JPS61267464A - Video camera - Google Patents

Abstract

PURPOSE:To obtain a vivid reproduced picture of not only the bright part but also the dark part of an object of high contrast by detecting the peak value of a video signal in case of image pickup of the bright part and detecting the average value of the video signal to obtain an iris control signal in case of image pickup of the dark part. CONSTITUTION:When the bright part of the object of high contrast is picked up with a proper quantity of light in case of image pickup of the object of high contrast, a switch 8 is closed to the side of a contact A, and the detection output of a peak value detecting circuit 6 controls an iris 1 as the iris control signal thereby. When the dark value is picked up with a proper quantity of light, the switch 8 is closed to the side of a contact B, and the detection output of an average value detecting circuit 7 controls the iris 1 as the iris control signal. Thus, the bright part and the dark part are picked up with the proper quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a video camera equipped with an iris controlled by the detection output of a video signal.

[Background of the invention]

Video cameras also respond to changes in the brightness of the subject.
An iris is provided to set the appropriate amount of light. Various methods of controlling the iris have been proposed in the past, and one such method is disclosed in Japanese Unexamined Patent Publication No. 57-10583, ``Unexamined Japanese Patent Application No. 56-16547.
As disclosed in Publication No. 1, etc., there is a method in which a video signal is peak-detected and the iris is controlled using the detected output.According to this iris control method, when the subject is bright as a whole, Since the peak value of the video signal is partly high, the level of the control tube signal becomes high and the iris is narrowed down.If the subject is dark overall, the peak value of the video signal is low, so the level of the control signal becomes high. The iris is lowered and opened, thereby controlling the iris according to the overall brightness of the subject, appropriately controlling the amount of light, and obtaining a reproduced image with appropriate brightness.

By the way, when capturing images indoors, for example, when capturing an image of a subject that has some bright areas on a dark background, such as a window in the capture screen, a conventional video camera that adopts the iris control method described in z6 above is used. In this case, the peak value of the video signal obtained is very large, and the iris is sufficiently narrowed down. For this reason, the amount of light is appropriate for bright parts, but the amount of light is insufficient for dark backgrounds, resulting in a very dark σ) on the playback screen.

In this way, when capturing a subject with a high contrast, with a conventional video camera, if there is even a slight bright part, the dark part of the subject will appear very dark on the playback screen, and the subject will appear very dark. It was not possible to image dark areas with an appropriate amount of light.

[Purpose of the invention]

An object of the present invention is to solve the problems of the above-mentioned prior art and to be able to photograph objects with high contrast.

To provide a video camera capable of selectively capturing images of both bright parts and dark parts with an appropriate amount of light.

[Summary of the invention]

In order to achieve this object, the present invention is designed to obtain an iris control signal by performing peak value detection on a video signal to capture an image of a bright part of a subject with a large contrast with an appropriate amount of light, and to obtain an iris control signal to capture a dark part with an appropriate amount of light. When taking an image, the feature is that the iris control signal is obtained by performing average value detection on the video signal.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a video camera according to the present invention, and 1 indicates an iris.

2 is an imaging section, 3 is a signal processing section, and 4 is an output terminal.

5 is an iris control signal forming circuit, 6 is a peak value detection circuit, 7 is an average value detection circuit, and 8 is a switch.

9 is an iris drive circuit.

In the figure, light from a subject (not shown) is incident on an imaging unit 2 via a lens 2 and an iris 1 (not shown). The imaging unit 2 generates a video signal according to this incident light,
This video signal is processed by the signal processing section 3 and then supplied to the output terminal 4 and the iris control signal forming circuit 5.

The iris control signal forming circuit 5 forms an iris control signal from the supplied video signal, and this iris control signal is supplied to the iris drive circuit 9, whereby the imaging unit 2
The iris 1 is controlled so that the zero incident light amount is appropriate.

The iris control signal forming circuit 5 includes a peak value detection circuit 6, an average value detection circuit 7, and a switch 8. The video signal from the signal processing unit 3 is detected by a peak value detection circuit 6 and an average value detection circuit 7, and one of these detection outputs is selected by a switch 8 as an iris control signal. When taking an image of a bright part, if you want to take an image of the bright part with an appropriate amount of light, close the switch 8 to the A side. Thereby, the detection output of the peak value detection circuit 6 controls the iris 1 as an iris control signal. On the other hand, when imaging a dark area with an appropriate amount of light, the switch 8 is closed to the B side. Thereby, the detection output of the average value detection circuit 7 controls the iris 1 as an iris control signal.

