JPH04287493A - Picture-in-picture circuit - Google Patents

Abstract

PURPOSE:To improve the picture-in-picture effect by generating a gate pulse for a burst signal period of a master pattern and inserting a burst signal whose frequency is coincident with a frequency of a chroma signal of a slave pattern signal to a correct position of the master pattern. CONSTITUTION:A burst detector 16 detects the presence of a burst signal as to a master pattern selected by a switch 3. A burst gate pulse generating circuit 17 generates a burst gate pulse for a burst signal period by the detection signal and the pulse signal is fed to an adder 18, in which the signal is added to a color difference signal B-Y and a slave pattern synthesis circuit 10 modulates a chroma signal to obtain a burst signal. A controller 13 synchronizes the signal read from a picture memory 9 with the master signal and the burst signal whose frequency is coincident with the frequency of the slave pattern chroma signal is inserted to a correct position of the master pattern signal. Thus, when the slave pattern signal is a color signal, the color signal is always reproduced independently of the master pattern as to whether the signal is a monochromatic signal or a color signal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a picture-in-picture circuit that has the function of inserting another screen (hereinafter referred to as a child screen) into a part of the main screen (hereinafter referred to as a parent screen) of a TV or the like. It is about improvement.

0002

2. Description of the Related Art FIG. 2 is a diagram showing the circuit configuration of a conventional picture-in-picture circuit. In the figure, 1, 2
3 is a video signal input terminal, 3 is a switch, 4 and 5 are for displaying a signal selected by switch 3, 4 is called a main screen signal, and 5 is called a sub-screen signal. 6 and 7 are synchronization separation circuits that separate the synchronization signals of the main screen signal 4 and child screen signal 5, respectively; and 8 is a luminance signal (Y) that converts the child screen signal 5 into a luminance signal (Y).
9 is an image memory, 10 is a small screen synthesis circuit that combines the signals from the image memory 9 into a small screen signal again, and 12 is a voltage control circuit. An oscillator (VCO), 11 an automatic phase adjustment circuit (APC circuit) for matching the oscillator frequency of the oscillator 12 with the burst signal frequency of the main screen signal, and 14 a sub-screen signal reproduced by the main screen signal and sub-screen synthesis circuit 10. A switch 13 is for controlling the timing of writing and reading from the image memory 9 and a controller for controlling the switch 14. A switch 15 is a synthesis output from the switch 14.

Next, the operation will be explained. The two video signals (composite video signals) input to video signal input terminals 1 and 2 are controlled by a switch 3 to be used as a signal 4 for the main screen, which becomes the main screen, and a signal 4 for the sub-screen, which is added to a part of the main screen as a separate screen. Selected by signal 5. For example, the input to the video signal input terminal 1 is a video signal from a TV tuner, and the input to the video signal input terminal 2 is a reproduced video signal from a VTR. The selection of the main screen signal and the sub-screen signal is arbitrarily selected according to the user's wishes. 6 and 7 are synchronization separation circuits which separate the synchronization signals from the video signals of the main screen signal 4 and the sub-screen signal 5, and provide the synchronization signals to the controller 13. This synchronization signal serves as a timing signal for reading and reading information into the image memory 9, as well as a timing signal for synchronizing the child screen with the main screen and inserting it into the position of the child screen.

The small screen signal 5 is input to a small screen demodulation circuit 8 . Here, signal conversion for writing into the image memory 9 is performed. If the composite video signal remains as it is, it will include a high frequency band such as a chroma signal frequency, making it difficult to write into the image memory 9, so conversion is performed. In this example, the luminance signal Y and the color difference signal (RY and B-Y)
It is demodulated and recorded. The demodulated signal is A/D
It is recorded in the image memory 9 in the form of a digital signal through a converter (not shown). The timing of this recording is controlled by the controller 13 to correspond to the frames of the TV screen.

The signals recorded in the image memory 9 are read out to the child screen synthesis circuit 10 according to timing signals from the controller 13 in order to reproduce them again as a child screen. The read speed needs to correspond to the size of the sub screen. That is, if the size is to be reduced to 1/3 on the TV screen, time axis conversion is performed to read out at three times the speed of recording, and the screen size is reduced. Further, this timing is set to be synchronized with the parent signal.

