JPS58182385A - Luminance signal separating circuit - Google Patents

Abstract

PURPOSE:To separate a luminance signal even if a PAL signal is fluctuated timewise without the reduction in the resolution, by generating a signal for cancellation in synchronizing with a chrominance carrier signal and eliminating a chroma signal from a PAL color video signal. CONSTITUTION:Since an Ev(t) component in a chrominance carrier signal is transmitted while balance-modulating a subcarrier signal of 180 deg. phase difference at each horizontal scanning line, only the Eu(t) component is outputted from a summing circuit 9. In a subtraction circuit 10, transmitted Eu(t) component is cancelled by balance-modulating the sub-carrier signal without phase difference at each horizontal scanning line and only the Ev(t)component is outputted. Each sub-carrier has 90 deg. phase difference. Thus, in forming rectifier circuits so as to make the output of both the rectifier circuit 11, 12 opposite, the output of an addition circuit 15 is a signal having a frequency double the basic frequency of the sub-carrier signal. Since this output is multiplied with the output of a 1H delay circuit 3 at a multiplication circuit 7, the chrominance carrier signal component in the output of a subtraction circuit 2 is cancelled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a luminance signal separation circuit, and particularly to a PAL (Ph
The present invention relates to a separation circuit that separates a luminance signal from a color video signal based on the Alternation Lin, e) method.

Such a separation circuit may be configured to remove the carrier color signal from the color video signal using a band-stop filter having a rejection band approximately equal to the frequency band of the carrier color signal and pass only the luminance signal, or to remove the carrier color signal from the color video signal and pass only the luminance signal. The phase of the color signal is IH (1 horizontal scanning period)
By using the fact that each shift is shifted by 9c,
There is a known structure in which the carrier color signals of two scanning lines spaced apart by H and having a phase difference of 180° are combined to cancel the carrier color signals. however,
In the former, the luminance signal components near the frequency of the carrier color signal are also removed, resulting in a reduction in horizontal resolution, which is a disadvantage, whereas in the latter, color video signals corresponding to two scanning lines separated by 2H from each other are combined. Therefore, the problem arises that the vertical resolution is significantly reduced. Therefore, a separation circuit as shown in FIG. 1 has already been devised, which can separate luminance signals without reducing the horizontal and vertical resolutions. In FIG. 1, a PAL color video signal is fed to a bandpass filter 1 and a subtraction circuit 2. In FIG. The bandpass filter 1 is configured such that its passband is approximately equal to the frequency band of a carrier color signal included in a PAL color video signal. The carrier color signal component is extracted by this bandpass filter l, and the carrier color signal component is extracted by the IH delay circuit 3. t
- and is supplied to the burst gate 4. Purst Gate 4
For example, the output of a P pulse generator (not shown) configured to obtain a pulse that exists for approximately the same period as the color burst signal by delaying the horizontal synchronizing signal is supplied as a burst gate pulse. There is. The burst gate 4 is made up of an analog switch circuit that turns on and off depending on the burst rate/solus, for example.
Separating the color burst signal from the carrier color signal, e.g.
The signal is supplied to a subcarrier generation circuit 5 using a PC (automatic phase control) method.

The subcarrier generation circuit 5 generates a color subcarrier signal synchronized with the color burst signal and supplies it to a color demodulation circuit (not shown), etc., and also to a doubling circuit 6. The doubler circuit 6 has a configuration similar to, for example, a double-wave rectifier circuit, and outputs a signal obtained by doubling the frequency of the color subcarrier signal. The output of this doubler circuit 6 is
The signal is supplied to a multiplication circuit 7. Multiplier circuit 7 and doubling circuit 6
A signal obtained by multiplying the output of the IH delay circuit 3 by the output of the IH delay circuit 3 is output and supplied to the low-pass filter 8.

In the low-pass filter 8, components with frequencies twice and three times the frequency of the color subcarrier signal included in the output of the multiplication circuit 7 are removed, and only components with a frequency equal to the frequency of the color subcarrier signal are output. It is supplied to the subtraction circuit 2. In the subtraction circuit 2, the output of the low-pass filter 8 is subtracted from the PAL color video signal to cancel the carrier color signal component, and the subtraction circuit 2 outputs only the luminance signal component.

In the above configuration, the PAL color video signal E□ corresponding to n (n is a natural number) grain scanning lines is expressed as follows.

