Chroma-signal processing system

Chroma-signal processing system is disclosed wherein a color television signal is sampled at a frequency equal to a sub-carrier frequency multiplied by an integer, and chroma-components of the sampled signals are sequentially stored in a plurality of storage means for each of the sample points, and the chroma-signals are retrieved from the storage means while omitting portions of the chroma signals whereby accomplishing the chroma-signal processing with a fewer number of storage means. The system can be used to reduce the size of a displayed color image without introducing phase discontinuities into the chrominance subcarrier. The reduced image may then be inset into another color image displayed on a CRT. The system may also be used to reduce the subcarrier frequency of a chrominance signal.

The present invention relates to a chroma-signal processing system in 
converting a picture image size of a reproduced picture image of a color 
television signal comprising a brightness signal and a chroma-signal. 
Referring to FIG. 1, as approaches to compress the picture size of the 
image signal picked up in a standard system as shown in (a), either 
horizontally as shown in (b) or both horizontally and vertically as shown 
in (c) and insert the compressed image signal in a portion of another 
image signal picked up in the standard system as shown in (d), it has been 
proposed to re-pick up an image, to use a continuous delay line and to 
sample picture elements using storage devices. 
Of those approaches, the picture element sampling method is explained 
below. In this method, picture elements arranged as shown in FIG. 2(a) are 
sampled by omitting the hatched picture elements and the sampled picture 
elements are rearranged in a manner shown in FIG. 2(b) and assigned with 
new numbers as shown in FIG. 2(c). They are then temporarily stored in a 
memory in accordance with the numbers shown in FIG. 2(c) and therafter 
read therefrom. In this manner the image conversion is accomplished. While 
FIG. 2 illustrates the picture elements along the horizontal scanning 
line, the principle can be applicable to the picture elements along the 
vertical line. 
When the above method is employed to selectively omit the picture elements 
at any desired positions of the sampled picture element unit, there occurs 
a problem in case the picture element signal is a composite signal such as 
NTSC signal, with regard to a color sub-carrier. It is, therefore, 
necessary to omit the picture elements for one cycle of the sub-carrier or 
to color demodulate the signal into simple brightness signal groups, 
conduct omission process and again modulate to reconstruct a necessary 
composite signal. 
The former method is practically not applicable because of large image 
distortion in the reproduced image because the picture elements are 
handled in the unit of one cycle of the sub-carrier. The latter method 
produces smaller image distortion but possesses another problem of 
increased number of storge means required to temporarily store the signals 
because the number of signal groups handled is large. 
It is an object of the present invention to provide a chroma-signal 
processing system for converting the picture image size while maintaining 
a distortion of a reproduced image to a minimum. 
It is other object of the present invention to enable the processing with a 
fewer number of storage means in a system wherein the omission process is 
conducted after color demodulation and the signal is again modulated to 
reconstruct a composite signal. 
It is other object of the present invention to facilitate the frequency 
conversion of sub-carrier of chroma signal.

Referring now to FIG. 3, an embodiment of a processing apparatus employing 
the chroma-signal processing system of the present invention is shown. The 
processing apparatus comprises a picture image signal input terminal 101, 
and A/D converter circuit 102, a picture element omission circuit 103, a 
memory unit 104, a D/A converter circuit 105, an omission control unit 106 
for controlling the picture element omission circuit 103, a write pulse 
generator 107 and a read pulse generator 108. 
A color television signal in NTSC standard system is received at the input 
terminal 101 and converted to a PCM signal by the A/D converter circuit 
102. The PCM signal is then supplied to the picture element omission 
circuit 103 which, under the control of the omission control unit 106 and 
the signal from the pulse generator 107, decompose the PCM signal to a 
brightness component and a chroma component for the picture element 
omission process. Thereafter the two components are again combined to 
reconstruct a PCM signal in NTSC standard system. The PCM signal is then 
written into the memory unit 104 under the control of the output pulse 
from the pulse generator 107. The written signal is then read out by the 
pulse from the read pulse generator 108 and converted to an analog signal 
by the D/A converter circuit 105. 
The picture element omission circuit 103 of the above embodiment is now 
explained below in detail. 
FIG. 4 shows a detailed construction of the picture element omission 
circuit 103 of FIG. 3. It comprises an input terminal 109 to receive the 
A/D converted picture image signal, an interdigital filter 110 for 
separating the brightness component and the chroma component from each 
other, a picture element omission circuit 111 for the brightness 
component, a picture element omission circuit 112 for the chroma 
component, a synthesizer circuit 113 for combining the brightness 
component and the chroma component after the omission process to 
reconstruct a composite signal, an output terminal 114 thereof, and a 
control circuit 115 for the omission control, which corresponds to the 
omission control unit 106 in FIG. 3. The reason for separately processing 
the brightness component and the chroma component in the picture element 
omission circuit 103 is that the simultaneous process is impossible by the 
reason to be described below and that it is intended to advantageously 
utilize the difference therebetween due to the fact that the change rate 
of the chroma component in the NTSC signal is smaller than the change rate 
of the brightness component. 
