JPS59103494A - Ntsc color television signal receiver - Google Patents

Abstract

PURPOSE:To receive a still picture without deterioration in picture quality and a chroma inverter from a video signal for one frame's share by demodulating a chroma signal with a subcarrier signal discontinuous at each frame. CONSTITUTION:A burst signal obtained from a burst separating circuit 606 is inputted as it is to a switch 608 and another is inputted to the switch 608 after being phase-shifted by 180 deg. at a phase shifter (1)607, and converted into a continuous wave phase-locked by an APC circuit, and one is inputted to a switch 611 as it is and the other is inputted thereto after being phase-shifted by 180 deg. at a phase shifter (2)610. When the input is a conventional video signal, an output of an AND gate 617 goes always to L for attaining conventional color demodulation. When the input signal is a still picture, a signal inverted with H and L at each frame is outputted from the AND gate and the switches 608, 611 are switched alternately to (a), (b) at each frame. Since the continuous burst is inputted to the APC circuit at all times regardless that the phase of the burst signal from the burst separating circuit is inverted by 180 deg. at each frame, the APC circuit acts the same when the conventional video signal is inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to improvements in NTSC color television signal receivers.

Conventional configurations and their problems In still image transmission, stealth playback on digital VTRs, etc., video signals are digitized, information for one frame is stored in memory, and this information is sequentially read out and transmitted to the receiver. There is a request to view still images. At this time, NTSC
The video signal of this system has a subcarrier frequency '8C and a frame frequency fr node.

Therefore, when the memory capacity is only for one frame, the phase of the phase carrier of the video signal read from the memory is reversed for each frame and becomes discontinuous. Therefore, chroma inverters have conventionally been used as a means to solve the above-mentioned disadvantages. That is, the continuity of the color signal is maintained by inverting the phase of only the color components of the video signal for each frame.

However, in order to use this chroma inverter, it is necessary to separate the luminance signal and chrominance signal, and in addition, since the chrominance signal is inverted and added to the luminance signal, the resolution deteriorates and the high-frequency components of the luminance signal deteriorate. etc. become a problem.

Figure 1 shows 3/, using a conventional chroma inverter.
,.

FIG. 2 is a block diagram of a one-frame still image transmission device.

The video signals sequentially read out from the frame memory 101 undergo various signal processing in the processor 102, and then one is sent to a switch 106 and the other is separated into a luminance signal Y (hereinafter abbreviated as Y) and a color signal C (hereinafter abbreviated as C). Circuit 1o3 (hereinafter referred to as Y
(abbreviated as C separation circuit). In the YC separation circuit, the Y signal and the C signal are separated by a comb filter or the like, and the C signal is inverted in phase by the next chroma inverter 104 and then added by an adder 105. The output of the processor 102 and the output of the adder 105 are connected to the switch 1
06. On the other hand, a control signal generator 111 is operated by a synchronization signal from a synchronization signal generator 110 to generate a switch changeover signal that is inverted every frame, thereby switching the switch 106. As a result, the output from switch 106 becomes a continuous video signal for each frame.

This video signal is returned to the original analog video signal through a digital-to-analog converter 107 and a low-pass filter 108, and is outputted from an output terminal 109.

In the above-described method, YC separation is generally performed using a comb filter or the like, but this degrades the resolution in the vertical direction. Furthermore, if this YC separation is not performed reliably, the high frequency components of the Y signal will also be extracted as the C signal,
Since the Y signal is inverted, the high frequency components of the Y signal deteriorate.

FIG. 2 shows a configuration example using a 1H (where H is one horizontal scanning period) type comb filter and a bandpass filter (hereinafter abbreviated as BPF) as an embodiment of a circuit for extracting the C signal. In FIG. 2, 201 is a 1H delay device;
20291 is a subtracter, and 203 is a band pass filter.

The comb-shaped characteristic shown by the solid line in FIG. 3 is the amplitude characteristic shown in FIG. 2, and the dotted line represents the spectrum where the Y signal exists. Therefore, the shaded part of the Y signal in the figure is extracted as the C signal by the comb filter in Figure 2, and its components are inverted and added to the original Y signal, so that the spectral range is The Y signal deteriorates.

Figure 4 shows the circuit configuration of a conventional NTSC color TV signal receiver. A video signal is input to the input terminal 401 from the output terminal 109 in FIG. Then, only the Y component is extracted by the low-pass filter 402, and the RG
It is input to the B output circuit 40.

On the other hand, a C signal is extracted by a bandpass filter 403 and is sent to two color demodulators (i'i circuits 404 and 406).
is input. Further, a burst signal is extracted from the burst separation circuit, and a reference subcarrier wave whose phase is synchronized with the burst signal is obtained in an automatic gain control circuit (hereinafter abbreviated as APC) 407. This reference subcarrier is then sent to the color demodulation circuit (1) 404 using a phase shifter 4o8.
The phase-shifted reference subcarrier is sent to the color demodulation circuit (2) 40 t
s to obtain color difference signals RY and BY, respectively. From these two color difference signals, three color difference signals of R-Y, B-Y, and G-Y are obtained in the matrix circuit 409, and these color difference signals and Y signal
Output circuits 4 and 1o provide R, G, and B three primary color signals.

