Image information signal transmitting system

An image information signal transmitting system of this invention is a system which divides an image information signal for one picture constituted by a set of picture element data into blocks each constituted by a predetermined quantity of picture element data, transmits the picture element data on each of the blocks on the basis of a mode selected from among a plurality of transmission modes each of which allows a different quantity of picture element data to be transmitted and a mode information signal indicative of the transmission mode of each of the blocks, and restores the picture element data on each of the blocks to the original image information signal. The system is arranged to store the transmitted picture element data, read out the stored picture element data at a data readout rate of one kind which is selected from among a plurality of different data readout rates and which corresponds to the kind of transmission mode indicated by the transmitted mode information signal, and implement a data restoring processing on the picture element data thus read on the basis of a data restoring processing of one kind which is selected from among a plurality of different data restoring processings and which corresponds to the kind of transmission mode indicated by the transmitted mode information signal. With this arrangement, it is possible to realize reductions in the size, weight and cost of the apparatus without deteriorating an image information signal to be transmitted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image information signal transmitting 
system for transmitting image information signals. 
2. Description of the Related Art 
In the field of transmission of information such as image information, it 
has consistently been desired to provide a transmission method which 
enables the original information to be faithfully reproduced with a 
transmission rate as small as possible and, to this end, a variety of 
transmission methods have been proposed. One proposed transmission method 
is an adaptive type variable-density sampling method in which sampling 
density, that is, the density of the information to be transmitted, is 
appropriately varied. One example of such an adaptive type 
variable-density sampling method will now be explained with reference to a 
time-axis transforming band-compression method (hereinafter referred to as 
"TAT") which is adapted to a one-dimensional TAT system. 
FIG. 1 is a view which serves to illustrate the basic concept of TAT. As 
shown by dashed lines in the figure, the original signal is divided into 
separate blocks at predetermined time intervals, and it is determined 
whether the information contained in each divided block is coarse or 
dense. If it is determined that the information of an arbitrary block is 
dense, all the data obtained by sampling the original signal corresponding 
to the block is transmitted as transmitted data, while, if it is 
determined that the information of an arbitrary block is coarse, only a 
portion of all the data obtained in a similar manner is transmitted as 
transmitted data. It is thus possible to reduce the amount of data to be 
transmitted per unit time and therefore to compress the bandwidth of a 
transmission signal. Simultaneously, a signal indicative of whether the 
original signal is dense or coarse is transmitted as transmission mode 
information. 
On the basis of the transmission mode information, a receiving side makes a 
decision as to whether all or a portion of the sampled data of each block 
has been received. For a block whose sampled data has been partially 
received, interpolated data is formed from the received data so as to 
interpolate the portion of the sampled data which has not been 
transmitted. It is thus possible to obtain a restored signal which closely 
approximates the original signal. 
The following is a description of a case where the above-described concept 
is applied to the transmission of image information. 
Image information has a two-dimensional extension and has correlations in 
the horizontal and vertical directions. Accordingly, if not only the 
horizontal sampling intervals but also the vertical sampling intervals are 
rendered variable, more effective compression is enabled. Such a method is 
hereinafter referred to as "two-dimensional TAT". 
FIG. 2 shows the data transmission patterns adopted in two-dimensional TAT. 
In two-dimensional TAT, a single picture is divided into picture element 
blocks consisting of m.times.n picture elements, and the amount of data to 
be transmitted is varied for each picture element block. FIG. 2 shows a 
picture element block which consists of 4.times.4 picture elements, and 
serves to illustrate the data transmission patterns used when each picture 
element block is to be transmitted selectively in either of two 
transmission modes 
In the figure, the symbols "o" represent picture elements to be 
transmitted, while the symbols "x" represent picture elements not to be 
transmitted. A pattern for transmitting all the picture element data is 
represented at E and a pattern for transmitting only a portion of the 
picture element data at C. The transmission modes using these transmission 
patterns are hereinafter referred to as the "E mode" and the "C mode", 
respectively. The picture elements which are transmitted from the picture 
element block in the C mode are hereinafter referred to as the "basic 
picture elements", and the remaining transmitted picture elements as the 
"high-fineness picture elements". As can be seen from FIG. 2, the density 
of information transmitted in the C mode is 1/4 that of information 
transmitted in the E mode. 
