in order to deal with large scale image, several tools have been developed to facilitate access to images.

Denote \(f \in \mathbb{R}^N\) where \(N\) is the dimension of the image \(N=N_x N_y\) with \(N_x, N_y\) are the number of pixels in direction \(X\) and \(Y\) respectively. \(f\) contains the pixel value.