JPS6214582A - Vertical emphasis circuit - Google Patents

Abstract

PURPOSE:To reduce the noise to prevent color fogging and blur by controlling the feedback quantity in accordance with the difference between the luminance signal of one horizontal period H before and the present luminance signal and correlations between signals of horizontal scanning periods adjacent to each other to perform preemphasis and deemphasis in the vertical direction. CONSTITUTION:If an input signal e1 is the luminance signal, the element of the constant of an attenuator in a fundamental circuit is included in a constant gamma of a level adjusting circuit 6, and an adder 7 is provided to perform operation, and a correlation detecting circuit consisting of a delay line 8, an attenuator 9, and a non-linear circuit 10 is formed, and the attenuation quantity of an attenuator 2 and the constant gammaof the circuit 6 are controlled by correlations obtained by said detecting circuit. The feedback quantity is controlled by the difference between the luminance signal of 1H before and the present luminance signal and correlations between signals of horizontal scanning periods adjacent to each other. Thus, the asymptotic characteristic of the outline part is converged more quickly to reduce the degradation of the response characteristic such as waveform dullness of rise and blur fall. The noise is reduced considerably by preemphasis and deemphasis effects in parts other than the outline part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a vertical emphasis circuit for a video signal in a magnetic recording/reproducing device (for example, a VTR, etc.).

[Background of the invention]

One of the means for improving the S/N of a VTR is pre-emphasis and de-emphasis in the vertical direction of the screen. this is,
For example, the 1H delay line (jH is 1 horizontal period, 63.5 μB in the case of NTSC) described in Japanese Patent Publication No. 55-19551.
) can be realized by developing a vertical contour enhancement circuit for a feedback type video signal.

However, when performing only pre-emphasis or only de-emphasis to simplify the circuit, increasing the amount of emphasis causes blurring in the vertical contour. Particularly in the case of color signals, there is a problem in that color bleeding occurs and image quality deteriorates.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a vertical emphasis circuit which can compensate for the above-mentioned drawbacks of the prior art, significantly suppress noise, and reduce the occurrence of vertical blur or color fringing.

[Summary of the invention]

The present invention develops a vertical contour enhancement circuit and performs vertical pre-emphasis and de-emphasis.

[Embodiments of the invention]

The present invention will be described below with reference to its embodiments, but before explaining the present invention, the principle of a feedper type contour emphasizing circuit will be explained.

FIG. 2 is an example of a feedback type video signal vertical contour enhancement circuit using a conventional 1H delay line. To explain the operating principle of this circuit, the input video signal e1 is 1
The positive feedback loop is added to a positive feedback loop composed of an H delay line 1, an attenuator 2 with an attenuation factor α times (α<1), and an adder 3. The output video signal of this circuit is 1H delay line 1
From the input signal e2 of the output signal e3, the attenuation rate is 1 times (
It is obtained by subtracting the signal that has passed through the attenuator 4 of 1) using the subtracter 5. The signals of each part are as follows, where the delay time of 1H delay line 1 is τ, e 2 =, a , stone wire, 1 bow 1
1Qx...Between songs ■a3 = exp(-Sr
) ・e t −=−■S is a Laplace transform operator, and the transfer function G (S) of the overall circuit is given by. The response 6tl to the step human force e3 decays as time τ elapses, as shown in FIG. 3, and becomes (1-β)
/(1-α). When α>β, there is no vertical contour enhancement circuit, and when α<β, the circuit has the opposite characteristics.

The present invention is based on an equivalent modification of the above-mentioned feedback type contour enhancement circuit, and further controls the amount of feedback based on the difference between the luminance signal 1H before and the current luminance signal, that is, the correlation between the signals in the horizontal scanning period that coincide with each other. By doing so, it is possible to realize a vertical emphasis circuit in which the emphasis characteristic at the contour portion is changed and blurring of the vertical contour or color blurring is reduced.

The vertical emphasis circuit of the present invention will be explained below using examples.