The non-transmitted picture elements contained in the picture element block 
transmitted in the C mode are restored to the original form on the 
receiving side by selecting picture element data close to the 
non-transmitted picture element data from the transmitted picture element 
data and forming interpolated picture element data by using the selected 
picture element data. 
FIG. 3 shows the construction of the sending side of a conventional 
two-dimensional TAT transmission system of the type which utilizes analog 
transmission. An input analog image signal is converted into a digital 
signal by an AD converter 10. A thinning-out circuit 12 implements 
thinning-out processing, corresponding to the C-mode pattern of FIG. 2, of 
all the picture element data supplied from the A/D converter 10, and 
outputs C-mode picture element data. An interpolation circuit 14 computes 
interpolated picture element data from the C-mode picture element data 
output from the thinning-out circuit 12. A mode identifying circuit 16 
compares the interpolated picture element data output from the 
interpolation circuit 14 with a true value from the A/D converter 10, and 
determines the transmission mode of each block (C or E mode). Concretely, 
the mode identifying circuit 16 calculates the total of the differences 
between the true values and the interpolated data in each block output 
from the interpolation circuit 14 (such a total is hereinafter referred to 
as the "block distortion"), and stores block distortions for one field in 
its memory. 
Then, while data for the succeeding field is being input, the distribution 
of the block distortions of all the picture element blocks is obtained. In 
this step, in order to make constant the compression rate per field, it is 
necessary to make constant the ratio of the number of picture element 
blocks to be transmitted in the C mode to the number of picture element 
blocks to be transmitted in the E mode. For example, if the proportion of 
picture element blocks to be transmitted in the C mode is set to 2/3 of 
the number of picture element blocks per field and if the proportion of 
picture element blocks to be transmitted in the E mode is set to 1/3 of 
the total number picture element blocks per field, the total amount of 
data to be transmitted (compression rate) becomes 
1/2=(2/3.times.1/4+1/3.times.1). Accordingly, in this step, a distortion 
threshold is determined which serves as a selection reference according to 
which selection of the transmission modes is carried out for each picture 
element block. 
At the timing that an image signal of the succeeding field is input, the 
block distortions stored in the mode identifying circuit 16 are 
sequentially read out, and the transmission mode is determined for each 
picture element block by comparing the block distortion with the 
distortion threshold. If the block distortion coincides with the 
distortion threshold, the transmission modes are allocated so that the 
ratio of the number of picture element blocks to be transmitted in the C 
mode to the number of picture element blocks to be transmitted in the E 
mode is set to the aforesaid predetermined ratio. The mode identifying 
circuit 16 outputs a mode identifying signal indicative of the allocation 
of the transmission modes. 
Reference numeral 18 denotes a buffer for E-mode picture element data and 
reference numeral 20 denotes a buffer for C-mode picture element data. In 
accordance with the mode identifying signal output from the mode 
identifying circuit 16, the switch 22 selects the output of the buffer 18 
or 20 in units of blocks. The picture element data selected by the switch 
22 is converted into an analog signal by a D/A converter 24 and output to 
a transmission path. The mode identifying signal is output through a 
buffer 26 to the transmission path as a mode information signal. This mode 
information signal is converted into an analog signal, 
frequency-multiplexed with an analog picture element signal, and then 
transmitted over the transmission path which is the same as that of the 
analog picture element signal. 
FIG. 4 diagrammatically shows a receiving side which corresponds to the 
sending side shown in FIG. 3. The picture element signal input from the 
transmission path is converted into digital picture element data by an A/D 
converter 28, and the digital picture element data is supplied to a C-mode 
interpolation circuit 30 and a switch 32. The C-mode interpolation circuit 
30 interpolates the non-transmitted picture elements of the picture 
element block transmitted in the C mode and outputs the result. If the 
mode information signal input to the switch 32 represents the C mode, the 
switch 32 is switched to a C contact, while if the input mode information 
signal represents the E mode, the switch 32 is switched to an E contact. 
Thus, all the picture element data including the E-mode picture element 
data, the C-mode picture element data, and the interpolated picture 
element data is stored in a frame memory 34. From the frame memory 34, all 
the picture element data is read out in the order conforming to, for 
example, a television signal, and is then converted into an analog image 
signal by a D/A converter 36. 
