Method and apparatus for transmitting a video signal, and apparatus for receiving a video signal

A video transmission apparatus that has a first input terminal for receiving a low-resolution TV signal. The apparatus also has a second input terminal for receiving a high-resolution TV signal and for outputting said high-resolution TV signal. The apparatus converts the low-resolution TV signal into a signal having a format which is equal to that of the high-resolution TV signal. The apparatus selects either the signal, which has been produced by converting low-resolution TV signal into a signal having a format which is equal to that of the high-resolution TV signal, or the high-resolution TV signal, which is outputted from the second input terminal The signal, which has been produced by converting low-resolution TV signal into a signal having a format which is equal to that of the high-resolution TV signal, is fitted into the high-resolution TV signal. The apparatus encodes the selected signal into a digital high-efficiency coded signal, and outputs a signal indicative thereof. Finally, the apparatus transmits the signal produced by encoding the selected signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for converting a video signal 
such as a television signal into a digital high-efficiency coded signal 
and transmitting it, a video signal transmission apparatus for use in the 
method, and a video signal reception apparatus. 
2. Description of the Related Art 
In recent years, a system for transmitting and receiving a high-resolution 
television signal (hereinafter referred to as a high-resolution TV signal) 
has been developed as a new method for transmitting and receiving a TV 
signal. The high-resolution TV signal has a larger number of scanning 
lines than that of scanning lines of a TV signal of the currently-used 
NTSC system (hereinafter referred to as a low-resolution TV signal), and 
allows an image to be formed more clearly. 
To watch high-resolution television, a high-resolution television set for 
receiving and demodulating a high-resolution TV signal is needed. Since, 
however, most of viewers have NTSC television sets, if they replace the 
NTSC television sets with high-resolution television sets, the NTSC 
television sets will be useless, as will be program sources of the NTSC 
system. Therefore, producers of TV programs wish to transmit the 
low-resolution TV signals as well as the high-resolution TV signals. If, 
however, a transmission path for the high-resolution TV signal and a 
transmission path for the low-resolution TV signal are formed separately 
from each other, it is difficult to assign transmission bands to these 
transmission paths. 
In order to popularize the methods for transmitting and receiving a 
high-resolution TV signal, television sets, such as HDTV (high definition 
television) sets and NTSC television sets, that the viewers possess at 
present, need to be used effectively. Further, it is necessary to devise 
the methods so as not to make program video sources of the NTSC system 
useless. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a method 
for transmitting a video signal, a video signal transmission apparatus for 
use in the method, and a video signal reception apparatus, in which a 
plurality of low-resolution TV signals can be transmitted with efficiency 
through a transmission path for a digital high-efficiency coded signal of 
a high-resolution TV signal, thereby effectively utilizing the 
transmission path and high-resolution TV sets without making program 
sources and currently-used low-resolution TV sets useless. 
According to a first aspect of the present invention, there is provided a 
method for transmitting a video signal, comprising: 
a step of synthesizing a plurality of low-resolution TV signals input from 
corresponding input terminals by synthesizing means, and outputting a 
multichannel low-resolution TV signal whose format is equal to that of a 
high-resolution TV signal; 
a step of converting the multichannel low-resolution TV signal into a 
digital high-efficiency coded signal by coding means, the multichannel 
low-resolution TV signal being processed in the same manner as the 
high-resolution TV signal is; and 
a step of transmitting the digital high-efficiency coded signal through A 
transmission path. 
According to a second aspect of the present invention, there is provided a 
video signal transmission apparatus comprising: 
input terminals from which a plurality of low-resolution TV signals are 
input; 
synthesizing means for synthesizing the plurality of low-resolution TV 
signals and outputting a multichannel low-resolution TV signal whose 
format is equal to that of a high-resolution TV signal; 
encoding means for converting the multichannel low-resolution TV signal 
into a digital high-efficiency coded signal; and 
transmitting means for transmitting a signal output from the encoding 
means. 
According to a third aspect of the present invention, there is provided a 
video transmission apparatus comprising: 
a first input terminal from which a low-resolution TV signal is input; 
a second input terminal from which a high-resolution TV signal is input; 
converting means for converting the low-resolution TV signal into a signal 
having a format which is equal to that of the high-resolution TV signal; 
selecting means for fitting the signal output from the converting means 
into the high-resolution TV signal; 
encoding means for converting a signal output from the selecting means into 
a digital high-efficiency coded signal; and 
transmitting means for transmitting a signal output from the encoding 
means. 
