System converter device for converting a video signal having a certain number of scan lines to a video signal having a lesser number of scan lines

A system converter device converts a video signal based on the MUSE system to a video signal based on the NTSC system. In the system converter device, two lines of scanning line signal based on the NTSC system are generated from three adjacent same numbered-type field lines of scanning line data included in the MUSE signal. The generated time-discontinuous scanning line signal is made continuous by an expanding circuit. The video information included in the MUSE signal is not lost by conversion, became a video signal based on the NTSC system is generated from all the scanning line signals forming 1 frame included in the MUSE signal. Therefore, it is possible to display the complete transmitted video on the display screen.

BACKGROUND OF THE PRESENT INVENTION 
1. Field of the Present Invention 
The present invention generally relates to system converter devices for 
video signals, and more particularly, to a system converter device for 
converting video signals having a certain number of scanning lines to 
video signals having a less number of scanning lines. The present 
invention has particular application to a system converter device for 
converting video signals based on the MUSE system to video signals based 
on the NTSC system. 
2. Description of the Background Art 
In the high definition television system, the number of scanning lines is 
1125 lines per frame, the interlace ratio is 2:1, and the aspect ratio is 
16:9. On the other hand, the NTSC system uses 525 scanning lines per 
frame, an interlace ratio of 2:1, and an aspect ratio of 4:3. Since one 
channel of satellite broadcasting has a bandwidth of 27 MHz, video signals 
based on a high definition television system are bandwidth compressed to 
the bandwidth of 8.1 MHZ. The bandwidth compressed signals are transmitted 
through one channel of the satellite broadcasting. This transmission 
system is called "Multiple Sub-Nyquist Sampling Encoding" (hereinafter 
referred to as MUSE). 
This MUSE transmission system is defined as a multiplexed subsample 
transmission system using offset subsampling between two fields and 
frames. Line sequential time axis integration (TCI) is employed in the 
MUSE transmission system, where the red color difference signal R-Y and 
the blue color difference signal B-Y have the time axis compressed to 1/4. 
The compressed signals are time axis multiplexed at the horizontal 
blanking period of the luminance signal Y. Furthermore, the red color 
difference signal R-Y and the blue color difference signal B-Y are 
multiplexed line sequentially on odd number lines and even number lines, 
respectively. 
When video signals of the high definition television system transmitted 
according to the MUSE transmission system, for example, are converted to 
video signals of the NTCS system, a conversion system is proposed in which 
the image portion of 1050 scanning lines and with the aspect ratio of 4:3 
is extracted from the 1125 lines of scanning line signals according to a 
high definition television system having the aspect ratio of 16:9, and 
further removing one half of the 1050 lines, i.e., 525 lines. 
However, when video signals are converted in such a manner, there was a 
problem that the image information on both sides of the display screen of 
the high definition television, that is to say, the right and left sides 
of the image that should be displayed on the display screen, for example, 
is lost. 
More specifically, the video signal according to the high definition 
television system comprises a video region A and video regions B adjacent 
to both sides of region A on a display screen 71, as shown in FIG. 10A. In 
the conventional converting system mentioned above, only video region A of 
FIG. 10A is displayed as video region A' on a display screen 72, as shown 
in FIG. 10B. In other words, video regions B on display screen 71 are lost 
in display screen 72. 
SUMMARY OF THE PRESENT INVENTION 
An object of the present invention is to have all the video information 
that is present in the video signal of the high definition television 
system contained in the converted video signal in a system converter 
device. 
Another object of the present invention is to generate a converted video 
signal on the basis of all video signals based on the high definition 
television system in a system converter device. 
A further object of the present invention is to have all video information 
that is comprised in the video signal based on the MUSE transmission 
system contained within the converted video signal based on the NTSC 
system. 
In summary, the system converter device in accordance with the present 
invention converts a first video signal having a first predetermined 
number of scanning lines per frame to a second video signal having a 
second predetermined number of scanning lines per frame. The first number 
is larger than the second number. The system converter device comprises a 
circuit for generating scanning line signals forming the second video 
signal in response to each group of scanning line signals of an adjacent 
third number of scanning lines in each frame of the first video signal, 
and a render-continuous circuit for making the generated 
time-discontinuous scanning line signal be time-continuous. 
