
output end of the code inverse transform circuit 14A,
for selectively connecting either the output end of the
adder 15 or that of the code inverse transform circuit 14A
to the input ends of the second frame memory 16 and of the
third orthogonal inverse transform circuit 20.
A third preferred embodiment of the present invention
consists of a time-varying image signal coding apparatus,
a time-varying image signal decoding apparatus and a
transmission path connecting these two apparatuses. The
time-varying image signal coding apparatus further comprises
a subtractor 2 one of whose input ends is connected to a
. .
time-varying image signal input end; an orthogonal transform
circuit 1 whose input end is connected to the output end
of the subtractor 2; a first quantizing circuit 3 whose
- 16 -
input end is connected to the outpu-t end of the orthogonal
transform circuit l; a first frame mernory 8; a first
adder 6 of whose input ends one is connected to the output
end of the ou-tput end of the first frame memory 8 and the
other is connected to the outpu-t end of the first quantizing
circuit 3; a second quantizing circuit 7 one of whose input
end is connected to the output end of the first adder 6;
a first switch SW2 for selectively connecting either the
output end of the second quantizing circuit 7 or that of
the first adder 6 to the input end of the first frame
memory 8; a code transfoxm circuit 4A whose output end is
connected to the transmission path; a second switch SWl
for selectively connecting either the output end of the
first quantizing circuit 3 or tha-t of the second quantizing
circuit 7 to the input end of the code transform circuit 4A;
and a control circuit 12 whose output end is connected to
the first and second switches SW2 and SWl, and the control
input ends of the second quantizing circuit 7 and of the
code transform circuit 4A.
The time-varying image signal decoding apparatus
comprises a code inverse transform circuit 14A whose input
end is connected to the transmission path; a second adder
15 one of whose input ends is connected to the output end
of the code inverse transform circuit 14A; a second frame
memory 16; a second orthogonal inverse transform circuit 20
whose output end is connected to the time-varying image
input end; and a third switch SW3, whose control input end
is connected to the control output end of -the code inverse
transform circuit 14A, for selectively connecting either
the ou-tpu-t end of the code inverse transform circuit 14A
of that of the second adder 15 to the input ends of the
second frame memory 16 and of the second orthogonal inverse
transform citcuit 20.
A fourth preferred embodiment of the present invention
consists of a first station 100, a second station 200, a
first transmission path connecting the first station and
the second station, and a second transmission path
connecting the second station and the first station.
The first station 100 further comprises a first coding
circuit 101 whose input end is connected to a first time-
~arying image signal input end; a second code transformcircuit 102 whose input and output ends are connected to
the output end of the first coding circuit 101 and the
first transmission path, respectively; a first switching
control circuit 103 whose output end is connected to the
control input ends of the first coding circuit lOl and
of the first code transform circuit 102; a first code
inverse transform circuit 104 whose input and first output
ends are connected to the second transmission path and
the input end of the first switching control circuit 103,
respectively; and a first decoding circuit 105 of whose
two input ends one is connected to the second, and the
other to the third, output ends of the first code inverse
transform circuit 104 and whose output end is connected to
a first time-varying image signal output end.
The second station 200 further comprises a firs-t coding
circuit 201 whose input end is conneeted to a second time-
varyinq image signal input end, a second code transform
circuit 202 whose input and output ends are connected to
the output end of the seeond eoding eircuit 201 and the
second transmission path, respectively; a second switching
control circuit 203 whose output end lS connected to the
control input ends of the seeond coding circuit 201 and
of the second code transform circuit 202; a second code
inverse transform circuit 204 whose input and first output
ends are eonneeted to the first transmission path and the
input end of the seeond switehing control circuit 203
respeetively; and a second deeoding eireuit 205 whose
two input ends are connected to the two output ends of
the second code inverse transform circuit 204 and whose
output end is eonneeted to a seeond time-Varying image
signal output end.
-~ FIG. 1 is a signal timing chart illustrating an example
of the aforementioned periodie refreshing in a time-varying
image signal eoding/deeoding system aceording to the prior
art. The frame is divided into two-dimensional bloeks,
each consisting of a plurality of lines and a plurality of
pixels, and bloek numbers from the first block Bl to the
-- 19 --
Nth block BN are assigned along the lines. FIG. 1 sho~,is
a case in which K blocks' equivalent is refreshed per
frame from the first frame period Tl til] the pth frame
Tp (N = P-K). In the first frame period Tl for instance,
blocks from the first Bl to the Kth BK are refreshed, and
this refreshing is represented by an abbreviation of
~Bl -K}- In each frame period, signals resulting from
the interframe coding of time-varying image signals are
transmit-ted except during the transmission of refreshed
signals.
