JPH08139989A - Television camera - Google Patents

Abstract

PURPOSE: To avoid white level deformation by arranging plural permeability variable means side by side in front of an image pickup element so as to set a signal of a highlight part within a dynamic range when a difference from luminance levels is extremely high. CONSTITUTION: Plural transmission type liquid crystal display devices 8 whose opposite party permeability is individually variable are arranged in front of an image pickup element 2 side by side. A video signal for revising permeability branched by an output amplifier 6 is given to a screen pattern division circuit 9, in which the signal is divided into plural block signals corresponding to the plural liquid crystal display devices 8. The luminance level of each block signal is calculated by an integration device 10 and the signal level of a portion with a high luminance whose video image output is 0.7Vp-p over is converted into a DC voltage by a detection circuit 11. The voltage is given to the transmission liquid crystal display devices 8 corresponding to the portion including the highlight portion to revise their permeability. Thus, white level deformation is prevented by decreasing the permeability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto iris device for a television camera.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional block diagram. Light incident from the auto iris lens 1 is photoelectrically converted by the image sensor 2 and amplified by the preamplifier 3. This signal is subjected to various corrections such as AGC by the correction / compensation circuit 4, and the gamma correction circuit 5 performs non-linear processing for changing the gain according to the input signal level. This video signal is amplified by the output amplifier 6 to a size sufficient for output to a monitor or the like, and branched into a video signal and an iris control video signal. The iris control video signal returns to the auto iris lens to control the iris and adjust the amount of incident light. In the prior art, the weighting circuit 7 lowers the level of the image signal for controlling the iris in the peripheral portion of the screen, and only the signal in the central portion of the screen is returned to the auto iris lens to reduce the influence of the background in the peripheral portion of the screen. A method such as controlling at the level of the main subject in the center of the screen was used. In this method, when the image is captured under the backlight condition, when the difference in the brightness level between the main subject at the center of the screen and the background at the periphery of the screen exceeds the dynamic range of the image sensor, it is affected by the high brightness background. The main subject may be underexposed and the background may be overexposed. Even if the main subject is exposed to light only by adjusting the amount of light by opening and closing the lens, the background is crushed in white and both exposures cannot be adjusted appropriately. Also, since the weighting position is fixed, the subject moves,
When the positions of the low-brightness part and the high-brightness part change, they cannot be automatically tracked.

[0003]

In the above-mentioned prior art,
Under conditions where the difference between the high brightness level and the low brightness level is extremely large, such as backlighting or excessive forward lighting, the exposure can only be adjusted to either one. An object of the present invention is to attenuate a signal in a high-brightness portion to a size that fits in a dynamic range and then input the signal to the image sensor when the difference in the brightness level is so large that it exceeds the dynamic range of the image sensor. The purpose is to provide a television camera that can eliminate the underexposure.

[0004]

In order to achieve the above object, the present invention inserts a polarizing filter such as a transmissive liquid crystal which adjusts the transmittance of light in front of an image pickup device, and polarizes the screen. It is divided into multiple areas corresponding to the filter, and the transmittance of the filter corresponding to each area is changed so that it falls within the dynamic range of the image sensor according to the integrated value of each area. This is to reduce the white crush.

[0005]

As a result, the main subject is not affected by the background, and the amount of light incident on the image sensor is always appropriate regardless of the size of the subject under the backlight condition or over-illumination condition. The exposure can be properly adjusted from the low brightness portion to the high brightness portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the same reference numerals as those in FIG. 3 denote the same circuit blocks, and a description thereof will be omitted. A plurality of transmissive liquid crystals 8 that can individually change the light transmittance are arranged and inserted immediately before the image sensor 2. The transmittance changing video signal branched by the output amplifier 6 is input to the screen division circuit 9, and a plurality of transmissive liquid crystals 8 are inputted.
Are divided into signals of a plurality of areas corresponding to. The brightness level of the signal in each of the divided areas is calculated by the integrator 10, and the signal level in the high-brightness area where the video output is 0.7 Vp-p or higher is converted into a DC voltage by the detection circuit 11, and this voltage value is increased. The transmittance is changed by inputting to the transmissive liquid crystal 8 corresponding to the area including the luminance portion. The auto iris lens is averaged.

[0007]

According to the present invention, the video output signal level, which has been controlled only by opening and closing the lens so far, is individually attenuated by the plurality of liquid crystals provided immediately in front of the image pickup element. The white output disappears and the dynamic range of the image sensor is exceeded, so that the video output becomes about 0.7 Vp-p even with a large signal.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing a video output according to the related art and a video output obtained by the present invention.

FIG. 3 is a configuration block diagram using a conventional technique.

[Explanation of symbols]

 1 Auto Iris Lens 2 Image Sensor 3 Preamplifier 4 Various Compensation Compensation Circuit 5 Gamma Correction Circuit 6 Output Amplifier 7 Weighting Circuit 8 Transmissive Liquid Crystal 9 Screen Division Circuit 10 Integrator 11 Detection Circuit

Claims (1)

[Claims] 1. A plurality of transmissivity varying means such as a polarization filter for individually varying the transmissivity of light are arranged side by side in front of an image sensor to detect a high brightness area where a video output signal level exceeds a predetermined value. The detecting means and the detecting means for detecting a DC voltage value corresponding to the detected light amount in the high brightness area, the transmittance of the transmittance varying means corresponding to the position including the high brightness portion by the detected DC voltage value. A television camera characterized by preventing white crushing by lowering.