JPH0287885A - Video signal circuit - Google Patents

Abstract

PURPOSE:To reproduce a stable sub-screen even if a video input level of a main screen is fluctuated by inserting a burst signal synchronized with a burst signal of a main screen video signal into a sub-screen chrominance signal, and executing a control so that it amplitude becomes equal to amplitude of the burst signal of the main screen video signal. CONSTITUTION:The title circuit is provided with a first level detector 20 for detecting a burst signal level of a first chrominance signal, and a burst inserting circuit 16 for inserting a burst signal synchronized with a burst signal of a first chrominance signal into a second chrominance signal. Also, said circuit is provided with a second level detector 18 for detecting an output burst signal level of an ACC circuit 17, and a level comparator 19 for comparing said signal level with an output of a first level detector 20 and controlling the gain of the ACC circuit 17 so that the burst signal level of the output of the ACC circuit 17 becomes the same as the burst signal level of a first chrominance signal. In such a way, even if amplitude of a main screen video signal is varied, it does not occur that a color of a sub-screen becomes too dark and the screen becomes unnatural relatively, and a stable reproducing image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal circuit, and more particularly to a video signal circuit having a two-screen synthesis circuit.

[Conventional technology]

Dual screen composition (hereinafter referred to as P-I N) built into VTRs, etc.
The P-INP circuit has the function of inserting a sub-screen video signal into a specific area of the main-screen video signal (for example, tuner output), and transfers the P-INP circuit output from the VTR to the T-INP circuit.
If input to a V receiver, an image with a sub-screen inserted into the main screen can be played back.

FIG. 3 is a block diagram for explaining a conventional video signal circuit.

As shown in FIG. 3, the main screen video signal is transferred to the switch 13
and is also input to the bandpass filter 1.

The carrier color signal separated by bandpass filter 1 is A CC
(automatic chromacontrol
) is input to a circuit 2, and its output forms a loop with a level detector 3 so that the amplitude is constant. The output of the ACC circuit 2 is further converted into an APC (automatic ph
control) is input to the circuit 4, passed through the low-pass filter 5, and converted to direct current, 4×f. Vco
input to circuit 7 (where rsc is the subcarrier frequency),
The output of the 4XfscVC○ circuit 7 is fs by the 1/4 frequency divider 6.
The frequency is divided into 4 x f and input to the APC circuit 4.
A loop is formed so that the 5cVc O circuit 7 performs accurate oscillation. The output of the 4×f scv CO circuit 7 is input to the memory processing circuit 8 as a clock forming signal. On the other hand, the chroma decoder 9 extracts a color difference signal R-Y, a color difference signal B-Y, a luminance signal Y, a horizontal synchronization signal HD, and a vertical synchronization signal VD from the sub-screen video signal, and inputs each to the memory processing circuit 8. be done. Memory processing circuit 8
The color difference signal R-Y, the color difference signal B-Y, and the luminance signal Y are A-to-D converted and written, and reading is performed at a timing synchronized with the main screen video signal. in this case,
If reading is performed at three times as many clocks as writing, the time axis of the sub-screen will be compressed to 1/3. The encoded carrier chrominance signal and luminance signal Y are output from the memory processing circuit 8, and are passed through a bandpass filter 10. Low pass filter 1
1 and is input to the adder 12. The main screen video signal is input to the other input of the switch 13, and the switching signal switches between the main screen video signal and the sub-screen compressed video signal output from the adder 12. In this case, the carrier color signal of the sub-screen compressed video signal has a phase based on the burst signal of the main-screen video signal.

[Problem to be solved by the invention]

In the conventional video signal circuit described above, when the output video signal is played back on a TV receiver, if the amplitude of the color subcarrier of the main screen video signal changes, the color density of the sub screen will also change. There were drawbacks. In other words, in a TV receiver, the ACC circuit works so that the burst signal of the input video signal has a constant value, so for example, when the amplitude of the burst signal of the main screen video signal is small, the main screen is
Due to the CC circuit, the color signal is corrected to normal and can be reproduced, but even though the amplitude of the compressed video signal for the sub screen is normal,
There is a problem in that the color of the sub-screen becomes darker due to the correction of the CC circuit, resulting in an unsightly screen.

[Means to solve the problem]

The video signal circuit of the present invention is a video signal circuit that synthesizes two video screens using a second carrier color signal synchronized with the phase of a burst signal of a first carrier color signal. a first level detector for detecting a signal level; a burst insertion circuit for inserting a burst signal synchronized with a burst signal of the first carrier color signal into a second carrier color signal; and an output of the burst insertion circuit. an ACC circuit that adjusts the amplitude of the parsed signal; a second level detector that detects the burst signal level of the ACC circuit output;
The outputs of the first level detector and the second level detector are compared so that the burst signal level of the ACC circuit output becomes the same as the burst signal level of the first carrier color signal. and a level comparator that controls the gain of the circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram for explaining a first embodiment of the present invention.

