JPS6359595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a luminance signal separation circuit for separating a luminance signal from a color video signal in which a luminance signal and a carrier color signal are frequency multiplexed.

Conventionally, in order to separate a luminance signal from such a color video signal, a trap circuit for trapping a carrier color signal has been used. However, this trap circuit has the disadvantage that not only the high-frequency luminance component deteriorates and the resolution decreases, but also cross color occurs.

In place of the trap circuit, when a comb filter 10 consisting of a delay circuit 11 of one horizontal period (1H) and a synthesizer 12 is used to separate the luminance signal as shown in FIG. 1, the above-mentioned disadvantages arise. However, dot interference peculiar to comb filters does occur.

That is, as shown in FIG. 2, three pixels a at the same horizontal position in three consecutive scanning lines,
The amplitude e′ of b and c is e′ _o-2 =Y _L(o-2) +Y _H(o-2) +C _(o-2)・P ₁ e′ _o-1 =Y _L(o-1) +Y _H(o-1) +C _(o-1)・P ₂ e′ _o =Y _L(o) +Y _H(o) +C _(o)・P ₁ …(1) Here, Y _L ; low range Luminance component Y _H ; High-frequency luminance component C; Carrier color signal component P; Phase term of color width carrier wave, when P ₁ = 1,
When expressed as P ₂ =-1, the frequency multiplexed regions are the second term and the third term. Assuming that the high-range luminance component and carrier color signal component between horizontal lines are equal,
If we set Y _H = Y ₀ and C = C ₀ , respectively, and set the carrier color signal component C _(o) to zero in n lines, the amplitude e of each pixel in this frequency multiplexing region is given by equation (2). It becomes like this.

e _o-2 = Y ₀ + C ₀ · P ₁ e _o-1 = Y ₀ + C ₀ · P ₂ e _o = Y ₀ ...(2) Color video signal Sa with amplitude e expressed by equation (2) is supplied to the comb filter 10, its separated output is the luminance signal Y (high-frequency luminance signal component)
teeth It is.

Therefore, when the (n-1), (n-2)... line is a vertical correlation section and the n line is a vertical non-correlation section, the luminance signal Y is formed from the line outputs of both of these correlation sections. In its components (in equation (3),
Since the carrier color signal component remains in Yn) without being canceled out, dot interference occurs due to the luminance signal at this time.

This dot interference becomes even more apparent when considering an image such as that shown in FIG. The figure shows an image in which the upper half is red, the lower half is black, and there is a vertical stripe in the center.
Q and pixel R on the red-white boundary line, the color video signal of the pixel P on the (n-2) line is the high-frequency luminance component Y ₀ (= Y _H ) and the carrier color signal C ₀ in Figure B, which represents the entire red color, are combined output (Figure C).

Therefore, the high-frequency color video signal Sa on each horizontal line including pixels P and Q becomes as shown in FIG. 5A,
Also, since the high-frequency color video signal Sb delayed by 1H becomes as shown in Figure B, the carrier color signal Sc output from the comb filter 10 becomes as shown in Figure C,
In particular, the signal formed from the (n-1) line and the n line should originally be only a luminance signal component, but since there is no vertical correlation between these lines with respect to color signals, the remaining carrier color signal C ₀ ( Same figure C
(shown with diagonal lines), dot interference occurs.

Therefore, the present invention proposes a luminance signal separation circuit that does not cause dot interference.

FIG. 6 shows an example of the separation circuit 20 according to the present invention, in which the color video signal supplied to the terminal 1 is
Si is supplied to high-pass filter 2 and the luminance signal
Signal Sa containing high frequency component Y _H in Y _W and carrier color signal
is separated and the separated high-frequency color video signal Sa
is supplied to a synthesizer 4 together with the original color video signal Si, and a low-band luminance signal _YL is separated.

The high frequency color video signal Sa is further processed by a delay circuit 21.
This delayed high-frequency color video signal Sb is supplied to the amplitude correlator 20 together with the previous color video signal Sa 1H, and the luminance signal Sd (=
Y _H ) is separated. This luminance signal Sd does not include a carrier color signal.

