im doing face recognition project.please explain the above coding in a step by step manner in how it works

%% illumination normalization

[x y] = ndgrid(1:size(I,1),1:size(I,2)); z = double(I); [Gx Gy] = gradient(z); mag = sqrt(Gx.^2+Gy.^2); h = fspecial('average',3); smooth = imfilter(z,h); norm_x = Gx./smooth; norm_y = Gy./smooth; niter = 10; kappa = 10; lambda = 0.25; im = double(norm_x+norm_y); figure,imshow(im),title('Smoothed image'); [rows,cols] = size(im); diff = im; var = 2;

for i = 1:niter diffl = zeros(rows+2,cols+2); diffl(2:rows+1,2:cols+1) = diff; %differences deltaN = diffl(1:rows,2:cols+1) - diff; deltaS = diffl(3:rows+2,2:cols+1) - diff; deltaE = diffl(2:rows+1,3:cols+2) - diff; deltaW = diffl(2:rows+1,1:cols) - diff;

    %conduction
    cN = exp(-(deltaN/kappa).^2);
    cS = exp(-(deltaS/kappa).^2);
    cE = exp(-(deltaE/kappa).^2);
    cW = exp(-(deltaW/kappa).^2);

    diff = diff+lambda*(cN.*deltaN+cS.*deltaS+cE.*deltaE+cW.*deltaW);

end

R = mat2gray(diff); bgImg = z;%Background Image fgImg = R;%Foreground Image

%Define Alpha Factor alphaFactor = 0.2;% 0 <= alphaFactor =< 1

%Size Validation bg_size = size(bgImg); fg_size = size(fgImg); sizeErr = isequal(bg_size, fg_size); if(sizeErr == 0) disp('Error: Images to be fused should be of same dimensions'); return; end

%Fuse Images fusedImg = FuseImages(bgImg, fgImg, alphaFactor); fusedImg = 25+uint8(fusedImg);

%Display Images figure; imshow(fusedImg);title('Illumination Normalized');

%% PCA feature extraction fusedImg=im2double(fusedImg); [Evalues, Evectors, x_mean]=PCA(fusedImg); figure,imshow(Evectors,[]);title('PCA');

features=entropy(x_mean)