The portion surrounded by the broken line in FIG. 1 is according to the present invention, and the structure other than the broken line portion is the same as that of the conventional example. The main screen video signal passes through a bandpass filter 1 to a first carrier color signal 1.
4 is taken out and input to the first level detector 20. The first level detector detects the amplitude of the burst signal of the first carrier color signal 14 and inputs it to the level comparator 19 . A burst signal is inserted into the second carrier color signal, which is the sub-screen carrier color signal, by a burst insertion circuit 16 . The burst insertion circuit 16 outputs the output (fsc) of the 1/4 frequency divider 6.
is input, a burst signal is inserted into the second carrier color signal only during the burst gate pulse period, and its output is input to the ACC circuit 17.

The gain of the ACC circuit 17 is controlled by the output of the level comparator 19, and the output of the ACC circuit 17 is controlled by the output of the second level detector 1.
8 detects the amplitude of the burst signal, and the level comparator 19 detects the amplitude of the burst signal.
is input. The level comparator 19 compares the amplitude of the burst signal of the carrier color signal for the main screen with the amplitude of the burst signal of the carrier color signal for the sub-screen, and controls the gain of the ACC circuit 17 so that the amplitudes are equal. . Therefore, A.C.
Since the amplitude of the carrier color signal output from the C circuit 17 changes in the same way as the amplitude of the burst signal of the main screen video signal, if the video output from the circuit configuration shown in FIG. 1 is played back on a TV receiver, Even if the amplitude of the main screen video signal changes, the color of the sub screen will not become too dark or the screen will look relatively unnatural, and a stable reproduced image can be obtained.

FIG. 2 is a block diagram for explaining a second embodiment of the present invention. The amplitude control signal 21 is transmitted to the burst insertion circuit 16
It has the same configuration as the first embodiment except that it is input to the second carrier color signal, and the amplitude of the burst signal to be inserted into the second carrier color signal can be arbitrarily set.

In the second embodiment, as in the case of the first embodiment, if the video output of the switching device 13 is played back on the TV receiver, a stable signal that is not affected by the amplitude of the main screen video signal can be obtained. This has the effect of not only being able to reproduce the sub-screen, but also allowing the color shading of the sub-screen to be arbitrarily adjusted independently of the main screen.

〔Effect of the invention〕

As explained above, the present invention inserts a burst signal synchronized with the burst signal of the main screen video signal into the sub-screen carrier color signal, so that the amplitude of the burst signal of the sub-screen carrier color signal is equal to the main screen video signal. By controlling the sub-screen carrier color signal using the ACC circuit so that it is equal to the amplitude of the burst signal, the sub-screen can be reproduced stably even if the main screen video input level fluctuates. .

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining a first embodiment of the present invention, FIG. 2 is a block diagram for explaining a second embodiment of the present invention, and FIG. 3 is a block diagram for explaining a conventional video signal circuit. FIG. 2 is a block diagram for explanation. 1...Band filter, 2...ACC circuit, 3...
Level detector, 4...APC circuit, 5...Low pass filter, 6-1/4 frequency divider, 7-4 X f scV
C0 circuit, 8...Memory processing circuit, 9...Chroma decoder, 10...Band filter, 11...Low pass filter, 12...Adder, 13...Switcher, 14...
...first carrier color signal, 15...second carrier color signal,
16... Burst insertion circuit, ]7... ACC circuit,
18... Second level detector, one... Level comparator, 20... First level detector, 21... Amplitude control signal. Shi7 purification issue

Claims (1)

[Claims] In a video signal circuit that synthesizes two video screens using a second carrier color signal that is synchronized with the phase of a burst signal of the first carrier color signal, a first carrier color signal that detects the burst signal level of the first carrier color signal is provided. a level detector; a burst insertion circuit that inserts a burst signal synchronized with the burst signal of the first carrier color signal into a second carrier color signal; and an ACC that adjusts the amplitude of the burst signal output from the burst insertion circuit.
a second level detector that detects the burst signal level of the ACC circuit output, and a second level detector that compares the outputs of the first level detector and the second level detector to detect the burst signal level of the ACC circuit;
the ACC so that the burst signal level of the C circuit output is the same as the burst signal level of the first carrier color signal;
A video signal circuit comprising: a level comparator for controlling the gain of the circuit.