Note that this high-frequency luminance signal Sd is supplied to the synthesizer 23 and synthesized into the reduced luminance signal _YL . Therefore, the synthesizer 23 obtains a broadband luminance signal Y _W that does not include a carrier color signal.

Now, in the above-mentioned amplitude correlator 20, the correlation between the amplitudes of the pair of signals Sa and Sb input thereto is determined,
When there is no correlation, that is, the amplitude (polarity) of one signal is positive and the amplitude of the other signal is negative, the output is zero; when there is correlation, the amplitude (polarity) of either signal is positive or negative. It is configured such that it is output only when it is negative, and in this case a signal with a particularly small amplitude is output.

For example, if the signals Sa and Sb are defined as shown in Figure 7A, the section where the signals Sa and Sb are absolutely the same is
Among Ta and Tb, the signals with smaller amplitudes in the sections Ta and Tb are the signal Sb in the sections Ta ₁ and Tb ₁ , and the signal Sa in the sections Ta ₂ and Tb ₂ , so the signal in the shaded area, Therefore, the signal Sd shown in Figure B is output.

Next, a separation operation using this amplitude correlator 20 will be explained with reference to FIG. Since the high-frequency color video signals Sa and Sb input to the amplitude correlator 20 are as shown in FIG. Since the polarities of Sa and Sb match and, in this case, the signal Sa has a smaller amplitude, a luminance signal Sd as shown in FIG. 5D is output.

Since both polarities match in the vertical non-correlation section (n line), the luminance signal Sd is output. in this case
Since Sa<Sb, the signal is output with the same amplitude as the signal Sa. In the vertical correlation section below the (n+1) line, both signals Sa and Sb are only luminance components and have the same amplitude, so either one of the signals is output.

In this way, by using the amplitude correlator 20, only the luminance signal can be completely separated even in the vertical non-correlation section, so that dot interference at the pattern boundary can be reliably removed.

Incidentally, the amplitude and phase of the luminance signal shown in FIG. 4A and the carrier color signal shown in FIG. . Therefore, the effects of this invention will be explained in a more general manner.

That is, if we focus only on the frequency multiplexed region in equation (1), the amplitude e of each pixel at that time can be expressed as follows.

e _o-2 ＝Y _Ho-2 ＋C _o-2・P ₁ e _o-1 ＝Y _Ho-1 ＋C _o-1・P ₂ e _o ＝Y _Ho ＋C _o・P ₁ ……(4) (4) C in the equation can be expressed as follows using a coefficient K representing the amount of color component and a coefficient M representing the amount of vertical correlation.

e _o-2 ＝Y _Ho-2 ＋K _o-2・M _o-2・Cu・P ₁ e _o-1 ＝Y _Ho-1 ＋K _o-1・M _o-1・Cu・P ₂ e _o ＝Y _Ho +K _o・M _o・Cu・P ₁ ...(5) Here, Cu: unit color component In equation (5), for convenience of explanation, the values of the luminance component Y _H and coefficient K are equal between scanning lines, Y _Ho-2 ＝Y _Ho-1 ＝Y _Ho ＝Y ₀ K _o-2 ＝K _o-1 ＝K _o ＝K ...(6) And as mentioned above, (n-2), (n- 1)
Letting the line be a correlation part and the n line be a non-correlation part, and setting M _o-2 = M _o-1 = 1 M _o =0 (7), equation (5) becomes as follows.

e _o-1 =Y ₀ +K・1・C _u・P ₁ e _o-1 =Y ₀ +K・1・C _u・P ₂ e _o =Y ₀ +K・0・C _u・P ₁ ……(8 ) Here, in order to see what value the output (amplitude) e _d of the amplitude correlator 20 becomes when the coefficient K is used as a variable, that is, when the amount of color components is changed, first
FIG. 8 shows the input signal e to the amplitude correlator 20 when the horizontal axis represents the input signal e. Figure A shows the amplitude characteristic when there is a correlation between the luminance signal and the color signal, and Figure B shows the amplitude characteristic when there is no correlation between the color signal and the color signal.
C in the same figure shows the amplitude characteristic when there is no luminance signal at all and when there is no correlation in some of the color signals.