In order to restore a television signal, the frame memory 34 having a 
storage capacity for at least one frame is needed on the receiving side of 
the aforesaid transmission system. In addition, the transmission rate of 
the C mode is four times as large as that of the E mode. Accordingly, if 
picture element data is to be transmitted at the rate of two samples per 
cycle time, it is necessary that the frame memory 34 have an 
8(2.times.4)-ply construction. As a result, the number of chips which can 
be selected becomes a multiple of 8, and the hardware construction of the 
memory frame 34 involves various difficulties such as a decrease in the 
utilization efficiency of memory and an increase in the number of chips. 
In addition, in recent years, the memory capacity per chip has been 
increasing, thereby making it possible to construct a frame memory with 
about 2 to 4 chips. However, in the case of the 8-ply construction, it is 
impossible to reduce the number of chips to 8 or less. 
Furthermore, if the above-described two-dimensional TAT method is used to 
transmit, for example, a motion image such as a television signal, the 
resolution of a still-image portion contained in the television signal 
deteriorates to a remarkable extent. To overcome the problem, it has been 
proposed to provide a transmission method whose transmission rate can be 
reduced by utilizing correlations in the direction of a time axis, since 
the still-image portion exhibits high correlation in the direction of the 
time axis. This transmission method is called a three-dimensional TAT 
method. In the three-dimensional TAT method, no image data corresponding 
to a still-image portion is transmitted and, on a receiving side, the 
received image data which precedes in time is utilized as the 
non-transmitted data. In other words, the transmission of the still-image 
portion is omitted, but the transmission density of the other portion is 
enhanced instead, thereby achieving the enhancement of image quality. 
In the three-dimensional TAT method, one picture is divided into a 
plurality of picture element blocks and, a mode for transmitting all the 
constituent picture element data (hereinafter referred to as the "e 
mode"), a mode for transmitting only data on picture elements which 
constitute a basic part of the constituent picture elements (basic picture 
elements) (hereinafter referred to as the "c mode"), and a mode for 
utilizing data on a corresponding block of a previously transmitted 
picture (hereinafter referred to as the "p mode") are selectively 
allocated under predetermined rules in order to make constant the amount 
of information transmitted per picture (for example, a compression rate of 
1/2). On a receiving side, signal processing corresponding to each mode is 
effected to restore the original image. A signal indicative of the 
allocation of the transmission modes is separately transmitted as mode 
information. In addition, in the p mode, basic picture element data alone 
may be transmitted in a manner similar to that used in the c mode and the 
receiving side may be arranged so that, if the transmitted data is the 
same as received data on the corresponding block contained in the 
preceding picture, it may be determined that not the C mode but the p mode 
is selected. 
In the three-dimensional TAT method, a block distortion Dc for c-mode 
transmission is calculated in advance and, in order to review correlation 
in the direction of a time axis, the image signal of the preceding picture 
is stored in a frame memory. For each picture element block, a block 
distortion (the degree of time correlation) Dp is calculated by comparing 
the picture element data on the preceding picture with the picture element 
data on the current picture. Then, Dc is compared with Dp to make a 
decision, for each picture element block, as to which of the c-mode 
transmission and the p-mode transmission is smaller in block distortion. 
If Dc&gt;Dp, the c mode is not selected and, if Dc&lt;Dp, the p mode is not 
selected. In a case where a picture element block which was transmitted in 
the c mode during the transmission of the preceding picture is transmitted 
in the p mode for transmission of the current picture, the effect of 
improving image quality is not expected. Accordingly, the picture element 
block transmitted in the e mode during the transmission of the preceding 
picture is transmitted in the p mode for transmission of the current 
picture. 
After the block distortions of all the picture element blocks which 
constitute one picture have been calculated in the above-described manner, 
the transmission modes are allocated for the respective picture element 
blocks and the picture element data on each picture element block is 
sequentially transmitted in accordance with the allocated transmission 
mode. 
