JPS5853809Y2 - Color/black and white detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a color and black-and-white detection device that can be used for video tape recorders (hereinafter simply referred to as VTRs), particularly simple VTRs, and provides an inexpensive and reliable device. .

In a VTR, color television signals are generally recorded by converting a carrier color signal to a low frequency of 700 KH, and combining this with a luminance and synchronization signal converted into a frequency modulated wave existing between approximately 1 and 4 MHz. I try to record it using

This is because by using the upper limit 1 of the frequency band that can be recorded and reproduced as the recording band for luminance and synchronization signals, the resolution can be improved and the band can be used effectively.

However, in such a VTR, the portion of the frequency band below about IMHz is only used for recording the carrier color signal during color recording, so when recording and reproducing black and white television signals, the recording and reproducing circuit for the luminance component is used. It is necessary to remove signals in this band in order to prevent noise signals from being mixed in.

Therefore, for this purpose, this type of VTR automatically detects whether the signal is a color television signal or a monochrome television signal, and the recording/reproducing circuit is switched and controlled as described above based on the detection output.

The present invention relates to a color/monochrome detection device used for such purposes in a VTR.

Hereinafter, a conventional color and monochrome device will first be explained with reference to FIG.

In FIG. 1, reference numeral 1 denotes an input terminal to which a composite video signal is input.

2 is a bandpass filter for extracting only the carrier color signal; 3 is a variable gain control circuit; and 4 is a color burst separation circuit, which performs a gate function by a color burst separation pulse inputted from a terminal 5.

6 is a narrow band filter such as a crystal resonator, and 7 is a rectifier circuit including a low-pass filter to obtain a control signal for the variable gain control circuit 3.

Terminal 8 is an output terminal for a carrier color signal whose gain is controlled, and is connected to a signal processing circuit such as a low frequency conversion circuit.

Reference numeral 9 denotes a color/monochrome detection circuit composed of a voltage comparison circuit such as a Schmitt circuit, and 10 outputs a high level or low level DC voltage as a discrimination output at its output terminal.

The carrier color signal extracted by the bandpass filter 2 is applied to a variable gain control circuit 3, gain-controlled, and output to an output terminal 8. At the same time, it is supplied to a color burst separation circuit 4, and the gate is turned off only during the burst period. It is opened and output.

However, a problem with power gourd detection is that during the period when the gate in the output signal of the burst separation circuit 4 is open, random noise in the passband of the bandpass filter 2 and the color burst separation circuit may be generated in addition to the color burst. In addition to the switching noise, the frequency components included in the trailing edge of the horizontal synchronization signal may include unnecessary components that have passed through the bandpass filter 2.

Among these unnecessary components, the influence of the trailing edge in the horizontal synchronization signal is particularly detrimental to detection.Since the band of the bandpass filter 2 is relatively narrow, ringing occurs over a long period of time, resulting in a burst period. Continue inside.

In the normal case where the level of the burst signal and the level of the synchronization signal are equal as determined by the tide path of the NTSC system, the magnitude is -15 d with respect to the level of the burst signal.
The value is about B.

On the other hand, visually on the screen of a television receiver, a good quality image can be obtained as a color image in the range of -25 dB 1 with respect to the normal burst level, so the color If the size of the burst is within the range of -25 dB relative to the amplitude of the synchronizing signal, it is determined that the signal is a color signal.

Therefore, if an unnecessary signal larger than the detection level of a color signal or a black and white signal is mixed in, it is recommended to directly determine whether it is a color signal or a black and white signal by adjusting the output signal amplitude of the color burst separation circuit. Since unnecessary components such as ringing are large, malfunctions may occur.

Conventionally, as shown in FIG. 1, a narrow band filter 6 such as a crystal oscillator with a very narrow band is used to suppress the unnecessary components, and the continuous wave output from the filter 6 is rectified by a rectifier circuit 7. , a gain control signal, and at the same time, a color/black/white detection circuit 9 comprising a voltage comparison circuit such as a Schmitt circuit compares it with a reference voltage to obtain a discrimination output.

