a corresponding width of the lenses 104 is 2 mm so that a 2 mm wide portion of an object results in a 1 mm wide corresponding image of that portion on the ccds 118 in addition to partial images from adjacent portions of the object a corresponding width of the black portions 302 and white portions 304 of the calibration pattern 300 is 2 mm the calibration process preferably takes place once preferably at the time that the scanner is manufactured however it may be necessary to recalibrate the scanner depending upon the effects of aging a scanner should have a modulation transfer function mtf of 50 or greater for a given line pattern at an appropriate distance from the lens array 102 to the object 108 20 mm in the above example as used herein mtf is typically measured for the captured image of an industry standard line pattern of equal width black and white bars with a periodicity denoted by the number of line pairs per inch lpi a typical line density for a 300 dpi scanner is 70 lpi for a 600 dpi scanner is 105 lpi and for a 1200 dpi scanner is 140 lpi the line pattern produces a modulation in the output of the converter 117 with a greater signal corresponding to the image of a white bar max and a lesser signal corresponding to the image of a black bar min the modulation transfer function mtf is defined as mtf max u2212.