FIG. 5 illustrates the manner of mode distribution for the block 
distortions Dc and Dp, and FIG. 6 shows a distribution ratio based on the 
time correlation of an image. A picture element block representing a 
larger motion is located at an upper position on the Dp axis, while a 
high-fineness picture element block, that is, a picture element block 
having a higher two-dimensional frequency is located on the more right 
side on the Dc axis. The c or p mode is specified on the basis of the 
relationship between the magnitudes of Dc and Dp. Accordingly, the c mode 
is selected in a region above a straight line Dc=Dp of FIG. 5, while the p 
mode is selected in a region below the straight line. The value of Dm of a 
picture element block located at Xc takes on the value on the Dc axis 
which is obtained when a perpendicular line is dropped with respect to the 
Dc axis. The value of Dm of a picture element block located at Xp takes on 
the value on the Dc axis which is obtained when a perpendicular line is 
dropped with respect to the Dp axis and a perpendicular line is further 
drawn to the Dc axis from the intersection point of the former 
perpendicular line and the straight line Dc=Dp. In FIG. 5, if a threshold 
T1 for selection of the e mode is selected on the Dm axis, a threshold T2 
is obtained on each of the Dc and Dp axes. That is to say, a picture 
element block represents a portion whose fineness is high and which shows 
a large motion is transmitted in the e mode. 
The distribution ratio of each mode is as follows. The data compression 
rate of one picture is fixed at, for example, 1/2 and, if the amount of 
picture element data to be transmitted in the c or p mode is 1/4 of the 
amount of picture element data which constitutes one picture element 
block, then the number of picture element blocks to be transmitted in the 
e mode occupies 1/3 of the total number of picture element blocks to be 
transmitted per field. In other words, as shown in FIG. 6, 1/3 of all the 
picture element blocks of one field is transmitted in the e mode and the 
remaining picture element blocks are transmitted in the p or c mode in 
accordance with the block distortion Dc or Dp. A straight line which 
constitutes the right side of FIG. 6 corresponds to a case where no 
correlated portion is present between two successive pictures and, in this 
case, processing identical to that used in the above-described 
two-dimensional TAT method is effected. The left side of FIG. 6 
corresponds to a case where a perfect still image is transferred, and the 
obtained resolution is the same as that obtained when all the picture 
element blocks are transferred in the e mode. The mode distribution rate 
for an arbitrary picture is represented by the length of a line segment 
defined, on a broken line shown at A in FIG. 6, in each of the e-, c- and 
p-mode regions. The position of the broken line A depends upon the time 
correlation of image information. 
FIG. 7 is a schematic block diagram showing a sending device according to a 
conventional three-dimensional TAT method of the type which employs an 
analog transmission path. An analog image signal to be transmitted is 
converted into a digital signal by an A/D converter 110. All the picture 
element data output from the A/D converter 110 is supplied to an 
thinning-out circuit 112, where all the data on the picture elements which 
exclude the aforesaid basic picture elements is eliminated. More 
specifically, the thinning-out circuit 112 outputs c-mode picture element 
data. An interpolation circuit 114 interpolates the picture element data 
eliminated by the thinning-out circuit 112 to reproduce the picture 
element block. A block distortion computing circuit 116 computes the block 
distortion Dc for each picture element block by comparing the picture 
element output from the A/D converter 110 with the interpolated c-mode 
data output from the interpolation circuit 114. 
The output of the A/D converter 110 is supplied also to a frame memory 118 
which serves as a delay element having delay time corresponding to one 
picture. More specifically, all the data on the preceding picture is 
stored in the frame memory 118 and a block distortion computing circuit 
120 calculates the difference between the picture element data on the 
current picture and the picture element data on the preceding picture 
supplied from the frame memory 118 for each picture element block. The 
block distortion computing circuit 120 outputs the total of the aforesaid 
differences (or block distortion Dp). This block distortion Dp represents 
the degree of similarity in the direction of the time axis. A comparator 
circuit 122 compares Dc and Dp with each other with a predetermined weight 
attached thereto, and outputs the result of the comparison as selection 
mode data Dc/Dp as well as a smaller block distortion as block distortion 
Dm for identifying the transmission mode. That is to say, for each picture 
element block, the comparator circuit 122 makes a decision as to which of 
the c-mode transmission and the p-mode transmission enables an image to be 
transmitted more faithfully with respect to the e-mode transmission. 
Concretely, if Dc&gt;Dp, the c mode is not selected, while if Dc&lt;Dp, the p 
mode is not selected. 
