Calculate the image gradient

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?

[naser telesi]

if Gx is zero then let Gx = 1 to avoid divide by zero problem

[Matt J]

if Gx is zero then let Gx = 1 to avoid divide by zero problem

But theta will be wrong...

Answer 1

[Matt J]

Use atan2 instead

 theta=atan2(Gy,Gx);

[Donghui Sun]

A big thanks.

[Image Analyst]

Like I said, imgradient() already gives that to you as Gdir - see the help. No need to do it yourself with atan2.

Answer 2

[Image Analyst]

Why do it yourself? Why not just use imgradient()?

[Donghui Sun]

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.