In operation, a scanning line signal forming the second video signal is 
generated in response to each group of the scanning line signals of an 
adjacent third number of scanning lines for each frame of the first video 
signal. That is to say, all the video information that is comprised in the 
first video signal will be contained in the second video signal because 
the scanning line signal forming the second video signal is generated in 
response to each group of the scanning line signals of an adjacent third 
number of scanning lines in the first video signal. 
In another aspect, the present invention converts a first video signal 
having a first predetermined number of scanning lines per frame to a 
second video signal having a second predetermined number of scanning lines 
per frame. The first number is larger than the second number. The method 
of the present invention includes the steps of receiving a first video 
signal, generating a scanning line signal forming the second video signal 
in response to each group of scanning line signals of an adjacent third 
number of scanning lines for each frame of the first video signal, and 
making the generated into a time-discontinuous signal scanning line signal 
time-continuous. 
The foregoing and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As an example of a signal according to the high definition television 
system, a MUSE signal transmitted via satellite broadcasting will be used 
below. Referring to FIG. 1, a satellite broadcasting signal received by an 
antenna 1 is applied to a tuner 2. The MUSE signal provided from tuner 2 
is converted to a digital signal by an A/D converter 3. This digital 
signal is applied to a de-emphasis circuit 4, where de-emphasis processing 
is performed. The output signal of the de-emphasis circuit 4 is provided 
to an adder 6 via an coefficient multiplier 5 and is also provided to 
adder 6 via a coefficient multiplier 8 after being delayed for 2 
horizontal periods (2H) by a delay element 7. 1H is equivalent to one 
horizontal period of the high definition television system, i.e., 1H=29.6 
.mu.sec. The number of scanning lines is converted from 1125 lines to 750 
lines which is 2/3 of the MUSE signal by coefficient multipliers 5 and 8, 
adder 6, and delay element 7. The coefficient multiplier 5 is shown in 
detail in FIG. 2. 
Referring to FIG. 2, coefficient multiplier 5 comprises a switching element 
51 connected so as to receive the output signal from the de-emphasis 
circuit 4, multipliers 52, 53 and 54 for multiplying predetermined 
coefficients, and a switching element 55 connected to the output of the 
multipliers. A timing signal generator 30 generates a clock signal .phi.5 
in synchronism with the horizontal scanning line of the MUSE signal. 
Switching elements 51 and 55 operate in response to this clock signal 
.phi.5. The coefficients of 1/4, 3/4, and 0 are previously set to 
multipliers 52, 53 and 54, respectively. 
FIG. 3 shows an example of coefficient multiplier 8 shown in FIG. 1. The 
coefficient multiplier 8 has a circuit configuration similar to that of 
coefficient multiplier 5 of FIG. 2, except that coefficients 3/4, 1/4, and 
0 are previously set to multipliers 82, 83, and 84, respectively. 
The conversion of the scanning lines by the system converter device of FIG. 
1 is described below referring to FIG. 4. The left side of the figure 
indicates the processing for the odd number field of the video signals, 
while the right side indicates the processing for the even number field. 
In this case, the odd number lines having the red color difference signal 
R-Y multiplexed, and the even number lines having the blue color 
difference signal B-Y multiplexed are individually added for the 
conversion of the number of the scanning lines. 
In other words, the first scanning line and the third scanning line of the 
MUSE signal are multiplied by the coefficients of 3/4 and 1/4, 
respectively, whereupon the two multiplied signals are added to form one 
scanning line. The 3rd scanning line and the 5th scanning line are 
multiplied by the coefficients of 1/4 and 3/4, respectively, whereupon the 
two multiplied signals are added to form one scanning line. The 7th 
scanning line and the 9th scanning line are multiplied by the coefficients 
of 3/4 and 1/4, respectively, whereupon the multiplied signals are added 
to form one scanning line. A likewise process is repeated so as to produce 
two scanning lines from every three adjacent odd numbered scanning lines 
of the MUSE signal. 
Similarly, the 2nd scanning line and the 4th scanning line of the MUSE 
signal are multiplied by the coefficients of 3/4 and 1/4, respectively, 
whereupon the multiplied two signals are added to form one scanning line. 