The child screen synthesis circuit 10 converts the digital signal read out from the image memory 9 into a D/A converter (not shown).
The chroma color difference signal is modulated again and combined with the luminance signal to create an analog signal and a composite video signal again.

When modulating the chroma color difference signal in the child screen synthesis circuit 10, the correct color will not appear on the child screen unless the modulation frequency correctly matches the frequency of the parent signal. Therefore, the burst signal is extracted from the parent signal 4, and the automatic phase adjustment circuit (APC circuit) 11 generates a voltage controlled oscillator (VC
O) Control 12 and accurately adjust the chroma modulation frequency to the parent signal 4
chroma signal frequency. The small screen signal thus obtained is applied to terminal b of switch 14. on the other hand,
A main screen signal is applied to terminal a of the switch 14, and the switch 14 is controlled by the controller 13.
A child screen signal is inserted into a fixed period of the main screen signal, and a composite signal of the parent and child screens is obtained from the composite signal output terminal 15.

Furthermore, although omitted in the above description, in the conventional configuration, the small screen composite signal applied to terminal b of the switch 14 does not include a synchronization signal and a burst signal. Recording to, reading from, etc. are also processed without including these signals.

[0009]

[Problems to be Solved by the Invention] The conventional picture-in-picture circuit is configured as described above, and as described above, the small screen composite signal applied to terminal b of the switch 14 includes a synchronization signal and a burst signal. It wasn't included. Therefore, if both the main screen signal and the child screen signal are color signals, it is possible to reproduce a color image on the child screen because the main screen signal includes a synchronization signal and a burst signal in advance. If the main screen signal is a monochrome signal and the child screen signal is a color signal, the main screen signal does not have a burst signal, so there is no burst signal in the parent and child composite signal output, and as a result, the child screen becomes a monochrome image,
There was a problem that color images could not be viewed on the sub-screen.

This invention was made to solve the above problems, and whether the parent signal is a color screen with a burst signal or a monochrome screen without a burst signal, the child screen is The purpose of the present invention is to provide a picture-in-picture circuit that can always reproduce a color screen.

[0011]

[Means for Solving the Problems] A picture-in-picture circuit according to the present invention includes means for detecting the presence or absence of a burst signal in a parent signal, means for generating a burst gate pulse during a burst signal period based on the detection output, and a means for detecting the presence or absence of a burst signal in a parent signal. This apparatus includes means for generating a burst signal matching the frequency of the sub-screen chroma signal by means of pulses, and means for inserting this burst signal as a substitute signal at the correct burst position of the main screen.

0012

In the picture-in-picture circuit of the present invention, when it is detected that there is no burst signal in the parent signal, a burst signal is automatically inserted as a substitute signal. Since this alternative burst signal exactly matches the chroma frequency of the sub-screen and is inserted at the correct burst position of the parent signal, a color image can be reproduced on the sub-screen.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a picture-in-picture circuit according to an embodiment of the present invention. An embodiment of the present invention will be described below. In FIG. 1, 16 is a burst signal detector, 17 is a burst gate pulse generator, 1
8 is an adder for adding the burst pulse with the color difference signal, and 19 is a switch switched by the burst gate pulse. Other components that are the same as those in the conventional example are given the same numbers, and their explanations will be omitted.

Next, the operation of this embodiment will be explained. As in the conventional example, the switch 3 is used to select the main screen signal and the sub-screen signal. If the selected main screen signal 4 is a color signal and there is a burst signal, the burst gate pulse 17 is not generated and the switch 19 remains on the a terminal side, and the operation is exactly the same as the conventional example. Explanation will be omitted.

On the other hand, consider the case where the main screen signal is a monochrome signal without a burst signal. In this case, the burst detector 16 first detects the presence or absence of a burst signal. The burst signal detector 16 has the same configuration as what is generally called a killer circuit, and can be configured relatively easily.

A burst gate pulse generating circuit 17 is controlled by a burst signal detector 16 to generate a burst gate pulse (BGP). The burst gate pulse is generated from a synchronization signal that is synchronously separated from the main screen signal.
It can accurately match the main screen signal burst period.

