function [Ix,Iy,It]=ComputeImageDerivs(imarray)

dxfilt = [1 0 -1];
dyfilt = [1 0 -1]';
dtfilt = permute(dyfilt,[3 2 1]);
Ix = convn(imarray,dxfilt,'same');
Iy = convn(imarray,dyfilt,'same');
It = convn(imarray,dtfilt,'same');