A mode identifying circuit 124 is a circuit in which the e mode is 
allocated for a predetermined number of picture element blocks in the 
order of magnitude of Dm. More specifically, the mode identifying circuit 
124 obtains the threshold of Dm on the basis of the distribution of Dm of 
all the picture element blocks. The circuit 124 selects the e mode if the 
value of Dm exceeds the threshold while, if the value of Dm is not greater 
than the threshold, any mode other than the e mode is selected. When the 
value of Dm is not greater than the threshold, if Dc&lt;Dp, then the c mode 
is allocated, while if Dc&gt;Dp, the p mode is allocated. In accordance with 
the allocation, the mode identifying circuit 124 outputs a mode 
identifying signal indicative of the e mode or any other mode. 
Regarding a picture element block to be transmitted in the p mode, its 
basic picture element data alone is transmitted in a manner similar to 
that used in the c-mode transmission. On a receiving side, the basic 
picture element data is compared with the basic picture element data on 
the corresponding picture element block in the preceding picture. If the 
basic picture element data of the current picture is the same as that on 
the preceding picture, it is determined that the basic picture element 
data was transmitted in the p mode, and the original image is restored by 
utilizing the picture element data on the preceding picture. If the basic 
picture element data on the current picture differs from that on the 
preceding picture, it is determined that the basic picture element data 
was transmitted in the c mode, and the original image is restored by an 
interpolation process. In addition, if a picture element block transmitted 
in the c mode during the transmission of the preceding picture is 
transmitted in the p mode for transmission of the current picture, the 
effect of improving image quality cannot be expected. It is determined, 
therefore, that the picture element block which was transmitted in the e 
mode during the transmission of the preceding picture is transmitted in 
the p mode for transmission of the current picture. 
A switch 126 is controlled by the output of the mode identifying circuit 
124. In the case of the e mode, the switch 126 delivers to a D/A converter 
132 all the picture element data on each picture element block which is 
supplied from the A/D converter 110 through a buffer 128 to the switch 
126. In the case of the c or p mode, the switch 126 delivers to the D/A 
converter 132 the basic picture element data on each picture element block 
which is supplied from the thinning-out circuit 112 through a buffer 130 
to the switch 126. The D/A converter 132 converts digital picture element 
data into an analog signal and transmits the result to a transmission 
path. In the case of e-mode transmission, it is not necessary to rewrite 
data on any corresponding picture element block of the frame memory 118. 
The frame memory 118 is therefore set to a write-inhibit state in 
accordance with the identification signal output from the mode identifying 
circuit 124. 
The mode identifying signal output from the mode identifying circuit 124 is 
further transmitted through the buffer 134 to the transmission path. 
FIG. 8 is a block diagram showing the construction of a receiving system 
which corresponds to the sending system of FIG. 7. The analog video signal 
transmitted over the transmission path is converted into a digital signal 
by an A/D converter 170. A switch 172 is controlled by the received mode 
information. If each picture element block is transmitted in the e mode, 
the switch 172 outputs all the picture element data in the state which is 
the same as the state when it was received. In any other mode, the switch 
172 outputs the picture element data interpolated by an interpolation 
circuit 174. Accordingly, the switch 172 always outputs all the picture 
element data on each picture element block, and this data is written into 
a frame memory 173 for all the picture elements. A switch 176 is likewise 
controlled by the received mode information. In the case of e-mode 
transmission, the switch 176 selects the output of a thinning-out circuit 
178 for extracting basic picture element data from the picture element 
block transmitted in the e mode and, in any other mode, the switch 176 
selects the output of the A/D converter 170. Accordingly, the switch 176 
always outputs basic picture element data, and this data is written into a 
frame memory 180 for basic picture elements. 
A block distortion computing circuit 182 computes the difference between 
the basic picture element data supplied from the switch 176 and the basic 
picture element data on the preceding picture supplied from the frame 
memory 180, thereby outputting the total of the differences for each 
picture element block (hereinafter referred to as the "block distortion 
Db"). The block distortion Db is compared with a threshold TH in the 
comparator circuit 184. If Db is smaller than TH, it is determined that 
the picture element block has been transmitted not in the c mode but in 
the p mode. An arithmetic circuit 186 generates a p identifying signal 
indicative of whether or not the p mode is selected, from the received 
mode information and the output of the comparator circuit 184, and 
supplies the p identifying signal to the frame memories 173 and 180. Thus, 
rewriting of the picture element blocks transmitted in the p mode is 
inhibited in the frame memories 173 and 180, and all the data on the 
preceding picture is held in the state which is the same as the state when 
the data was transmitted. In this fashion, the data of the frame memory 
173 is up-dated and read into the D/A converter 188. The D/A converter 188 
provides a high-resolution analog video signal. 
