Method and apparatus for converting radiant energy levels to digital data

Abstract

A method and apparatus for converting radiant energy levels to digital data wherein an image sensor is provided having at least one row of sensor elements each including a light sensitive capacitor and an access switch and which changes state produces a corresponding binary output signal when a predetermined charge threshold is exceeded by the capacitor whose charge is a function of intensity and period of an illumination. The row of elements is first calibrated by illuminating same with a reference light source and sensing at a first frequency (F) such that approximately one half of the elements change state and counting the digital output signals corresponding to the changes of state to obtain a first number (B). Thereafter, the row is illuminated with an unknown light source which has a lower radiant energy level than that of the reference light source and senses at a frequency F/2. The digital output signals corresponding to the changes of state are counted to obtain a second number (A). The numbers A and B are compared to produce a digital '1' signal when A>B and a digital '0' when A<B corresponding to digital data bit N.sub. 1. The sensing and comparing are repeated for each successive bit N.sub.2, N.sub.3 . . . N.sub.k of a K bits of digital data at successive sensing frequencies in accordance with ##EQU1##