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This paper describes a black and white photographic chart called the 'Scanner Analyzer Target' developed as a practical aid toward analyzing scanned image quality produced by binary digital document scanners used as input devices in document image processing systems. The target is used by factory-line personnel as an 'adjustment-set' tool, by the quality control department as an image quality judgement tool, and by customers as an incoming inspection tool. The scanner uses a rotary drum paper transport to move the document in front of a fixed scan line. The document is illuminated by a pair of fluorescent lamps and reflected through a reduction type camera to a CCD image sensor. Scanning speeds range from 7 in./s to 12 in./s and scanning resolutions range from 200 to 300 dpi. The scanner control panel allows image quality adjustments by using 9 levels of darkness and 10 levels of sensitivity. The darkness setting controls the level of optical reflectance at which the scanner shifts its output from white to black. At low darkness setting a scanned image appears lighter than the original and at high darkness setting the resulting image is dark. The sensitivity setting controls the amount of adaptive thresholding included in the binary decision. Low sensitivity setting is adequate for high contrast originals; high sensitivity setting allows the scanner to detect low contrast information contained in different background shades (or colors). At maximum sensitivity, the scanner is extremely sensitive to high frequency (text) and tends to drop out the background information. The purpose of the target is to give the user the ability to measure a number of scanned image parameters: text legibility, resolution, focus, darkness range, shading distortion, sensitivity range, photograph dithering, vertical and horizontal pixel count, document or CCD skew, vertical resolution linearity, aspect ratio, video noise and page registration.
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