On the use of hash functions for defect detection in textures for in-camera web inspection systems

Hash functions are one way functions which are used in cryptography to ensure integrity of files by creating a binary signature specific to that file. A family of special hash functions are developed, which are simple enough to fit into a small FPGA and can generate one dimensional signatures of repeating texture images. While these hash functions are sensitive enough to detect small changes and defects in texture, they are immune to change in illumination and contrast. Analyses of these signatures and determination of the parameters of the hash functions are presented.