Next will be described preferred embodiments of the
present invention with reference to drawings.
FIG. 2 illustrates the configuration of a first
preferred embodiment of the invention. The time-varying
image signal coding apparatus comprises an orthogonal
transform circuit l; a subtractor 2; a quantizing circuit 3;
a frame memory 8; another quantizing circuit 7, a switch SWl;
and another switch SW2. The time-varying image signal
decoding apparatus comprises a code inverse transform
circuit 14i an adder 15; a frame memory 16; an orthogonal
inverse transform circuit 17; and a switch SW3.
The operation of the time-varying image signal coding
apparatus will be descrlbed below.
The orthogonal transform circuit 1 supplies the
subtractor 2 wlth a signal obtained by orthogonally
transforming an inputted time-varying image signal on
' " ' ' ' ' , '
.'~ ~ : : ' ,-
., ~ .
' ... , ' ' ' :
:
- 20 -
a block-by-block basis, each bloc~ consisting of a plurality
of pixels (to be described in further detail below~. The
subtractor 2 subtracts from the signal supplied by the
orthogonal transform circuit 1 its predicted signal given
by the frame memory 8 to generate a prediction error signal
in the transform region, and supplies it to the quantiziny
circuit 3. The quantizing circuit 3 supplies a quantized
signal obtained by quantizing the prediction error signal
to the terminal Al of the switch SWl and the adder 6. The
adder 6 generates a local decoded signal by adding the
predicted signal from the frame memory 8 and the quantized
signal from the quantizing circuit 3, and supplies it the
terminal A2 of the switch SW2 and the quantizing circuit 7.
The quantizing circuit 7 supplies a quantized signal
obtained by quantizing the local decoded signal to the
terminal Bl of the switch SWl and the terminal B2 of the
switch S~2. The frame memory 8 delays the signal,
selectively connected by the switch SW2, by writing it in,
temporarily storing it and reading it out after the lapse
of a one-frame time, and thereby generates said predicted
signal.
The code transform circuit 4 subjects the quantized
signal, selectively connected by the switch S~l, to
variable-length coding, and codes a switching control
signal provided from ~he switchi.ng control circuit 12,
and transmits the coded signals to the time-~arying image
~ 21 -
signal decoding apparatus via the transmission path. The
switching control circuit 12 generates said switching
control signal which gives an instruction to the switches
SWl and SW2 as to which of the two terminals on the inpu-t
side is to ~e selected for connection to the terminal on
the output side. For the selective connection of the
terminals Al and A2, the signal resulting from the
quantizing of the prediction error signal, supplied from
the quantizing circuit 3, is transmitted from the code
transform circuit 4 as the sequence of codes or, for the
- selection of the terminals B1 and B2, the quantized signal
supplied from the quantizing circuit 7 is transmitted from
the code transform circuit 4 as the sequence of refreshing
codes.
15Next will be described the operation of the time-
varying image signal decoding apparatus.
The code inverse transform circuit 1~ decodes and
separates the sequence of codes received from the
transmission path, and supplies a prediction error signal
or a local decoded signal to the adder 15 and to the
terminal B3 of the switch SW3 and a switching control
signal to the switch SW3. The switch SW3, like the
switches SWl and SW2 on the transmitting side, selectively
connects either the terminal A3 or the terminal B3 as
instructed by the switching control signal. When the
terminal A3 is selectively connected, the prediction error
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signal supplied from the code inverse transform circuit 14,
after being added to the predicted signal by the adder 15,
is returned to the space region to reproduce said time-varying
image signal. The result of addition by the adder 15 is
delayed by being temporarily stored in the frame memory 16
and read out after the lapse of a one-frame time, and sent
to the adder 15 as a reproduced predicted signal. On the
other hand, when the terminal B3 is selectively connected,
the local decoded signal for the refreshing purpose,
supplied from the code in~erse transform circuit 14, is
written into the frame memory 16 to perform refreshing.
FIG. 3 is a structural diagram illustrating an example
of the block formation of transform coefficients in the
first preferred embodiment, and FIG. 4 is a signal timing
chart for describing the periodic refreshing in the first
embodiment.
