A device for detection of the image figee on a liquid crystal screen has

摘要

A detection device of the image is fixed on a liquid crystal screen (12) comprises at least one photoelectric cell (4) able to provide a luminance signal i (t) to the means (8) for processing said signal. The cell is disposed facing a display zone (z) of the screen. In this display area, it controls the display of a variable pattern to a characteristic frequency fc. The processing means are adapted to detect the characteristic frequency in the signal i (t). In the event of detection, they cause a corresponding alarm.