JPH03214973A - Aperture compensation circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to reduce the cost by providing an edge detection circuit, a gamma correction circuit and an adder means adding an edge signal to a video signal after gamma correction and applying aperture correction to the video signal subjected to gamma correction in response to a level of an input video signal. CONSTITUTION:An amplified video signal is amplified by a gamma correction section 3 and its video signal is inputted also to an edge detection section 4. Thus, an edge signal in response to a level change in the input video signal is outputted from the edge detection section 4 as an aperture signal. In this case, a high frequency level of the video signal before gamma correction is high, while the low frequency level component (including noise component) is low, that is, the aperture due to the noise component is suppressed. The aperture signal and the video signal subjected to gamma correction are added at an adder 7 and the added signal is outputted to an automatic gain controller 8. Since the edge signal is obtained from the video signal before gamma correction, that is, a signal whose high frequency level is not compressed, a detection section and a voltage controlled amplifier are not required.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention amplifies the aperture according to the input video signal in order to increase the amplification of the high frequency component of the video signal from the image pickup tube etc. compared to the low frequency component. This relates to an aperture compensation circuit that changes the amount of (aperture). [Conventional Example] Conventionally, this type of aperture compensation circuit has a configuration shown in FIG. 3, for example.

In this figure, the aperture compensation circuit includes an amplifier 2 that amplifies the output signal (video signal) of an imaging unit (for example, a TV camera tube) 1, and a gamma correction unit 3 that performs gamma correction on the amplified video signal. An edge detection section 4 that obtains an aperture signal from a gamma-corrected video signal, a detection section 5 that detects the level of the gamma-corrected video signal, and a voltage control amplifier (VCA) that amplifies the aperture signal according to this detection level. 6 and an adder 7 that adds the amplified aperture signal and the gamma-corrected video signal, and outputs the added video signal, that is, the aperture-corrected video signal, to the automatic gain control circuit 8. It's like this. By aperture correcting the video signal, the outline of the image created by the video signal can be made clearer. [Problems to be Solved by the Invention] By the way, it is desired that the price of a TV camera equipped with the above-mentioned aperture compensation circuit be further reduced. Therefore, even in the aperture compensation circuit mentioned above, a circuit that can be made cheaper is desired. The present invention has been made in view of the above problems, and its object is to provide an aperture compensation circuit that has a simple circuit configuration and can reduce costs.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides an aperture compensation circuit for a TV camera that detects the level of an input video signal and changes the aperture amount according to the detected level. An edge detection circuit that obtains an aperture signal according to the signal level, a gamma correction circuit that gamma-corrects the input video signal, and an adder that adds the aperture signal to the gamma-corrected video signal. The gamma-corrected video signal is subjected to aperture correction according to the level of the video signal. [Function] With the above configuration, the aperture signal for aperture correction is obtained according to the level of the incoming video signal before gamma correction, and the aperture signal and the video signal after gamma correction are added. ．． Since the obtained aperture signal is based on an input video signal that has not been compressed by Takagi, the aperture amount increases as the Takagi level increases and decreases as the low frequency level increases. Therefore, by adding the aperture signal to the gamma-corrected video signal, it is possible to perform aperture correction in the same way as before, eliminating the need for conventional detection circuits and voltage-controlled amplifiers (VCAs), and eliminating low-frequency noise. It will be suppressed.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 and 2. In Fig. 1, the same parts and corresponding parts as in Fig. 3 are denoted by the same reference numerals, and redundant explanation will be omitted. In the aperture compensation circuit shown in FIG.
Before performing gamma correction on the video signal amplified by ing. Therefore, in the aperture compensation circuit, the video signal amplified by the amplifier 2 is input to the gamma correction section 3 and the edge detection section 4, and the edge signal obtained by edge detection is added to the gamma-corrected video signal by the adder 7. It will be done. Note that the edge detection section 4 is composed of, for example, a differentiating circuit, an inverting circuit, etc., and has a function of differentiating an input signal, inverting this differential signal, and adding the differential signal and the inverted differential signal. There is. As described above, the 7-virtual compensation circuit of the present invention includes the detection section 5 and the voltage controlled amplifier (VCA) shown in FIG.
)6 can be omitted. Next, the operation of the aperture compensation circuit with the above configuration will be explained based on the time chart shown in FIG. First, the imaging section 1
It is assumed that a video signal obtained in 1 is input and that this video signal is amplified in amplifier 2 (shown in FIG. 2(a)). Then, the amplified video signal is amplified in the gamma correction section 3 as in the conventional case, but since the video signal is also input manually to the edge detection section 4, the level of the incoming video signal is detected from the edge detection section 4. An edge signal corresponding to the change is output as an aperture signal (shown in (b) of the same figure). At this time, as shown in a, b, c (a<b<c) of the same figure (c), the video signal before gamma correction has a high Takagi level, and the edge detection unit 4 The edge signal becomes high in the Takagi level part, while it becomes low in the low level part (including the noise component), which means that the aperture amount due to the noise component is suppressed. The aperture signal is input to the adder 7, and the aperture signal and the gamma-corrected video signal are added in the adder 7, and this additional signal is output to the automatic gain control 8 (see figure (c)). ) 6 In this way, since the edge signal is obtained from the video signal before gamma correction, that is, the signal whose Takagi level is not compressed, the detection unit 5 and the voltage control amplifier (VC
A) 6 can be omitted, the aperture compensation circuit can have a simple configuration, and the cost can be reduced.

[Effects of the Invention] As described above, the aperture compensation circuit of the present invention includes an edge detection circuit that obtains an aperture signal according to the level of an input video signal, a gamma correction circuit that gamma-corrects the input video signal, and an addition means for adding the edge signal to the gamma-corrected video signal, and the gamma-corrected video signal is subjected to aperture correction according to the level of the input video signal, so that the detection circuit and voltage control amplifier are This has the effect of simplifying the circuit configuration and reducing costs.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an aperture compensation circuit showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of the aperture compensation circuit, and FIG. 3 is a diagram of a conventional aperture compensation circuit. This is a schematic block diagram. In the figure, 1 is an imaging unit, 2 is an amplifier, 3 is a gamma correction unit, and 4
is an edge detection section, 7 is an adder, and 8 is an automatic gain controller (A
GC).

Claims (1)

[Claims] (1) In an aperture compensation circuit for a TV camera that detects the level of an input video signal and changes an aperture amount according to the detected level, an edge detection means for obtaining an aperture signal according to the level of the input video signal, and the input video comprising: gamma correction means for gamma-correcting a signal; and addition means for adding the aperture signal to the gamma-corrected video signal; An aperture compensation circuit for a TV camera, characterized in that: