Problem adding two numbers

I'm trying to write a function for blurring images. (I'm aware of imfilter command. Just trying to implement it in my own way). I've the following function which takes a uint8 matrix as argument img.

function output=bl(img,w)
row=size(img,1);
col=size(img,2);
g_size=(2*w+1)^2;

output=uint8(zeros(row,col));
for ii=1:row
    for jj=1:col
        s=0;
        corner=[ii jj]-w;

        for r=corner(1):(corner(1)+(2*w))
            for c=corner(2):(corner(2)+(2*w))
                if((r>0 && r<=row) && (c>0 && c<=col))
                    s=s+img(r,c); %PROBLEMATIC LINE
                    fprintf('The value of s is %d\n',s);
                end
            end
        end     
        m=s/g_size;
        output(ii,jj)=fix(m);
        s=0;
    end
end
end

I'm having trouble with the line marked as "PROBLEMATIC LINE". The line of code was supposed to add previous value of s with img(c,r). But surprisingly each time the line runs, the previous value of s becomes 0. What am I doing wrong here? How can I solve this?

[Adam Danz]

What's a typical value of w?

[Image Analyst]

There are so many other problems with how to do the b lurring manually. Just search for blur.

[John D'Errico]

Another important question is what is the class of the variable img? Let me guuess, is this an image? If so, is the array img a uint8 array?

[Adam Danz]

The OP described the input as a uint8 matrix.

@Sneha Fariha, Image Analyst brings up a good point. My answer doesn't address the blurring proceedure. It just addresses the probem you described in the value of s.

Answer 1

[Sneha Fariha]

Well, I actually found the problem. The problem was that, s=s+img(r,c); in this line I was trying to add variables of two different types. And the maximum value of uint8 cannot exceed 255. So, after updating s for first time (s=255) it was unable to add numbers anymore and I was thinking that s is being initialized to 0 each time the line s=s+img(r,c); runs. Casting to double solves the problem.

[Adam Danz]

Well done. Thanks for the follow-up.