Therefore, A in the same figure corresponds to the amplitude characteristic near point P in Fig. 3, B in the same figure corresponds to the amplitude characteristic in the vicinity of point Q in Fig. 3, and C in the same figure corresponds to the amplitude characteristic near point R in Fig. 3. handle.

When a signal with such amplitude characteristics is separated using a conventional comb filter, the output is
e _c becomes as shown in Figure 9. A, B, and C in the same figure are the 8th
Corresponds to that in the figure. According to FIG. 9A, the luminance signal is completely separated regardless of the value of the carrier color signal component, which is natural since it is a signal from the vertical correlation section. Also, according to C in the same figure, this area is originally an area where there is no luminance component. However, since the comb filter 10 outputs an amplitude proportional to the carrier color signal component as a luminance component, this output
All e _{and c} become dot interference components.

According to FIG. 9, the luminance component must be a constant value regardless of the magnitude of the carrier color signal component, but if the comb filter 10 is used, the amplitude e _c of the luminance signal will change as shown in the figure. It varies depending on the ingredients.

On the other hand, according to the separation circuit according to the present invention using the amplitude correlator 20, for the input amplitude characteristics shown in FIGS. 8A, B, and C, the input amplitude characteristics shown in FIG.
Outputs like B and _C are obtained.

Therefore, when the input amplitude characteristic is as shown in FIG. 8B, the amplitude e _d of the luminance signal is suppressed from changing significantly due to the carrier color signal component, and when the input amplitude characteristic is as shown in FIG. 8C, is the amplitude even if there is a carrier color signal component.
Since e _d is always zero, there is no dot interference.

FIG. 11 is a waveform diagram similar to FIG. 5 when the phase of the color subcarrier is opposite to that in FIG. 4;
FIG. 12 is a waveform diagram for explaining the separation operation when the luminance component is smaller than the color component. In either case, only the luminance signal can be separated.

FIG. 13 shows a specific example of the amplitude correlator 20, which is composed of four differential amplifiers. Transistors Q ₁ , Q ₃
A predetermined DC bias E _B (for example, 1/2
A signal Sa superimposed on Vcc) is supplied, and the bases of transistors Q ₂ and Q ₄ are also supplied with a DC bias E _B
A signal Sb superimposed on the signal Sb is supplied. Since the first differential amplifier 21 operates as a logical sum, when the pair of signals _Sa and _Sb are input in the state shown in FIG. The sum output) x is shown in B in the same figure.
Further, since the second differential amplifier 22 operates as a logical product, the common emitter output (first logical product output) y of the transistors Q ₃ and Q ₄ becomes as shown in FIG.

The third differential amplifier 23 to which the first OR output X is supplied is configured to operate as an AND, and therefore the second AND output obtained therefrom
Sd ₁ becomes D in the same figure. Also, the first logical product output y
The fourth differential amplifier 24 to which is supplied is configured to operate as a logical sum, and therefore, the second logical sum output Sd ₂ shown in FIG. These outputs
A composite output Sd of Sd ₁ and Sd ₂ is obtained from the output terminal 26. This combined output Sd is the same as the output shown in FIG. 7B, and it is therefore understood that if the high frequency color video signals Sa and Sb are supplied to the amplitude correlator 20, the luminance signals can be separated.

FIG. 15 shows a case where a separation circuit 30 is configured by combining a conventional comb filter 10 and an amplitude correlator 20, and the high frequency color video signal Sa is passed through the comb filter 1.
0 and its output Sc is supplied to the amplitude correlator 20. Therefore, a part of the output Sc is sent to the delay circuit 21.
The output is delayed by 1H with respect to the output Sc.
Se is formed, and these outputs Sc and Se are supplied to the amplitude correlator 20.