With such a device, a reliable discrimination output can be obtained during recording, so color and black-and-white detection during playback can be performed only by detecting the color burst level, eliminating the need for discrimination by phase comparison using an A20 circuit, and performing jitter correction. This is particularly effective when performing the following using only the AFC circuit.

Here, the AFC circuit is used to inversely convert the reproduced low frequency converted carrier color signal of the VTR to obtain the regular carrier color signal frequency.
The A20 circuit is a circuit for making the carrier color signal frequency output to the television monitor equal to the frequency of a reference oscillator without jitter, and the A20 circuit is a circuit for making the carrier color signal frequency output to the television monitor equal to the frequency of a reference oscillator without jitter. This is to synchronize with the phase of the reference oscillator, and both remove jitter components.

Therefore, if the response of the AFC circuit is sufficiently fast, APC is not necessary for jitter correction, but it is difficult to determine whether the reproduced signal is a color signal or a monochrome signal if an uncertain color killer operation is performed during recording. In many cases, it is difficult to do this except by using a method of determining whether or not the A20 circuit is in a synchronous state.

Furthermore, although the conventional color/black and white detection device using a crystal filter has the above-mentioned advantage in that discrimination is reliable, it has the disadvantage that the crystal filter that is required separately is expensive and is not suitable for simple VTRs. .

Therefore, the present invention solves this problem by sharing a delay line (hereinafter referred to as a 1H delay line) with a delay time of one horizontal period, which is required in the reproduction signal processing circuit system of a VTR, etc., during recording. The object of the present invention is to provide a color/monochrome detection device that operates reliably and can be easily obtained at low cost.

Hereinafter, the present invention will be explained with reference to FIGS. 2-3 showing an embodiment thereof.

FIG. 2 shows a part of a recording system of a VTR including an embodiment of the color/monochrome detection device of the present invention.

Circuit portions that perform operations similar to those of the conventional example are indicated by the same numbers as in FIG. 1, and description thereof will be omitted.

Here, 11 is a 1H delay line, 12 is a subtraction circuit such as a differential amplifier, 13.degree.14 is a switch circuit, and 15.16 is a terminal connected to a predetermined reproduction signal processing circuit.

During the period when the gate of the color burst separation circuit output is open, the bandpass filter 2 generates an unnecessary component other than the color burst.
A ringing component exists due to random noise in the passband of , switching noise during color burst separation, and the trailing edge of the horizontal synchronization signal.

Of these, the ringing and switching noises are synchronized with the horizontal synchronization signal because the color burst separation pulse is created using the horizontal synchronization signal.

Therefore, when the 1H delay line 11 and the subtraction circuit 12 are connected as a comb filter as shown in FIG.
The current output from the burst separation circuit 4 and the output from one horizontal period before are applied as the two inputs of the burst separation circuit 4, and the ringing components with the same phase and amplitude and the gate time are applied to both outputs. When the switching noise of 1 is included, these are canceled out by the subtraction circuit 12, and the ringing component and the switching noise are not output in the output.

On the other hand, as for the random noise component, since there is no canceling effect, the noise level of the output of the subtraction circuit 12 is four times the output noise level of the color burst separation circuit 4.

On the other hand, in the NTSC system, the phase of the color burst signal is inverted every horizontal period, so the subtraction circuit 12
The output voltage is twice the voltage of the output burst signal from the burst separation circuit 4.

As is clear from the above explanation, the output of the subtraction circuit 12 does not include ringing components and switching noise, and the S/N of the color burst signal is also improved by 3 dB.

Therefore, by rectifying the output of the subtraction circuit 12 to obtain a control voltage for gain control and comparing it with the reference voltage in the voltage comparison circuit of the color/black-and-white detection circuit 9, it is possible to accurately detect and discriminate whether the signal is a color signal or a black-and-white signal. The output can be output to the terminal 10.

FIG. 3 shows another embodiment of the color/monochrome detection device of the present invention.