Referring to FIG. 3, a frame F is divided into two-
dimensional blocks, each consisting of eight lines by eight
pixels, and block numbers from the flrst block Bl to the
Nth block NN are sequentially ~ssigned in the direction of
the lines. Each block (for lnstance the ith block Bi) is
a two-dimensionaI block of eight lines by eight pixels, and
further divided into seven groups, the first Gl to the
seventh G7, from the upper left corner, the lowest in
; 25 sequence, toward the lower right corner, the highest in
sequence. Refreshing is carried out, as typically
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,
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illustrated in FIG. 4, upon L groups of each block per frame
period between the first frame period Tl till the mth frame
period Tm (N = Lm). In the first frame Tl, for instance,
-the first group Gl from the first block Bl through the Lth
block BL are refreshed. This is represented by an
{ 1(1) ~ l(L)~ ~ In each frame period
signals resulting from the coding of prediction error
signals are transmitted except during the transmission
of refreshed signals.
FIG. 5 is a block diagram illustrating an example of
the configuration of the quantizing circuit 7 in the first
preferred embodiment. The quantizing circuit 7 is provided
to quantize the local decoded signal to match it with an
input value acceptable by the code transform circuit 4
when refreshed signals are to be transmitted. The local
decoded signal pro~ided by the adder 6 is distributed by
a distributing circuit 70 among quantizers 71 through 77
for the first group Gl through the seventh group G7,
respectively. Since picture quality deterioration is
usually greater in the lower part of the sequence, the
quantizing steps are the finest in the quantizer 71, and
become coarser in the order of the quantizers 72, 73, 74,
75, 76 and 77. A selecting circuit 78, receiving the
switching control signal from the switching control
circuit 12 for indicating the reference number of the
group to be refreshed, selects the quantizing output for
- 2~ -
the group, and supplies it to the terminal Bl of the
switch SWl and the terminal ~2 of the switch SW2.
In the first preferred embodiment so far described:
(1) No difference occurs in received pic-ture quality be-
tween the refreshed part and the remaining part because thelocal decoded signals are transmitted as refreshed signals.
(2) Since the blocks of transform coefficients are further
divided into pluralities of groups for the transmission of
refreshed signals, the time taken to refresh a whole frame
is longer than according to the prior art, and accordingly
the quantity of refreshing information per unit time is
reduced, resulting in an improved coding efficiency.
Whereas the first embodiment is a case in which all the
groups are refreshed at an equal frequency, the codlng
efficiency can be further improved by refreshing less
fre~uently the groups higher in the sequence, which
affect the picture quality less, lower than those lower
n sequence.
FIG. 6 illustrates the configuratlon of a second
preferred embodiment of the invention, an example in
which motion compensation is lntroduced~ into interframe
differential orthogonal transform coding.
A time-~arying image signal coding apparatus is
: provided with an orthogonal transform circuit 1, a
subtractor 2, a quantizing circuit 3, a code transform
circuit 4A, a motion detecting circuit 5, an adder 6,
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another quantizing circuit 7, a frame memory 8, an
orthogonal inverse transform circuit 9, a variable delay
circuit 10, another orthogonal transform circuit 11, and
a switching control circui-t 12. A time-varying imaye
signal decoding apparatus comprises a code inverse
transform circuit 14A, an adder 15; a switch SW3, a frame
memory 16, an or-thogonal inverse transform circuit 17,
a variable delay circui-t 18, an orthogonai transform
circuit 19, and another orthogonal inverse transform
circuit 20.
The operation of the time-varying image signal coding
apparatus will be described below.
The motion detecting circuit 5, into which a time-
varying image signal has been entered, detects a moving
vector signal by interframe block matching. The moving
vector signal is supplied to the code transform circuit 4A
and the variable delay circuit 10. Meanwhile, the
subtractor 2 supplies the orthogonal transform circuit 1
with a prediction error signal obtained by subtracting
from the time-varying image signal, provided to one of
the input ends, a predicted signal supplied to the other
input end from the variable delay circuit 10. The
orthogonal transform circuit 1 applies orthogonal transform
to the prediction error signal for each block consisting
of a plurality of pixels, and supplies the resultant signal
to the quantizing circuit 3. The quantizing circuit
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quantizes the transform coefficient obtained by orthogonal
transform, and supplies the quantized signal to the
terminal Al of the swi-tch SWl and the adder 6.
The adder 6 generates a local decoded signal by adding
the signal orthogonally transformed by the orthogonal
~transform circuit 11 and the quantized signal supplied
from the quantizing circuit 3, and supplies this local
decoded signal to the terminal A2 of the switch SW2 and
the quantizing circuit 7. The quantizing circuit 7
quantizes the local decoded signal, and supplies the
quantized signal to the terminal Bl of the switch SWl
and the terminal B2 of the switch SW2. The frame memory 8
delays the signal, selectively connected by the switch SW2,
. by writing it in, temporarily storing it and reading it
out after the lapse of a one-frame time, and supplies the
resultant predicted signal to the orthogonal inverse
transform circuit 9, which returns this predicted signal
: from the transform region to the space region. The
variable delay circuit 10 suppli.es the predicted signal,
obtained by giving the output signal of the orthogonal
: inverse transform circuit 9 a delay corresponding to the
moving vector, to the subtractor 2 and the orthogonal
transform circuit ll, which applies orthogonal transform
to the preaicted signal and supplies the resultant signal
to the adder 6.