The burst gate pulse signal generated above is added to the adder 18, added to the (B-Y) color difference signal, and chroma signal modulated by the small screen synthesis circuit to obtain a burst signal. The level of this burst signal can be freely selected by adjusting the amount of interpolation of the burst gate pulse, that is, the pulse height. Here, the selection is made according to the (RY) color difference signal obtained from the image memory 9.

[0018] This embodiment uses the NTSC system, and the above (
B-Y) If a pulse is applied to the burst position of the color difference signal,
It is generally well known that a burst signal is obtained during chroma modulation.

What is important here is that the main screen signal and the child screen signal are synchronized in both the horizontal and vertical periods; if they are not synchronized, the burst signal cannot be generated at the correct position. Therefore, in this embodiment, the signal read out from the image memory 9 by the controller 13 is synchronized with the parent signal.

The burst signal modulated by the small screen synthesis circuit 10 and the chroma signal of the small screen are both modulated by the oscillator 12, so that they have exactly the same frequency. In this case, since there is no burst signal of the main screen signal, the APC circuit 11 does not work, and the oscillator 12 is in a free-run frequency state. The free run frequency of the oscillator 12 is generally designed to match the chroma frequency, and there is no problem in performing chroma modulation in this state.

The burst signal and the small screen signal obtained by the small screen synthesis circuit 10 as described above are applied to the b terminal sides of the switch 19 and the switch 14. The switch 19 is connected to the burst period b generated by the burst gate pulse generation circuit 17.
It is switched to the terminal side and a burst signal is inserted into the main screen signal.

A burst signal is inserted into the main screen signal and is applied to the a terminal side of the switch 14. switch 1
A child screen signal is applied to the b terminal side of 4, a switch 14 is switched by a signal from a controller 13, and a composite output of parent and child signals is obtained from a composite output terminal 15. Since the burst signal is correctly inserted into this composite output as described above, a color image can be reproduced on the child screen.

[0023] In the above embodiment, an example was shown in which the switch 14 and the switch 19 were used, but the switch could be controlled by adding the burst gate pulse and the control signal of the controller. For example, it is possible to use even one switch.

Furthermore, although the above embodiment refers to the NTSC system, it can also be applied to the PAL system by adding a circuit for adding the burst gate pulse to the (R-Y) color difference signal, and the same effects as in the above embodiment can be obtained. Obtainable.

[0025]

As described above, according to the present invention, a burst signal of a main screen signal is detected, a burst gate pulse is generated during the burst signal period by this detection signal,
This pulse generates a burst signal that matches the frequency of the sub-screen chroma signal and inserts it at the correct position of the main screen signal, so regardless of whether the main screen is monochrome or color, the sub-screen chroma signal If it is a color signal, color reproduction is always possible and the picture-in-picture effect can be enhanced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a picture-in-picture circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional picture-in-picture circuit.

[Explanation of symbols]

1 Video signal input terminal 2 Video signal input terminal 3 Switch 4 Main screen signal 5 Sub-screen signal 6 Sync separation circuit 7 Sync separation circuit 8 Sub-screen demodulation circuit 9 Image memory 10 Sub-screen synthesis circuit 11 Automatic phase control circuit (APC circuit) 12 Voltage controlled oscillator (VCO) 13 Controller 14 Switch 15 Synthetic output 16 Burst detector 17 Burst pulse generator 18 Adder 19 Switch

Claims (1)

[Claims] Claim 1. A picture-in-picture circuit having a function of inserting another screen (hereinafter referred to as a child screen) into a part of a main screen (hereinafter referred to as a parent screen) on a TV or the like,
burst signal detection means for detecting the presence or absence of a burst signal on the main screen; and burst gate pulse signal generation means for generating a burst gate pulse signal corresponding to a burst period when the burst signal detection means detects that there is no burst signal. , comprising means for generating a burst signal matching the frequency of the chroma signal of the child screen using the burst gate pulse signal, and means for inserting the burst signal into a correct burst position of the main screen. picture-in-picture circuit.