METHOD AND APPARATUS FOR PROCESSING SIGNALS FROM PHOTOCONDUCTIVE SENSOR

A signal processing method for detecting a point of change from a first signal level to a second signal level, outputted from a line sensor having a photoconductive bit element array including setting a threshold level between the first signal level and the second signal level. A pair of bit elements are detected which have outputs that are larger than and smaller than the threshold level. A first line is determined based on the outputs of the pair of bit elements or a pair of bit elements which have a specific relationship to the above-mentioned pair of bit elements. A zero-cross bit element located at an intersecting point of the first line with a zero level is obtained. A second line, which has an inclination angle that is smaller than that of the first line, is determined based on the outputs of the zero-cross bit element and a bit element having a specific relationship to the zero-cross bit element or the outputs of a pair of bit elements having a specific relationship to the zero-cross bit element. A point of change is determined by the intersecting point of the first line and the second line.