KR890004227B1 - Devices for processing colour signals - Google Patents

Abstract

The processor is to rationalize the recording level of a colour signal by detecting the level of the input colour signal, comparing the output with a reference level, synchronizing the output signal of the compared result with a vertical synchronous signal, and controlling a gain switching circuit. The level of the colour signal input to a terminal (11) is detected by a level detector (14) and compared with the reference level of a reference level generator (16) by a level comparator (15). If the colour signal level is lower than the reference level, a high level signal is output from the comparator. On the contrary, a low level signal is output.

Description

Color signal processing device

1 is a block diagram showing an embodiment of a conventional ACC circuit.

2 is a block diagram showing the configuration of an embodiment of the present invention.

3 is a block diagram showing the configuration of another embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

12: gain switching circuit 14: level detector

15: Level comparator 17: D flip flop

31: ACC circuit

The present invention relates to a color signal processing apparatus that can be used for a video tape recorder or the like.

In a public video tape recorder, a method of recording and reproducing a video signal by dividing it into a luminance signal and a color signal is used. In such a method, conventionally, a method of making the burst level of a color signal to be recorded constant so that the recording level of the color signal is corrected during recording is used.

Next, a conventional example will be described with reference to FIG. FIG. 1 is a block diagram of an auto chromamer control circuit (hereinafter referred to as an ACC circuit) conventionally used to make the burst level of a color signal constant during recording. In recording, a color signal is input from the input terminal 1 to the variable gain amplifier 2. The output of the variable gain amplifier 2 is taken out of the output terminal 6 and sent to the recording circuit, while the burst level detector 4 detects the level of the burst signal. The burst level obtained by the burst level detector 4 is compared with the reference level generated by the reference level generator 5 in the level comparator 3, the output of which controls the variable second amplifier 2. As a result, the output terminal 6 can obtain a color signal whose burst level is always the same as the reference level.

However, the above structure has a drawback that the SN ratio deteriorates when the color signal level is low in order to keep the burst level constant.

An object of the present invention is to change the gain of the color signal amplification when the color signal level is low at the time of recording so that the recording level is increased so that the SN ratio of the color signal is always maintained, and the switching timing is synchronized with the vertical synchronization signal to thereby reproduce the reproduction screen. An object of the present invention is to provide a color signal processing apparatus in which the effect of the level change in gain switching is not conspicuous.

In addition, the present invention improves the SN ratio of the color signal by switching the reference level of the conventional ACC circuit so that the output level of the ACC circuit increases when the color signal level is low and increasing the recording level. In addition, the timing of switching the reference level is to provide a color signal processing apparatus which synchronizes with the vertical synchronization signal so that the effect of the change of the recording level on the reproduction screen is not conspicuous.

The color signal processing apparatus of the present invention includes a level detector for detecting a level of a color signal, a level comparator for comparing the output of the level detector with a reference level, a reference level generator for generating a reference level, and an output of the level comparator. A synchronization circuit for synchronizing with the ong signal and a gain switching circuit for switching the gain of the color signal by the output of the synchronization circuit and amplifying the gain, so that when the color signal level is low in recording, the amplification gain of the color signal is synchronized with the vertical synchronization circuit. To change the color signal level and to record.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings.

2 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, the color signal inputted to the input terminal 11 is detected by the level detector 14, and is compared with the reference level generated by the reference level generator 16 and the level comparator 15. As a result, for example, when the color signal level is lower than the reference level, a signal of high level and vice versa appears at the output of the level comparator 15. This output becomes a signal synchronized with the vertical synchronizing signal input from the input terminal 18 at the D flip-flop 17, and switches the id of the gain switching circuit 12. FIG. In this case, the gain switching circuit 12, for example, has a gain greater than 1 when the output Q of the D flip-flop 17 is at a high level, and the gain is 1 when at a low level. When low, the color signal inputted from the input terminal 11 is amplified and appears on the pull terminal 13. In addition, by making the level detector 14 have a low pass filter characteristic, it is possible to delay the change of the output of the level detector 14, thereby preventing frequent switching of the gain. In addition, the level comparator 15 has hysteresis characteristics to prevent chattering from occurring when the output of the level comparator 15 is equal to the output level of the level detector 14 and the output of the reference level generator 16. Can be. In addition, the color signal processing bag apparatus of the present embodiment may be used together with the conventional ACC circuit described above, and in this case, the same effect can be obtained even if the present embodiment is placed before and after the conventional ACC circuit.

