JPS63175593A - Color decoder - Google Patents

Abstract

PURPOSE:To prevent undesired coloring surely in regenerating a black/white VTR signal or the like by discriminating the black/white and color signals depending on the presence of a color burst signal and using a luminance signal as R.G.B outputs directly in case of the black/white signal while not using the R.G.B signal obtained from a matrix circuit. CONSTITUTION:A burst signal detection means 17 detecting the presence of the color burst signal in an inputted video signal and a changeover circuit 11 outputting by switching the luminance signal as the R.G.B output in place of the R.G.B output in place of the R.G.B output from a matrix circuit 8 when no burst signal is detected, are provided. When a black/white VTR regenerating signal is inputted as an input to a color decoder, since the burst signal detector 17 detects no burst signal, its output goes to a low level. Thus, the output of a switching circuit 11 is a luminance signal Y'. Thus, the RGB output signal uniform in time phase and voltage level is obtained and the coloring is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a color decoder for reproducing color, black and white VTR tapes, etc.

(Prior art) In this type of color decoder, a color difference signal (RY signal, B-Y signal) obtained from a video signal and a luminance signal Y are input to a matrix circuit to generate R, G, and B signals. It is supposed to be done.

Here, in order to obtain the color difference signal, a color burst signal is detected from the video signal, and a reference signal locked to the phase and frequency of this color burst signal is input to a demodulator for extracting the color difference component. I was letting it happen.

(Problem to be solved by the invention) By the way, for example, in recent years, color Doppler has appeared in ultrasound diagnostic equipment, and color decoders such as those shown in (a) above have come to be used, but images recorded on a VTR using a conventional black and white device cannot be used. The color decoder is also used to reproduce .

At this time, there is no color burst signal in the black and white VTR reproduction signal. In addition to the brightness signal of the image, the black and white VTR playback signal includes pulse-like signals such as dots and markers (approximately 1/2 to 1/4 wavelength of the subcarrier). 3 near the fall.
58 MHz (subcarrier frequency) component is generated. At this time, the PLL is in free oscillation because there is no color burst signal, and a color difference signal is momentarily generated through a demodulator and an LPF (low pass filter).

Due to the slight difference in time phase between this and the Y signal, the dots and markers, which should normally be white, are colored unstable at the left and right edges in the horizontal direction (the hue is often yellow or magenta). There was a problem that a phenomenon in which votes also change over time occurred.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a color decoder that can reliably prevent unnecessary coloring when reproducing black and white VTR signals or the like.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides burst signal detection means for detecting the presence or absence of a color burst signal in an input video signal, and when the burst signal is not detected, the matrix circuit A color decoder is constructed by providing a switching circuit that switches and outputs the luminance signal as R, G, and B outputs instead of the R, G, and B outputs from the color decoder.

(Function) It distinguishes between black and white and color depending on whether or not there is a color burst signal in the bank pouch of the video signal, and when it is black and white, it uses the luminance signal without using the R, G, and B signals obtained through the matrix circuit. are directly switched as R9G and B outputs.

Therefore, in the case of black and white input, the time phases of the R, G, and B signals,
Signals with uniform voltages can be obtained, and unnecessary coloring will not appear.

(Examples) Hereinafter, the present invention will be specifically described based on illustrated examples.

FIG. 1 is a block diagram of a color decoder according to the present invention.

In the figure, the video signal is filtered by a bandpass filter (hereinafter abbreviated as BPF) 1. The signal is input to a notch filter 2 and a synchronization separation circuit 3. Said BPF
1 passes the band of subcarriers (3, 5) of the video signal 6, and the output of this filter is the 1st . The signal is input to second demodulators 4 and 5. The first demodulator 4 detects the filter output based on a signal obtained by shifting a reference signal of the PLL 16, which will be described later, by a 90' shifter, while the second demodulator 5 detects the filter output based on the reference signal of the PLL 16. It detects the wave.

The outputs of both demodulators 4 and 5 are passed through low-pass filters (hereinafter abbreviated as LPF) 6 and 7 to color difference signals R-Y,
It is generated as B-Y and input to the matrix circuit 8 at the subsequent stage.