The code transform circuit 4A applies variable-length
coding -to the quantized signal selectively connec-ted by
the switch SW], at the same -time encodes the moving vector
signal provided from the motion detecting circuit 5 and
a switchinq con-trol signal provided from the switching
control circuit 12, and transmits the coded signals to
the time-varying image signal decodiny apparatus via the
transmission path. The switching control circuit 12
supplies the switching control si.gnal, which yives an
instruction as to which of the terminals Al, A2 and Bl, B2
of the switches SWl and SW2 are to be selected for connection.
When the terminals Al and A2 are selectively connected,
the signal supplied from the quantizing circuit 3, resulting
from the quantizing of the prediction error transform
coefficient, is subjected to coded transmission from the
code transform circuit 4A, and the local decoded signal is
not quantized but supplied as it is to the frame memory 8.
On the other hand, when the terminals Bl and B2 are
selectively connected, the signal supplied from the
quantizing circuit 7, resulting from the quantizing of
the local decoded signal, is subjected to coded transmission
from the code transform circuit 4A for the refreshing
purpose, and also supplied to the frame memory 8.
Next will be described the operation of the time-
varying image signal decoding apparatus.
The sequence of codes received from the transmission
path is decoded and separated by the code inverse transform
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circuit 14h; either the prediction error transform
coefficient or the local error signal is supplied to the
adder 15 and the terminal B3 of the swi-tch SW3, the
switching control signal is to -the switch SW3, and the
moving vector signal is -to -the variable delay circuit 18,
The switch SW3, like the switches SWl and SW2 of the
time-varying image coding apparatus, selectively connects
either the terminal A3 or the terminal B3 as instructed
by the switching control signal. When the terminal A3 is
selectively connected, the predicti.on error transform
coefficient is supplied from the code inverse transform
circuit 14A, and a predicted coded signal, obtained as
the result of the addition of a predicted transform
coefficient to the prediction error transform coefficient
by the adder 15, is returned to the space region to be
reproduced as the time-varying image signal. The result
; of addition by the adder 15 is delayed by being temporarily
stored in the frame memory 16 and read out after the lapse
of a one-frame time, returned to the space region by the
orthogonal inverse transform circuit 17, given a delay
corresponding to the moving vector by the variable delay
circuit 18, further turned into the predicted transform
coefficient by the orthogonal transform circuit 19, and
fed back to the adder 15. On the other hand, when the
- 25 terminal B3 is selectively connected, the local decoded
signal for the refreshing purpose is supplied from the
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code inverse transform circuit 14A, and written directly
into the frame memory 16 to perform refreshiny.
The block formation of the transform coefficient and
the periodic refreshiny operation in the second preferred
embodiment are the same as in the first embodiment described
with reference -to FIGS. 3 and 4.
FIG. 7 illustrates the configuration of a third
preferred embodiment of the invention.
This third embodiment is structured by removing from
the second embodiment the functions related to motion
compensation, and this configuration also provides the
same effect as the second embodiment.
~ IG. 8 is a block diagram illustrating a fourth
preferred embodiment of the invention, adopting a demand
refresh system using a group-divided block structure as
shown in FIG. 3. In this embodiment, a sequence of codes
is transmitted and recei~ed between a station 100 and
another station 200. In the time-varying image signal
coding apparatus of the station 100, a time-varying image
signal is subjected to orthogonal transform and interframe
coding by a coding circuit 101, and a code transform
clrcuit 102 applies variable-length coding to a quantized
signal supplied from the coding circuit 101 to turn it
into a sequence of codes, which is transmitted to the
code inverse transform circuit 204 of the time-varying
image signal decoding apparatus of the station 200.
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The code inverse transform circuit 204 decodes the sequence
of codes to reproduce the signal having undergone orthogonal
transform and interframe coding, and a decoding circuit 205,
into which this signal is entered, reproeuces the time-
varying image signal.
