A system and method for controlling a video display blanking signal so as to maintain a full display screen while minimizing interference with the displayed picture. To control the blanking signal one or more photosensors are placed at the periphery of the display screen. When a CRT overscans the screen at a sensor's location, the light from the CRT is incident on the sensor and the sensor generates a signal proportional to the amount of incident light. The sensor signal is used to adjust the CRT scan such that the CRT scan covers the screen but does not degrade the displayed picture.