Television – Image signal processing circuitry specific to television – Chrominance-luminance signal separation
Reexamination Certificate
1999-03-01
2001-02-13
Kostak, Victor R. (Department: 2611)
Television
Image signal processing circuitry specific to television
Chrominance-luminance signal separation
C348S664000
Reexamination Certificate
active
06188445
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a luminance signal and chrominance signal separating circuit for separating composite color video signal of NTSC color television system into luminance signal and chrominance signal.
BACKGROUND ART
A composite video signal of NTSC system is composed by superposing a chrominance signal on a luminance signal in an interleaving relation. It hence requires a process of separating the two signals, but if a chrominance signal component is mixed in the separated luminance signal, it appears as dot interference (caused by chrominance signal) on the screen, or if a luminance signal component is mixed in the chrominance signal, it results in cross color interference, and it is therefore ideal to separate them without causing such mixing. As a method of separating, recently, it is the mainstream to separate by a comb filter using a 1H (H being a horizontal scanning period) delay circuit.
FIG. 6
is a schematic diagram showing an example of signal processing circuit for separating a composite video signal of a conventional NTSC color television system into luminance signal and chrominance signal (hereinafter called Y/C separation). In
FIG. 6
, a video signal
701
is entered, and is fed into a 1H delay circuit CCD HDL
702
of CCD (charge coupled device), and is delayed by a horizontal scanning period, and the 1H delayed signal is delivered from the 1H delay circuit
702
into a subtractor
703
. In the subtractor
703
, the input video signal
701
is also supplied, it is subtracted in relation to the 1H delayed signal. As known well, since the chrominance signal is inverted in phase, according to the principle of interleaving, in every adjacent scanning line, and therefore if the video signal has correlation between lines, the luminance signals are mutually canceled by the subtraction process, and the component of chrominance signal is separated as the output signal of the subtractor
703
.
On the other hand, the input video signal
701
is also supplied into a subtractor
704
. The subtractor
704
is also provided with a chrominance signal obtained by passing the output signal of the subtractor
703
through a band pass filter circuit BPF
705
, and therefore by subtracting this chrominance signal from the video signal
701
, only the luminance signal is separated and obtained.
This operating function is the principle of separation of luminance signal and chrominance signal by the known comb filter. However, since perfect separation is impossible in the position not having correlation between signals (between lines) before and after 1H, dot interference or cross color interference may occur. Accordingly, by detecting a signal not separated in a comb filter circuit, it is attempted to process so as to decrease such interference.
That is, in the prior art in
FIG. 6
, the output signal of the subtractor
703
is supplied into a low pass filter LPF
711
and a band pass filter BPF
713
, and a luminance signal component of lower frequency than the chrominance signal component is taken out from the LPF
711
, and a chrominance signal component is taken out from the BPF
713
. If there is no correlation in signal between lines, the luminance signal component is issued through the LPF
711
, and is put into a YL correlation detecting circuit
712
, and a signal showing absence of correlation is issued from the YL correlation detecting circuit
712
.
On the other hand, if the entered video signal has a chrominance signal, a chrominance signal component is issued from the BPF
713
, and is put into a chrominance detecting circuit
714
. This chrominance detecting circuit, if the chrominance signal component is entered, issues a signal showing its detection.
Between thus obtained no-correlation detection signal and the detection signal of chrominance signal, the AND (logical operation) is calculated in an AND circuit
715
. By the output signal of the AND circuit
715
, switch operations of trap circuit
707
and switch circuit
706
are controlled.
That is, if there is no correlation in signal between lines and a chrominance signal is present, a switch
708
of the trap circuit is closed, and the chrominance signal component superposed on the luminance signal is removed by the trap effect, so that the dot interference is lessened. At this time, the switch circuit
706
operates so that a chrominance signal may be directly obtained from the video input signal
701
.
However, since the chrominance signal is detected directly from the signal obtained from the output signal of the subtractor
703
in FIG.
6
through the BPF
713
, if there is no correlation between lines, a luminance signal component is present in the output signal of the subtractor
703
, and hence the precision of chrominance signal detection is lowered. Accordingly, depending on the pattern of the image, the Y/C separation may not be realized at high precision.
To enhance the precision further, in a prior art, for example, the luminance signal obtained in the comb filter circuit is passed again through other comb filter circuit, and presence or absence of chrominance signal component contained in the luminance signal is detected (not shown in a drawing). In this case, however, one more 1H delay circuit for color video signal is needed, and the cost is increased.
If there is no correlation in signal between lines, as mentioned above, since a luminance signal component is contained in the chrominance signal obtained from the output signal of the subtractor
703
in
FIG. 6
, it is passed through the band pass filter circuit BPF
705
, and the cross color interference is lessened. Although such filter circuit can lessen the cross color interference in the narrower band characteristic, the transient characteristic of chrominance signal is impaired, and the response of chrominance signal is sacrificed in the signal high in correlation between lines and free from cross color interference.
DISCLOSURE OF THE INVENTION
The invention is intended to process signal in order to solve the above problems more specifically, and presents a luminance signal and chrominance signal separating circuit for separating color video signal into luminance signal and chrominance signal in a circuit system comprising a first band pass filter for obtaining a first signal by passing a predetermined band width of a color video signal through said first band pass filter, a first 1H delay circuit for delaying said color video signal by one horizontal scanning period and a second band pass filter for obtaining a second signal by receiving the output signal from said first 1H delay circuit and passing said predetermined band width of the delayed color signal, thereby taking out a chrominance signal from said first signal and second signal.
In the above-explained circuit system, a first aspect of the invention is characterized in that it comprises:
a correlation detecting circuit for detecting the correlation between said first signal and second signal;
a second 1H delay circuit for delaying the output signal from said correlation detecting circuit by one horizontal scanning period;
a first logic circuit for receiving the output signal from said correlation detecting circuit and the output signal from said second 1H delay circuit, and performing a logical operation; and
an operation processing circuit for receiving said first signal and second signal, and taking out a chrominance signal from the difference between said first signal and second signal or from the first signal only, depending on the output signal of said first logic circuit.
According to the invention, whether the color video signal has a correlation before and after one horizontal scanning period, or not having correlation, by detecting the absence of correlation at high precision, the signal processing circuit capable of separating into luminance signal and chrominance signal can be presented.
The second aspect of the invention is characterized in that the correlation detecting circuit described in the first aspect comprises:
a v
Kostak Victor R.
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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