Information signal transmission system

An information signal transmission system is arranged to divide an original image information signal which consists of information signals representing a number k.times.l (k and l: positive integers) or picture elements into a plurality of small blocks, each grouping a number m.times.n (m and n: positive integers) of picture elements to have a plurality of compressing modes of different information compressing rates; and to compress the information signal for each of the blocks in one of the plurality of compressing modes in transmitting these information signals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an information signal transmission system of the 
kind arranged to transmit information signals by compressing them. 
2. Description of the Related Art 
The conventional information compressing transmission methods include, for 
example, a method called the time axis transform method (hereinafter 
referred to as the TAT method). In the TAT method, an information signal 
is compressed for transmission by utilizing the fact that, in compressing 
the band-width of an information signal, the density of the information 
signal in one part thereof differs from another. 
FIG. 1 of the accompanying drawings shows the operating principle of the 
TAT method as applied to a case where a signal is processed in a 
one-dimensional manner. Referring to FIG. 1, as indicated with broken 
lines, an original signal is divided into groups or blocks of picture 
elements by a given account of information. Each of the divided groups is 
subjected to a discrimination between a dense state and a sparse state of 
information. For a group which is thus determined to be dense, all data 
that are obtained by sampling the original signal are transmitted as 
transmission data. Meanwhile, in the case of a group determined to be 
sparse, only a part of data obtained by sampling is transmitted while the 
remainder of the same group is not transmitted and regarded as skipped 
data. In the illustration, marks " " represent the transmitted picture 
element data or data to be transmitted. Marks "X" represent data not 
transmitted (or skipped data). The band of the transmitted information 
signal is compressed as the number of data transmitted per unit time is 
decreased by the arrangement of transmitting the data marked " " at 
intervals of a given length of time. 
With the picture element data thus transmitted, the skipped picture 
elements which are not transmitted are proximately restored by using the 
transmitted data to obtain interpolating data which are as indicated with 
marks " " in FIG. 1. The interpolating data thus obtained corresponds to 
the sparse parts of information and has a close resembrance to the skipped 
data. Therefore, the signal thus restored virtually shows no difference 
from the original information signal, in comparison with a case where all 
the data are transmitted, despite of a great degree of compression 
effected on the transmitting band of the information signal. 
In this instance, each of the data (or picture element) groups is examined 
to determine whether all the picture elements within the group is to be 
transmitted or only a part of the picture elements included in the group 
is to be transmitted. This determination is made by checking the fineness 
or elaborateness of the original signal. Information on this determination 
is transmitted as a transmitting mode signal concurrently with the 
information signal. 
Further, in the case of image information signal, the transmitting band of 
the image information can be compressed by changing not only the 
horizontal sampling intervals but also vertical sampling intervals in a 
two-dimensional manner. 
In two-dimensionally processing a signal, like in the case of an image 
information signal, one image plane is divided into blocks, each having an 
m.times.n number of picture elements. Then, the image density of each 
block is examined. A block which is determined to be dense is processed to 
have all the picture elements included in the block sampled and 
transmitted as transmission data. A block determined to be sparse is 
processed to have only some of the picture elements thereof sampled and 
transmitted as transmission data while the rest are not transmitted and 
processed as skipped data. 
Assuming that the processing or transmitting mode in which all the picture 
elements are to be sampled is called "mode E" and the mode in which only a 
part of picture elements are to be sampled is called "mode C", the picture 
elements to be transmitted and the picture elements not to be transmitted 
in each of these different modes E and C are as shown in FIGS. 2(a) and 
2(b). 
FIGS. 2(a) and 2(b) show the picture element blocks, each consisting of 
4.times.4 picture elements. The block shown in FIG. 2(a) is to be 
processed in the mode E while that of FIG. 2(b) to be processed in the 
mode C. The image information of one image plane to be transmitted is 
divided into blocks, each having 4.times.4 picture elements, from a left 
upper part to a right lower part of the image plane one after another. One 
of the above-stated two different transmitting modes is selected for each 
of these blocks according to the density of image carried. Sampling is 
performed in the mode selected. 
FIG. 3(a) shows one field of TV image plane of the NTSC system divided by 
the above-stated method into picture element blocks, each of which 
consists of 4.times.4 picture elements. The transmitting modes E and C 
which are as shown in FIG. 2(a) and 2(b) are allocated to these divided 
blocks as applicable. Marks " " indicate picture elements to be 
transmitted and marks "X" picture elements not transmitted. With the 
picture elements sampled in this manner, the transmitting band of the 
information signal is compressed by transmitting at given intervals the 
data thus obtained through sampling. 
