discretization methods for continuous line or matrix (not linear polynomial function)

I am working with 2D and 1D pictures of wave phase. I need to make leveling/discretization/quantization (all same), see example. Something looking like in example of c2d function examples. But in my case there is no time dependent well defined function with which c2d works. Also I want better descretization than dividing to equal sections.

My question is: How to make discretization for general 2d or 1D matrix ?

Example of such as matrix (zmod): z=peaks(512); zmod=mod(z, 2*pi);

Thanks