Next, the present invention will be described with reference to FIG. 3 with respect to another embodiment. 3 is a block diagram showing the configuration of another embodiment of the present invention.

The color signal input to the input terminal 20 is a variable gain amplifier 21 and a burst level detector 29. By the ACC circuit 31 composed of the level comparator 28 and the reference level generator 27, the burst level is controlled to be equal to the reference level generated by the reference level generator 27 as described in the conventional configuration. It is output to the terminal 22 and sent to the recording circuit. On the other hand, the color signal input from the input terminal 20 is level detected by the level detector 23, and compared with the reference level generated by the reference level generator 25 and the level comparator 24, as described in the first embodiment. do. This output becomes a signal synchronized with the vertical synchronization signal input from the input terminal 30 at the D flip-flop 26 and is obtained at the output Q. This output is used to determine the reference level at which the reference level generator 27 is generated. Switch. As described above, since the ACC circuit 31 is controlled such that the burst level of the output color signal is equal to the reference level generated by the reference level generator 27, by switching the reference level generated by the reference level generator 27. The color signal level obtained at the output terminal 22 can be switched. As a result, when the color signal level input to the input terminal 20 is low, the signal level obtained by the output terminal 22 can be increased.

Moreover, it has the function of the conventional ACC circuit in this embodiment, that is, the function which keeps a burst level constant.

As in the first embodiment, the level detector 23 may have a low pass filter characteristic, and the level comparator 24 may have a hysteresis characteristic.

As apparent from the above description, the present invention can switch to increase the gain of the gain switching circuit when the color signal level is low at the time of recording, thereby increasing the recording level of the color signal, thereby improving the SN ratio. Also, by synchronizing the switching timing with the vertical synchronization signal, the level change at the time of switching is performed by the operation of the ACC circuit (circuit which makes the burst level of the reproduction color signal constant) during reproduction even when the portion where the recording level is switched is reproduced. There is an effect that makes the effect of inconspicuous.

In addition, by having the low pass filter characteristic in the level detector and the hysteresis characteristic in the level comparator, it is possible to prevent frequent gain conversion of the color signal amplification or chattering at the output of the level comparator.

In addition, the present invention uses a method of switching the reference level of the conventional ACC circuit as a means for switching the color signal gain, so that when the color signal level is low, it can increase the recording level of the color signal and also have the function of the conventional ACC circuit. have.

Claims (4)

A level detector 14 for detecting the level of the color signal, a first level comparator 15 for comparing the output of the level detector with a reference level, a first reference level generator 16 for generating the reference level, and And a gain switching circuit (12) for switching the gain of the first level comparator to the vertical synchronization signal and the gain switching circuit (12) for switching the gain of the color signal by the output of the synchronization circuit. . The gain switching circuit (12) according to claim 1, wherein the gain switching circuit (12) detects a variable gain amplifier (21) for amplifying a color signal with a gain determined according to a control signal, and a burst level of the color signal obtained at the output of the variable gain amplifier. A second level comparator 28 which compares the bias level detector 29 with the output of the burst level detector and a reference level, and obtains a signal for controlling the gain of the variable gain amplifier; and controls the reference level. A second reference level generator 27 is generated which switches in accordance with a control signal given as an input, wherein the input and output of the gain switching circuit 12 are respectively input and output of the variable gain amplifier 21. And a reference level generated by the second reference level generator (27) as a gain switching method of the gain switching circuit (12). The color signal processing apparatus according to claim 1, wherein the level detector (14) has a low pass filter characteristic in the level detector. 2. The color signal processing apparatus according to claim 1, wherein the first level comparator (16) has hysteresis characteristics.

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