The transmission of the image data sampled from within each block is 
arranged to be effected one after another in sequence either in the 
horizontal direction or in the vertical direction. FIG. 3(b) shows a case 
where these data are transmitted one after another in the horizontal 
order. FIG. 3(c) shows a case where the transmission is effected in the 
vertical order. The reference symbols and numerals in FIGS. 3(b) and 3(c) 
correspond to those used for the picture elements shown in FIG. 3(a). 
These data are transmitted in the direction of arrows. 
The picture elements which are not transmitted are proximately restored 
during reproduction by using the adjacent picture elements which are 
transmitted. Therefore, despite of the great extent of compression 
effected on the transmitting band of the information signal, there takes 
place not much changes in the amount of information as compared with a 
case where all the data are arranged to be transmitted. 
However, there arises some difference in information level among the 
picture element because of positional relation, on the image plane, 
between the picture elements before and after transmission change-over 
from one block to another. For example, picture elements a and 16 which 
are neighboring each other across a border line between two blocks as 
shown in FIGS. 3(b) and 3(c) are separated as shown in FIG. 3(a) by one 
picture element in the horizontal direction and by four picture elements 
in the vertical direction. Therefore, their correlativity becomes weak, 
particularly in the vertical direction. This results in information level 
difference between one picture element and another. In other words, the 
probability of having a high frequency component at a boundary between one 
block and another becomes high. In the case of the two-dimensional TAT 
system in particular, there are a large number of blocks. Therefore, the 
probability of having a high frequency component at the boundary between 
adjacent blocks further increases. An image signal converted by the the 
two-dimensional TAT method, therefore, tends to have as a whole many high 
frequency components included therein. 
In transmitting such an image signal, the high frequency component thereof 
greatly deteriorates if the transmissible band of the transmission line is 
narrow. 
This tends to result in transmission errors and generation of noises. That 
trouble may be avoidable by widening the transmissible band of the 
transmission line. Then, however, it increases the cost of the 
transmission system. 
Further, in the conventional information compressing transmission system, 
only a part of picture elements within some block to be processed in the 
mode C are sampled and transmitted as information data. In decoding the 
whole picture element information data of the block thus transmitted, an 
interpolating process is performed by using transmitted picture element 
information data for the non-transmitted picture elements. It has been 
inevitable, therefore, to have a certain degree of deterioration of the 
information. In the case of a fine image information signal in particular, 
it has been necessary to carry out a complex process of interpolation 
during a decoding operation for the purpose of minimizing the 
deterioration of information because of the above-stated poor 
correlativity among the picture elements sampled for transmission. 
SUMMARY OF THE INVENTION 
It is a general object of the present invention to provide an information 
signal transmission system which is capable of solving the above-stated 
problems. 
It is a more specific object of this invention to provide an information 
signal transmission system wherein the generation of high frequency 
components is minimized and the deterioration of information signals can 
be prevented even in the event of a transmission line allowing only a 
narrow transmissible band. 
Under this object, an information signal transmission system arranged 
according to this invention to divide an original image information signal 
which consists of information signals including a number k.times.l (k and 
l: positive integers) of picture elements into a plurality of small 
blocks, each block grouping a number m.times.n (m and n: positive 
integers) of picture elements; to have a plurality of compressing modes of 
different information compressing rates; and to compress the information 
signal for each of the blocks in one of the plurality of compressing modes 
in transmitting these information signals comprises: first compressed 
information signal forming means for forming and producing for every one 
of the blocks, a first compressed information signal consisting solely of 
information signals for specific picture elements included in the block; 
first memory means for storing the first compressed information signal; 
second compressed information signal forming means for forming and 
producing, at least for some of the blocks,a second compressed information 
signal consisting of information signals for picture elements other than 
the specific picture elements; second memory means for storing the second 
compressed information signal; compressing mode signal generating means 
arranged to determine one of the plurality of compressing modes to be used 
in compressing the information signal of each block and to produce a 
compressing mode signal representing the compressing mode thus selected; 
and transmission signal forming means arranged to read out, according to 
the compressing mode signal generated by the compressing mode signal 
generating means, the first and second compressed information signal 
corresponding to the sequence of picture elements horizontally aligned 
within the original image information signal from the first and second 
memory means and to form a transmission signal by using the first and 
second compressed information signals thus read out. 
It is another object of this invention to provide an information signal 
transmission system which is capable of transmitting an image information 
signal in a manner whereby the original image information signal is 
restorable to an adequate degree without necessitating any process for 
discrimination of the above-stated compressing mode. 