According to a fourth aspect of the present invention, there is provided a 
video reception apparatus comprising: 
an input terminal supplied with a multichannel low-resolution TV signal 
generated by synthesizing a plurality of low-resolution TV signals; 
decoding means for decoding the multichannel low-resolution TV signal; 
display processing means for converting a signal output from the decoding 
means, which corresponds to one of the plurality of low-resolution TV 
signals, into a display signal; and 
display means for displaying a signal output from the display processing 
means. 
In the above method and apparatuses, the transmission path and 
high-resolution TV sets can be utilized effectively, without making 
currently-used low-resolution TV program sources useless.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described, with reference 
to the accompanying drawings. 
FIG. 1 schematically shows a system for transmitting and receiving a video 
signal according to one embodiment of the present invention. FIG. 2 shows 
channels ch1 to ch4 of low-resolution TV signals in order to explain an 
operation of the system shown in FIG. 1. 
In FIG. 1, the low-resolution TV signals of the channels ch1 to ch4 are 
supplied to their respective terminals 101 to 104. The terminals 101 to 
104 are connected to a picture synthesizing circuit 110. Pictures P1 to P4 
of the low-resolution TV signals of the channels ch1 to ch4 are 
synthesized by the picture synthesizing circuit 110 in such a manner that 
they are fit into a single picture PM as shown in FIG. 2 to generate a 
multichannel low-resolution TV signal (which is a four-picture signal in 
FIG. 2). The multichannel low-resolution TV signal is then supplied from 
the picture synthesizing circuit 110 to one input terminal of a selection 
circuit 118. The other input terminal of the selection circuit 118 is 
supplied with a high-resolution TV signal from a terminal 107. The 
selection circuit 118, which is controlled by a control signal supplied 
from a control terminal 108, selects a signal from the picture 
synthesizing circuit 110 or the terminal 107 and supplies the selected 
signal to a high efficiency encoding circuit 111 included in an HDTV (high 
definition television) encoder 120. The HDTV encoder 120 also includes a 
buffer circuit 112 for receiving a signal output from the high efficiency 
encoding circuit 111. 
The high efficiency encoding circuit 111 converts a signal output from the 
selection circuit 118 into a high-efficiency-encoded signal and supplies 
it to the buffer circuit 112. The buffer circuit 112 is intended to smooth 
the encoded signal so as to have a fixed transmission rate and send it to 
a transmission path 113. When the amount of information of the encoded 
signal becomes large, the buffer circuit 112 controls the 
high-efficiency-encoding circuit 111 to reduce the amount. 
The signal transmitted through the transmission path 113 is supplied to a 
buffer circuit 114 arranged in an HDTV decoder 121 and stored therein. A 
signal having a fixed transmission rate is supplied from the buffer 
circuit 114 to a decoding circuit 115 and decoded therein. The decoded 
signal is supplied to a display processing circuit 116. 
When the display processing circuit 116 detects that the signal decoded by 
the decoding circuit 115 is a high-resolution TV signal, it supplies the 
decoded signal to an HDTV monitor 117 as it is. When the display 
processing circuit 116 detects that the decoded signal is a multichannel 
low-resolution TV signal, it processes an image in response to a control 
signal supplied to a terminal 106 from a user. 
FIGS. 3A and 3B show examples of display pictures formed in accordance with 
a processing mode of the display processing circuit 116. FIG. 3A shows a 
display of four pictures synthesized by the picture synthesizing circuit 
110, FIG. 3B shows a display of an enlarged one of the four pictures 
synthesized on the transmission side, and FIG. 3C shows a display of a 
main picture (master picture) obtained by enlarging one of the four 
pictures synthesized on the transmission side and a sub-picture (slave 
picture) corresponding to another one of the four pictures. 
An operation of the picture synthesizing circuit 110 will be described, 
with reference to FIGS. 4 and 5A to 5C. 
In FIG. 4, low-resolution TV signals of channels ch1 and ch4 are supplied 
to the terminals 101 to 104. The signal from the terminal 101 is supplied 
to memories 610 and 611, the signal from the terminal 102 is supplied to 
memories 612 and 613, the signal from the terminal 103 is supplied to 
memories 614 and 615, and the signal from the terminal 104 is supplied to 
memories 616 and 617. The memories 610 and 611 are controlled alternately 
by a control circuit (not shown) that one of them is set in a write mode 
and the other is set in a read mode. Similarly, the memories 612 and 613 
are controlled alternately by the control circuit, as are the memories 614 
and 615 and the memories 616 and 617. An input signal is written to the 
memories in the write mode, and a stored signal is read out from the 
memories in the read mode. The outputs of the memories 610 and 611 are 
supplied to a switch 620, the outputs of the memories 612 and 613 are 
supplied to a switch 621, the outputs of the memories 614 and 615 are 
supplied to a switch 622, and the outputs of the memories 616 and 617 are 
supplied to a switch 623. These switches 620 to 623 are controlled by a 
control circuit (not shown) so that a signal is selectively read out from 
the memories in the read mode. The read speed is faster than the write 
speed, and a picture corresponding to the read-out signal is reduced to, 
for example, 1/4 of a picture corresponding to the input signal. The 
output signals from the switches 620 to 623 are transmitted to a selecting 
circuit 630. 
