Digital fourier transforms as means for scanner evaluation

This brief paper is presented as an illustration of the possible use of the Fourier transform as an aid in evaluating the performance of digital image scanners. A discussion is presented on the interpretation of Fourier energy along the horizontal and vertical frequency axes, and it is suggested that such perfectly aligned energy is most often man-induced (purposefully or unknowingly). Windowing, scanner jitter, and aperture effects are described; specific examples are presented illustrating all these points for a laser scanner system on some scanned imagery. In addition to the main theme of scanner evaluation, a peripheral example of the use of a priori knowledge for image enhancement is presented. A nonlinear space domain transformation (amplifier) is described, based on a priori knowledge, as a tool for noise reduction in the above-mentioned imagery examples.