Applying SAD on image using matlab - image

Question

Hello so I have an original image and I cropped a part of that image(template) and wrote a code with SAD algorithim to detect on the original image the part i cropped (template) where it exists and draw a rectangle on it.
The code doesnt have any errors , but the rectangle draw doesnt match the template , so I guess the 'output ' variable is the problem can you please help me
I2=imread('img.PNG');
I2=rgb2gray(I2);
[r,c]= size(I2);
%padding the image
%padding
B = padarray(I2,[24 24],'replicate' ,'both');
%imshow(B);
%creating template
temp=imread('crop_img.PNG');
temp= rgb2gray(temp);
%imshow(temp)
size(temp)
output = zeros (size(I2));
K = size(temp)
x=1;
y=1;
for i = 25 : r-24
for j = 25: c-24
%dif = temp -I2(i:i+47,j:j+47) ;
K = imabsdiff(temp,B(i-24:i+24,j-24:j+24));
output(i-24, j-24) = sum (K(:));
end
end
%gettting min value in output
min_value = output(1,1)
for i=1 : r
for j=1 :c
if(output(i,j)<min_value)
min_value=output(i,j);
row=i;
col=j;
end
end
end
row
col
output(1,465)
output(6,200)
%draw rectangle on matching area
%Create the shape inserter object.
shapeInserter = vision.ShapeInserter;
%Define the rectangle dimensions as [x y width height].
rectangle = int32([row col 24 24]);
%Draw the rectangle and display the result.
J = step(shapeInserter, I2, rectangle);
imshow(J);

Answer 1

There is an issue with image coordinates vs. matrix coordinates - you need to flip your row and column variables. Also, with shapeInserter, the coordinates are for the corner of the rectangle, so to make something centred on your output, you'd need something along the lines of:
rectangle = uint8([col-12 row-12 24 24]);
In MATLAB, it is usually not required to loop over every pixel of an image - it's much more efficient to work on the whole image at once. For example, you don't need a loop here:
min_value = output(1,1)
for i=1 : r
for j=1 :c
if(output(i,j)<min_value)
min_value=output(i,j);
row=i;
col=j;
end
end
end
This can be replaced by:
min_value = min(output(:));
[row,col] = find(output==min_value,1,'first');