"A signal output from the CCD image sensor is an analog signal. To use the signal for various measurements and differentiations, the analog signal must be first converted into a digital signal. To convert from analog to digital, a threshold (binary level) is set for the signal from the CCD image sensor, as shown below. Areas brighter than the threshold are defined as "bright", and areas darker than the threshold are defined as "dark". Thus, all areas are defined as either "bright" or "dark". This process is termed binarization, and digital signals corresponding to "bright" are defined as "1" (= HI), and those corresponding to "dark" are defined as "0" (= LO). The intersection of the signal from the CCD image sensor and the threshold is termed "edge". Detection of this "edge" is applied for various measurements and differentiations."