ABSTRACT
This chapter describes the process known as fast Fourier transform (FFT). Repetitive background patterns such as dots or lines often obscure detail in fingerprints or other impressions. FFT would display the components in the frequency domain, where they would occupy different positions. Perhaps the most underutilized image optimization technique today is removal of obstructive patterns with fast FFT, which can routinely make the difference between an indecipherable area of obstructed ridge detail and an identifiable fingerprint. Footwear and fingerprint impressions located on exhibits and at crime scenes are routinely developed with chemistry or powder, or they are simply photographed in situ as they are found. All elements of the pattern signature in the periodic display are removed. The signatures of the fingerprint and obstructive pattern can be more easily recognized. The obstructive dot pattern is uniform in that it displays little or no variation in the area occupied by the fingerprint.
