How do I calculate the directional derivative of an image in the north, east, west and south directions?

To implement the anisotropic diffusion of Perona and Malik (1987), we can use an explicit scheme (Euler forward method), where the formula

where c is the diffusion function, I is the image and x, y and y are the parameters of both c and I (where x and y are the spatial coordinates of the image and t is time).

In this formulation, we need to find the gradient of the image in the north, east, west and south direction and c is also computed as a function of the direction. In Matlab, there are at least two functions to compute the derivative of a function, imgradient and imgradientxy, where the second seems to be the function I am looking for, but it calculates the directional gradient in the x and y direction. However, I am looking for the gradient in the north, east, west and south directions! So, how can I calculate the gradient of an image in the N, E, W and S directions in Matlab?