What's the problem in implementing this MATLAB Prewitt operator?
I am trying to code an implementation of the Prewitt operator for edge detection. So far I have tried:
openImage = im2double(rgb2gray(imread(imageSource)));
[rows,cols] = size(openImage);
N(1:rows,1:cols)=0;
for i=1:rows-2;
for j=1:rows-2;
N(i,j)=-1*openImage(i,j)-1*openImage(i,j+1)-1*openImage(i,j+2)+0+0+0+1*openImage(i+2,j)+1*openImage(i+2,j+1)+1*openImage(i+2,j+2);
end;
end;
O(1:rows,1:cols)=0;
for i=1:rows-2;
for j=1:rows-2;
O(i,j)=-1*openImage(i,j)+0+1*openImage(i,j+2)-1*openImage(i+2,j)+0+1*openImage(i+1,j+2)-1*openImage(i+2,j)+0+1*openImage(i+2,j+2);
end
end
Z = N + O;
For which I can get:
As you can see, this image received half the processed image and half the space. What am I doing wrong?
This is the original image:
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2 answers
Consider the following code:
I = im2double(rgb2gray(..));
[rows,cols] = size(I);
N = zeros(size(I));
for i=2:rows-1;
for j=2:cols-1;
N(i,j) = 1*I(i-1,j-1) + 1*I(i-1,j) + 1*I(i-1,j+1) + ...
0 + 0 + 0 + ...
-1*I(i+1,j-1) + -1*I(i+1,j) + -1*I(i+1,j+1);
end
end
O = zeros(size(I));
for i=2:rows-1;
for j=2:cols-1;
O(i,j) = 1*I(i-1,j-1) + 0 + -1*I(i-1,j+1) + ...
1*I(i,j-1) + 0 + -1*I(i,j+1) + ...
1*I(i+1,j-1) + 0 + -1*I(i+1,j+1);
end
end
Z = sqrt(N.^2 + O.^2);
imshow(Z)
Then compare it to:
Gx = conv2(I, [-1 0 1; -1 0 1; -1 0 1]); Gy = conv2(I, [-1 -1 -1; 0 0 0; 1 1 1]); G = sqrt(Gx.^2 + Gy.^2); T = atan2(Gy, Gx); imshow(G)
Note. You may need to use imshow(result,[])
outside the range of [0,1] to display results correctly.
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