Automatic white balance circuit for color TV cameras having means for interrupting whitening operation upon viewing mono-colored non-white object fields

摘要

A circuit arrangement comprises a process amplifier which inputs primary color signals and a luminance signal from an image sensor and which outputs color difference signals each corresponding to a difference between each of said primary color signals and said luminance signal with an amplitude determined by gain control signals; a balance control circuit which generates the gain control signals responsive to said color difference signals to control the process amplifier so as to keep a white balance; and a detecting circuit for detecting a condition where a field of vision of the image sensor is substantially occupied with one color, the detecting circuit producing and supplying a hold signal to the balance control circuit while the detection of the condition is made. When the hold signal is supplied to, the balance control circuit holds each of the gain control signals to a value at a moment right before the hold signal is supplied, and keeps holding until the hold signal stops. In one embodiment the detecting circuit detects the colors green or magenta by level detecting the chrominance signal. In another embodiment the detecting circuit detects the close-up position of the lens by using a switch actuated by the lens moving lever.