JPS59114986A - Color television signal decoding method and decoder circuit device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

TECHNICAL FIELD The present invention relates to a method of decoding a color television signal and a decoder circuit device implementing the method.

The method for demodulating the NTS (! signal is described, for example, in the book "
Pr1nciples of Co1or Te1ev
isio, n J, K, McIIwain, Ch.
arles Dean, J., Wiley & 5o
ns, 1956, chapter 15, page 385 (especially page 396, number 158, figure) vc. The quadrature amplitude modulated color signal is roughly separated into a luminance signal and a chrominance signal by a bandpass filter, and then quadrature modulated by a regenerated subcarrier. The demodulated signal is
After being filtered by a low-pass filter, it is supplied to a matrix circuit. In this matrix circuit, the demodulated signal is combined with the luminance signal in a linear relationship to reproduce the reduced primary color signals R, G, B.

Commonly transmitting the color signals in the color signal channels results in an undesirable superposition of the spectra of the two signals. The luminance spectral components transmitted together with the chrominance signal components through the chrominance bandpass filter are demodulated together during synchronous demodulation, resulting in disturbance voltages in the chrominance channel.

Such fault voltages were unavoidable in conventional color television devices. In very expensive commercial decoders, the disturbance voltage can be removed by a comb filter. This comb filter is provided, for example, to remove a color signal from a luminance signal. These comb filters require expensive broadband delay lines. These lines delay all luminance signals by one scan line (or multiple scan #s). More expensive detection equipment is used. These detection devices adaptively switch between two modes, i.e. low-pass filtering or comb filtering, depending on the image content, and vertically interpolate at the transition of the horizontal scan line. Avoiding the formation of tethered structures. Color television signals are transmitted on these lines on a carrier wave (in the case of acoustic delay lines) or
Processed under clock control (in the case of a charge-coupled delay network). In some cases the carrier frequency must have a high value, for example 27 MHz, and in other cases the clock frequency must have a value of at least 2.2×f7. In this case, f? represents the highest signal frequency of the transmitted signal. Typically, to ensure these conditions,
A high-order low-pass filter with group travel time is required.

The object of the invention is to effectively reduce color signal crosstalk by a simple and economically easy-to-implement method.

Effect of the invention (
The present invention having the features set forth in claim 1 includes:
It has the advantage that color signal crosstalk reduction can be achieved at low cost.

The invention is applicable in all color television signals, such as NTSO signals, where the frequency of the color subcarrier is an odd multiple of the line frequency.

Description of examples Next, embodiments of the present invention will be described in detail using the drawings.

A color television signal is supplied to terminal 1 of the circuit arrangement of the known decoder shown in FIG.

In the channel provided for the luminance signal Y, a delay element 2 and a chrominance subcarrier trap 3 are provided to compensate for the transit time in the chrominance signal channel. The color signal components are separated and detected using a bandpass filter 4. As mentioned at the beginning, the luminance component present in the frequency range of the color subcarriers leads to color signal crosstalk. The chrominance signal is demodulated in two synchronous demodulators. Color difference signal U and VCP
For these synchronous demodulators, in order to obtain the
A phase-shifted optical color subcarrier voltage (fsc) is provided. By means of the low-pass filters 9 and 10, residual color subcarriers are eliminated from the signals U and V or (2) and Q. Signal Y
.

In another known circuit, illustrated in FIG. 2, the chrominance and luminance signal components of a color television signal are separated by a comb filter.

For broadband delay of color television signals, the modulator 11
．． An acoustic delay line 12, an amplifier 13 and a demodulator 14 are required. An acoustic delay line 12 connects the input transducer and the output transducer. The delay of delay line 12 is one scan period.

When the delayed and undelayed color television signals are summed in circuit 18, a luminance signal component appears. This luminance component, however, has, at the vertically occurring transitions or edges, the string-of-pearl structure mentioned at the beginning. To avoid this phenomenon, an oat 9-wrap device 15 is provided. This oat wrap device 15
supplies the luminance signal blown out by the low-pass filter 17 to the output 16 if such an edge appears. Furthermore, the auto-ratuzo device 15 is controlled by an adaptive control circuit 19.

The color signal is output by subtraction of the delayed and non-delayed color television signals using (9) path 20 and subsequent bandpass filtering.

The other parts of the decoder shown in FIG. 2 correspond to the other parts of the decoder shown in FIG.

The comb filter decoder shown in FIG. 2 is considerably more expensive than the simple decoder shown in FIG. This comb filter decoder is therefore used in equipment where noise-free decoding is particularly important, such as television studio equipment.

In the decoder according to the invention shown in FIG. 3, the luminance signal channel is configured in the same way as in the decoder shown in FIG. The chrominance signal channel is composed of a bandpass filter 21, a transnormal filter 22, 23, a synchronous demodulator 5.6 and a low-pass filter 9, 1o. having a delay time of 2275 times the color carrier period;
In the case of the NTSC system, the transnormal filters 22, 23 separate the color signal from the luminance component in the frequency range of the color signal in the same way as the comb filter shown in FIG.

But it's very simple. This is because in this case only the relatively narrow band color signals that have already been modulated are delayed. Furthermore, the adaptive control-ohno-wrap circuit shown in FIG. 2 can be omitted.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of a known decoder circuit;
The figure is a schematic circuit diagram of a decoder device according to the invention. 2... Delay element, 3... Color printing carrier wave trap, 4...
... Bandpass filter, 5, 6 ... Synchronous demodulator, 9, 1° ... Low-pass filter, 11 ... Modulator, 12 ... Acoustic delay line, 13 ... Amplifier, 14 ...・Demodulator, 1
5...Automatic wrap device, 17...Low pass filter, 19...Adaptive control circuit.

Claims (1)

[Claims] 1. A chrominance signal is extracted from a chrominance television signal by a wave using a band limit and a transversal filter, and a luminance signal is extracted from a frequency existing in the region of chrominance subcarriers, as is known. A method for decoding color television signals, characterized by suppressing and extracting the signals. 2. A color subcarrier trap (3) is provided in the luminance signal channel, and a bandpass filter (21L!:) and a lance nose filter (22, 23) are provided in the color channel. TV signal decoder circuit device. 3 The transparsal filter has two color subcarrier periods.
Decoder circuit arrangement for NTSO signals according to claim 2, comprising a delay device (22) having a delay time of 27.5 times. 4 The transparsal filter has two color subcarrier periods.
The decoder circuit device for PAL signals according to claim 2, having a delay time of 83.7516 times.