Calculate the image gradient

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Donghui Sun
Donghui Sun 2013-9-23
评论： Matt J 2017-3-1
I use the function imgradientxy to get the Gx and Gy firstly. Then obtain the direction of the gradient.
some codes like:
% code
b = zeros(100);
b(1:4:end,:) = 1;
[Gx, Gy] = imgradientxy(b);
theta = atan(Gy./Gx);
The image only has some horizontal lines. So The Gx is all zeros and the theta have a lot NAN. What should I do to get the gradient for this image and for other?
  2 个评论
naser telesi
naser telesi 2017-3-1
if Gx is zero then let Gx = 1 to avoid divide by zero problem
Matt J
Matt J 2017-3-1
if Gx is zero then let Gx = 1 to avoid divide by zero problem
But theta will be wrong...

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采纳的回答

Matt J
Matt J 2013-9-23
Use atan2 instead
theta=atan2(Gy,Gx);
  2 个评论
Image Analyst
Image Analyst 2013-9-23
Like I said, imgradient() already gives that to you as Gdir - see the help. No need to do it yourself with atan2.

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更多回答（1 个）

Image Analyst
Image Analyst 2013-9-23
Why do it yourself? Why not just use imgradient()?
  1 个评论
Donghui Sun
Donghui Sun 2013-9-23
Haha, I just want to try another method. In addition, the gradient direction in imgradient() contains angles in degrees within the range [-180 180]. I need the angle in radians.

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