5.1. Image Smoothing. Smoothing is the action of simplifying an image while
preserving important information. The goal is to reduce noise or useless details
without introducing too much distortion so as to simplify subsequent analysis.
It was realized that the process of smoothing is closely related to that of pyramiding
which led to the notion of scale space. This was introduced by Witkin [97],
and formalized in such works as [53, 46]. Basically, a scale space is a family of images
{St | t ≥ 0} in which S0 = I is the original image and St, t > 0 represent the
different levels of smoothing for some parameter t. Larger values of t correspond
to more smoothing.