How to write the Gaussian Surround Function in MATLAB

F(x,y) = k* exp(-r2 / c2 ) here the function f is a gaussian function.this function used in retinex algorithm.

R(x,y)=log[I(x,y)]-log[I(x,y)*F(x,y)] R is the retinex output,I is the input image,r=x2+y2; c is the surround space constant and k is such that ∫∫ F(x,y) dx dy =1. what is mean by surround space constant

please help me about the values of c and k

[Walter Roberson]

Duplicates http://www.mathworks.com/matlabcentral/answers/127813-how-to-determine-the-value-of-k-and-c-in-gaussian-surround-function