why wont it show after the decimal point values?

I'm trying to find correlations between letters and text pngs by creating a zeros the same size as the text image size and checking every possible place for the picture to be. to show if a place has a good correlation the end matrix will have at that position a value of around if not exactly zero (0) which will show a white color at that position. the problem is when I do the calculation to check for corelation it only returns 1 or 0 nothing in between. *I know there a dedicated function that does just that but my intention to try and make it myself. this is my code:

letter_GR = rgb2gray(letter);
text_GR = rgb2gray(text);
[text_row,text_col] = size(text_GR);
[letter_row,letter_col] = size(letter_GR);
num_cols = round((text_col/letter_col)); 
num_rows = round((text_row/letter_row));
positions = zeros(text_row,text_col);
%%compare critical locations
for row=1:num_rows
  for col=1:num_cols%the first two loops gives me the start places for the first pixel comparison

        for z=1:11
            for k=1:11
                x= double((text_GR(row+z-1,col+k-1)-letter_GR(z,k))/255);
               positions(row+z-1,col+k-1) = double(positions(row+z-1,col+k-1) + x);
            end
        end

    end 
end
figure;
imshow(positions);

thanks:)

Answer 1

[Walter Roberson]

Try

               x = double((text_GR(row+z-1,col+k-1)-letter_GR(z,k)))/255;
               positions(row+z-1,col+k-1) = double(positions(row+z-1,col+k-1)) + x;