In the picture synthesizing circuit 110, the data writing frequency of each 
of the memories is, for example, 13.5 MHz, and the data reading frequency 
thereof is, for example, 54.0 MHz. 
FIG. 5 are timing charts for explaining an operation of the selecting 
circuit 630. The selecting circuit 630 is supplied with control signals C1 
and C2 from a control circuit (not shown) through terminals 606 and 607. 
The terminals 606 and 607 are supplied with control signals C1 and C2 
shown in FIGS. 5A and 5B, respectively. In FIG. 5B, T4 and T5 each 
represent a one-line period of a low-resolution TV signal, and T6 
represents a period of the sum of periods T4 and T5 which is a one-line 
period of the multichannel low-resolution TV signal shown in FIG. 2 (a 
picture PM). In FIG. 5A, T1 and T2 each represent a 1/2 vertical period of 
the multichannel low-resolution TV signal shown in FIG. 2 (a picture PM), 
and T3 represents one vertical period (one-frame period) of the 
multichannel resolution-low TV signal shown in FIG. 2. The selecting 
circuit 630 selectively outputs the signals from the switches 620 and 621 
during the period T1, and outputs the signal from the switch 620 during 
the period T4 and the signal from the switch 621 during the period T5. 
Further, the selecting circuit 630 selectively outputs the signals from 
the switches 622 and 623 during the period T2, and outputs the signal from 
the switch 622 during the period T4 and the signal from the switch 623 
during the period T5. As a result, channel signals are output from an 
output terminal 605 of the selecting circuit 630 in the sequence shown in 
FIG. 5C. More specifically, signals of channels ch1 and ch2 are output 
alternately for each line during the period T1 in which the control signal 
C1 is at a low level, and signals of channels ch3 and ch4 are output 
alternately for each line during the period T2 in which the control signal 
C1 is at a high level, with the result that a picture of the multichannel 
low-resolution TV signal includes pictures of the channels ch1 and ch2 
arranged on the upper side and those of the channels ch3 and ch4 arranged 
on the lower side. More specifically, in the picture synthesizing circuit 
110, the same lines of a plurality of low-resolution TV signals are 
sampled in sequence to generate a signal corresponding to one line of a 
high-resolution TV signal, with the result that the low-resolution TV 
signals are synthesized into a multichannel low-resolution TV signal. 
The multichannel low-resolution TV signal is the same as the 
high-resolution TV signal in line frequency, vertical frequency, and the 
like. Therefore, like the high-resolution TV signal, the multichannel 
low-resolution TV signal can be encoded and decoded. 
The multichannel low-resolution TV signal output from the terminal 605 is 
high-efficiently encoded by the high-efficient encoding circuit 111. If, 
when the picture signals of the four channels are high-efficiently 
encoded, the amount of information of a picture signal of one of the 
channels is increased and the amount of information of picture signals of 
the other channels is decreased, the total amount of information is not 
decreased, and the encoded signals can be transmitted without degrading 
the image quality of the picture signal of the channel having a large 
amount of information. 
In a low-resolution TV signal transmission mode, the signal output from the 
picture synthesizing circuit 110 is input to the HDTV encoder 120 through 
the selecting circuit 118. In a high-resolution TV signal transmission 
mode, the high-resolution TV signal supplied from the input terminal 107 
is selected by the selecting circuit 118 and then supplied to the HDTV 
encoder 120. During the selection of the high-resolution TV signal, the 
selecting circuit 118 is able to select one of the low-resolution TV 
signals to produce a video signal representing a picture of the selected 
low-resolution TV signal which is fit into a picture of the 
high-resolution TV signal and, in this case, a control signal is supplied 
from a timing control circuit (not shown) to the control terminal 108 of 
the selecting circuit 118. Assuming that a picture of the low-resolution 
TV signal of channel ch1 is fit into a picture of the high-resolution TV 
signal, the memories 610 and 611 and switches 620 and 630 in the picture 
synthesizing circuit 110 operate as converting means for converting the 
low-resolution TV signal so that it can be fit into part of the picture of 
the high-resolution TV signal. This operation is substantially the same as 
the above-described picture synthesizing operation. Therefore, one 
low-resolution TV signal output from the switch 620 is selected by the 
selecting circuit 630 and then supplied to the selecting circuit 118. 
