On the Use of Hash Functions as Preprocessing Algorithms to Detect Defects on Repeating Definite Textures

Abstract

Hash functions are one way functions and often used in cryptography to ensure the integrity of files by creating a binary signature specific to that file. In a similar way, a family of special hash functions can be developed and used to generate one dimensional signatures of an image. The resultant signatures can then be used to compare the image either to a golden template or, if the image consists of repeating definite patterns, then to the texture itself. While such hash functions are sensitive enough to detect small changes and defects in repeating texture, they are immune to changes in illumination and contrast. In this paper we discuss the generation of suitable hash functions for textured images, which are simple enough to fit into a very small FPGA, and provide several examples of their use.