Under that object, an information signal transmission system arranged 
according to this invention to divide each field portion of an original 
image information signal which consists of information signals including a 
number k.times.l (k and l: positive integers) of picture elements into a 
plurality of small blocks, each block grouping a number m.times.n (m and 
n: positive integers) of picture elements; to have a plurality of 
compressing modes of different information compressing rates; and to 
compress the information signal of each of the blocks in one of the 
plurality of compressing modes in transmitting these information signals 
comprises: suppressing means for suppressing the high frequency component 
of each field portion of the original image information signal; first 
compressed information signal forming means for forming and producing for 
every one of the blocks of the original image information signal having 
the high frequency component thereof suppressed by the suppressing means, 
a first compressed information signal consisting solely of information 
signals for specific picture elements included in the block; first memory 
means for storing the first compressed information signal; second 
compressed information signal forming means for forming and producing, at 
least for some of the plurality of blocks of each field portion of the 
original image information signal, a second compressed information signal 
consisting of information signals for picture elements other than the 
specific picture elements; second memory means for storing the second 
compressed information signal; compressing mode signal generating means 
arranged to determine one of the plurality of compressing modes to be used 
in compressing the information signal of each block and to produce a 
compressing mode signal representing the compressing mode thus selected; 
reading means arranged to read out from the first memory means the first 
compressed information signal for every one of the plurality of blocks of 
each field portion of the original image information signal and to read 
out from the second memory means the second compressed information signal 
according to the compressing mode signal produced from the compressing 
mode signal generating means; and transmitting means for transmitting the 
first and second compressed information signals read out from the first 
and second memory means by the reading means and also for transmitting the 
compressing mode signal. 
It is a further object of this invention to provide an information signal 
transmission system which is capable of transmitting an information signal 
in a manner whereby the original image information signal is restorable to 
an adequate degree even in cases where it becomes impossible to detect one 
of the compressing modes in which the information signal for each of the 
blocks is transmitted. 
Under this object, an information signal transmission system arranged 
according to this invention to divide each field portion of an original 
image information signal which consists of information signals including a 
number k.times.l (k and l: positive integers) of picture elements into a 
plurality of small blocks, each block grouping a number m.times.n (m and 
n: positive integers) of picture elements; to have a plurality of 
compressing modes of different information compressing rates; and to 
compress an information signal representing each of the blocks in one of 
the plurality of compressing modes in transmitting these information 
signals comprises: suppressing means for suppressing the high frequency 
component of each field portion of the original image information signal; 
first compressed information signal forming means for forming and 
producing, for every one of the blocks of the original image information 
signal having the high frequency component thereof suppressed by the 
suppressing means, a first compressed information signal consisting solely 
of information signals for specific picture elements included in the 
block; first memory means for storing the first compressed information 
signal; second compressed information signal forming means for forming and 
producing, at least for a part of plurality of blocks of each field 
portion of the original image information signal, a second compressed 
information signal consisting of information signals for picture elements 
other than the specific picture elements; second memory means for storing 
the second compressed information signal; compressing mode signal 
generating means arranged to determine one of the plurality of compressing 
modes to be used in compressing the information signal for each block and 
to produce a compressing mode signal representing the compressing mode 
thus selected; reading means arranged to read out from the first memory 
means the first compressed information signal for every one of the 
plurality of blocks of each field portion of the original image 
information signal and to read out from the second memory means the second 
compressed information signal according to the compressing mode signal 
produced from the compressing mode signal generating means; transmitting 
means for transmitting the first and second compressed information signals 
read out from the first and second memory means by the reading means and 
also for transmitting the compressing mode signal; compressing mode signal 
error detecting means for detecting any error in the compressing mode 
signal transmitted by the transmitting means; and restoring means which, 
in the event of detection of any error by the compressing mode signal 
error detecting means, restores the original image information signal by 
using only the first compressed information signal out of the first and 
second compressed information signals transmitted in relation to the 
compressing mode signal detected as in error. 
Further objects and features of this invention will become apparent from 
the following detailed description of embodiments thereof taken in 
connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A VTR to which this invention is applied as an embodiment thereof is 
arranged as described below with reference to the accompanying drawings: 
In this case, in dividing one field of a TV image plane of the NTSC system 
into a plurality of blocks, each block is arranged to consist of 4.times.4 
picture elements. 
FIG. 5 shows in outline the arrangement of the recording system of the VTR 
embodying this invention. Referring to FIG. 5, one field portion of 
incoming analog video signal has all the picture element information 
signals thereof converted into a digital video signal by an A/D converter 
17. The digital video signal thus obtained is supplied to a field memory 
18, a skipping or thinning-out circuit 19 and a mode discriminating 
circuit 20. 
