how to get Image of same size after processing - matlab

Question

I am estimating ridge orientation of an fingerprint image by dividing it into blocks of 41*41..image is of size 240*320..here is my code and the problem is that I am getting output image size different than input image.
% matalb code for orientation
im =imread('D:\project\116_2_5.jpg');
im = double(im);
[m,n] = size(im);
% to normalise image
nor = im - mean(im(:));
im = nor/std(nor(:));
w = 41;
% To calculate x and y gradient component using 3*3 sobel mask
[delx,dely] = gradient(im);
% Ridge orientation
for i=21:w:240-41
for j=21:w:320-41
A = delx(i-20:i+20,j-20:j+20);
B = dely(i-20:i+20,j-20:j+20);
Gxy = sum(sum(A.*B));
Gxx = sum(sum(A.*A));
Gyy = sum(sum(B.*B));
diff = Gxx-Gyy;
theta(i-20:i+20,j-20:j+20) = (pi/2) + 0.5*atan2(2*Gxy,diff);
end;
end;
but in this process i am loosing the pixels at the boundries so as to avoid the "index exceed" error i.e size of theta is m = 240-41 = 199 and n = 320-41=279..Thus my input image size is 240*320 and output image size is size 199*279..How can i get output image same as size of input image.
one more thing that i dnt have to use "blockproc" function...Thanks in advance

Answer 1

You can use padarray to add zeros onto your matrix:
A1 = padarray(A,[7 8],'post'); % 240+7=41*7, 320+8=41*8
B1 = padarray(B,[7 8],'post');
then generate Gxx, Gyy, and Gxy with A1 and B1.
Method 2:
Besides, I tried to simplify your code a little bit by removing the loops, for your reference:
% Ridge orientation
Gxy = delx .* dely;
Gxx = delx .* delx;
Gyy = dely .* dely;
fun = #(x) sum(x(:))*ones(size(x));
theta_Gxy = blockproc(Gxy,[41 41],fun, 'PadPartialBlocks', true);
theta_diff = blockproc(Gxx-Gyy,[41 41],fun, 'PadPartialBlocks', true);
theta0 = pi/2 + 0.5 * atan2(2 * theta_Gxy, theta_diff);
theta = theta0(1:240, 1:320);
You may check blockproc for more details.