How to multiply a 3x3 kernel to a gray scale image (uint8) ?

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theblueeyeswhitedragon
评论： Sonny Revell 2021-12-14
Gx = [-1 0 1;-2 0 2;-1 0 1];
Gy = [-1 -2 -1; 0 0 0; 1 2 1];
img = imread('Bikesgray.jpg');
[rws, cls] = size(img);
mag = zeros(rws, cls);
for i = 1:rws - 2
for j = 1 : cls - 2
S1 = sum(sum(Gx.*img(i:i+2, j:j+2))); *
S2 = sum(sum(Gy.*img(i:i+2, j:j+2)));
mag(i+1, j+1) = sqrt(S1^2 + S2^2);
end
end
  • I get an error on this line saying: "Error using .* Integers can only be combined with integers of the same class,or scalar doubles." Converting img to double solves this problem, but it also makes the image white for some reason. Is there a way to multiply uint8 gray scale images to a 3x3 matrix?

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采纳的回答

Rik
Rik 2018-8-1
编辑：Rik 2018-8-1
You should indeed cast your image to double to avoid underflow and overflow. Another way to do this is to simply use the conv function family to do this convolution.
The reason for your image looking white is that a double is expected to have a value range from 0 to 1 and not 0 to 255. Casting back to uint8 will fix that, as would explicitly setting the caxis.
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Rik
Rik 2018-8-3
The internal convolution method is about 250 times faster than a nested loop by the way.
Sonny Revell
Sonny Revell 2021-12-14
We know its faster but every image processing class makes you do the raw convolution process.

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