The present invention is a method, circuit and system for erasing one or more non-volatile memory cells in an NVM array or array segment. The source voltage controller changes the source voltage according to temperature. A camera, the lens, the ophthalmic lens and the reflecting means are arranged on the same main optical axis. An analog to digital converter receives the amplified modified array signal and provides as an output a sequence of digital values. In one embodiment, an image color adjustment may be determined by adjusting the image of the reference color marker to the predetermined color.