Pixel intensity transformations
Pixel intensity transformations are a class of techniques for enhancing visual appearance of images. These techniques are referred to as spatial domain techniques since they directly operate on the image pixels. There are two major classes of spatial domain techniques – point intensity transformations and neighborhood intensity transformations. Point intensity transformations change the intensity of a pixel based on just the current intensity value of the pixel. In contrast, neighborhood intensity transformations change the intensity of a pixel by considering a neighborhood of pixels around the pixel under consideration.
For simplicity, we refer to point intensity transformations as intensity transformations and neighborhood intensity transformations as spatial filtering. Note that both these transformations change the value of a single pixel at a time. In the first case, the new value of a pixel is based just on its current value. On the other hand, the intensity of a pixel is a functions of the intensity values in the neighborhood.
Spatial domain techniques have many uses including image sharpening, image blurring, boundary extraction, and edge detection. In general, spatial domain techniques are computationally more efficient and require less computer processing time.
Intensity transformation functions
Commonly used pixel intensity transformation functions. All these functions are variations of the Power-law (aka Gamma) transformation function, which is of the form \(s = cr^\gamma\). For all the functions \(c=1\) but the value of \(\gamma\) is varied.