JPH0413895Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a synthesis circuit suitable for superimposing another signal onto a PAL television signal.

[Summary of the idea]

This invention is applicable to a device that superimposes an image signal to be displayed using R, G, and B signals on a PAL video signal that is input from the outside.
G, B, signals are converted to PAL output video signals by a PAL encoder, and this converted
PAL output video signal and externally supplied
The PAL encoder is configured to compare the phases of color burst signals of PAL video signals and control the PAL encoder based on the comparison signal. Therefore, when both video signals are combined, it is possible to always output an image with the same hue.

[Conventional technology]

2. Description of the Related Art In recent years, with the development of image communication services, various types of information are being transmitted or received in the form of image signals, and synthesis devices that superimpose such image information on video signals have also been developed.

In this case, especially when the video signal is in the PAL format, as is well known, the color difference signal R-Y signal is assumed to be phase-inverted for each scanning line, and the color burst signal is also R-Y signal. The angle is selected to be ±135° from the B-Y axis in response to signal switching.

Therefore, when converting a video text signal or character information output from a microcomputer etc. into a video signal and superimposing it on a PAL video signal, if you directly combine it as a composite TV signal, there will be a hue mismatch. Therefore, it may not be possible to obtain a normal color screen.

Therefore, for example, as shown in FIG. 3, the _PAL video signal V
G, B, signals and input them to, for example, video switch circuits _SR , _SG , _SB , and also form signals to be superimposed on the video switch circuits _SR , _SG , _SB . For example, it consists of CPU, RAM, video ram, CRT controller, modem, etc.
The text information output from the TEXT signal generator TG is input into signals separated into R, G, and B signals, and the R, G, and B signals are synthesized by each video switch circuit S _R , S _G , and S _B .
The G, B, and B signals are input again to the PAL encoder E _PAL , and at the same time, a synchronizing signal, subcarrier, etc. are supplied from the separation circuit S to produce a composite video signal.

[Problem that the invention attempts to solve]

However, this method requires a decoder (DEM) and several video switches to demodulate the externally input PAL video signal, which increases the overall circuit scale.
There is a problem in that it increases costs.

This invention was made in view of these problems, and is a PAL video signal that can accurately combine video signals of the PAL format with image signals output from videotexes or microcontrollers using a simplified circuit. The present invention provides an apparatus for synthesizing standard television signals.

[Means for solving problems]

This device for synthesizing PAL video signals has the following features:
An encoder converts the R, G, B signals to be combined into PAL video signals, and detects the phase of the output video signal output from the encoder and the burst signal of the PAL video signal input from the outside. A burst phase detection circuit is provided, and the phase information of the burst phase detection circuit is used to detect the
Chroma modulation carrier signal of PAL ender,
and configured to control the phase of the color burst.

[Effect]

formed from R, G, B signals to be combined
The PAL television signal is controlled to have the same phase as the burst phase of the externally supplied PAL television signal using the phase information output from the burst phase detection circuit. The image can also always be displayed in normal colors.

〔Example〕

Figure 1 is a block diagram showing an example of a PAL television signal synthesis circuit of this invention. 1 is a block diagram showing an example of a PAL TV signal synthesis circuit of this invention. 1 is a block diagram showing image information consisting of characters, graphics, etc. transmitted via a telephone line etc., or generated by a computer etc. image information (hereinafter referred to as videotex signal)
2 is the TEXT signal generation circuit that outputs the above
R, G, output from the TEXT signal generation circuit
A PAL encoder that forms the B signal and the synchronization signal into a second PAL video signal, and 3 and 4 a carrier reproducing circuit that reproduces a subcarrier signal from the first PAL video signal supplied from the input terminal _T1 . and a burst phase detection circuit that detects the burst phase.

Reference numeral 5 denotes a gate circuit for outputting the detection signal outputted from the burst phase detection circuit 4 only during the burst period, and its opening/closing control is performed by a synchronization signal inputted from the terminal _T2 .

6 is the first input from the terminal _T1 .
A video switcher for combining, switching, or superimposing a PAL video signal and a second PAL video signal output from the PAL encoder, and the switching control is as described above.
This is performed using an insertion timing signal outputted from the TEXT signal generation circuit 1.