In the receiving system used in the conventional example described above, 
both picture element information and mode information need to be 
accurately received and a memory address is calculated and determined in 
accordance with the mode information. It is, therefore, necessary to 
transmit the mode information simultaneously with or prior to the picture 
element information. 
Where the mode information is to be transmitted prior to the picture 
element information by using, for example, a transmission path constituted 
by a magnetic tape, as shown in FIG. 9, a situation may be encountered in 
which the mode information cannot be received due to dropout. In such a 
situation, an image signal of the succeeding field may be fatally 
adversely affected. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an image 
information signal transmitting system capable of overcoming the 
above-described problems. 
It is another object of the present invention to provide an image 
information signal transmitting system which makes it possible to realize 
reductions in the size, weight and cost of the overall apparatus without 
deteriorating an image information signal to be transmitted. 
To achieve the above objects, in accordance with the present invention, 
there is provided an image information signal transmitting system which is 
arranged to divide an image information signal for one picture constituted 
by a set of picture element data into blocks each constituted by a 
predetermined quantity of picture element data, transmit the picture 
element data on each of the blocks on the basis of a mode selected from 
among a plurality of transmission modes each of which allows a different 
quantity of picture element data to be transmitted and transmit a mode 
information signal indicative of the transmission mode of each of the 
blocks, and restore the transmitted picture element data on each of the 
blocks to the original image information signal. The present image 
information signal transmitting system is provided with storage means for 
storing the transmitted picture element data, data readout means for 
reading out the picture element data stored in the storage means at a data 
readout rate of one kind which is selected from among a plurality of 
different data readout rates and which corresponds to the kind of 
transmission mode indicated by the transmitted mode information signal, 
and data restoring means for implementing a data restoring processing on 
the picture element data read from the storage means on the basis of a 
data restoring processing of one kind which is selected from among a 
plurality of different data restoring processings and which corresponds to 
the kind of transmission mode indicated by the transmitted mode 
information signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described below with 
reference to the accompanying drawings. 
In the following description, it is assumed that an image information 
signal transmitting system according to a first embodiment of the present 
invention has a sending system which has the same construction as that 
shown in FIG. 3 and that a picture element signal including two samples is 
transmitted over an analog transmission path during one cycle time of a 
memory. 
FIG. 10 is a block diagram showing the construction of the receiving system 
of the image information signal transmitting system according to the first 
embodiment of the present invention. In the figure, a picture element 
signal 240, which is input through the transmission path, is converted 
into picture element data by an A/D converter 242 and input to a buffer 
memory 244, whereas the mode information input through the transmission 
path is converted from mode information on a block basis to mode 
information on a line basis by a block/line (B/L) conversion circuit 246. 
The mode information thus converted is supplied to a memory control 
circuit 248 and a switch 252. Incidentally, the B/L conversion circuit 246 
temporarily stores the mode information, which is input on a block basis 
in a field memory or the like, and reads the same mode information from 
the field memory every four lines to convert the mode information 
allocated in units of blocks into mode information allocated in units of 
lines, then outputting the result. The memory control circuit 248 controls 
the buffer memory 244 in the following manner: The memory control circuit 
248 writes the output data of the A/D converter 242 into the buffer memory 
244 at the rate of 2 samples/cycle-time and converts the output data into 
signals in the order conforming to a television signal (raster scan). The 
buffer memory 244 is controlled to output, in the E mode, picture element 
data at a rate which is twice the rate of writing and, in the C mode, at a 
rate which is 1/2 of the rate of writing. Accordingly, in the E mode, the 
data of the buffer memory 244 is read out at the rate of 4 
samples/cycle-time, while, in the C mode, the data is read out at the rate 
of 1 sample/cycle-time. 
The picture element data output from the memory 244 is supplied to a C-mode 
interpolation circuit 250 and a switch 252. The C-mode interpolation 
circuit 250 computes picture element data for interpolating the 
non-transmitted portion from the basic picture element data, converts the 
result and the basic picture element data into raster scan data, and 
supplies the raster scan data to the switch 252. If the output of the B/L 
conversion circuit 246 assumes the C mode, the switch 252 is switched to a 
C contact, while if the output assumes the E mode, the switch 252 is 
switched to an E contact. Accordingly, all the picture element data on 
each picture element block is provided at the output of the switch 252, 
and the picture element data is converted into an analog signal by a D/A 
converter 253. 