Ey,=EYC1) +BU(t)cmwct +Ev
(t) S stone wct・・・・・・・・・(1) wc = 2 yr (284-/4) /H--・(
2) Here, EY(t) is the luminance signal, Ev(t) and E
U(t) indicates color difference signals R, , -Y, and BY, respectively.

Further, fH is a horizontal scanning frequency.

Here, EY(t) is the fundamental frequency component Y1(
2) (2πfR・1゛・t) and its high frequency component Y2a
lXs(2π8・2・t),・・・・・・・・・Y
t possible (2π8・t・t).

Since it can be considered as the sum of . . . , EY(t) is expressed as the following equation.

EY(t) - ΣYt low (2π8・t・t) ・・・・・・
...Similarly to (3), EU(t) and Ev(t) are expressed as in the following equations.

BU(t)=Σ〜P12π8・m・t) ・・・・・・
...(4) Ev(t)-ΣBr-(2π/,-r-t
)--=-(5) Next, (n-1) wood grain PAL' color video signal E signal-Mn is expressed as the following equation.

BMn-1=By (t - tH) 10Eu (t -
tH) crswc (i −LH) −Evs1! Iw
C(t-tH)=EY(t)-FjU(t)dnwct
−Frv(t)ayawct −・−(6) Here,
The elm indicates the time corresponding to IH.

Therefore, the output 5In2u)Ct'Ey of the multiplier 7 outputs the signal obtained by multiplying the signal gk2wct obtained by doubling the frequency of the color subcarrier signal by the output of the IH delay circuit 3.
(n-1) is as shown in the following equation.

5ln2 ”l ”EM(n-11”'Ey ('
)' 5In211)CIEUCt)stnwct-
=n2wct-Ev(C)cLswct-siAlvc
t18. '-, (7) Substituting equation (3) into equation (7) and rearranging it, we get the following equation.

5fn2 wC6-EM(B-1') -p:, u(t) mwc t-sIn2wc t'-
Bv(t) ctswc t ・sin 2wc by 1,000tr (2wc 2 rc / B −Z l
t) + (Vz) EuCt) [cxs3wct -as
wct ) 10C'A) Ey(t-)C 3wct +
tnwct) ---・-(s) Output E,', 7B+ 1, 14 of the low-pass filter 8 that removes components of frequencies twice and three times the frequency of the color subcarrier signal from the output of the multiplier 7. It becomes as follows.

('A) E, J(t) cIyswc t-(%>
F-vct, ) stnWcL.

-(k) Eu(t)aswct -('A) E, (
t) stnwct...α1 (1) From equation 01, the following equation holds true.

Es5n+ 2 EM(71-1) = Ey(t) ten Σ
Yl 5irL2π(z X 284'/2)
In ・'-”・('1ap type #) Subtraction circuit 2 that synthesizes the PAL color video signal and the output of the low-pass filter 8
It can be seen that one color feed signal component in the output of can be canceled.

In addition, since the angular frequency of the fundamental frequency component in the component indicated by α and the second term of the equation is different from the angular frequency of the fundamental frequency component in the luminance signal EY(t), the angular frequency of the fundamental frequency component in the component indicated by α and the second term of the equation is The impact is thought to be small.

However, in the conventional separation circuit as described above, the signal output from the low-pass filter 8, that is, the signal for canceling the carrier color signal, is generated in synchronization with the color burst signal. When a reproduced PAL color video signal with time axis fluctuation is input, a phase difference occurs between the carrier color signal and the signal for canceling the carrier color signal, resulting in insufficient cancellation of the carrier color signal. Therefore, the purpose of the present invention is to sufficiently remove the carrier color signal from the PAL color to video signal even if the signal has time axis fluctuations, without causing a decrease in horizontal resolution or vertical resolution. An object of the present invention is to provide a separation circuit that can separate luminance signals.

The separating circuit according to the present invention is configured to remove the carrier color signal from the PAL color video signal and separate the luminance signal by generating a signal for canceling the carrier color signal in synchronization with the carrier color signal.

Hereinafter, the present invention will be explained in detail with reference to FIGS. 2 to 4.