FIG. 2 is a block diagram illustrating the outline of the PAL encoder 2, in which 7 is an R, which forms an image signal.
A color encoder which forms color difference signals R-Y and B-Y from the G and B signals, and 8 is also a luminance signal Y.
This is a matrix circuit that forms a Color difference signal R
-Y and B-Y are first and second balanced modulators 9a, respectively, balanced modulated by subcarriers;
9b. Reference numeral 10 denotes a color subcarrier generation circuit (PLL circuit) synchronized with the output of the carrier regeneration circuit 3, and one of its outputs is connected to the phase shifter 1.
1a, the color difference signal B-Y is phase-shifted by 90°.
The other output is input to the balanced modulator 9b of the color difference signal R-Y, which is switched by the switch 12 which inverts the signal whose phase is shifted by 180° by the phase shifter 11b and the line signal. 9a. Then, the color difference signal RY is modulated so as to be inverted by 180° for each line. Reference numeral 13 denotes a flip-flop circuit which is reset by the output (mismatch signal) of the burst phase detection circuit 4 shown in FIG. 1, and the Q output of this flip-flop 13 drives the switch 12.

14 is an adder circuit that forms a composite chroma signal;
5 is an adder that adds a luminance signal and a burst signal, and 16 is a color burst signal forming circuit.

Since the PAL video signal synthesis circuit of this invention has the above-mentioned configuration, the first PAL video signal input from terminal _T1 and TEXT
The video text signals (R, G, B, and synchro signals) output from the signal generation circuit 1 are as described above.
The second PAL video signal converted into a PAL television signal by the PAL encoder 2 is
First, a synchronization relationship is established by the carrier regeneration circuit 3, and then the phase relationship of the chroma signals is corrected by the output of the burst phase detection circuit 4, which detects the burst phase of both signals. .

In other words, when the color burst phase of the output video signal output from the PAL encoder 2 and the color burst phase of the PAL video signal input from the outside do not match, the burst phase detection circuit 4 outputs a mismatch. The signal is applied via gate circuit 5 to flip-flop 13 in the PAL encoder. Therefore, reversing switch 12 will result in a 180° phase shift, but this control allows
When the phase of the color burst of the output video signal of the PAL encoder 2 matches, the mismatch signal disappears, and from then on, both video signals, which are in a synchronous relationship, are supplied to the video switcher 6.

A video text signal is superimposed on an external PAL video signal by a control signal supplied to the video switcher 6, and a composite video signal with matching color bursts is output.

Although the detection signal of the burst phase detection circuit is output for each line in the embodiment, for example, a counter or an integrating circuit may be provided on the output side to output a mismatch signal when the mismatch period continues for a predetermined period of time. In addition, the counter or the integrating circuit may be reset when a matching signal is obtained.

[Effect of idea]

As explained above, the PAL video signal synthesis circuit of this invention uses color burst phase detection to synthesize or superimpose and output a video text signal and an external PAL video signal.
Since the subcarrier phase within the PAL encoder is controlled, the effect is that color synchronization can be realized with a simple circuit configuration. Therefore, there is an advantage that a composite image output with correct hue can always be obtained.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a PAL video signal synthesis device showing one embodiment of this invention, and Figure 2 is
Block diagram showing an example of a PAL encoder, Part 3
The figure is a block diagram showing an example of a conventional video signal synthesis device. In the figure, 1 is a TEXT signal generation circuit, 2 is a PAL encoder, 3 is a carrier reproducing circuit, 4 is a burst phase detection circuit, 5 is a gate circuit, and 6 is a video switcher.

Claims (1)

[Scope of utility model registration request] A video signal indicated by R, G, B signals and a first
superimposes and outputs the PAL format video signal.
In image synthesis equipment for PAL television signals,
The above R, G, B signals are input, and the color difference signal R-
a matrix circuit that forms Y, a color difference signal B-Y, and a luminance signal Y, and a second carrier wave whose phase is reversed by 180° for each line with respect to the first carrier wave signal based on the subcarrier signal of the above-mentioned PAL video signal. a carrier wave forming circuit that forms a signal; a first modulator that parallel modulates the first carrier signal with the color difference signal B-Y; and a first modulator that parallel modulates the second carrier signal with the color difference signal R-Y. a second modulator; a forming circuit for forming a color burst signal based on the second carrier signal; and adding an output signal of the first modulator and an output signal of the second modulator; an adding circuit for adding the luminance signal Y and the color burst signal, and a video switcher for synthesizing and outputting the first PAL video signal and the second PAL video signal; Based on the output of the burst phase detection circuit, the carrier wave forming circuit detects the second carrier wave when the phase of the color burst of the first PAL video signal and the color burst of the second PAL video signal do not match. An image synthesizing device for PAL video signals, characterized in that it is configured to invert the phase of a PAL video signal by 180°.