The maximum value of the access rate of the buffer memory 244 is 4 
samples/cycle-time and the buffer memory 244 can therefore be constructed 
with four plies. In addition, since the stored data is compressed data, 
the required memory capacity is reduced to 1/2 in accordance with a 
compression rate (in this case, 1/2). 
FIG. 11 is a block diagram showing the construction of the receiving system 
of an image information signal transmitting system according to a second 
embodiment of the present invention. A detailed description of only the 
portions which differ from those shown in FIG. 10 will be given here, and 
it is assumed that the second embodiment is arranged to separately 
transmit E-mode picture element data and basic picture element data 
(C-mode picture element data). The picture element data digitized by the 
A/D converter 254 is supplied to buffer memories 256 and 258. If an input 
mode information signal represents the E mode, a memory control circuit 
260 allows corresponding E-mode picture element data to be written into 
the buffer memory 256 and inhibits writing operation of the buffer memory 
258. If an input mode information signal represents the C mode, the memory 
control circuit 260 allows corresponding basic picture element data to be 
written into the buffer memory 258 and inhibits a writing operation of the 
buffer memory 256. A B/L conversion circuit 261 converts input mode 
information on a block basis to mode information on a line basis in a 
manner similar to that used in the B/L conversion circuit 246 described 
above in connection with FIG. 10. The B/L conversion circuit 261 is 
provided with a delay circuit of a one-field delay period so as to give a 
delay for one field to the input mode information. If the output of the 
B/L conversion circuit 261 represents the E mode, the memory control 
circuit 260 controls the buffer memory 256 so that the stored signal may 
be read out at a rate which is twice the rate of writing (4 
samples/cycle-time) in the order conforming to a television signal. 
The buffer memory 256 converts picture element data on a block basis into 
raster scan data under the control of the memory control circuit 260. 
Simultaneously, the buffer memory 256 outputs the E-mode picture element 
data in the preceding field at a rate which is twice the rate of writing 
(i.e., at the rate of 4 samples/cycle-time) to supply the thus-read E-mode 
picture element data to a switch 264. Similarly, the buffer memory 258 
converts basic picture element data on a block basis into raster scan data 
under the control of the memory control circuit 260. Simultaneously, the 
buffer memory 258 outputs the basic picture element data in the preceding 
field at a rate which is 1/2 of the rate of writing (i.e., at the rate of 
1 sample/cycle-time) to supply the data read to a C-mode interpolation 
circuit 262. The C-mode interpolation circuit 262 computes picture element 
data for interpolating a non-transmitted portion from the basic picture 
element data, converts the result and the basic picture element data into 
raster scan data, and supplies the raster scan data to the switch 264. The 
picture element block transmitted in the C mode is restored. 
If the output of the B/L conversion circuit 261 assumes the C mode, the 
switch 264 is switched to a C contact, while if the output assumes the E 
mode, the switch 264 is switched to an E contact. The output of the switch 
264 is converted into an analog signal by a D/A converter 266. 
In the second embodiment described above in connection with FIG. 11, the 
maximum values of the write or read rates of the respective buffer 
memories 256 and 258 are 4 samples/cycle-time and 2 samples/cycle time and 
the buffer memories 256 and 258 may be constructed with four plies and two 
plies, respectively. In addition, the required memory capacities can be 
reduced to 1/3 and 1/4, respectively, 7/12 in total, which is about half 
the memory capacity required in the conventional system. 
In addition, if high-fineness picture element data of the E mode an basic 
picture element data are to be transmitted separately, the capacity of the 
buffer memory 256 becomes 1/4 (=1/3-1/4.times.1/3) and the total capacity 
of the buffer memories 256 and 258 becomes 1/2 (=1/4+1/4). In this case, 
as shown in FIG. 12 which illustrates a third preferred embodiment, the 
switch 264 shown in FIG. 11 is replaced with a switch 268, and a switch 
control circuit 270 is disposed for controlling the switch 268 so that, in 
the case of basic picture element data of the E mode, the switch 268 is 
switched to a B contact. 