The notch filter 2 separates the video signal into a luminance signal Y, and outputs this to the matrix circuit 8 via a delay circuit 9. Further, in this embodiment, the output of the notch filter 2 is also output to an attenuator 10, so that a luminance signal Y' is obtained as the attenuator output. Note that the luminance signal @Y' is an attenuated luminance signal @Y before passing through the delay.

The matrix circuit 8 receives the aforementioned color difference signals RY,
It generates and outputs R, G, and B signals from the 8-Y and luminance signals. In addition, in this embodiment, the output of the matrix circuit 8, R,
A switching circuit 11 is provided which selectively selects and outputs the G, B signals and the luminance signal Y' which is the output of the attenuator 10. This switching operation will be described later.

On the other hand, the output of the synchronization separation circuit 3 is input to horizontal and vertical synchronization signal generators 12 and 13, and the output is horizontal.

It is used for generating vertical synchronization signals.

In addition, the horizontal synchronization signal is generated by the burst signal timing generator 1.
4 and is used for generating the burst position signal @BF. This burst position -〇- signal BF is generated at the timing of the horizontal synchronization signal as shown in FIG. 2, and is generated at T1. T2 can be adjusted depending on the VTR used.

The gate amplifier 15 to which this pressure reduction signal is input is connected to the BP
The color burst signal corresponding to the liver signal from the output of F1 is separated and output. As a result, only the color burst signal is transmitted to the PLL' during 1H synchronization.
16, and the reference signal @fRE[ which is locked to the phase and frequency of this color burst signal is generated.

Further, in this embodiment, a burst signal detector 17 is provided which detects the presence or absence of a color burst signal based on the output of the gate amplifier 15. This burst signal detector 17
If there is a burst signal for 1H cycle, its output 8FO
1 is set as HIGI-1, and when this output BFO1 is HIGH, the switching circuit 11 selects the R, G, and B signals. Conversely, when a burst signal is not detected, such as when a black and white VTR playback signal is manually input, the output BFO 1 is set to LOW and the switching path 11
The luminance signal @Y' is selected with .

According to the color decoder described above, when a color VTR reproduction signal is input, the burst signal detector 1
7, a burst signal is always detected, so its output BO
F1 is always HIGH.

Therefore, R, G, and B signals are obtained as the output of the switching circuit 11, so that color display is possible.

On the other hand, when a black and white VTR playback signal is input to the color decoder, the burst signal detector 1
Since the burst signal is not detected at 7, its output BOF
1 becomes LOW. Therefore, the output of the switching circuit 11 becomes the luminance signal Y'.

Therefore, the R, G, and B outputs have the same time phase and voltage level, and the above-mentioned coloring can be prevented. As mentioned above, the luminance signal Y' is an attenuator of the luminance signal Y before passing through the delay, but this is because the f-characteristic deteriorates when passing through the delay, etc., and this is intended for gain correction. I'll go to market.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the gist of the present invention.

[Effects of the Invention] As described above, according to the present invention, even when a black and white video signal is reproduced by a color decoder, unnecessary coloring does not appear, and the quality of the image is improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color decoder according to the present invention, and FIG. 2 is a timing chart showing detection of a color burst position signal. 8... Matrix circuit, 11... Switching circuit, 17
...Burst signal detection means. Agent Patent Attorney Norihiro Chika Kenshu Daigo Norifu −〇−

Claims (2)

[Claims] (1) A color difference signal obtained by detection based on a reference signal locked to the phase and frequency of a color burst signal in a video signal and a luminance signal separated from the video signal are input to a matrix circuit, A color decoder that obtains G and B outputs includes a burst signal detection means for detecting the presence or absence of the color burst signal, and when the burst signal is not detected, the luminance signal is changed to the R, G, and B outputs from the matrix circuit. A color decoder comprising a switching circuit that switches and outputs R, G, and B outputs. (2) A patent claim in which the luminance signal output from the switching circuit is obtained by attenuating the luminance signal separated from the video signal before passing it through a delay circuit to match the time phase with the color difference signal. The color decoder according to range 1 above.