The 4th scanning line and the 6th scanning line are multiplied by the 
coefficients of 1/4 and 3/4, respectively, whereupon the two multiplied 
signals are added to form one scanning line. The 8th scanning line and the 
10th scanning line are multiplied by the coefficients of 3/4 and 1/4, 
respectively, whereupon the two multiplied signals are added to form one 
scanning line. A likewise process is repeated so as to produce two 
scanning lines from every three adjacent even numbered scanning lines of 
the MUSE signal. 
Thus, each odd number line and even number line of the MUSE signal are 
converted to produce 375 lines of odd number lines and 375 lines of even 
number lines. This means that the 1125 scanning lines of the MUSE signal 
are converted to 750 lines. 
In order to convert the number of the scanning lines as described above, 
the output signal of de-emphasis circuit 4 is multiplied by the 
coefficients shown in FIG. 5A in coefficient multiplier 5. That is, the 
3rd scanning line and the 4th scanning line are multiplied by the 
coefficient of 1/4, the 5th scanning line and the 6th scanning line are 
multiplied by the coefficient of 3/4, and the 7th scanning line and the 
8th scanning line are multiplied by the coefficient of 0. In a likewise 
manner, the coefficients are switched every two horizontal periods. The 
output signals of delay element 7 are multiplied by the coefficients shown 
in FIG. 5B in coefficient multiplier 8. That is, the 1st scanning line and 
the 2nd scanning line are multiplied by the coefficient of 3/4, the 3rd 
scanning line and the 4th scanning line are multiplied by the coefficient 
of 1/4, and the 5th scanning line and the 6th scanning line are multiplied 
by the coefficient of 0. In a likewise manner, the coefficients are 
switched every two horizontal periods. 
Accordingly, adder 6 provides a signal having the number of scanning lines 
converted as shown in FIG. 4. In this case, the red color difference 
signal R-Y and the blue color difference signal B-Y are separated from 
each other. 
The output signal of adder 6 is provided to a time axis expanding circuit 
9. In expanding circuit 9, the line having the blue color difference 
signal B-Y multiplexed is extracted from the output signal of adder 6, 
where one horizontal period (1H) of the extracted line has the time axis 
expanded to 1 horizontal period (1H') based on the NTSC system. 1H' 
corresponds to 63.5 .mu.sec. 
The output signal of adder 6 is provided to delay element 10 having a delay 
time of 1 horizontal period (1H). The output signal of delay element 10 
(shown in FIG. 5D) is provided to a time axis expanding circuit 11. The 
expanding circuit 11 extracts the line having a red color difference 
signal R-Y multiplexed from the output signal of delay element 10. 1 
horizontal period (1H) of the extracted line has the time axis expanded to 
1 horizontal period (1H') of the NTSC system. The delay element 10 makes 
the timing of the line having the red color difference signal R-Y 
multiplexed coincide with the timing of the line having the blue color 
difference signal B-Y multiplexed. The scanning lines extracted from 
expanding circuits 9 and 11 having the color difference signals R-Y and 
B-Y multiplexed, respectively, appear intermittently as shown in FIG. 6A. 
For the purpose of expanding the time axis of such intermittent data, it is 
customary to use two field memories. First, data from each field is 
written into the field memory, where the written data is read out from 
each field memory in response to a clock signal according to the NTSC 
system. This means that the configuration of conventional circuits are 
large due to the fact that four field memories are required. 
On the contrary, expanding circuits 9 and 11 of FIG. 1 each have a random 
access memory (hereinafter referred to as RAM) that can store scanning 
line data of 49 horizontal periods, in which the time axis is expanded. 
There are 1032 lines of effective scanning lines of the MUSE signal, so 
the effective scanning lines EL of the 375 scanning lines are defined as 
in the following equation: 
EQU EL=375.times.(1032/1125)=344 lines (1) 
Since there are 172 lines of effective scanning lines in one field, the 
scanning line signals of 172 lines for each field are continuously read 
out from the RAM. 
An example of a circuit that is applicable to expanding circuits 9 and 11 
are shown in FIG. 7. Referring to FIG. 7, expanding circuit 90 comprises a 
RAM 91, a writing address counter 92, and a readout address counter 93. 