Since the second and third embodiments of the present invention utilize 
separate buffer memories for E-mode picture element data and basic picture 
element data, those embodiments are suited for use in a system for 
separately transmitting E-mode picture element data and basic picture 
element data (C-mode picture element data). 
Incidentally, although the above description is made with reference to the 
arrangement in which picture element data is transmitted in units of 
blocks, the picture element data may be transmitted in the order 
conforming to a television signal. In this case, the B/L conversion 
circuits 246 and 261 shown in FIGS. 10, 11 and 12 are not needed, and 
sorting of picture element data in the buffer memories 244, 256 and 258 is 
not needed. In addition, a mode information signal may be transmitted as 
digital data over a transmission path which differs from that of an analog 
picture element signal. 
As can be understood from the above explanation, in each of the first to 
third embodiments, image information including a non-transmitted portion 
is stored in memory means in order to effect interpolation of the image 
information, whereby the capacity of the memory means can be reduced 
according to the proportion of the nontransmitted portion in transmitted 
image information. Accordingly, it is possible to manufacture image 
information processing systems with simplified hardware constructions at 
low cost. 
FIG. 13 is a block diagram showing the construction of the receiving system 
used in an image information signal transmitting system according to a 
fourth embodiment of the present invention. In FIG. 13, the same reference 
numerals are used to denote the constituent elements which are the same as 
those shown in FIG. 8. In FIG. 13, reference numeral 290 denotes a 4-ply 
high-fineness picture element frame memory, reference numeral 291 a 2-ply 
basic picture element frame memory, reference numeral 292 a c-mode 
interpolation circuit, reference numeral 293 a switch which is switched in 
response to input mode information, and reference numeral 294 a memory 
used for delaying an input mode information signal by a predetermined time 
period in order to cause the input mode information signal among the input 
mode information signal and a picture element information signal, which 
are supplied at mutually different timings as shown in FIG. 9 mentioned 
above, to correspond in time to input picture element information as shown 
in FIG. 14. Incidentally, in the embodiment shown in FIG. 13, the frame 
memory 173 has a 4-ply construction and each of the frame memories 173, 
290 and 291 has a cycle time t.sub.1, and the A/D converter 170 effects 
sampling at the rate of 2 picture elements per t.sub.1. Of the outputs of 
the A/D converter 170, basic picture element data is written into the 
frame memory 291 via the switch 176, while high-fineness picture element 
data is written into the frame memory 290. After writing into the frame 
memory 290 has been completed, the basic picture element data of the frame 
memory 291 is read out at a rate which is 1/2 of the rate of writing, that 
is, at the rate of one picture element per t.sub.1, and supplied to the 
c-mode interpolation circuit 292. The c-mode interpolation circuit 292 
effects interpolation of non-transmitted picture elements and outputs 
serial data of four picture elements per t.sub.1. 
The output of the frame memory 290 is 4-picture-element parallel data which 
is read out at a rate which is twice the rate of writing, that is, at the 
rate of four picture elements per t.sub.1. In accordance with the input 
mode information signal temporarily stored in the memory 294, the switch 
293 selects the output of the frame memory 290 in the e mode and, in any 
mode other than the e mode, the output of the c-mode interpolation circuit 
292. The signal selected by the switch 293 is supplied to the D/A 
converter 188 through the frame memory 173, and the D/A converter 188 
outputs a corresponding analog image signal. 
Also, the frame memory 291 supplies picture element data on the preceding 
picture to the block distortion computing circuit 182 for the purpose of 
arithmetic operations in the block distortion computing circuit 182. 
As described above, the fourth embodiment realizes a method of transmitting 
mode information in correspondence with image information for one field 
and is arranged such that basic picture element data and high-fineness 
picture element data are temporarily stored in memory means. Accordingly, 
after all the picture element data for one field has been received, it is 
possible to carry out allocation of the e, c and p modes. 
Although the above explanation has been made with illustrative reference to 
three-dimensional TAT, the fourth embodiment can of course be applied to 
two-dimensional TAT. 
As can be readily understood from the foregoing, in the fourth embodiment, 
received picture element information and mode information are made to 
correspond to each other in time and, therefore, even if dropout or the 
like occurs during transmission, influence upon the succeeding field can 
be minimized.