GB1278742A - White balance control systems - Google Patents

Abstract

1278742 Colour television camera SONY CORP 19 Feb 1970 [22 Feb 1969] 8060/70 Heading H4F A white balance control system for a colour television camera 1, Fig. 1, comprises gain control circuits 3a and 3b in the red and blue signal paths, the control signals for which are derived from subtraction circuits 5a and 5b in which the red and blue signals are respectively subtracted from the green signal and any difference is fed to a memory circuit which maintains the optimum gains in circuits 3a and 3b for white balance. Ganged switches S1 and S2 are only closed when a white object is televised, since for a white object the red, green and blue signals should be equal for correct white balance. The subtraction circuits include integration circuits. The memory circuits preferably comprise a memory capacitor and a field effect transistor (Fig. 2, not shown). In a second embodiment, Fig. 3, the colour difference signals R - Y and B - Y are applied via clamp circuits 14a and 14b and integration circuits 15a and 15b to memory circuits 16a and 16b when a white object is being televised, ganged switches S3 and S4 being then closed. The clamp circuits are provided for eliminating a level change resulting from a change of the dark current in the image pick-up tube, and are gated in synchronism with the horizontal sync. pulses.