FIG. 5 shows further details of the construction of the chroma component 
processing circuit of FIG. 4. A serial-to-parallel converter circuit 112a 
converts the separated chroma component to parallel data for the picture 
elements corresponding to the sample amount of one cycle of the 
sub-carrier. The sampling frequency is shown to be equal to the triple of 
the sub-carrier frequency f.sub.s. (In the following embodiments, the 
sampling frequency is assumed to be equal to the triple of the sub-carrier 
frequency.) The parallel-converted chroma component (parallel data) is 
stored in a temporary storage 112b which maintains the chroma component 
for one sub-carrier period. A parallel-to-serial converter circuit 112c 
switches or scans the temporarily stored chroma component to eliminate the 
discontinuity of the sub-carrier in the omission process and reconverts 
the parallel chroma component to serial data. Before the explanation of 
the operation of the converter circuit 112c, basic properties of the NTSC 
signal are described. 
FIG. 6 shows a small portion of a plot on the scan lines for the brightness 
component and the chroma component of the NTSC signal. The brightness 
component and the chroma component are shown in superimposed on each other 
and the phases of the sampling points are shown by dots assuming that 
there are no changes in the brightness component and the chroma component 
at corresponding phase points because of the small portion. The sampling 
frequency is three times as high as the sub-carrier frequency, and the 
sampling points are represented by a.sup.0, b.sup.0, c.sup.0, a.sup.1, 
b.sup.1, c.sup.1, -- . FIG. 7 shows the results of the omission process 
shown in FIG. 2 for the brightness signal and the chroma signal, wherein 
the magnitudes of the sampled brightness signal and the chroma signal are 
represented by Ya.sub.0, Yb.sup.0, Yc.sup.0, Ya.sup.1, Yb.sup.1, Yc.sup.1, 
-- Ca.sup.0, Cb.sup.0, Cc.sup.0, Ca.sup.1, Cb.sup.1, Cc.sup. 1. 
In FIG. 7, (a) shows a group of picture elements before the omission 
process, and (b) and (c) show the arrangements of the picture elements 
after the omission process of FIG. 2 has been applied to the brightness 
component and the chroma component. That is, (b) shows the arrangements of 
the picture elements after 3/4 compression in length and (c) shows the 
arrangement after 1/2 compression. 
As seen from FIG. 7, the brightness signal is converted to Ya.sup.0, 
Yb.sup.0, Yc.sup.0, Yb.sup.1, Yc.sup.1, Ya.sup.2, Yc.sup.2, Ya.sup.3, 
Yb.sup.3 -- for the 3/4 compression and to Ya.sup.0, Yc.sup.0, Yb.sup.1, 
Ya.sup.2, Yc.sup.2, Yb.sup.3, Ya.sup.4, Yc.sup.4, Yb.sup.5, -- for the 1/2 
compression. Thus, the intermediate picture elements are omitted in such a 
manner as to severely deteriorate the contents of the image. On the other 
hand, the chroma component is converted to Ca.sup.0, Cb.sup.0, Cc.sup.0, 
Cb.sup.1, Cc.sup.1, Ca.sup.2, Cc.sup.2, Ca.sup.3, Cb.sup.3, -- or to 
Ca.sup.0, Cc.sup.0, Cb.sup.1, Ca.sup.2, Cc.sup.2, Cb.sup.3, Ca.sup.4, 
Cc.sup.4, Cb.sup.5, --. Thus, the arrangements are similar to those of the 
brightness component and the color phase is quite disturbed and the 
continuity of the sub-carrier is lost. Accordingly the color reproduction 
is impossible in this system. In the NTSC signal, the frequency band for 
the brightness signal greatly differs from that for the chroma signal, and 
the change rate for the brightness component is relatively high while the 
change rate for the chroma component is relatively low and can be 
considered constant for several or more cycles of the sub-carrier. 
