How to make a contour plot when difference in data values is small?

Question

I have a function z=f(x,y), I can plot the contour of z. But the problem is that the values of z for pairs of (x,y) are very close to each other. And when you plot the contour or surf of the data or any other representation of them, the continuous but small difference does not become sensible.

What would be the best way to have a contour-like representation of data which are close to each other in their values?

Does MATLAB has some variations of contour function to handle this type of data?

Or do you suggest any pre-processing of the data before plotting it?