JPS58196790A - Detection circuit of color difference signal - Google Patents

Abstract

PURPOSE:To designate precisely the specific color difference signal, by discriminating a level between preset upper and lower limits arranged preliminarily to two kinds of color difference signals by using two comparators. CONSTITUTION:A chrominance signal I is inputted to comparators 3 and 5 from an input terminal 1, and compared with the upper limit L1 and lower limit L2 of the color difference signal. Logical products are outputted out of the output of the comparators 3 and 5 by AND gate 6. A color difference signal Q is inputted to comparators 13 and 15 from an input terminal 11, and compared with the upper limit L3 and lower limit L4 of the color difference signal Q. Logical products are outputted by an AND gate 16 from the outputs of the comparators 13 and 15. Outputs from AND gates 6 and 16 are inputted to an AND gate 30 and taken out as chroma key signals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color difference signal detection circuit for television video signals.

In general, the video signal of 2-TV TV is orthogonally balanced modulated using two color difference signals l and Q, which are synthesized from the three primary color signals of red (Bi, Ennichi, and blue), and a luminance signal equivalent to a black and white video signal. This is a superimposed color subcarrier. On the other hand, chromakey is used for the ``inset'' technique as a special effect of the Eirin signal, and a line chromakey signal generator is a device that demodulates and extracts this chromakey signal from the Eirin signal. A color difference signal detection circuit is used in this line chromakey generator.

Conventionally, this kind of color difference signal detection system, -Ratio IIR-
This color difference signal detection circuit can only detect color difference signals above a certain level (Lo) on the vector scope shown in Figure 1. It was only possible to detect the shaded area. For this reason, in addition to the range of specific 0 colors (for example, blue) to be chroma-keyed, there is also the disadvantage that ζ-O is also detected, and chroma-keying is also performed outside the range of p-makey.

An object of the present invention is to eliminate the above-mentioned drawbacks by using a ratio IIR device of two levels t between two types of color difference signals I and Q between preset upper and lower limit values, and to eliminate the above drawbacks. It is an object of the present invention to provide a color difference signal detection circuit capable of detecting color difference signals from a specific range.

The color difference signal detection circuit of the present invention includes a first comparison circuit that detects that a first color difference signal I of a color television signal is within a level range 1 once set in advance; fa to detect that the second color difference signal Q that is orthogonal to 6 is within a preset second level range.
The second comparison circuit includes two comparison circuits, and a gate circuit that takes the logical product of the respective outputs of the first and aI2 comparison circuits.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the invention.

This embodiment consists of two comparison circuits 10, 20 and one AND gate 30. This comparison circuit 10
inputs the color difference signal I from input terminal 1, and inputs the color difference signal I from input terminal 2.
The upper limit level L1 and the lower limit level L2 of the Maruhoshi color difference signal I inputted from the comparators 3.
5, and the output tube AND gate 6 of each comparator 3.5 outputs the AND gate 9. 9, the comparison circuit 2o inputs the color difference signal Q from the input terminal 11, and inputs the color difference signal Q from the input terminal 12゜1.
The upper limit level Ls of the color difference signal Q input from 4.
and its lower limit level L4 are compared with the comparator 13.15, and the outputs of these comparators 13.15 and 16
Outputs the logical product.

That is, the color difference signal I is compared with the upper limit level L1 in the comparator 3, and the color difference signal I is compared with the upper limit level L1.
1 When the signal is small, it outputs a high level "1", and when it is large, it outputs a low level "0" @ On the other hand, the comparator 5 compares the color difference signal with the lower limit level L11, and the color difference signal ■ outputs a level L snow. When it is larger than the high level rlJ ttti force L, /J\, it outputs the low level "0". The output obtained from these two ratio*devices 3 and 5 is the AND gate 6
The logical product is taken by . This operation means that a signal with a color difference between the upper limit level Ll of the color difference signal I and its lower limit level L can be discriminated.The color difference polarization Q also has the same ratio as this color difference signal I. The soft circuit 20 discriminates a signal having a certain color difference between the upper limit levels l, s and the lower limit level L4. The outputs of the color difference signals I and Q thus determined are ANDed by an AND gate 13 and output as a chromakey signal.

Figure 2 shows a color difference signal engineer corresponding to the color bar signal.

It is a waveform diagram in which a yellow (1) portion is extracted as Q.

That is, yellow (1) in the color bar signal is at level L1. During Ll, the color difference signal Q is at level L3. , La. Therefore, in a circuit that discriminates levels higher than level Ltt, the force 2-(M, R
), etc., but by taking the logical product of levels L1-L2 and levels L3-L4, the range S
Figure 3 is a vector scope showing the operating range of this embodiment. That is, 1 between the levels L+ and La of the color difference signal I (horizontal line part) and between the levels Ls and L4 of the color difference signal Q (vertical line part).
It is possible to output a specific color range as a chromakey signal.

Note that color difference signals I, Q and upper and lower limit levels L1 to L
4 may be an analog signal or a digital signal.

As explained above, in the present invention, the upper limit level (L4) and lower limit level (LL) of the color difference signal detection range can be freely set using the four comparators and three AND circuits. It becomes possible to specify a specific color difference signal precisely. Also, the color difference signal level I is compatible with the power 5-/<-st signal.

By setting Q and inputting a signal corresponding to the burst flag to ANDG 30, it is also possible to detect a burst signal.

[Brief explanation of drawings]

JI1 diagram is a vector scope showing the conventional color difference signal detection range, 1s2 diagram is a 10-step diagram of the embodiment of the present invention, 311
Figure 3 is a waveform diagram in which the color bar signal is divided into color difference signals I and Q, and Figure j14 is a vector scope showing a color difference signal according to this embodiment. In the figure, 1.11... color difference signal input terminal, 2
゜4, 12.14...Upper limit, lower limit setting level input terminal, 3, 5.13.15...Comparator, 6.1
6.30...Group/AND gate, 10.20...Comparison circuit, 31...Output terminal. High 4 figure

Claims (1)

[Claims] a comparison circuit of jllll for detecting that the color difference signal ■ of the rattan 1 of the color television signal is within a preset level range f of 1g1, and a second color difference signal Q orthogonal to the color difference signal of the rattan 1. JIE20 with preset
a second comparator circuit that detects jin in level range 11;
A color difference signal detection circuit including a gate circuit for ANDing the respective outputs of the first and second comparison circuits.