JPH0498655A - Video emphasis circuit - Google Patents

Abstract

PURPOSE:To satisfactorily transmit video signals while reducing a signal component to be missed and reducing the degradation of picture quality by clipping the video signals at the front step of low frequency emphasis. CONSTITUTION:An emphasis characteristic is formed by the characteristic for synthesizing the first characteristic of short time constant emphasis and the second characteristic of low frequency emphasis, the video signal is taken out through the serial circuit of a first circuit 2 having the first characteristic and a second circuit 4 having the second characteristic, and a white/dark clip circuit 3 is provided in the front step of the second circuit. Then, the emphasis characteristic is divided into short time constant emphasis and low frequency emphasis, and clipping is executed in the front step of this low frequency emphasis. Thus, the video signals can be satisfactorily transmitted while reducing the signal component to be missed and reducing the degradation of picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video emphasis circuit used in a video signal recording system in, for example, a VTR.

[Summary of the invention]

The present invention relates to a video emphasis circuit, and the emphasis characteristics are divided into short time constant emphasis and low frequency emphasis, and clipping is performed before the low frequency emphasis to reduce missing signal components and achieve good quality with less deterioration of image quality. It is designed to transmit video signals.

[Conventional technology]

For example, when recording/reproducing (transmitting) a video signal in a VTR, the luminance signal component in the video signal is usually transmitted as an FM signal.

In this case, in FM transmission, so-called triangular noise occurs due to waveform distortion during transmission. Therefore, emphasis is performed to reduce this triangular noise. That is, V.T.
A video emphasis circuit is provided in the R recording system, and a corresponding de-emphasis circuit is provided in the reproduction system.

However, in such a device, when emphasis is applied, a so-called overshoot occurs, for example, at the edge portion of the signal, and the amplitude is thereby expanded. On the other hand, in the case of FM transmission of a signal, due to band limitations on the transmission path, etc., if a signal with an amplitude greater than a predetermined value is supplied, an inversion phenomenon may occur. Conventionally, therefore, the overshoot caused by emphasis is clipped at an arbitrary level to prevent the amplitude from exceeding a band limit or the like.

That is, in FIG. 7, (11) is an input terminal for, for example, a luminance signal to be recorded, and a signal from this input terminal (11) is supplied to a white and dark clip circuit (13) through an emphasis circuit (12). A signal from this clip circuit (13) is taken out to an output terminal (14) which is supplied to an FM modulator (not shown).

This allows the emphasis circuit (
A signal as shown in FIG.
3) to the output terminal (14).

Alternatively, in Fig. 9, the signal from the input terminal (11) is passed through the bypass filter (15) to the coefficient circuit (
16), and the signal from this coefficient circuit (16) is supplied to an AC clip circuit (17). Then, the signal from the clip circuit (17) and the signal from the input terminal (11) are added together in an adder (18), and the signal is sent to the output terminal (14).
is taken out.

That is, in this circuit, the bypass filter (15)
The characteristic function of s'ro/me 1 + S T @/ m .

However, T is a time constant S, m is a coefficient, and when K=m-1, the signals V and A supplied to the input terminal (11) and the signal v0 taken out to the output terminal (14) The relationship with is 1 + S T .

1+sT, 7m0, and this equation is a characteristic function of a so-called video emphasis circuit. ``Thus, when a signal as shown in FIG. 10A is supplied to the input terminal (11), a signal as shown in FIG. 10B is taken out from the bypass filter (15), and this signal is AC at lip level as shown in the diagram
Clipped. This clipped signal and the input terminal (
11) are added by an adder (18) and taken out to an output terminal (14).

[Problem to be solved by the invention]

However, in these circuits, the overshoot is clipped, so that the signal component in the shaded area in FIG. 11A is lost. For this reason, when this clipped signal is de-emphasized, the edge portion of the signal becomes a waveform that is shaved off, as shown in Figure B, and especially in the case of a luminance signal, the sharpness decreases and the image quality is significantly degraded. It was something to put away.

This application has been made in view of these points, and the object is to provide a video emphasis circuit that has a simple configuration, reduces missing signal components, and can transmit good video signals with little deterioration in image quality.

[Means to solve the problem]

The present invention provides a video emphasis circuit for transmitting a video signal with a predetermined emphasis characteristic, in which the emphasis characteristic is formed by a composite characteristic of a first characteristic of short time constant emphasis and a second characteristic of low frequency emphasis. The video signal (input terminal (1)) is connected in series between a first circuit (2) having the first characteristic and a second circuit (4) having the second characteristic. Take out through the circuit (
This video emphasis circuit is characterized in that a clip circuit (3) is provided in the preceding stage of the second circuit together with a five-output terminal (5).

[Effect]

According to this, the emphasis characteristics are divided into short time constant emphasis and low-frequency emphasis, and clipping is performed before the low-frequency emphasis, which reduces missing signal components and produces a good video signal with less image quality deterioration. transmission can be performed.

〔Example〕

In FIG. 1, (1) is an input terminal for, for example, a luminance signal to be recorded, and the signal from this input terminal (1) is supplied to a white and dark clip circuit (3) through a short time constant emphasis circuit (2). and this clip circuit (
The signal from 3) is taken out through a low frequency emphasis circuit (4) to an output terminal (5) which is fed to an FM modulator (not shown).