Counters 92 and 93 are connected to receive predetermined clock signals 
.phi.1 and .phi.2 from timing signal generators 30 and 40, respectively. 
Clock signal .phi.1 has a frequency of 8.1 MHz according to the MUSE 
transmission system. Clock signal .phi.2 has a frequency of a 
approximately 4 MHz according to the NTSC system. 
172 lines of scanning line signals are sequentially written into each RAM 
provided in expanding circuits 9 and 11 at a timing shown in FIG. 6A. 
Also, the commencement of readout is delayed so that 172 lines of scanning 
line data will be continuously readout by each field. In other words, by 
commencing the readout of the written data after the beginning data of the 
171th scanning line signal is written, the 1st to 172nd scanning line 
signals may be readout continuously. The readout of the first scanning 
line signal commences at time t1 between the writing of the 49th and the 
50th scanning line signals. The readout of the first scanning line signal 
commences after the writing of the 49th scanning line signal is completed. 
As a result, the 1st to 172nd scanning line signals are readout 
continuously by providing a RAM that can store data corresponding to 49 
horizontal periods in circuits 9 and 11. 
Since the 173rd scanning line signal shown in FIG. 6B is not yet written at 
the timing of the readout of the 173rd scanning line signal, the readout 
data does not indicate the data of the 173rd scanning line signal. 
Therefore, this data is not used. 
In the above expanding circuits 9 and 11, scanning line signals according 
to 172 lines per field, 344 lines per frame according to the NTSC system 
is produced, and blankings of 181 lines are added to the relevant position 
of the scanning lines simultaneously. This results in the generation of 
525 lines of scanning line signals according to the NTSC system. 
The output signals from expanding circuits 9 and 11 are multiplied by the 
coefficient of 1/2 by means of coefficient multipliers 12 and 13, 
respectively. The multiplied two signals are added by adder 14 to produce 
a luminance signal Y. It is noted that the produced luminance signal Y has 
the interlaced related position between the odd number field and the even 
number field, as shown in FIG. 4. The luminance signal Y provided from 
adder 14 is converted to an analog signal by D/A converter 15 to be 
applied to a matrix circuit 16 and a NTSC encoder 17. 
The output signal of expanding circuit 9 is provided to time axis expanding 
circuit 18, where the the blue color difference signal B-Y having the time 
axis compressed to 1/4 is expanded. The blue color difference signal B-Y 
provided from expanding circuit 18 is provided to an intra-field 
interpolation circuit 19. The interpolation circuit 19 comprises a delay 
element 191 having a delay time of 1 horizontal period (1 H'), 1/2 
coefficient multipliers 192 and 193, and an adder 194. In interpolation 
circuit 19, weighted mean processing is performed between two continuous 
scanning line signals. The blue color difference signal B-Y provided from 
interpolation circuit 19 is converted to an analog signal by D/A converter 
20 to be applied to matrix circuit 16 and NTSC encoder 17. 
The output signal of expanding circuit 11 is applied to a time axis 
expanding circuit 21, where the red color difference signal R-Y having the 
time axis compressed to 1/4 is expanded. The red color difference signal 
R-Y provided from expanding circuit 21 is provided to an intra-field 
interpolation circuit 22. The interpolation circuit 22 has a circuit 
configuration similar to that of the above mentioned interpolation circuit 
19. Interpolation circuit 22 performs weighted mean processing between 
continuous two scanning line signals. The red color difference signal R-Y 
provided from interpolation circuit 22 is converted to an analog signal by 
D/A converter 23 to be provided to matrix circuit 16 and NTSC encoder 17. 
As a result, original color signals G, B, R indicating green, blue and red, 
are provided via the output terminals 24G, 24B, 24R of matrix circuit 16, 
respectively. A video signal SV according to the NTSC system produced by 
adding a carrier chrominance signal C formed by quadrature two-phase 
modulation of the color difference signal R-Y and B-Y, and a luminance 
signal Y are provided via the output terminal 25 of NTSC encoder 17. The 
luminance signal Y and the carrier chrominance signal C are provided from 
the output terminals 26Y and 26C of NTSC encoder 17. 