At the field memory 18, the digital video signal is stored in a state of 
carrying all picture element information for one field, i.e. in a state of 
a mode C digital video signal, with one address data added to each signal 
corresponding to one line of each block. The skipping circuit 19 is 
arranged to adjust the mode E digital video signal to an amount of 
information corresponding to the mode C. More specifically, the mode E 
digital video signal which is in a state as shown in FIG. 2(a) is thinned 
out to carry a number of picture elements into a mode C digital video 
signal as shown in FIG. 2(b). The mode C digital video signal which is 
thus obtained from the skipped or thinning-out circuit 19 is supplied to a 
mode discriminating circuit 20 and a memory 21. At the memory 21, the mode 
C digital video signal is stored with one address data added to each 
signal corresponding to one line of each block. 
The mode discriminating circuit 20 receives both the digital video signals 
of the modes E and C. An interpolating process is performed on the mode C 
digital video signal. After the interpolation, comparison is made for 
every block between an image signal obtained from the mode E digital video 
signal and another image signal obtained from the mode C digital video 
signal. The mode E is allotted to the block if a difference obtained by 
this comparison exceeds a given threshold value. The mode C is allotted to 
the block if the difference is less than the threshold value. A mode 
information signal is generated to effect this allotment. In other words, 
the mode information signal is generated to represent the mode E for a 
block which is dense on a field image plane and the mode C for a block 
which is sparse on the image plane. 
The mode information signals generated at the mode discriminating circuit 
20 are stored at a mode memory 22 and at the same time are also supplied 
to a counter 23. The counter 23 is arranged to receive a block 
synchronizing signal in addition to the mode information signal. This 
block synchronizing signal is in the form of clock pulses which are 
synchronized with a signal length corresponding to the number of picture 
elements of one block in the horizontal direction. At the counter 23, with 
the mode information signal and the block synchronizing signal received, 
the pulses of the block synchronizing signal are first counted. In case 
that the mode E is detected from the mode information signal, a counted 
value obtained up to that point of time is produced and supplied to a skip 
memory 24. The counter 23 is then reset. In other words, a counted value 
which corresponds to the number of mode C blocks preceding a mode E block 
is stored at the skip memory 24. 
An address signal generator 25 is arranged to receive the block 
synchronizing signal and a horizontal synchronizing signal. The horizontal 
synchronizing signal is a pulse signal synchronized with a line scanning 
process on the image plane. After detection of a pulse of the horizontal 
synchronizing signal, the address signal generator 25 up counts the pulses 
of the block synchronizing signal every time one pulse is detected. The 
counted value thus obtained is supplied from the generator 25 to a 
parallel-to-serial converter 26 as low order address data. 
The horizontal synchronizing signal is supplied also to an initial value 
setting circuit 27. At the circuit 27, high order address data 
corresponding to each line is generated every time one pulse of the 
horizontal synchronizing signal is detected. The address data thus 
generated is supplied to the parallel-to-serial converter 26. 
At the parallel-to-serial converter 26, the address data of high and low 
orders obtained in the above-stated manner are put otgether into one 
address data. The address data is supplied to the skip memory 24 as 
writing-in address data. At the skip memory 24, the counted value which is 
produced from the counter 23 is stored at an address designated by this 
writing-in address. 
FIGS. 4(a) and 4(b) show the mode information signal to be supplied to the 
mode memory 22 and the contents of the data to be written in the skip 
memory 24 in relation to each other. In the case of FIG. 4(a), a mode 
information signal which corresponds to the left end block of one line is 
in the mode E. FIG. 4(b) represents another case in which the same block 
is in the mode C. In both of these cases, a value which is obtained by 
adding the number "1" of the mode E block is added to the number of mode C 
blocks preceding each mode E block is stored. 
Next, a process for rearranging the digital video signal into the 
transmitting sequence as shown in FIG. 3(d) is as follows: The mode 
information signal which is stored at the mode memory 22 is continuously 
read out and supplied to a memory control circuit 28. Concurrently with 
this, a line discriminating circuit 29 detects whether the line being 
transmitted is an odd number line or an even number line by detecting the 
horizontal synchronizing signal. A discrimination signal which is thus 
produced from the circuit 29 is supplied to the memory control circuit 28. 
If the signal from the line discriminating circuit 29 represents an odd 
number line, the memory control circuit 28 continuously generates reading 
addresses of the field memory 18 at a speed which is 1/2 of the writing 
speed in case that the mode information signal represents the mode E. 
