Still video camera with common circuit for color balance and exposure

Abstract

A video still camera includes a common integrating circuit for measuring light level in relation to both color balance and exposure control. An exposure photodiode generates an exposure signal from a small sample of image light diverted from the optical section of the camera. Broadly oriented red, green and blue photodiodes generate three color balance signals corresponding to the color characteristics of the illuminant. The photodiodes are selectively multiplexed into the input of the integrating circuit for the measurements. In one embodiment, the exposure photodiode remains connected to the integrating circuit for exposure measurement. The color balance measurement is unaffected because the small photocurrent from the exposure photodiode is effectively swamped by the much larger color photocurrent from a multiplexed color photodiode.