FIG. 1 shows the basic configuration of a vertical emphasis circuit as a first embodiment of the present invention.
is the case of the luminance signal. The difference from the basic form in FIG. 2 is that the constant β of the attenuator 4 is replaced by the constant γ of the level adjustment circuit 6.
In addition, an adder 7 is provided to perform calculations, and a correlation detection circuit consisting of a delay &18, an attenuator 9, and a nonlinear circuit 10 is configured, and according to the amount of correlation obtained from the correlation detection circuit. Attenuation amount of attenuator 2 and fixed value γ of level adjustment circuit 6
The structure was designed to control the This makes it easier to specify the emphasis constant as described later, and also reduces the amount of de-emphasis in the contour area to reduce excessive naoher shoot during pre-emphasis and blurring during de-emphasis that occur on the contour. Features such as being able to do so occur.

For the input e1, 62+eB is given by the above-mentioned equations (1) and (2), and as a result, e4 becomes. When the gain of the level adjustment circuit 6 is r, the transfer function G (S) is expressed as 1-α. If r=1=7 in equation 0, the characteristics match the characteristics shown by equation (2), and the equivalent pre-emphasis characteristic Gp(S) of this circuit is as follows. Between both characteristics, Gp(S)・Gd('S) = 1...
・・・・・・・・・・・・・・・・・・・・・・・・
Because of the relationship . . . , it is possible to completely satisfy the matching conditions for both circuits. 1 for emphasis coefficient. K
z and the emphasis element X are established as two independent variables according to the above matching condition relational expression, and the circuit characteristics can be determined by determining both the emphasis coefficients or one of them and the amount of emphasis.

here, It has a characteristic that the lower limit is maximum for each fH.

The vertical frequency spectrum component of the luminance signal exists centered on the horizontal spectrum nfH (n is an integer, fH is the horizontal frequency), and from the characteristics shown in Figure 4, the pre-emphasis is 1Gp (7
It can be seen that the vertical frequency spectrum component is emphasized by ω)1 and suppressed by de-emphasis 1Gd(/ω)1. FIG. 5 shows the step response of briefphasis, and FIG. 6 shows the step response of de-emphasis. By pre-emphasizing the luminance signal and recording it on tape, etc., and de-emphasizing it during playback, the vertical frequency spectral components match the original signal, and noise mixed in the playback system is suppressed by de-emphasis, resulting in a low S/N ratio. Improved. The improvement effect spans the entire signal band from low frequencies to high frequencies.

Next, when we input a step-like signal as shown in Figures 5 and 6, which describe the response characteristics at the contour, the pre-emphasis creates an overshoot at the rise of the signal and gradually approaches the signal level. , de-emphasis] has a characteristic that the rise 9 is gradual and gradually approaches the signal level. In the falling portion, as shown in FIGS. 7 and 8, even if the input signal becomes 0, the emphasis output has a characteristic that gradually approaches 0. In the present invention, the contour is detected by a correlation detection circuit consisting of a delay line 8, an attenuator 9, and a nonlinear circuit 10, and the attenuation amount of the attenuator 2 and the level adjustment circuit 6 are controlled to reduce the values of 0 or 2 and X. This speeds up the convergence speed of the asymptotic characteristics of the contour and reduces deterioration in response characteristics such as waveform blunting at the rising edge and blurring at the falling edge. In this case, only the contour portion is affected, and the noise suppression effect due to the above-mentioned emphasis characteristic is maintained in areas other than the contour portion. Also, an attenuator 2, a level adjustment circuit 6
A configuration in which only one of the two is controlled is also possible, and in this case, the above-mentioned response characteristic improvement effect becomes small.

This vertical emphasis circuit will be described in detail as a circuit that applies it to chromaticity signals. In the case of the NTSC system, the chromaticity signal is multiplexed with the luminance signal by a chrominance subcarrier with a frequency of 227.5 fH (fH is the horizontal frequency) with a 1/2 fH frequency offset, resulting in a horizontal vector (n+7) fH (
There are vertical frequency spectral components centered around the frequency (n is an integer). Therefore, in the vertical direction assist, it is necessary to correct the phase of the color subcarrier so that the component circuit shown in FIG. 1 operates according to the principle for the spectral component centered at (n+-)fH. In other words, whether 227.5fH delay correction is added to 10.5H delay line 1 or
The output phase of H delay line 1 is inverted. Or adder 3
9 is an example of a vertical emphasis circuit for NTSC chromaticity signals. In this example, adder 3 is used as a subtracter, and subtracter 5 is used as an adder. The pre-emphasis characteristic Gp (S) resulting from this is the de-emphasis characteristic Gtics)h, and these frequency characteristics 1Gp (7ω) are shown in Figure 10.
I, 1Gd(7ω)l is shown. IGp(j”)
1Gd(,2ω)I has the characteristic that it becomes the maximum for each fH with Q in the Io formula as the upper limit, and 1Gd(,2ω)I has the characteristic that it becomes the minimum for each fH with 1/Q as the lower limit.