Then, the digital video signal is read out in the mode E. In the case of 
the mode C, the reading address is continuously generated at a speed equal 
to the writing speed and the digital video signal is read out in the mode 
C. The read out digital video signal is supplied to a switch circuit 30. 
When the output of an AND gate 31 is at a high level (hereinafter referred 
to as H level), the connecting position of the switch circuit 30 is on one 
side H thereof. In this instance, the digital video signal read out from 
the field memory 18 is supplied to a D/A converter 32. If the output of 
the AND gate 31 is at a low level (hereinafter referred to as L level), 
the position of the switch circuit 30 is on the other side L thereof. In 
that instance, the digital signal read out from the memory 21 is supplied 
to the D/A converter 32. The AND gate 31 is arranged to receive the mode 
information signal from the mode memory 22 and the discrimination signal 
from the line discriminating circuit 29. In case that the discrimination 
signal indicates an odd number line (L level), the digital video signal is 
supplied to the D/A converter 32 from the field memory 18 when the mode 
information signal is in the mode E (at an H level) and is supplied from 
the memory 21 when the mode information signal is in the other mode C (at 
an L level). Further, in case that the discrimination signal indicates an 
even number line (at an H level), the digital video signal is supplied to 
the D/A converter 32 from the field memory 18 irrespective as to whether 
the mode information signal represents the mode E or the mode C. 
In the case of the even number line, the block of the mode C does not 
include any digital video signal as shown in FIG. 3(a). Therefore, in that 
case, the signal of the mode E block is continuously read out for the 
purpose of keeping a data rate unvarying. First, at the memory control 
circuit 28, an address within the skip memory 24 is designated for a block 
corresponding to the left end of the image plane and the content of the 
skip memory is read out. The term "content" means the above-stated stored 
value obtained by adding the number of the mode E block "1" to the number 
of mode C blocks preceding the mode E block. Therefore, the content of the 
skip memory 24 thus read out is added to the initial value of address of 
the field memory 18. Then, by using the result of this addition as a 
reading address, an address of the field memory 18 is designated and the 
digital video signal of a next mode E block is read out. After that, every 
time a mode E block is detected, the content of an address corresponding 
to the position of that block is read out from the skip memory 24. Then, 
the content thus read out is added to the address of the mode E block 
within the field memory 18. The result of this addition is used as a 
reading address and an address of the field memory 18 is designated. With 
the address thus designated, the digital video signal of the next mode E 
block is read out. 
With the signals of the odd and even number lines processed by controlling 
the process of read-out from the field memory 18, the memory 21 and the 
skip memory 24 by means of the memory control circuit 28, a signal of 
constant data rate can be obtained. The digital video signal thus 
processed is supplied to an D/A converter 32 to be converted into an 
analog signal with the band thereof compressed by 1/2. The compressed 
signal is applied to a low-pass filter (hereinafter referred to as LPF) 33 
for band limitation. After this, the signal is subjected to a recording 
process accomplished for recording on a tape at a recording part 34 
together with the mode information signal produced from the mode memory 
22. 
The above-stated operation of this embodiment is arranged to divide the 
signal into blocks which have four lines of picture elements in the 
vertical direction. Therefore, the mode information signals for these 
lines are stored at the mode memory 22 and are read out from th e memory 
22 every time one line is processed. 
FIG. 6 shows in outline the arrangement of the reproducing system of the 
VTR arranged to reproduce the information signal recorded by the recording 
system shown in FIG. 5. Referring to FIG. 6, the analog video signal which 
is compressed to have 1/2 of its original bandwidth and the mode 
information signal are reproduced by a reproducing part 35 from a tape 
which is not shown. The reproduced analog video signal is supplied to an 
A/D/ converter 36 to be converted into a digital video signal while the 
reproduced mode information signals are supplied to and stored at a mode 
memory 37. The digital video signal produced from the A/D converter 36 is 
supplied to a field memory 38. A process of writing into the field memory 
38 is performed under the control of a writing time control circuit 39. 
The writing time control circuit 39 is arranged to receive also the 
reproduced mode information signals. When the digital video signal is 
detected to be of the mode E by means of the mode information signal 
supplied, the digital video signal is written into the field memory 38 at 
a normal speed. If the digital video signal is detected to be of the mode 
C through the mode information signal, the digital video signal is written 
into the field memory 38 at a speed which is 1/2 of the normal speed. 
The digital video signal which is thus written into the field memory 38 is 
read out block by block by means of a reading control circuit 40 and is 
supplied to a switch 41. 
The switch 41 is arranged to have it connecting position changed from one 
position over to the other according to the mode information signal which 
is produced from the mode memory 37 concurrently with commencement of 
reading from the field memory 38. The position of the switch 41 shifts to 
one side E in case that the mode information signal represents the mode E 
and to the other side C if it represents the mode C. 