FIG. 6 specifically shows the display processing circuit 116. Assume that a 
plurality of low-resolution TV signals are decoded by the decoding circuit 
115 of the HDTV decoder 121. The signals output from the decoding circuit 
115 in FIG. 1 are supplied to an input terminal 801 and then a switch 810. 
When the low-resolution TV signals are supplied, the switch 810 directly 
guides the signals from the input terminal 801 to a switch 821 in response 
to a control signal (mode selection signal) from the terminal 106, or 
supplies it to a memory 811 or a memory 813. When the display mode shown 
in FIG. 3A is selected in response to the control signal from the terminal 
106, the signal of the input terminal 801 is supplied to the switch 821 as 
it is, and the switch 821 guides the input signal to an output terminal 
802. 
When the display mode shown in FIG. 3B is selected, the switch 810 supplies 
one of four picture signals of the input terminal 801 to the memory 811 in 
response to the control signal inputted from the input terminal 106. The 
memory 811 receives the picture signal under control of a write control 
circuit (not shown). The output signal of the memory 811 is supplied to an 
interpolation circuit 812. The interpolation circuit 812 interpolates the 
scanning lines of the signal supplied from the memory 811 in order to 
convert it into a signal to be displayed on a high-resolution display. The 
output of the interpolation circuit 812 is supplied to the output terminal 
802 through the switches 820 and 821. 
When the display mode shown in FIG. 3C is selected, one of four picture 
signals of the input terminal 801, which is designated as a master 
picture, is written to the memory 811, and another one of the picture 
signals, which is designated as a slave picture, is written to the memory 
813. The output signal of the memory 811 is input to the interpolation 
circuit 812. The data writing frequency of each of the memories 811 and 
813 is 54 MHz, and the data reading frequency thereof is also 54 MHz. The 
interpolation circuit 812 interpolates the scanning lines of the signal in 
order to convert it into a master picture signal. The output signal of the 
memory 813 is supplied to a reduction/expansion circuit 814 and 
reduced/expanded in the time basis direction in order to convert it into a 
slave picture signal. The switch 820 selects the output signal of the 
reduction/expansion circuit 814 during a period corresponding to the slave 
picture, and selects the output signal of the interpolation circuit 812 
during a period corresponding to the master picture. The output signal of 
the switch 820 is transmitted to the output terminal 802 through the 
switch 821. The write clocks of the memories 811 and 813 are synchronized 
with each other by a timing control circuit (not shown), as are the read 
clocks thereof, and the read start timing is controlled in order to 
determine display positions of the master and slave pictures. Furthermore, 
the switch 820 is controlled by the timing control circuit. 
When the high-resolution TV signal is decoded, the signal of the input 
terminal 801 is supplied to the output terminal 802 through the switches 
810 and 821. 
In the system of the above embodiment, a plurality of low-resolution TV 
signals can be synthesized and the synthesized signal can be transmitted 
as a multichannel low-resolution TV signal from the transmission side, and 
the multichannel low-resolution TV signal can be processed and displayed 
in an arbitrary mode on the reception side. This system can be applied to 
a system for transmitting and receiving a high-resolution TV signal. More 
specifically, since a plurality of low-resolution TV signals can be 
transmitted efficiently through a transmission path for a digital 
high-efficiency coded signal into which the high-resolution TV signal is 
converted, the transmission path and high-resolution television sets can 
be used effectively, and program sources of the NTSC system recorded on 
magnetic tapes or the like can be prevented from being made useless. 
FIG. 7 is a block diagram showing a system for transmitting and receiving 
video signal according to another embodiment of the present invention. 
This embodiment is intended to offer a convenience to a user having a 
low-resolution TV signal monitor 213. In FIG. 7, the descriptions of the 
elements denoted by the same numerals as those in FIG. 1 are omitted. When 
the low-resolution TV signals of channels ch1 to ch4 are supplied to 
terminals 101 to 104, respectively, a high-efficiently encoded 
multichannel low-resolution TV signal is supplied to a selecting circuit 
210 through a transmission path 113 at a fixed transmission rate. The 
selecting circuit 210 selects one picture signal from the multichannel 
low-resolution TV signal in response to a user's control signal from a 
control terminal 206. The output signal of the selecting circuit 210 is 
supplied to a buffer circuit 211. The buffer circuit 211 stores a signal 
supplied from the selecting circuit 210 and then supply it to a decoding 
circuit 212. A picture signal is supplied from the decoding circuit 212 to 
the low-resolution TV monitor 213.