Automatic calibration system for video displays in vision testing

摘要

A calibration circuit and method for instructing an instrument operator on how to adjust the brightness and contrast controls of a video display in order to achieve a precise display intensity directly proportional to the video drive signal input to the video display. A photometer detects the display intensity as the video drive is modulated and a differential amplifier compares the video drive to the photometer output signal thereby generating an analog offset signal highly representative of brightness and contrast offsets. The analog offset signal is converted to numerical offset values from which independent brightness and contrast offsets are computed. For raster-scanned video displays only a one-bit analog-to-digital converter, a comparator, is required and a multi-bit numerical value of the video offset may be obtained from the comparator output by the method of counting the number of scan lines in each frame giving a positive comparator output.