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Chapter 4:
Spatial Filtering and Fourier Frequency Methods
Filtering of an image is an important aspect of electronic image processing. It provides a means of reducing the noise present in an image and sharpening of a blurred image. Filtering of an image can be implemented in either the spatial or frequency domain. This chapter first discusses several types of noise that occur commonly within images, followed by several types of spatial filters that can be used to reduce the noise. Next, Fourier frequency filtering methods are presented and then used to restore images that have been degraded by a known degradation process. Both inverse filtering as well as Wiener filtering methods are presented. The reduction of noise present in images is an important aspect of electronic image processing. Noise applied to a noise free image can degrade the image to such a point that important features are no longer observable. Images acquired with an electronic camera are typically corrupted with noise due to the camera's sensor and its associated electronics. Photographs of images contain noise due to the finite size of the silver halide grains that are part of the chemical photographic process. This type of noise is very predominant in images acquired with high speed film due to the film's large silver halide grain size. Another source of photographic noise is due to dust that collects on the optics and the negatives during the development process
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