Unless a transmission path error arises while this
sequence of codes is being transferred, no refreshing
takès place. If a transmission path error occurs durdiny
a transfer, for instance, from the station 100 to the
station 200, the code inverse transform circuit 204 will
become unable to perform correct decoding, and trouble
information indicating the inability is conveyed from the
code inverse transform circuit 20~ to a switching control
circuit 203. In accordance with this trouble information,
the switching control circuit 203 supplies a code transform
circuit 202 with a refresh transmit demand signal for the
station 100, and the code transform circuit 202 transmits
this demand signal to the station 100. A code inverse
transform circuit 104, having received this refresh transmit
demand signal, transfers this signal to a switching control
circuit 103. In accordance with this, the switching
control circuit 103 supplies a re~resh control signal for
having the local decoded signal o~ the coding circui-t 101
supplied to the code transform circui-t 102 as a refreshing
signal. The code transform circuit 102 subjects the local
decoded signal for the refreshing purpose to variable-
- 31 ~
length coding and transmits it, together with a signal
supplied from the switchiny control circuit 103, resulting
from the encoding of the refresh control signal, to the
station 200. The code inverse transform circuit 204,
having received the refresh control signal, so controls
the decoding circuit 205 as to have the refreshing signal,
which follows -the refresh control signal, written into
the frame memory of -the decoding circuit 205.
Whereas this round of demand refresh operations
refreshes the frame memory of the decoding circuit 205
only when the code inverse transform circuit 204 has failed
to perform correct decoding, each block of the frame F is
further divided into groups Gl through G7 as illustrated in
FIG. 3; the reference numbers of the group including the
transfer coefficient having become unable to be decoded
and of its block are indicated, together with the trouble
information, from the code inverse transform circuit 204
to..the switching control circuit 103 via the switching
control circuit 203, the code transform circuit 202 and
the code inverse transform circuit 104; and a refreshing
signal only for the block and the part of the group referred
to by this indication is transferred. Therefore, the time
required for refresh transfer is very short. Furthermore,
when the code inverse transform circuit 204 has failed to
; 25 perform correct decoding, the deterioration of the
reproduced picture qualit~ can be better restrained by
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fixing the output value of the code inverse transform
circuit 204 pertaining to the group of the block concerned
or the transform coefficient of the group of the block
concerned decoded by the decoding circuit 205 at a
predetermined value (0 for instance) than by decoding
by the decoding circuit 205 using a wrong prediction
error signal.
The coding circuits 101 and 201 are each composed, as
illustrated in FIG. 2, of an orthogonal transform circuit 1,
a subtractor 2, a quantizing circuit 3, a code transform
circuit 4, another quantizing circuit 7, a frame memory 8,
a switch SWl and another switch SW2. The code transfer
circuits 102 and 202 have the same constitutions as that
of the code transform circuit 4 shown in FIG. 2,,and the
switching control circuit 103 and 203 have the same
constitutions as that of the switching contro]. circuit 12
shown in FIG. 2. The decoding circuits 105 and 205 are
each composed, as illustrated in FIG. 2, of an adder 15,
a frame memory 16, an orthogonal inverse transform cirGuit 17
and a switch SW3. The code inverse transform circuits 104
and 204 have the same constitutions as that of the code
inverse transform circuit 14 shown in FIG. 2.
On the other hand, where moti.on compensation is to
be combined with the interframe differential orthogonal
transform coding method, coding circuits 101 and 201 are
each composed, as illustrated in FIG. 6, of an orthogonal
transform circult 1, a subtractor 2, a quantizing circuit 3,
a code transform circuit 4, a motion compensatiny circuit 5,
an adder 6, another quantizing circuit 7, a frame memory 8
an orthogonal inverse transform circuit 9, a variable delay
circuit 10, still another quan-tiziny circuit 11, a switch
SWl and another switch SW2, and the decodiny circuits 105
and 205 are each composed, as illustrated in FIG. 6, of
an adder 15, a frame memory 16, an orthoyonal inverse
transform circuit 17, a variable delay circuit 18, an
orthogonal transform circuit 19 and a switch SW3.
As hitherto described, according to the present
invention, an equal refreshing effect to what is given by
the prior art can be achieved with less refresh information
than by the prior art because the local decoded signal in
the transform reyion is refresh-transferred on a component-
by-component basis and the minimum required refreshiny
frequency is ensured for those components whose picture
quality deterioration tends to be particularly conspicuous.
Furthermore, where the demand refresh method is used,
only the components of the group in which an error has
arisen in the erroneous block need to be sent as refresh
information, resultiny in a siynificant improvement in the
overall codiny efficiency.
Although the invention has been described with
reference to specific embodiments, this description is
not meant to be construed in a limiting sense. Various
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modifications of the disclosed embodiments, as well as
other embodiments of the invention, will become apparent
to persons skilled in the art upon reference to the
description of the invention. I-t is -therefore contemplated
tha-t the appended claims will cover any such modifications
or embodiments as fall within the true scope of the invention.
