Gain control for scanning arrays

The method of operating a raster scanner having plural arrays, each of said arrays having a plurality of image viewing elements for scanning an original, the viewing areas of said arrays overlapping to assure an uninterrupted scan line, with crossover from a viewing element of one array to the next succeeding viewing element in the adjoining array being made within said overlapping area, the steps which comprise:

• (a) scanning a calibration image;
• (b) using the signal output of only the array viewing elements where crossover between said arrays is made to provide a calibration signal output and comparing the calibration signal output of said crossover viewing elements with a preset reference signal to provide a corrective signal for each array;
• (c) adjusting the image signal level of each array in accordance with the corrective signal for that array;
• and
• (d) repeating steps a-c on each scan.

The method of calibrating an image scanning array having plural image viewing elements to provide a preset array signal output level, the steps which comprise:

• (a) repeatedly scanning a calibration image;
• (b) after each scan, comparing the signal output of at least one viewing element of said array with a predetermined reference signal to provide an array corrective signal;
• (c) increasing in relatively large increments said array corrective signal until said array signal output level equals or exceeds said predetermined reference signal;
• (d) where said array signal output level exceeds said predetermined reference signal, decreasing said array corrective signal in relatively smaller increments until said array signal output equals or is below said predetermined reference signal;
• and
• (e) repeating steps c and d with smaller and smaller increments of said array corrective signal until said array signal output level is substantially equal to said predetermined reference signal.