Furthermore, the phase of the sub-carrier changes by 180.degree. for each 
scanning line. Bearing those facts in mind, in the present invention the 
brightness component is separated from the chroma component and a special 
process is applied only to the chroma component. The operation of the 
converter circuit 112c in FIG. 5 is characterized by a switching circuit 
for effecting the compression process while producing the chroma component 
in conjunction with the converter circuit 112a and the temporary storage 
112b in such a manner to assure the continuity of the sub-carrier. The 
switch circuit is rotatably operated by the omission pulse from the 
omission control circuit 115 utilizing the fact that the chroma signal 
does not change over at least several cycles of the sub-carrier. The 
signals applied from the control circuit 115 to the circuit 111 and the 
converter circuit 112c are timing pulses for omitting or sampling the 
picture elements, by which in the circuit 111, a latch circuit is actuated 
only when the required picture elements are to be transmitted. These 
pulses are also applied to the converter circuit 112c to step the switch 
circuit. That is, the switch circuit is shifted each time a pulse is 
applied from the control circuit 115 so that it selects the input pulses 
to the converter circuit 112c in the sequence of l, m, n, l, m, n -- . On 
the other hand, the chroma signal to the converter circuit 112a is updated 
or renewed for each sampling pulse of the repetion frequency 3f.sub.s and 
parallel converted for each one cycle of the sub-carrier f.sub.s and 
stored in the temporary store 112b. Thus, the chroma signal is updated for 
each one cycle of the sub-carrier f.sub.s and does not change within one 
cycle of the sub-carrier. As a result, the output from the conversion 
circuit 112c is Ca.sup.0, Cb.sup.0, Cc.sup.0, Ca.sup.1, Cb.sup.1, 
Cc.sup.2, Ca.sup.2, Cb.sup.3 , Cc.sup.3, -- and Ca.sup.0, Cb.sup.0, 
Cc.sup.1, Ca.sup.2, Cb.sup.2, Cc.sup.3, Ca.sup.4, Cb.sup.4, Cc.sup.5, -- 
as shown in the lower rows of (d) and (e) in FIG. 7. Thus, the continuity 
of the sub-carrier is maintained in the arrangement and the chroma 
information has deviated from the corresponding brightness information by 
up to two sampling points. In the NTSC signal, as stated before, the 
change rate of the chroma component is relatively low and it can be 
assumed that the chroma signal remains unchanged for at least one cycle of 
the sub-carrier. Therefore, the deviation from the brightness signal, that 
is, two sampling point distance, is considered to include no problem. 
In the above embodiment, the chroma signal is processed based on the 
serial-to-parallel conversion for one period of the sub-carrier. However, 
the chroma component to be serial-to-parallel converted need not be 
limited to one period of the sub-carrier. When the chroma signal extends 
over more than one cycle, a circuit for digitally color-demodulating the 
signal utilizing the nature of adjacent sampling points and remodulating 
the signal, or a circuit for averaging the chroma change rate between the 
sampling points of the same phase may be additionally provided between the 
temporary storage 112b and the converter circuit 112c in FIG. 5. 
Furthermore, the number of the sampling points in one cycle of the 
sub-carrier need not be limited to three but any number of sampling points 
may be used provided that the serial-to-parallel converter circuit and the 
parallel-to-serial converter circuit for the chroma component are 
modified. 
Another application of the present invention is a frequency converter of 
the sub-carrier of the chroma signal. An embodiment thereof is now 
explained. FIG 8 again shows the parallel-to-serial converter and the 
switch circuit which perform the chroma signal processing operation 
described above. The difference of the construction shown in FIG. 8 from 
that of FIG. 5 resides in that the frequency of the switching signal 
applied to the converter circuit 112c is n times (three times) as high as 
the frequency of the sub-carrier and the switching signal is made 
continuous. 
The operation is explained below in detail. It should be noted that the 
following explanation relates to typical one bit of coded television 
signal although a plurality of parallel circuits which are equal in number 
to the number of bits are actually provided. The signal b applied to the 
converter circuit 112a is sampled at the frequency (3f.sub.s) which is n 
times (three times) as high as the frequency of the sub-carrier frequency 
of the chroma signal to produce the coded chroma signal of the television 
signal. This signal is stored in a shift register forming the conversion 
circuit 112a by the clock pulses at 3f.sub.s and stored in a D-type 
flip-flop in the temporary storage 112b, after having been 
serial-to-parallel converted, by the clock pulses at one thirds of 
3f.sub.s clock pulses. As a result, the input signal b continuously 
applied to the converter circuit 112a is stored in the temporary storage 
112b for one cycle and all the stored information is substantially updated 
for each of the cycles. 
The outputs from the temporary storage 112b are applied to the converter 
circuit 112c which multiplexes them to produce serial output. The 
operation described so far is the same as that described before, but since 
the frequency of the switching input signal applied to the converter 
circuit 112c is n times (three times) as high as the frequency of the 
sub-carrier to be converted, the switching operation is not intermittent 
but continuous. For example, when a signal is to be converted to the 
NTSC signal, f.sub.s ' is 3.58 MHz. FIG. 9 shows the manner of conversion 
on a time chart of the signal b applied to the conversion circuit 112a to 
the signal b' at the output thereof. In FIG. 9, (a) shows the manner in 
which the input signal b changes, and (b) shows three outputs l, m, n, of 
temporary storage 112b. These outputs are multiplexed by 3f.sub.s ' 
applied to the converter circuit 112c to produce output as shown in (c), 
in which (i) shows the output b' when f.sub.s ' = 7/8 f.sub.s and they are 
in phase and (ii) shows the output b' when f.sub.s ' = 2 f.sub.s and they 
are out of phase. Since the change rate of the chroma signal is 
sufficiently high as compared with the period of the carrier due to an 
inherent nature of the television signal, it can be considered that 
Ca.sup.k = Ca.sup.K+1 = Ca.sup.k+2, Cb.sup.k = Cb.sup.k+1 = Cb.sup.k+2, 
Cc.sup.k = Cc.sup.k+1 = Cc.sup.k+2 (where k is a positive integer). 
