I need MatLab code to compute gradient direction atan(y/x) for image at each pixel.
Hi,
you can obtain the gradient direction for each pixel by using the second output argument of the "imgradient" function (in image processing toolbox):
[Gmag, Gdir] = imgradient(I)
The principle behind the function is to compute finite differences in x and y directions, to store the result in two arrays with same size as original image, and then to combine them by using atan2 function.
Thank you my colleague David, but I could not understand the last speech "to store the result in two arrays with same size as original image, and then to combine them by using atan2 function."
Also, these arguments, Gmag and Gdir in X-direction or Y-direction?
Gmag and Gdir are both computed from the directional gradients in X and Y directions.
Chao Xing provided a good summary of the method.
Maybe the detailed code can help:
img = double(imread('rice.png')); % convert to double to avoid truncation problems with gradient on uint8 data
dx = imfilter(img, [-1 0 1], 'replicate'); % gradient in x direction
dy = imfilter(img, [-1 0 1]', 'replicate'); % gradient in y direction
Gmag = hypot(dx, dy); figure; imshow(Gmag, []);
Gdir = atan2(dy, dx);
hue = (Gdir + pi) / (2 * pi); % convert angle to [0 1] interval
hsv = cat(3, hue, ones(size(img)), min(Gmag/100, 1)); % compute color representation of directional gradient
rgb = hsv2rgb(hsv);
figure; imshow(rgb)
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