The digital video signal which is read out block by block from the field 
memory 38 is supplied to a field memory 42 if it is determined to be in 
the mode E by the mode information signal. In case that the video signal 
is in the mode C, the signal is subjected to an interpolation process 
which is performed at a C mode interpolation circuit 43 block by block to 
interpolate for the picture element information not transmitted by 
utilizing the picture element information which has been transmitted. 
After completion of the interpolation, the interpolated signal is supplied 
to the field memory 42. 
At the field memory 42, one field portion of the digital video signal is 
processed and stored in a manner as mentioned in the foregoing. After 
that, the signal is read out from the field memory 42 by the reading 
control circuit 40 and is supplied to a D/A converter 43. The signal is 
converted into an analog video signal and is produced from the D/A 
converter 43 as a video signal. 
The analog video signal and the mode information signal which are recorded 
on the tape are reproduced through the operation described above in the 
same form of signal as the form in which they are supplied during 
recording. 
In the embodiment described, a number 4.times.4 of picture elements are 
grouped into each of the blocks forming one image plane. However, in 
accordance with this invention, this block arrangement may be changed in a 
suitable manner. 
The VTR arranged according to this invention as described in the foregoing 
is capable of transmitting an information signal in a state of having it 
high frequency component suppressed with simple structural arrangement. 
Another embodiment in which this invention is also applied to a VTR is 
arranged as follows: In dividing one field of a TV image plane of the NTSC 
system into a plurality of blocks, each block is arranged to include 
4.times.4 picture elements in the same manner as in the case of the VTR 
shown in FIG. 5. 
FIG. 12 shows in outline the arrangement of the recording system of the VTR 
which is arranged as the above-stated another embodiment. One field 
portion of an incoming analog video signal is converted into a digital 
video signal by the A/D converter 44. The digital video signal is supplied 
to a field memory 45, a pre-filter 46 and a mode discriminating circuit 
47. At the field memory 45, the digital signal is stored in a state of 
including all the picture elements of one field portion of the signal. In 
other words, a digital video signal having all the picture element blocks 
in the mode E is stored at the field memory 45. The pre-filter 46 is a 
two-dimensional low-pass filter which is arranged to remove the high 
frequency component of the digital video signal. The digital video signal 
of the mode E is averaged by this filter 46. The averaged digital video 
signal of the mode E is thinned out into a digital video signal of the 
mode C to have 1/4 of the picture elements by a skipping or thinning out 
circuit 48 as shown in FIG. 2(b). The digital video signal of the mode C 
which is thus obtained from the circuit 48 is supplied to a mode 
discriminating circuit 47 and a memory 49. The memory 49 then stores the 
digital video signal of the mode C. 
The mode discriminating circuit 47 is arranged to receive both the digital 
video signal of the mode E and that of the mode C. An interpolating 
process is performed on the digital video signal of the mode C. After 
that, the circuit 47 compares for every block an image signal obtained 
from the digital video signal of the mode E with an image signal obtained 
from the interpolated digital video signal of the mode C and temporarily 
stores information on an error or difference between the two. Then, the 
mode E is allocated at a predetermined rate to the block in case that the 
difference is large and the mode C is allocated to the block at a 
predetermined rate in the event of a small difference. The circuit 47 then 
generates a mode information signal according to the allocation. In other 
words, the mode information signals are generated to represent the mode E 
for a block having dense information within the one-field image plane and 
to represent the mode C for a block having sparse information. 
In order to made unvarying the length of time required in transmitting each 
field portion of the video signal, the ratio between the number of blocks 
to be transmitted in the mode C and that of blocks to be transmitted in 
the mode E must be fixed. 
In the case of this embodiment, with one image plane divided into a 
plurality of blocks, all the blocks are sampled in the mode C. After that, 
the blocks in a dense part of the image are further sampled in the mode E. 
In this instance, if the transmitting band is to be compressed to a degree 
of 1/2 as a whole, for example, the desired rate of compression is 
attainable by allocating the mode E to 1/4 of all the blocks to be 
transmitted. Further, in allocating the mode information signal to these 
blocks, the difference information values off all the blocks stored are 
arranged in the order of largeness of the value and the mode E is 
allocated to 1/4 of the blocks having larger difference values by setting 
a threshold value at a suitable value for that purpose. Then, the 
threshold value is compared with error or difference information. The mode 
E is allocated to the blocks having difference values larger than the 
threshold value. With the modes E and C allocated in this manner for 
transmission, the transmitting band compressing rate becomes 1/2 as a 
whole. 