In FIG. 2, a bandpass filter 1, a subtraction circuit 2, an IH delay circuit 3, a multiplication circuit 7, and a low-pass filter 8 are connected in the same way as in FIG. However, in this example, the output of the bandpass filter 1 is supplied to the LH delay circuit 3, an addition circuit 9 as a first signal synthesis means, and a subtraction circuit 10 as a second signal synthesis means. In addition circuit 9, a signal obtained by adding the output of bandpass filter 1 and the output of IH delay circuit 3 is synthesized. Further, in the subtraction circuit 10, a signal obtained by subtracting the output of the IH delay circuit 3 from the output of the bandpass filter 1, for example, is synthesized. The outputs of the adder circuit 9 and the subtracter circuit 10 are respectively supplied to double-wave rectifier circuits 11 and 12 as first and second frequency doubling stages. The outputs of the double-wave rectifier circuits 11 and 12 are amplitude-limited by limiters 13 and 14, respectively, and then added by an adder circuit 15. These limiters 13
, 14 and the adder circuit 15 form a third signal synthesis means. Then, the output of the adder circuit 15 is multiplied by the output of the IH delay circuit 3 in the multiplier circuit 7.

In the above configuration, the Ev(t) component of the carrier color signal in the PAL color video signal is transmitted by balanced modulation of subcarrier signals having a phase difference of 180° for each horizontal scanning line. Addition circuit 9
, the EV(t) component is canceled and only the BU(t) component is output from the adder circuit 9.

Furthermore, in the subtraction circuit 10, the sent EU(t) component is canceled by balanced modulation of the subcarrier signal with no phase difference for each horizontal scanning line, and only the -(t) component is output from the subtraction circuit 10. be done. The subcarriers of each of these Ev(t) and EU(t) components are 90% each other.
It has a phase difference of °. Therefore, when the EU(t) component as shown by the solid line a in FIG. It is output from the subtraction circuit 10. The outputs of the double-wave rectifier circuits 11 and 12 that double-wave rectify each of the EU(t) component and the Ev(t) component are shown in FIG.
dotted line a' in the same figure and dotted line l in 00 in the same figure or dotted line C' in 0 in the same figure
If each of the double-wave rectifier circuits 11 and 12 is configured so that the polarities are opposite to each other as shown in each of FIG. This results in a signal having a fundamental frequency component of the frequency.

Since the output of the adder circuit 15 is multiplied by the output of the IH delay circuit 3 in the multiplier circuit 7, the carrier color signal component in the output of the subtracter circuit 2 can be canceled out in the same way as the circuit shown in FIG. .

In the above operation, the signal for carrier color signal cancellation obtained by extracting a component of the same frequency as the frequency of the subcarrier signal from the output of the multiplication circuit 7 by the low-pass filter 8 is synchronized with the carrier color signal. Therefore, even if the phase of the carrier color signal fluctuates when a reproduced PAL color video signal output from a video teso recorder or the like with time axis fluctuation is input, the phase of the signal for canceling the carrier color signal also fluctuates in the same way. In particular, the carrier color signal is sufficiently canceled and a luminance signal that does not contain the carrier color signal component is obtained.

FIG. 4 is a block diagram showing a color demodulation circuit based on the PALN (1'bWPAL) demodulation method, which is formed by sharing parts of the luminance signal separation circuit according to the present invention.

In FIG. 4, a bandpass filter 11, a subtraction circuit 2, an IH delay circuit 3, a multiplication circuit 7, a low-pass filter 8, an addition circuit 9,
15. The subtraction circuit 10, the double-wave rectification circuit 11, and the 12° limiters 13 and 14 are connected in the same manner as in FIG. 2 to form a luminance signal separation circuit. However, in this example, the output of the bandpass filter 1 is also supplied to the burst dart 4. The burst dart 4 receives the burst gate pulse, separates a color burst signal from the carrier color signal supplied from the bandpass filter 1, and supplies it to the subcarrier generation circuit 5. The subcarrier generation circuit 5 generates a 4.43 MHz color subcarrier signal synchronized with the color burst signal and supplies it to the subcarrier combination circuit 16 having an APC circuit configuration. The subcarrier combination circuit 16 is supplied with a signal having a fundamental frequency component having a frequency (8.35 MHz) twice the frequency of the subcarrier signal output from the adder circuit 15. Subcarrier coupling circuit 1
A 4.43 MHz signal synchronized with the output of the 6-υ addition circuit 15 is output and supplied to the color demodulation circuit 17. The color demodulation circuit 17 is also supplied with the EU(t) component output from the addition circuit 9 and the Ev(t) component output from the subtraction circuit 10. The color demodulation circuit 17 includes, for example, a phase shifter that phase-shifts the output of the subcarrier combination circuit 16 to generate a subcarrier signal for detection, and a detection circuit that receives the supply of each of the EU(t) component and the Ev(t) component. It consists of a synchronous detector and the like that demodulates each of the color difference signals B-Y and R-Y using a subcarrier signal.

