JPS5917591B2 - Color television signal transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color television signal transmission system in which a color signal is time-base compressed, time-division multiplexed to a luminance signal, and transmitted, and particularly relates to an improvement in a color signal transmission system. be.

In a color television signal, the signal amplitudes of the luminance signal Y and color signals I and Q used in the NTSC 3C system are expressed by the following equations.

0.300.590.11 0.60-0.28-0.32 0.21-0.520.31 Now, if the R, G, and B signals vary between amplitudes 0 and 1, Yku1 -0.6≦1≦0.6 --- 0.52≦Q≦+0.52.

The maximum signal change width of the color signal is 1.2. The 1Vpp composite video signal has a synchronization signal amplitude of 0, 3V, 0 video (luminance)
It consists of a signal amplitude of O and 7V.

At this time, the maximum signal change width of the color signal is 1.2V x 0.7-
O, 84V. Conventionally, color television signals are transmitted by compressing the color signal in the time axis and time-division multiplexing it into the luminance signal; in the transmission system, as shown in Figure 1, the color signal is The DC reference level XL for I and Q was set at approximately 0.84 x 1/2 = 0.42V with respect to the pedestal level XL for brightness for transmission.

Alternatively, the color signals I and Q are limited to variations of ±O, 35V, and the DC reference level XL of the color signal is set at a position of approximately O, 35V with respect to the luminance pedestal level YL, and transmitted. Therefore, if the transmission line is overloaded,
Along with changes in the white level of luminance/signal Y, color signals I,
There was a drawback that color change occurred due to Q overload.

Although the visual effect of a change in the vicinity of the white level of the luminance signal Y is slight, a change in color causes a large visual deterioration because the hue itself changes. In order to eliminate these drawbacks, the present invention takes advantage of the fact that the S/N ratio standard for chrominance signals is looser than that for luminance signals, lowers the signal amplitude of chrominance signals, and lowers the DC reference level of chrominance signals. This device is designed to suppress color changes due to overload, and will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, where A is the luminance signal amplitude,
B is the color signal amplitude, and C is the color signal DC reference level.

S/N required for brightness signal of color television signal
It is a well-known fact that the S/N ratio required for color signals is about 10 dB lower than that for color signals.

The present invention focuses on this point, and transmits the color signal by lowering the level of the color signal by αDB at the transmitter, and amplifies it by αDB at the receiving end.

That is, in the transmission path, A. B. Set the value of C.

FIG. 3 shows an embodiment for realizing this. 1 is I
Signal input terminal, 2 is Q signal input terminal, 3 is Y signal input terminal, 4 is switch, 5 is clamper 6 is time axis compression circuit,
7 is an attenuator, 8 is a clamper, 9 is a switch, 10 is a color television signal output terminal, 11 is a color television signal input terminal, 12 is a clamper, 13 is a switch, 14
is an amplifier, 15 is a time axis expansion circuit, 16 is a color signal interpolation circuit, 17 is an I signal output terminal, 18 is a Q signal output terminal, 1
9 is a Y signal output terminal.

In addition, FIG. 3A represents a transmitting section, and the opening represents a receiving section. Color signals 1 and Q are input to input terminals 1 and 2, and converted into line sequential signals by a switch 4.

The clamper 5 key-clamps a part of the blanking period of the line sequential signal, and performs 1. Match the DC level of the Q signal. Further, the DC output voltage is set so that the output of the clamper 5 is biased approximately at the center of the allowable change range of the input signal of the memory of the time axis compression circuit 6. In the time axis compression circuit 6, the color signal is written using a low speed clock and read out using a high speed clock, thereby compressing the time axis. Time axis compression circuit 6
The output of the compressed color signal is kept at the ground potential during the DC reference level (achromatic color level) and the period when the compressed color signal is not present, and the color signal changes between positive and negative with respect to the ground potential. Attenuator 7 is the main point of the invention and attenuates the compressed color signal by about 5 dB. On the other hand, the brightness signal is output by the clamper 8.
The DC output voltage is set so that the level of about +0.2V from the pedestal level or +0.5V from the bottom of the synchronizing signal becomes the ground potential. The switch 9 switches between the output of the attenuator 7 and the output of the clamper 8, and outputs the signal shown in FIG. 2 from the terminal 10. On the other hand, in the receiving section, the signal shown in FIG. 2 is input to the terminal 11.

The clamper 12 performs DC regeneration and sets the DC output voltage so that the DC reference level of the color signal is at ground potential.
The switch 13 separates the luminance signal and the color signal. In the separated luminance signal, the portion where the color signal was multiplexed is replaced with the black level (pedestal) of the luminance signal sent during the vertical retrace period. The compressed signal is kept at the DC reference level and at ground potential during the period when the compressed color signal is not present, and is input to the amplifier 14, where it is amplified by 5 dB.

This compensates for the attenuation due to attenuator 7. Amplifier 14
The DC output voltage of is set approximately at the center of the allowable change range of the input signal of the memory of the time axis expansion circuit 15. Since the color signal whose time axis has been expanded by the time axis expansion circuit 15 is a line sequential signal, the color signal is processed by the color signal interpolation circuit 16 in 1. Convert to simultaneous Q signal. Therefore, the I signal is at terminal 17, and the I signal is at terminal 1.
8 is the Q signal, terminal 19 is the Y signal, terminals 1, 2, 3
output at the same amplitude level as the input signal level. As explained above, the direct reference level of the color signal is set to the ground potential, and in the case of the compressed color signal, the period when the compressed color signal does not exist is set to the ground potential to attenuate and amplify the signal. Only the amplitude of the signal can be attenuated or amplified without changing the level.

Note that in the above explanation, the color signal is 1. I explained about the Q signal, but the R-Y. The B-Y signal may be used, or any other suitable color signal may be used.

In addition, the amount by which the amplitude level of the color signal is lowered by 5 dB in the transmitting section is
There is no need to limit the DC reference level of the color signal to +0.5V from the bottom of the synchronization signal, as long as the above conditional expressions (1), (2), and (3) are satisfied. good. As explained above, since the signal amplitude of the color signal is lowered and the DC reference level of the color signal is lowered, even if an overload occurs on the transmission path, the color can be maintained within an acceptable range for a monochrome image. No change occurs. Furthermore, if the present invention is applied to a method of time-divisionally transmitting color signals and luminance signals, it is highly effective in reducing color changes caused by nonlinear distortion occurring in the transmission path.

[Brief explanation of drawings]

Figure 1 is a waveform diagram showing the amplitude level of the color signal of the conventional color signal.
3 is a waveform diagram showing an example of the amplitude level of a color signal according to the present invention, and FIG. 3 is a block diagram showing an example of a circuit for obtaining the signal according to the present invention. 1...I signal input terminal, 2...Q signal input terminal, 3...Y signal input terminal, 4...
...Switch, 5...Clamper, 6...
・Time axis compression circuit, 7... Attenuator, 8...
...Clamper, 9...Switch, 10...
...Color television signal output terminal, 11...
・Color television signal input terminal, 12...
Clamper, 13...Switch, 14...
・Amplifier, 15... Time axis expansion circuit, 16...
...Color signal interpolation circuit, 17...I signal output terminal, 18...Q signal output terminal, 19...
...Y signal output terminal.

Claims (1)

[Claims] 1. In a color television signal transmission system that compresses the color signal in the time axis and transmits it by time-division multiplexing with the luminance signal, the maximum amplitude of the color signal is set lower than the maximum amplitude of the luminance signal amplitude, and the DC reference level of the color signal is A color television signal transmission system characterized in that the luminance signal amplitude is lower than 50% of the luminance signal amplitude.