Abstract: An apparatus that receives input video which includes picture video and test signals that occur periodically between segments of picture video. The test signals contain video distortion errors dependent on at least one varying property of input video. The system automatically generates corrected picture video, the degree of correction depending on errors extracted from the test signals. In a preferred embodiment of the invention, separate storage units are provided to store error signals associated with differential gain and differential phase. Stored error signals, which are updated every video frame, are selectively used in corrective fashion, the instantaneous correction amount depending on the instantaneous luminance level of video picture information.