OBJECTS OF THE INVENTION The object of the present invention is to provide an improved NTSC system capable of receiving still images without image quality deterioration even from one frame worth of video signals as described above without using a chroma inverter.
The purpose of the present invention is to provide a color television signal receiver.

Structure of the Invention In order to realize the above object, the present invention
This is a partial improvement to the color television signal receiver. In other words, the NTS read from the memory for one frame
In the C color TV signal, the burst and color signals are in the same phase in each frame, and the subcarriers obtained from the burst are discontinuous in each frame. Therefore, the present invention is configured to demodulate the color signal using discontinuous subcarrier signals for each frame.

Description of examples Next, examples of the present invention will be described.

As mentioned above, using the conventional chromine inverter, the 7t-
] In still image transmission, image quality inevitably deteriorates. Therefore, the present invention aims to write a color TV signal as it is into a frame memory by simply improving a color TV receiver without using a chroma inverter, and to obtain a still image that does not cause image quality deterioration even when sequentially read out. .

FIG. 6 shows an example of the configuration of the transmission device.

501j: frame memory, 602 is a processor, 60
3 is a digital-to-analog converter, 5o4 is a low-pass filter, and 606 is an output terminal.

The signal read from the frame memory passes through the processor, is converted into an analog signal, and is output.

Therefore, no degradation occurs in the transmitted signal.

FIG. 6 shows the configuration of a receiver according to the present invention.

One of the burst signals obtained from the burst separation circuit 606 remains unchanged, while the other is phase-shifted by 1800 in the phase shifter (1) 607 and enters the switch 608. After being converted into a phase-synchronized continuous wave by the APC circuit, One is inputted as is, and the other is phase-shifted by 180° by a phase shifter (2) 610 and inputted to a switch 611.

The above two switches 608 and 611 are AND gates 61
It is controlled by a switching signal from 7. Signals from a control signal generator 616 and a control signal input terminal 618 are input to this AND gate 617 . In other words, the synchronization signal from the synchronization signal separation circuit allows the
A switching signal that repeats 'H' and 'L' is obtained from the control signal generator, and from the control signal input terminal, if the input to the receiver is a normal video signal, 'L',
H for still image signals read from 1 frame memory
A control signal is input that changes depending on the input signal so that

When the control signal is “L”, the switches 608 and 611
When it is "H" to the side, it works to be connected to the b side. In other words, if the input is a normal video signal, the AND gate 617
The output is always °'L'', and FIG. 6 coincides with FIG. 4, and normal color demodulation is performed.

Next, when the input signal is a still image, the AND gate outputs a 9-page signal in which 1H" and "L" are inverted for each frame, and switches 608 and 611 are alternately connected to a and b for each frame. In this way, the phase of the burst signal from the burst separation circuit will vary by 180 degrees for each frame.
Since continuous bursts are always input to the APC circuit even though the 0 phase is inverted, the APC circuit operates in the same way as when a normal video signal is input. Further, from the output of the switch 611, a reference subcarrier whose phase is inverted by 1800 for each frame is obtained, which is then directly passed through the color demodulation circuit (1) 6o4 and phase shifted by 90° through the phase shifter (3) 612. color demodulation circuit (
2) Supplied to e o 6. Note that in FIG. 6, a circuit other than that described above, that is, a low-pass filter 60
2. Bandpass filter 603, matrix circuit 61
3. The RGB output circuit 614 operates in the same manner as the corresponding circuits in FIG.

As described in detail of the invention, if the receiver is configured as in the present invention, it is possible to operate a normal video receiver by simply adding a phase shift circuit, a switch circuit, and a simple switch control circuit to a conventional receiver. In addition to signals, there is no need to pass through a color inverter on the transmission equipment side, even for still images read out from one frame memory and where the color signal is inverted for each frame, so there is no deterioration in image quality. It is possible to receive an image and stably perform color demodulation.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a still image transmission device in a conventional example.
Figure 2 is a block diagram of a comb filter for extracting color signals, Figure 3 is the amplitude characteristic of the comb filter shown in Figure 2, and Figure 4 is a diagram of the still image transmission device in the conventional example. The block diagram, FIG. 6, is an NTSC in one embodiment of the present invention.
FIG. 1 is a block diagram of a color television signal receiver. 101.601...Frame memo IJ, 103
... YC separation circuit, 1o4 old... Chroma inverter, 406.606 ... Burst separation circuit, 4o7゜11bae; 609 --- APC circuit, 607, 610 ... Group 18o0 phase shifter. Name of agent: Patent attorney Toshio Nakao and 1 other person: Castle 594-

Claims (1)

[Claims] means for phase shifting the burst signal by 1800 every frame;
means for obtaining successive color subcarriers from the transferred burst signal;
00 phase shifting means, and means for demodulating the color signal using the phase-shifted color subcarrier.
TSC color television signal receiver.