Image restoration

2.5 Image Restoration:
Image restoration methods are used to improve the appearance of an image by application of a restoration process that use mathematical model for image degradation.
Example of the type of degradation:
1. Blurring caused by motion or atmospheric disturbance.
2. Geometrics distortion caused by imperfect lenses.
3. Superimposed interface patterns caused by mechanical systems.
4. Noise from electronic source.

2.5.1 What is noise?
Noise is any undesired information that contaminates an image. Noise
appears in image from a variety of source. The digital image an acquisition
process, which converts an optical image into a continuous electrical
signal that is then sampled is the primary process by which noise appears
in digital images.
At every step in the process there are fluctuations caused by natural phenomena that add a random value to exact brightness value for a given pixel. In typical image the noise can be modeled with one of the following distribution:
1. Gaussian (“normal”) distribution.
2. Uniform distribution.
3. Salt _and _pepper distribution.