This color demodulation circuit 17 outputs a BY signal and a RY signal.

In the above configuration, bandpass filter 1. IH delay circuit 3
, addition circuits 9, 15 . Subtractor circuit 101 Double wave rectifier circuit 11
, 12 , and limiters 13 and 14 form a part of the luminance signal separation circuit according to the present invention, and also double-wave rectify the two carrier chrominance signals before demodulation to take out the 8.86■ h component. A PALN configured to obtain a detection subcarrier signal synchronized with the component and demodulate the color difference signal.
It forms part of a color demodulation circuit using a demodulation method. In this manner, each part of the luminance signal separation circuit according to the present invention can be used in common with the color demodulation circuit, so that the number of parts used in a video reproducing device or the like can be reduced.

As described in detail above, the luminance signal separation circuit according to the present invention is configured to remove the carrier color signal using a signal for canceling the carrier color signal synchronized with the carrier color signal, so that a decrease in horizontal resolution or vertical resolution can be avoided. Even if the PAL color video signal has time axis fluctuations, the carrier color signal can be sufficiently removed from the signal, and the occurrence of dot interference caused by minute black and white dot arrays can be prevented. At the same time, it is possible to reduce the number of parts used in a video playback device or the like that employs the PALN demodulation method. Furthermore, according to the present invention, even when a color burst signal having a steady phase error, such as a reproduced color video signal output from a video tape recorder or the like, is input, the carrier color signal can be sufficiently removed. This means that it is possible to obtain a luminance signal that is

In the above embodiment, a bandpass filter I is used as the carrier color signal separating means, but other circuits such as a comb-shaped filter may be used as the carrier-color signal separating means. Further, in the above embodiment, the third signal synthesis means includes the limiter 13, 14 and the adder circuit 15.
However, in addition to the above-mentioned configuration, the third signal synthesizing means is provided with a tuning circuit for extracting a signal having a frequency twice the frequency of the subcarrier signal before or after each of the limiters 13 and 14. It may be configured. Furthermore, this third signal synthesizing means is the limiter 1
A configuration may be adopted in which a phase adjustment circuit is provided at the subsequent stage of each of 3 and 14, and in such a case, the reliability of the effect obtained can be improved. Further, in the above embodiment, the subtraction circuit 2 and the low-pass filter 8 functioned as the fourth signal synthesizing means, but the fourth signal synthesizing means has a phase adjustment circuit installed before or after the low-pass filter 8 in addition to the above structure. , amplitude adjustment circuit, or both may be provided, and even in such a case, the reliability of the effect obtained can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional luminance signal separation circuit;
FIG. 2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a waveform diagram showing the operation of the circuit in FIG. 2, and FIG. FIG. 2 is a block diagram showing a color demodulation circuit according to the present invention. Explanation of symbols of main parts 1...Band filter 2, 10...Subtraction circuit 3...IH delay circuit 7...Multiplication circuit 8...Low pass filter 9, 15...Addition circuit 11, 12...Double wave rectifier circuit 13
, 14...Limiter applicant ・Motohiko Fujimura, patent attorney representing Ionia Co., Ltd.

Claims (1)

[Claims] A separation circuit that separates and outputs a luminance signal from a PAL color video signal in which one of the carrier color signals and the color burst signal is phase-inverted every horizontal scanning period;
a carrier color signal separating means for separating and outputting a carrier color signal from an AL color video signal; a signal delaying means for delaying the output of the carrier color signal separating means for a predetermined time; and a signal delaying means for adding the input and output of the signal delaying means. a first signal synthesizing means for synthesizing the signals obtained by the first signal synthesizing means, a second signal synthesizing means for synthesizing the signals according to the difference between the input and output of the signal delaying means, a first frequency doubling means for generating a signal of twice the frequency; a second frequency doubling means for generating a signal of twice the frequency of the output of the second signal synthesizing means; a third signal synthesizing means for synthesizing a signal obtained by adding the outputs of the two frequency doubling means; a multiplication means for multiplying the third signal synthesizing means and the output of the signal delaying means; and an output of the multiplication means. and a fourth signal synthesizing means for synthesizing a signal obtained by adding or subtracting a relatively low frequency component of the PAL color video signal and the PAL color video signal.