In accordance with the above embodiment, it is possible to display a 
picture on the display screen of a television according to the NTSC system 
without losing the video information included in the MUSE signal, due to 
the fact that 375 lines of scanning line signals forming the video signal 
based on the NTSC system are produced from 1125 lines of scanning line 
signals of the MUSE signal. Referring to FIG. 10C, video regions A" and B" 
are provided on the display screen 73 of the NTSC system. Respective video 
regions A" and B" correspond to the video information included in the 
transmitted MUSE signal, i.e., correspond to the video regions A and B of 
FIG. 10A. It is noted that image B" corresponding to the video region B 
contained in the MUSE signal is displayed on the display screen 73 of the 
NTSC system of FIG. 10C. 
Furthermore, since 375 lines of scanning line signals (the effective 
scanning lines are 344) forming the video signal of the NTSC system is 
produced from 1125 lines of scanning line signals of the MUSE signal, the 
aspect ratio of the image displayed on the television receiver under the 
NTSC system comes closer to the aspect ratio of the high definition 
television system. As a result, a good image is displayed on the display 
screen. 
Furthermore, field memories are not required as in conventional circuits 
since expanding circuits 9 and 11 each have a RAM that can store data of 
49 horizontal periods. The size of the circuit configuration may be 
reduced to lower the cost. 
The number of scanning lines may be converted as shown in FIG. 8, instead 
of converting the scanning lines of 1125 of the MUSE signal to 750 lines 
as shown in FIG. 4. In the processing of odd number fields, one scanning 
line is produced from the first scanning line of the MUSE signal. The 3rd 
scanning line and the 5th scanning line are each multiplied by the 
coefficient of 1/2, whereupon the two multiplied signals are added to 
produce one scanning line. One scanning line is produced from the 7th 
scanning line. By repeating the process in a similar manner, two scanning 
lines are produced from the three odd number scanning lines of the MUSE 
signal. 
Similarly, in the processing of even number fields, one scanning line is 
produced from the second scanning line of the MUSE signal. The 4th 
scanning line and the 6th scanning line are each multiplied by the 
coefficient of 1/2, whereupon the two multiplied signals are added to 
produce one scanning line. One scanning line is produced from the 8th 
scanning line. By repeating the process in a similar manner, two scanning 
lines are produced from the three even number scanning lines of the MUSE 
signal. 
The odd number lines and the even number lines of the MUSE signal are each 
converted to 375 lines, causing the number of 1125 lines to be converted 
to 750 lines. It will be appreciated that only the value of the 
coefficients to be multiplied in coefficient multipliers 5 and 8 of FIG. 1 
need to be changed for the conversion of the scanning lines shown in FIG. 
8. In the case of FIG. 8, the coefficient multiplier 5 multiplies the 
output signal of de-emphasis circuit 4 by the coefficients shown in FIG. 
5E. More specifically, the 3rd scanning line and the 4th scanning line are 
multiplied by the coefficient of 0. The 5th scanning line and the 6th 
scanning line are multiplied by the coefficient of 1/2. The 7th scanning 
line and the 8th scanning line are multiplied by the coefficient of 0. The 
coefficients are switched every 2 horizontal periods. The coefficient 
multiplier 8 multiplies the output signal of delay element 7 by the 
coefficients shown in FIG. 5F. More specifically, the 1st scanning line 
and the 2nd scanning line are multiplied by the coefficient of 1. The 3rd 
scanning line and the 4th scanning line are multiplied by the coefficient 
of 1/2. The 5th scanning line and the 6th scanning line are multiplied by 
the coefficient of 0. The coefficients are switched every 2 horizontal 
periods. 
The intra-field interpolation circuits 19 and 20 of FIG. 1 may be replaced 
by the circuit 70 shown in FIG. 9. Referring to FIG. 9, the intra-field 
interpolation circuit 70 comprises delay elements 71 and 72 having a delay 
time of 1 horizontal period (1 H'), 1/4 coefficient multipliers 73 and 74, 
1/2 coefficient multiplier 75, and an adder 76. The weighted mean 
processing of three continuous scanning line signals are carried out in 
inter-field interpolation circuit 70. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.