The separation operation when the separation circuit 30 is configured in this way will be explained using the pattern shown in FIG.
The result will be as shown in FIGS. 5, 11, and 12. That is, if the output of each circuit is determined as shown in FIG. 15, the finally obtained luminance signal Sf will be as shown in FIG. 5F, FIG. 11F, and FIG. 12F. FIG. 16 shows output characteristics similar to those shown in FIG. 10.

As is clear from these figures, the separation circuit 3 is constructed by combining the comb filter 10 and the amplitude correlator 20.
When 0 is configured, even in the case of an input amplitude characteristic as shown in FIG. 8A, the luminance component will not be output with a degraded state.

FIG. 17 shows a modification of FIG. 15, in which two comb filters 40 and 50 are used, and the first comb filter 40 is composed of a 1H delay circuit 41 and a synthesizer 42. The second comb filter 50 is composed of a 1H delay circuit 51 and a synthesizer 52. Even if the separation circuit 30 is configured in this way, the luminance signals can be separated as in the case of FIG. 15. That is, in FIG.
When calculating the transfer function of the signals Sc _{and Se} input to the
When e _c (t)=e(t)/2(ε ^-j 〓 ^TH -1) ...(9) e _e (t)=e(t)/2(ε ^-j 〓 ^TH -ε ^{- j2} 〓 ^TH )…
…(10) However, T _H is the horizontal period and ω=2πf. On the other hand, in the configuration shown in FIG. 17, the transfer function of the signals Sc' and Se' input to the amplitude correlator 20 similarly converts the amplitudes of the signals Sc' and Se' into e _c ', e _e ', and the signal Sa
When is e(t), e _c ′(t)=e(t)/2(ε ^-j 〓 ^TH −1)……(11) e _e ′(t)=e(t)/2(ε ^-j 〓 ^TH −ε ^-j2 〓 ^TH )
...(12) becomes. That is, it can be seen that even if the structure is as shown in FIG. 17 with Sc'=Sc and Se'=Se, the signal separation similar to that shown in FIG. 15 can be achieved.

As explained above, according to the present invention, it is possible to reliably eliminate dot interference occurring in the vertical non-correlation section. Therefore, image quality can be improved compared to a conventional separation circuit using a comb filter. If the separation circuit 30 is constructed by also using comb filters 10, 40, and 50 as shown in FIG. 15 or FIG. 17, it is possible to prevent deterioration of the luminance component, thereby further improving the image quality. Can be done.

[Brief explanation of drawings]

Figure 1 is a connection diagram of a comb filter, Figures 2 to 5 are diagrams for explaining the luminance signal separation operation,
6 and 15 are system diagrams showing an example of the separation circuit according to the present invention, FIG. 7 is an explanatory diagram of the operation of the amplitude correlator, and FIGS. 8 to 12 and 16 are diagrams for explaining the separation operation. FIG. 13 is a connection diagram showing a specific example of the amplitude correlator, FIG. 14 is an explanatory diagram of its operation, and FIG. 17 is a system diagram showing another example of the present invention. 10, 40, and 50 are comb filters, 20 is an amplitude correlator, and 21 is a delay circuit.

Claims (1)

[Claims] 1. An amplitude correlator configured to output a signal with a smaller amplitude only when a pair of signals of equal polarity is input, and the amplitude correlator is configured to output a signal with a smaller amplitude. A color video signal including a gamut component and a carrier chrominance signal and a color video signal one horizontal period before this color video signal are supplied, and the amplitude correlator separates a luminance signal not including a carrier chrominance signal. This is a luminance signal separation circuit. 2. It has an amplitude correlator that outputs a signal with a smaller amplitude only when a pair of signals of equal polarity is input, and a comb filter, and a carrier color signal output from the comb filter. The luminance signal containing the carrier color signal and the luminance signal delayed by one horizontal period are supplied to the amplitude correlator, and the luminance signal not containing the carrier color signal is separated from the amplitude correlator. Separation circuit.