Since the vertical frequency spectral component of the color signal exists around (n←)fH, the S/N is the same as in the case of the luminance signal.
An improvement effect can be obtained. In the embodiment shown in FIG. 9, the luminance signal eg is added to the input of the correlation detection circuit, and the contour of the luminance signal is detected to control the attenuator 2 and the level adjustment circuit 6. This is because it is easier to adjust the detection circuit by detecting the contour of a luminance signal than by detecting a chromaticity signal modulated by a chrominance subcarrier.

When detecting a contour by inputting a chromaticity signal to es, the attenuator 9 is changed to an adder.

In the case of vertical emphasis in the PAL system, the chromaticity signal is multiplexed with the luminance signal by a color subcarrier with a frequency of 28175 fH at a frequency offset of F) 1/4 fH.
The signal has a horizontal spectrum (n-7)fH, and the RY signal has a vertical frequency spectrum component centered on (n+a)fH.

Therefore, the vertical emphasis must be corrected so that the component circuit in Figure 1 is centered at (n±'')fH.In other words, the 1H delay line of 0.5 in Figure 1 is changed to a 2H delay line. , 283.75J'H-
Add delay correction or invert the output phase of that 2H delay line. The correlation detection circuit may have a configuration similar to that of the NTSC system when a luminance signal is input. When inputting a chromaticity signal, either use the 1H delay 0.5 extension line as a 2H delay line and add a delay correction of 285.75fH, or invert the output phase of the 2H delay line.
Alternatively, a 2H delay line may be used to replace the subtracter 9 with an adder.

〔Effect of the invention〕

As described above, by applying the vertical direction assist according to the present invention to a VTR, etc., it is possible to
/N improvement effect can be obtained.

In particular, it is effective even in the low frequency region of 200 KHz or less, where it is difficult to improve the S/N by other means, so it greatly contributes to improving image quality.

Further, the vertical emphasis circuit according to the present invention changes the emphasis coefficient at the vertical contour portion, so that
It is possible to minimize the deterioration of response characteristics of the reproduced output signal and excessive overshoot that occur when de-emphasis is performed without pre-emphasis or when de-emphasis is performed without pre-emphasis.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the vertical emphasis circuit of the present invention, FIG. 2 is a block diagram of a conventional vertical edge enhancement circuit, and FIG. 3 is an input/output waveform diagram of FIG. 2. Figure 4 is an emphasis characteristic diagram of the circuit in Figure 1, Figures 5, 6, 7, and 8 are input/output waveform diagrams of the circuit in Figure 1,
FIG. 9 is a block diagram showing a second embodiment of the present invention;
FIG. 0 is an emphasis characteristic diagram of the circuit of FIG. 1.8... 1H delay line, 2... Attenuator, 6... Level adjustment circuit, 10... Nonlinear circuit.

Claims (1)

[Claims] 1. A first delay circuit that delays an input video signal, and a first delay circuit that positively feeds back the output video signal of the first delay circuit to the input side of the first delay circuit to calculate an input video signal and an output video signal. 1
an arithmetic circuit 1, a second arithmetic circuit that obtains an amplitude difference signal between an input video signal and an output video signal, a linear circuit that changes the magnitude of the amplitude difference signal of the second arithmetic circuit, and an output of the linear circuit. a third calculation circuit that calculates an input video signal; a second delay circuit that delays the input video signal; and a fourth calculation that obtains an amplitude difference signal between the output video signal of the second delay circuit and the input video signal. circuit, and a nonlinear circuit that detects a constant amplitude or more of the amplitude difference signal of the fourth arithmetic circuit, and controls the amount of positive feedback and the attenuation amount of the linear circuit by the output of the nonlinear circuit, and the output of the third arithmetic circuit. A vertical emphasis circuit characterized in that the output signal is