The configuration shown in FIG. 3 replaces the color burst separation circuit 4 in the embodiment shown in FIG. It operates similarly to that of FIG. 2, except that the switching noise in the output of circuit 4 is hardly canceled out.

Switching noise is generated by the transient response of the color burst separation circuit 4, so if a circuit configuration with good transient characteristics is selected as the gate circuit for the color burst signal, it will not affect the gain control operation and the color/monochrome detection operation. It is possible.

On the other hand, two 1H delay lines are normally used in a VTR reproducing circuit system.

The first is a 1H delay line for replacing and outputting an output signal from 1H period before when the output signal drops out, and the second is used together with a subtraction circuit to form a comb filter.

This comb-shaped fin letter is used to improve the S/N ratio of the carrier color signal or to suppress unnecessary carrier color signals detected from adjacent recording tracks.

Therefore, the 1H delay line 11 and two switch circuits 13 and 14 necessary for the color and monochrome detection device of the present invention as described above are required.
Therefore, the filters used in the reproduction circuit can be switched and connected, and the subtractor circuit 12 and the 1H delay line 11 connected together are generally used as a comb filter in the reproduction color signal processing circuit. , 2nd, 3rd
As shown by the broken line in the figure, the connection position of the switch circuit 14 is provided on the output side of the subtraction circuit 12, so that this subtraction circuit 12 can also be used in common with the one in the reproduced color signal processing circuit.

In such a case, connecting the terminals 15 and 16 to the connection part between the circuits before and after the 1H delay line or the combination circuit of the 1H delay line and the subtraction circuit in the reproduction circuit or reproduction color signal processing circuit is referred to as 1. not.

In the above explanation, the amplitude of the signal is not attenuated in the 1H delay line 11, but when an ultrasonic delay line or the like is used, the attenuation of the amplitude of the signal is large.
It is necessary to make the magnitudes of the two input signals to the subtraction circuit 12 as equal as possible by amplifying the delayed output or by amplifying it in advance and then delaying it.

As described above, the color/black-and-white detection device of the present invention combs out the ringing component of the trailing edge of the horizontal synchronizing signal, the gate noise of the color burst signal, and other random noise contained in the output signal of the color burst separation circuit. The color burst of the output of the comb filter is detected and a signal corresponding to the amplitude is obtained to detect whether the signal is a color signal or a black and white signal. The combination circuit of a delay line or a 1H delay line and a subtraction circuit is shared and switched with those used in the reproduction signal processing circuit of a magnetic recording/reproduction device such as a VTR, so it has an extremely simple configuration. It can be obtained at low cost.

Furthermore, since the comb filter is provided in the color killer detection path located outside the passage path of the carrier color signal to be recorded, there is no possibility that the vertical resolution of the carrier color signal will be degraded and the image quality will be degraded.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional color and monochrome detection device, and FIGS. 2 and 3 are block diagrams of a color and monochrome detection device according to an embodiment of the present invention. 1...Input terminal, 4...Band filter,
3... Variable gain control circuit, 4... Color burst separation circuit, 5... Color burst separation pulse input terminal, T... Rectifier circuit, 8・
...Output terminal, 9...Color and black and white detection circuit, 10...Output terminal, 11...1H
Delay line, 12... Subtraction circuit, 13, 14...
...Switch circuit, 15, 16... terminal.

Claims (1)

[Scope of utility model registration request] A comb filter consisting of a 1H delay line and a subtraction circuit is provided in the color killer detection path, and the input television signal or the color burst signal extracted from it is input to this comb filter, and the color output side of this comb filter is The amplitude of the burst signal is detected to determine whether the television signal is a color signal or a monochrome signal, and a 1H delay line and a subtraction circuit are used during reproduction signal processing of a magnetic recording and reproduction device. A color/black-white detection device configured to share a comb-shaped filter or a 1H delay line consisting of the above with a switch circuit so as to be used as a comb-shaped filter for color/black-white discrimination or a 1H delay line constituting the comb-shaped filter. .