Spatial filtering, edge enhancement and equalization
X-ray medical imaging. 2D image processing

Filtering an image consists, for each pixel, in replacing the measured value (the gray level supplied by the detector) by a linear combination of the values measured on the surrounding pixels. This operation is the algebraic equivalent of a convolution (a multiplication in Fourier space of spatial frequencies). The surrounding pixels are chosen from a square whose side is an odd number of pixels 2N + 1, the central pixel being the one to which the result of the operation applies. The square is called the template, and the set of (2N + 1)² pixels it covers is called the kernel. In each box of the template, a number indicates the weight of the underlying pixel in the filtering operation. Several types of template are possible, depending on the type...