The mode information signal which is thus produced at the mode 
discriminating circuit 47 in the manner as described above is stored at a 
mode memory 50. 
FIG. 7 shows by way of example the above-stated mode information signals as 
allocated to blocks on an image plane. The allocation on the image plane 
of the picture elements within each of the blocks to be transmitted 
according to the mode information signals becomes as shown in FIG. 8. 
In actuality, however, it is the information on the picture elements of the 
mode C blocks which are as shown in FIG. 9 and the information on the 
picture elements of the mode E blocks which are as shown in FIG. 10 that 
is actually transmitted. These data are read out from a memory 49 and a 
field memory 45 by means of a memory control circuit 51 which will be 
described later. For example, one field portion of the mode C picture 
elements is transmitted during the first half of one field period while 
one field portion of the mode E picture elements is transmitted during the 
latter half of the same one-field period in a separate manner as shown in 
FIG. 11. 
As apparent from FIGS. 9 and 10, for the groups or blocks to which the mode 
E is allocated have all of their picture elements transmitted. Therefore, 
considering each block in a one-dimensional manner, the transmitting band 
in the mode E is four times as much as the transmitting band of the mode C 
within one block. However, since the modes E and C are allocated in the 
ratio of 1:4 within one field image plane, the transmitting band of the 
first half of one field period becomes equal to that of the latter half of 
the same field period with the picture element information data arranged 
to be transmitted at a constant speed and at equal intervals. 
The memory control circuit 51 is arranged to operate as shown in a flow 
chart in FIG. 13. Referring to FIG. 13, upon completion of writing the 
information signals of all the picture element blocks of one field portion 
into the memory 49 and the field memory 45 in the manner as described 
above, the memory control circuit 51 begins to read out the signals from 
the memories. At the memory control circuit 51, reading address signals 
are first generated for reading from the memory 49 the information signals 
representing the mode C picture elements included in the blocks of one 
field. An address of the memory 49 is designated by using the address 
signal thus generated. The information signals representing the mode C 
picture elements are read out and supplied to a change-over switch 52. The 
memory control circuit 51 has been supplied with a synchronizing signal 
generated by a synchronizing signal generating circuit 53. The addresses 
are up counted in synchronism with this synchronizing signal. Then, 
according to these addresses, the information signals representing the 
mode C picture elements are read out one after another during the 1/2 
field period at a speed which is twice as fast as the speed at which these 
signals have been written in. This synchronizing signal is a pulse signal 
of such a frequency that enables the information signals of all the mode C 
picture elements to be completely read out during the 1/2 field period. At 
the memory control circuit 51, the mode information signals are stored at 
the mode memory 50 are also read out while the information signals 
representing the mode C picture elements are read out from the memory 49. 
The mode information signals are supplied also to the memory control 
circuit 51. The memory control circuit 51 is provided with a mode E 
detector, an address counter and a counter memory for the purpose of 
detecting the addresses of the information signals representing the 
picture elements of blocks designated to be in the mode E among the 
information signals representing all the picture elements stored at the 
field memory 45. This address counter up counts the addresses in 
synchronism with the reading clock pulses applied to the mode memory 50. A 
counted value obtained at the address counter when a mode information 
signal representing the mode E is detected by the E mode detector is 
stored at the counter memory. Upon completion of reading the information 
signals representing the mode C picture elements from the memory 49, the 
information signals representing the mode E picture elements are 
continuously read out from the field memory 45 according to the addresses 
stored at the counter memory. The information signals thus read out are 
supplied to the change-over switch 52. The process of reading, from the 
field memory 45, the information signals for the mode E picture elements 
also comes to an end within 1/2 field period. 
The information signals for the mode C and mode E picture elements which 
are thus read out from the memory 49 and the field memory 45 are supplied 
via the change-over switch 52 to a D/A converter 54 in the state as shown 
in FIG. 11. The operation of the change-over switch 52 is under the 
control of the memory control circuit 51. The connecting position of the 
change-over switch 52 is on one side C thereof while the information 
signals for the mode C picture elements are being read out and on the 
other side E thereof while the information signals for the mode E picture 
elements are read out. 
The output of the change-over switch 52 is converted into an analog signal 
by the D/A converter 54. The analog signal thus obtained is supplied to a 
lowpass filter 55 for band limitation. After this band limiting process, 
the signal is recorded by a recording part 56 together with the mode 
information signals. 
