Automatic color-temperature compensator with guest-host liquid-crystal filter for video image sensing

A color-temperature compensating system with an electrically controllable liquid-crystal filter and a color sensor mounted on a video camera has been developed for color image sensing. The filter contains two guest-host liquid-crystal devices with dichroic dyes that have strong light absorption for shorter-wavelength light; two devices are necessary because of the spectral difference between the sun and an incandescent lamp as light sources. The filter's absorption is continuously controlled by the voltage applied to the filter. Because the filter is driven according to spectral information about the illumination detected by the color sensor, the color balance of the video image to be sensed can be compensated automatically and rapidly. This is especially useful for video image shooting in which a video camera experiences changes in illumination color temperatures.