Simple image edge enhancement/detection filters.

Implement Box (Average), Median, Sobel, Prewitt, DoG, 3/9 and Nagao-Matsuyama filters.

It also provisions functions to add noise (uniform and salt&pepper), for normalization, equalization and thresholding.

Finally it implements two simple contour detection algorithms and two functions for linear convolution along the X and Y axis.

Read and write single channel PGM files.