As described above, an image information signal is divided for transmission 
into information signals for the mode C picture elements and information 
signals for the mode E picture elements for all the divided blocks. By 
virtue of this arrangement, the information signals for the mode C picture 
elements can be decoded without necessitating any mode information signal 
during the process of decoding. In other words, in the event of occurrence 
of any error in the mode information signal during a transmission process, 
the decoding process can be accomplished by means of the information 
signals for the mode C picture elements. 
FIG. 14 shows in outline the arrangement of the reproducing system for 
reproducing the information signal recorded by the recording system of the 
VTR shown in FIG. 12. The reproducing operation of the system is as 
follows: Referring to FIG. 14, a reproducing part 57 reproduces an image 
information signal and a mode information signal. These signals are 
respectively supplied to an A/D converter 58 and a mode error detecting 
circuit 59. The image information signal which is an analog signal is 
converted into a digital signal by the A/D converter 58. The digital 
signal is supplied to a switch 60. Meanwhile, a synchronizing signal which 
is reproduced by the reproducing part 57 has been supplied also to the 
switch 60. The switch 60 divides the recorded digital image information 
signal into mode C picture element information signals and mode E picture 
element information signals. These divided information signals are stored 
at a mode C memory 61 and a mode E memory 62 as applicable. The connecting 
position of the switch 60 is shifted from one side C to the other side E 
thereof at intervals of 1/2 field period in synchronism with the 
above-stated synchronizing signal. 
The reproduced mode information signal on the other hand is stored at a 
mode memory 63. Meanwhile, the mode error detecting circuit 59 detects the 
number of signals representing the mode E included in all the mode 
information signals reproduced. The circuit 59 counts this number. The 
number of blocks to which the mode E is allocated within one field during 
recording is predetermined and fixed. Therefore, with the number of the 
mode E blocks counted during the reproducing operation, the circuit 59 
determines that there is no error in the mode information when the count 
number coincides with the predetermined number and determines that the 
mode information is in error if the count number differs from the 
predetermined number. 
In case that the mode information signal is determined to be in error at 
the mode error detecting circuit 59, an error detection signal is supplied 
from the mode error detecting circuit 59 to a mode conversion circuit 64. 
In response to this error detection signal, the mode conversion circuit 64 
reads out the mode information signals stored at the mode memory 63 and 
converts all the mode information signals into mode information signals 
representing the mode C. If the mode information signal is determined to 
be correct at the mode error detecting circuit 59, the signals read out 
form the mode memory 63 is produced as they are through the mode 
conversion circuit 64. 
The mode information signals which are thus produced from the mode 
conversion circuit 64 are supplied to a reading control circuit 65. The 
reading control circuit 65 reads out picture element information signals 
stored at the mode C memory 61 and the mode E memory 62 respectively 
according to the mode information signals received. The information of the 
mode C picture elements read out from the mode C memory 61 is interpolated 
at a mode C interpolating circuit 66 with the transmitted picture element 
information for the picture element information not transmitted. The 
interpolated picture element information is stored at a field memory 67 
while the mode E picture element information is stored as it is at the 
field memory 67. One field portion of the image information signal is 
stored at the field memory 67 in this manner. 
After that, the image information signal stored at the field memory 67 is 
read out according to a control signal produced from the reading control 
circuit 65. The signal thus read out is supplied to a D/A converter 68 to 
be converted into an analog video signal before it is produced from the 
reproducing system. 
While this invention is applied to a VTR in the case of the embodiment 
described, the invention is applicable also to apparatuses of other kinds 
such as a video disc apparatus, various recording/reproducing apparatuses, 
communication apparatuses, etc. 
In the embodiment described, each of the divided picture element blocks is 
arranged to include 4.times.4 picture elements. However, this block 
arrangement may be changed as desired. Further, in generating the data of 
the mode C picture elements, the whole picture element data of each block 
are first subjected to band limitation before thinning out the mode C 
picture element data. Therefore, during reproduction, even if the mode C 
picture elements are restored using only the mode C data with the mode 
information signal incorrectly reproduced due to an error or drop-out or 
the like, the quality of a reproduced picture can be prevented from 
deteriorating. 
In accordance with this invention, as described in the foregoing, even in 
cases where only a part of picture elements within one block are 
transmitted during the recording and reproducing operation of the VTR, 
information can ba prevented from deteriorating during a decoding process. 
Even in the event of occurrence of an error in the mode information signal 
during a transmission process, at least a portion of picture element 
information signals are transmitted, so that the deterioration of the 
information thus transmitted can be minimized. 
As apparent from the foregoing description of the embodiment of this 
invention, the VTR according to this invention is capable of minimizing 
deterioration of information with simple structural arrangement, so that 
information can be reproduced in a satisfactory state.