By the way, as shown in FIG. 2, the white part 11 and the dotted part 1
2, the peak value of the video signal for this object is determined by the ratio of the area of the white part 110 to the area of the dotted part 12 (hereinafter referred to as
Since the detection output level of the peak value detection circuit 6 is constant, the aperture area of the iris 1 controlled by this detection output is determined by the straight line 13 in FIG. As shown in , it remains constant even if the W/B ratio changes. Therefore, in this case, even if the area of the white portion 110 changes, that portion is always imaged with an appropriate amount of light. .

On the other hand, when the W/B ratio changes, the average level of the video signal also changes, so the detection output of the average value detection circuit 7 also changes, and the aperture area of the iris 1 controlled by this changes as well.
It changes as the B ratio changes. Therefore, when there are very few white parts 11, the average level of the video signal is very low, and when there are many white parts 11, the average level of the video signal is very high, so the average value detection circuit White part 110 when the detection output of 7 is used as the iris control signal
The iris aperture area relative to the ratio is curve 14 in Figure 3.
It changes like this.

Therefore, when photographing a dark subject indoors or in backlit conditions, even if a slightly bright part enters the subject, the iris opening area becomes extremely large, and these dark parts are captured with the appropriate amount of light. will be done.

As described above, in this embodiment, by operating the switch 8 for a subject with a large contrast, it is possible to image the bright and dark parts of the subject with an appropriate amount of light.

When imaging a subject with low contrast, either detection output may be used as the iris control signal, but in order to prevent blooming, burn-in in the imaging section, and collapse of white peaks, it is preferable to use the peak detection circuit 6. It is preferable to use the detected output of the iris as the iris control signal.

FIG. 4 is a circuit diagram showing a specific example of the iris control signal forming circuit 5 in FIG.
are transistors, 17, 18, and 19 are resistors, 20 is a capacitor, 21 is a switch corresponding to switch 8 in the vJ1 diagram, and 22 is an output terminal.

In the figure, a video signal is inputted to the input terminal 15Vc from the signal processing section 3 (FIG. 1). Resistance 18, 19
and capacitor 20 constitute a time constant circuit. Now, let the resistance values of resistors 17, 18.19 be Rx, Rz, and R, respectively.
3, there is the following relationship between them.

Therefore, when the switch 21 is closed, the time constant of the time constant circuit becomes small, and by setting this to about one field or one frame, this iris control signal forming circuit operates as an average value detection circuit. Also, open switch 21.

The time constant of the time constant circuit becomes large and operates as a peak value detection circuit. Although these do not exhibit average value detection characteristics or peak value detection characteristics exactly, they approximately exhibit these characteristics. The obtained detection output is supplied from the output terminal 22 to the iris drive circuit 9.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a clear reproduced image even for a bright part of an object with high contrast, and it is possible to obtain a clear reproduced image even for a dark part. θ), in which an average value detection circuit and a switch are added to the video camera, does not make the configuration particularly complicated, and it is possible to solve the problems of the above-mentioned prior art and provide a video camera with excellent functions.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an embodiment of the video camera according to the present invention, and Figs. 2 and 3 show the peak value detection output and the average value for the ratio of the white part to the black part of the subject. FIG. 4 is an explanatory diagram showing the value detection output. FIG. 4 is an explanatory diagram showing the iris control signal formation in FIG. - Imaging section 5...Iris signal forming circuit 6...Peak value detection circuit 7...Average value detection circuit 8...Switch 9...Iris drive circuit

Claims (1)

[Claims] A video camera comprising means for forming a control signal from a video signal and controlling an iris using the control signal, the means comprising: a peak value detection circuit for peak value detection of the video signal; and a peak value detection circuit for detecting the peak value of the video signal; It consists of an average value detection circuit that performs value detection, and a switch that selects the detection output of the peak value detection circuit and the detection output of the average value detection circuit, and the detection output selected by the switch is used as the control signal. A video camera featuring: