JPS6372269A - Video camera - Google Patents

Abstract

PURPOSE:To raise an alarm to an object condition having a large brightness change such as backlight by providing a means detecting a peak value of a luminance signal and a means detecting a mean value so as to detect the difference of the two output levels. CONSTITUTION:A signal current obtained from an image pickup tube 2 is inputted to a gain control circuit 4 via a preamplifier 3, the gain is controlled at the gain control circuit 4 in response to the luminance signal level and the result is inputted to a gain switching circuit 5. Then gamma correction is applied by a gamma correction circuit 6, a period signal, a burst signal and a color signal are added by an encoder circuit 7 and the result is outputted. Moreover, the output signal of the gain control circuit 4 is inputted to a peak detection circuit 9 and a mean value detection circuit 10, and each output signal is fed to a differential amplifier 11. Thus, the difference between the peak value and the mean value is extracted and the cases having a large and a small brightness change are distinguished depending on the output signal level of the differential amplifier 11.

Description

[Detailed Description of the Invention] [Industrial Application] The present invention relates to a brightness signal circuit for a video camera, and in particular to a video camera with a backlight warning device suitable for photographing under subject conditions where the brightness is greatly reduced, such as when backlit. Regarding the camera.

[Conventional technology]

Normally, a video camera has an automatic gain control circuit that detects a luminance signal and suppresses the luminance signal low when the luminance signal level is high in the detected output, and increases the luminance signal level when the luminance signal level is low. It is provided. Alternatively, detect the brightness signal in the same way, and if the detected output shows that the brightness signal is high, the iris is automatically narrowed down to suppress the brightness signal, and if the brightness signal is low, the iris is automatically opened to increase the brightness signal. Such a device is provided.

However, in the past, there was no video camera with a backlight warning device, and devices that discriminate the amount of light and issue a warning are disclosed in Japanese Patent Application Laid-Open Nos. 50-157029 and 50-5161.
There was only No. 5 etc.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, the brightness signal level is controlled by focusing only on high brightness areas under subject conditions with large brightness changes such as backlighting, and as a result, relatively low brightness areas become dark. It often sinks. Generally, in such cases, the center of photography is often in a low-luminance area (person), for example, when a person is standing in front of a light and the person is focused on the person.

In such a case, the conventional technique causes a very inconvenient situation, such as the person appearing dark. Also recently,
As prices have become lower and video cameras have become more handy, instead of using an electric vinyl finder, which simply converts the photographed image into an electrical signal and then displays it on the vinyl viewfinder, it is possible to directly convert the photographed image into an electric signal and display it on the lens. In such a case, the above-mentioned problem becomes even more serious. An object of the present invention is to provide a video camera with a backlight warning device that issues a warning to prevent the screen from becoming dark (sunken) under subject conditions with large brightness changes such as when backlit.

[Means for solving the problem] The above purpose is to have a means for detecting the peak value of a luminance signal and a means for detecting the average value, and to amplify and detect the difference between the two output levels. Be achieved by this.

[For production]

That is, the means for detecting the peak value of the 14 degree signal detects only the signal level of the high brightness portion, and the means for detecting the average value of the luminance signal detects the average level of the entire signal. Therefore, if we focus on the difference between the output level when detecting the peak value and the output level when detecting the average value,
Subject condition with large brightness changes 1 For example, in subject conditions where the subject is backlit, with a high-brightness part entering a part of the screen and most of the other part of the screen being dark, the difference in temperature will be large and the overall The difference becomes smaller under subject conditions such as extremely bright or dark conditions. Therefore, by amplifying this difference, it is possible to distinguish whether the luminance change is large or small.

[Example]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is an example of a smoke tube video camera.

First, to explain the symbols in the figure, 1 is the iris, 2 is the image pickup tube, 5 is the preamplifier, 4 is the gain control circuit, 5 is the gain switching circuit, 6 is the γ correction circuit, 7 is the encoder circuit, and 8 is the iris drive circuit, 9 is a peak value detection circuit, 10 is an average value detection circuit, 11 is a differential amplifier, 12 is a voltage comparison circuit, and 15 is after obtaining the output signal of 12, the gain of the luminance signal is determined by the photographer's judgment. This is a SW for switching.

A signal current obtained from the image pickup tube 2 is amplified by a preamplifier 5 to a level sufficient for signal processing, and then input to a gain control circuit 4. After the gain control circuit 4 performs gain control according to the luminance signal level, the signal is input to the gain switching circuit, subjected to γ correction in the γ correction circuit 6, and converted into a synchronization signal, burst signal, color signal, etc. in the encoder circuit 7. It is added and output. 4, while controlling the gain,
The output signal of the gain control circuit generates an iris control signal for iris control, is input to the iris drive circuit 8, and controls the opening of the iris 1 according to the luminance signal level. The output signal is the input signal of the differential amplifier 11. In this way, cases where the peak value and the average value are significantly different, that is, cases where the brightness change is large and cases where the brightness change is small can be distinguished by the output 1-signal level of the difference #J amplifier. Therefore, the output signal of the differential booster 1 can be input to the pressure ratio regulator @12, and it can be determined whether it is higher or lower than a desired threshold level, and can be used as a warning signal.

In this way, only when it is determined that the brightness change is large due to the warning signal (the screen is dark and sunken), the gain of the brightness signal is increased by SW1 5 to prevent the screen from sinking.

〔Effect of the invention〕

According to the present invention, under subject conditions with large brightness changes, such as when backlit, the brightness signal level is controlled by focusing only on high brightness parts, so that relatively low brightness parts become dark. Get a warning signal so that you can easily detect that the ship is sinking.

FIG. 1 is a block diagram showing one embodiment of the present invention.

1...Iris 2... Shooting IJ! tube 3...Preamplifier 4...Gain control circuit 5...Gain switching circuit 6...γ Boou Kai゛烙 7...Encoder circuit 8...Iris drive circuit 9...Peak value detection circuit 10... Average detection frequency 11...Difference amplification device 12...1 pressure comparator 15...Gain selection switch /-), (Pa \　・ Agent Masu Burier Masaru Ogawa (Male) Figure 1 Mail

Claims (1)

[Claims] 1. It has a peak value detection circuit that detects the peak value of the luminance signal and an average value detection circuit that detects the average value, and the output signal of the peak value detection circuit, the output signal of the average value detection circuit, and the It has a differential amplifier that receives the output signal of the average value detection circuit as an input signal, and it has a voltage comparator that compares the output signal level of the differential amplifier with a predetermined threshold level,
A video camera characterized in that the output signal of the voltage comparator is used as a warning signal.