Video camera exposure control method and apparatus for preventin

Details Video camera exposure control method and apparatus for preventin Video camera exposure control method and apparatus for preventin

1990-04-06

1991-09-17

Groody, James J.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358228, 358209, 35821319, H04N 314, H04N 5335

Patent

active

050499971

ABSTRACT:
A photometry of a scene divided into a plurality of areas is carried out by using an image area sensor of a video camera. An average luminance value of each area is calculated, and the luminance distribution is estimated on the basis of the average luminance value and a threshold value to thereby discriminate the type of scene. A calculation equation prepared for each type of scene is selected to calculate a luminance value of the scene by using at least one of the average luminance values. The light amount incident to the image area sensor is adjusted in accordance with the scene luminance value. If a scene is divided into a central area and a peripheral area, the scene is discriminated as a rear light scene or a spot light scene on condition that the average luminance value of each area is equal to or larger than a threshold value. For the rear light scene, using as a reference value a median between average luminance values of two areas, luminance values smaller than the reference value are selected for the calculation of the scene luminance value. For the spot light scene, luminance values larger than the median are selected for the calculation of the scene luminance value. In order to eliminate the influence of white or black clothes, very high or low luminance components are clipped. A higher clip level is used for clipping the high luminance components for the spot light scene. The threshold values to be used for a scene discrimination are determined by a preceding scene discrimination result.

REFERENCES:
patent: 4695894 (1987-09-01), Saito et al.
patent: 4829382 (1989-05-01), Hess et al.

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