Carrier chrominance signal separating circuit

Details Carrier chrominance signal separating circuit Carrier chrominance signal separating circuit

1983-06-22

1986-02-11

Masinick, Michael A.

Facsimile and static presentation processing

Static presentation processing

Attribute control

H04N 964

Patent

active

045701776

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Filed
This invention relates to such a technique that in a comb filter for separating a carrier chrominance signal from a color video signal, even if the carrier chrominance signal contains portions having no vertical correlation, the carrier chrominance signal can be correctly extracted.
2. Background Art
A comb filter is known as a filter for separating a luminance signal and a carrier chrominance signal from a color video signal. Further, a comb filter has been proposed which can avoid a dot interference and a cross color.
FIG. 1 is a block diagram showing an example thereof. A color video signal, or a composed signal (Y.sub.L +Y.sub.H +C) consisting of a low frequency band component Y.sub.L and a high frequency band component Y.sub.H of a luminance signal Y and a carrier chrominance signal C is supplied to a terminal 1. The signal (Y.sub.L +Y.sub.H +C) is supplied to a band-pass filter 2 which passes therethrough a signal (Y.sub.H +C). This signal (Y.sub.H +C) and the signal (Y.sub.L +Y.sub.H +C) are both supplied to a subtracting circuit 3 from which is derived the low frequency band component Y.sub.L. This low frequency band component Y.sub.L is supplied through a phase compensation delay circuit 4 to an adding circuit 5.
The signal (Y.sub.H +C) from the filter 2 is supplied to a delay circuit 6 and delayed by one horizontal period so that the delay circuit 6 delivers a signal (Y.sub.H -C) consisting of the high frequency band component Y.sub.H of one horizontal period before and a carrier chrominance signal -C of opposite phase. The signal (Y.sub.H -C) and the signal (Y.sub.H +C) from the filter 2 are supplied to an amplitude correlating circuit 7.
The correlating circuit 7 is an analog-AND circuit the example of which will be described later. When this circuit is supplied with two signals Sa and Sb as, for example, shown in FIG. 4A, it produces correlated portions (hatched areas) of both the signals Sa and Sb as shown in FIG. 4F. Accordingly, the correlating circuit 7 delivers the high frequency band component Y.sub.H.
The high frequency band component Y.sub.H is then supplied to the adding circuit 5 which then delivers the luminance signal Y (=Y.sub.L +Y.sub.H) to a terminal 11.
The signal (Y.sub.H -C) from the delay circuit 6 is supplied further to an inverter 8 from which a signal (-Y.sub.H +C) of inverted phase is derived. The signal (-Y.sub.H +C) and the signal (Y.sub.H +C) from the filter 2 are supplied to a correlating circuit 9 which delivers the carrier chrominance signal C to a terminal 12.
FIG. 3 is a circuit diagram showing an example of the correlating circuits 7 and 9. When the signals Sa and Sb as shown in FIG. 4A are supplied to terminals Ta and Tb, transistors Q.sub.1 and Q.sub.2 generate a signal Sm as shown in FIG. 4B so that from transistors Q.sub.3 and Q.sub.4 is derived a portion Sn corresponding to the correlated portion of the negative half cycle period of the signals Sa and Sb as shown in FIG. 4C. Since from transistors Q.sub.5 and Q.sub.6 is derived a signal S.sub.p as shown in FIG. 4D, transistors Q.sub.7 and Q.sub.8 produce a correlated portion S.sub.q corresponding to a positive half cycle period of the signals Sa and Sb as shown in FIG. 4E. Accordingly, the correlated portions between the signals Sa and Sb, namely, a correlated signal (Sa Sb) shown in FIG. 4F is delivered to a terminal Tc.
Thus, according to the comb filter shown in FIG. 1, the luminance signal Y and the carrier chrominance signal C can be separated from the color video signal. In addition, in this case, no dot interference and no cross color occur.
However, in the comb filter shown in FIG. 1, if the carrier chrominance signal C in the color video signal supplied to the terminal 1 is that as shown in FIG. 2A, or only lines (n+1) to (n+4) thereof are colored, the carrier chrominance signals C at the respective circuit elements become as shown in FIGS. 2A to 2C and the carrier chrominance signal C which will appear at the terminal 12 becomes as shown in FIG. 2D. In other words,

REFERENCES:
patent: 4263612 (1981-04-01), Gibson et al.

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