Therefore, the output signal C a.sup.0, Cb.sup.0, Cc.sup.1, Ca.sup.1, 
Cb.sup.2, Cc.sup.2, -- and the output signal Ca.sup.0, Cb.sup.0, Cb.sup.1, 
Cc.sup.1, Cc.sup.2;l , C a.sup.2;l , C b.sup.2, Cb3, -- transmit the 
substantially same chroma component and hence they may be considered to be 
a continuous signal. Cb.sup.0, Cb.sup.1, Cc.sup.1, Cc.sup.2 show that the 
output of the temporary storage 112b has changed during or at intermediate 
of the operation of the switch forming the converter circuit 112c, but 
this does not substantially affect to the transmitted chroma component by 
the same reason as described above. 
In this manner, the carrier frequency of the chroma signal can be 
converted. In the circuit of FIG. 8, by replacing the converter circuit 
112a with an analog shift register, the temporary storage 112b with an 
analog memory and the converter circuit 112c with an analog switch, the 
signals b and b' can be analog signals. FIG. 10 conceptionally shows the 
circuit of FIG. 8, in which the operation of the converter circuit 112a 
and the temporary storage 112b, which is considered as a combination of a 
switch and an analog memory, and the switch operation of the converter 
circuit 112c are consolidated. The circuit of FIG. 10 basically differs 
from the circuit of FIG. 8 in that the sampled data are sequentially 
stored in the analog memories shown by capacitors C and maintained therein 
for one cycle of the carrier, while in the circuit of FIG. 8 the sampling 
points are maintained in parallel for one cycle (1/f.sub.s) of the carrier 
by the parallel-to-serial converter. In the present case, the relation 
between the input signal b and the output signal b' is shown in FIG. 11. 
The potentials of the outputs l, m, n of the analog memories differ in the 
manner as shown in (b), but assuming that the relation of f.sub.s and 
f.sub.s ' is same as that in FIG. 9, the output signal b' remains 
substantially unchanged because of the slow change of the chroma 
component. Thus, by sequentially storing in n memories the magnitudes of 
the chroma signals of a first television signal sampled by the clock 
signal which is synchronized with the color carrier of the first 
television signal and has a frequency n times as high as the frequency of 
the color carrier, maintaining the stored data for one cycle of the color 
carrier, and sequentially switching to read out the respective data at the 
frequency n times as high as the frequency of a second desired color 
carrier while eliminating harmonic components, a chroma signal having its 
color carrier frequency converted can be produced. 
This method of converting the sub-carrier frequency makes use of the 
property of the chroma signal and it is based on a novel idea. 
While the processing of the chroma component on the horizontal scanning 
line has been described, the application of the present invention to the 
vertical line is now explained. In the NTSC signal, when the sub-carriers 
on the adjacent scanning lines are compared for each horizontal cycle, 
they differ in phase by 180.degree.. Accordingly, when the method shown in 
FIG. 2 (the picture image compression method by the omission of picture 
elements) is to be applied to the vertical direction (where one picture 
element is regarded as one scan line), the phase of the sub-carrier on the 
scan line must be shifted by 180.degree.. Noting a particular scan line, 
the scan line number originally assigned to that scan line and the scan 
line number assigned to that scan line after the compression operation has 
been effected are compared, and only when such scan line number changes 
from an odd number to an even number or vice versa before and after the 
compression, the polarity of the sub-carrier on the scan line is changed, 
where no odd to even change or even to odd change of the original scan 
line number occurs through the compression operation, the polarity is not 
changed. In this case, there is imposed a limitation to the phase of the 
sampling pulse. That is, it is required that the sampling pulses are in 
phase in two continuous scanning lines. 
This can be automatically attained when the sampling frequency is even 
number times as high as the color sub-carrier, but when it is odd number 
times as high as the color sub-carrier, the adjustment by a horizontal 
cycle signal is required. 
The change of the polarity of the chroma signal may be effected at any time 
after the chroma signal has been separated by the interdigital filter of 
FIG. 5 and before it is combined in the synthesizer circuit 113. In FIG. 
5, it may be readized by changing the polarity of the chroma signal (or 
changing a sign bit) when adding the brightness component and the chroma 
component together in the synthesizer circuit.