Here, the characteristic function of the short time constant emphasis circuit (2) is, for example, 1+5T1 1 +ST I/m+, whereas the characteristic function of the low frequency emphasis circuit (4) is, for example, 1 + S T+/m+ 1 +S TOl
+S T, r +S To/meHowever, T 1. T o is a time constant, T + < T 11
S, m, , no are coefficients, and are expressed as m, q&m@.

Therefore, in this circuit, the composite characteristics of the entire circuit are obtained by multiplying these two characteristic functions, and as described in the prior art, 1+ST.

1 + S T o/m (1 is the characteristic function of the video emphasis circuit.

That is, in the above-mentioned circuit, the characteristic curve of the short time constant emphasis circuit (2) is, for example, as shown by the broken line a in FIG. As a result, these composite characteristics become, for example, a characteristic curve of a video emphasis circuit as shown by a solid line C in the figure.

In this circuit, when a signal as shown in FIG. 3A is supplied to the input terminal (1), a signal as shown in FIG. 3B is taken out from the short time constant emphasis circuit (2). . Here, this short time constant emphasis circuit (2
) has a large-amplitude overshoot, but its effect is short-lived. For example, this signal is DC-clipped at the white and dark clip levels as shown in the figure, and this clipped signal is supplied to the low frequency emphasis circuit (4), thereby producing a signal as shown in C in the figure. taken out. Here, the signal from the low frequency emphasis circuit (4) has a long influence time, but almost no overshoot occurs. A signal from this low frequency emphasis circuit (4) is taken out to an output terminal (5).

In other words, in this circuit, the overshoot is clipped by the signal from the short time constant emphasis circuit (2), so the effect of this clipping does not extend over a long period of time, and the loss of signal components is indicated by the diagonal lines in Figure 4A. Only the portion shown with is reduced in size compared to the conventional one shown by the broken line. Therefore, even if this clipped signal is de-emphasized, the edges of the signal are improved as shown in Figure B, and the reduction in sharpness is improved, especially in the case of luminance signals, resulting in improved image quality. Deterioration is prevented.

In this way, according to the above-mentioned device, the emphasis characteristic is divided into short time constant emphasis and low-frequency emphasis, and clipping is performed before the low-frequency emphasis, thereby reducing the number of missing signal components and improving image quality with less deterioration. This enables transmission of video signals.

That is, according to this circuit, triangular noise, inversion phenomenon, and sharpness can all be improved, and an extremely good video signal can be transmitted.

Note that in the above explanation, the characteristic functions of the short time constant emphasis circuit (2) and the low frequency emphasis circuit (4) are not limited to the above examples, and desired emphasis characteristics can be applied to arbitrary high and low frequencies. It is fine as long as it is divided.

FIG. 5 shows the configuration of another example, in which the signal from the input terminal (1) is filtered through the bypass filter (
6) to a coefficient circuit (7), and the signal from this coefficient circuit (7) is supplied to an AC clip circuit (8). The signal from the clip circuit (8) and the signal from the input terminal (1) are then supplied to the adder (9),
The signals added by the adder (9) are taken out to the output terminal (5) through the low frequency emphasis circuit (4).

That is, in this circuit, the characteristic function of the bypass filter (6) is S T ,/m.

1+STl/ml and K=m-1, the characteristic function up to the adder (9) is equal to the short time constant emphasis circuit (2) mentioned above, and the clip circuit (8) has the same characteristic function as the short time constant emphasis circuit (2). As shown by the solid line in FIG. 6, overshading with a large amplitude and a short period of time is clipped. Note that the broken line is the conventional bypass filter output. The signals added by the adder (9) are then supplied to the low frequency emphasis circuit (4), whereby a signal similar to that described above is taken out to the output terminal (5).

In this way, also in this circuit, the number of missing signal components is reduced, and a good video signal with little deterioration in image quality can be transmitted.

[Effects of the Invention] According to the present invention, the emphasis characteristic is divided into short time constant emphasis and low frequency emphasis, and clipping is performed before the low frequency emphasis, thereby reducing missing signal components and reducing image quality deterioration. It is now possible to transmit a good video signal with less noise.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an example of a video emphasis circuit according to the present invention, FIG. 2 is a characteristic diagram for explaining its operation, and FIG.
Figure 4 is a waveform diagram for explaining the operation, Figure 4 is a waveform diagram for explaining the effect, Figure 5 is a configuration diagram of another example of the video emphasis circuit according to the present invention, and Figure 6 is an explanation of its operation. FIG. 7 is a configuration diagram of a conventional video emphasis circuit, FIG. 8 is a waveform diagram for explaining its operation, and FIG. 9 is a waveform diagram for explaining its operation.
Figure 1 is a block diagram of another conventional video emphasis circuit.
0 and 11 are waveform diagrams for explaining the operation. For example, (1) is an input terminal for a luminance signal to be recorded, (2) is a short time constant emphasis circuit, (3) is a white and dark clip circuit, (4) is a low frequency emphasis circuit, and (5) is a short time constant emphasis circuit.
) is the output terminal. 4118 Figure 1 of BuQ Manwaike

Claims (1)

[Claims] In a video emphasis circuit for transmitting a video signal with a predetermined emphasis characteristic, the emphasis characteristic is a composite characteristic of a first characteristic of short time constant emphasis and a second characteristic of low frequency emphasis. the video signal is taken out through a series circuit of a first circuit having the first characteristic and a second circuit having the second characteristic; A video emphasis circuit characterized in that a clip circuit is provided at the front stage of the circuit.