Well Known Gradients

Filt = fspecial(‘sobel’)
Filt = 
         1     2     1
         0     0      0
        -1     -2     -1
Outim = imfilter(double(im), filt);
imagesc(outim);
Colormap grey;

** imfilter uses convolution by default

% gradient Difrection
Pkg load image;

Img = double(imread(‘octagon.png’)) /255.;
imshow(img);

%computer x, y gradients
[gx gy] = imgradientxy(img, ‘sobel’);
imshow((gx + 4 ) /8); % or imshow((gy +4 )/8); %

% Obtain gradient magnitude and direction
[gmag gdir] = imgradient(gx, gy);
imshwo(gmag / (4 * sqrt(2)));

% Find pixels with desired gradient direction
My_grad = select_gdir(gmag, gdir, 1, 30, 60); % 45 +/- 15
imshow(my_grad)

Function result = select_gdir(gmag, gdir, mag_min, angle_low, angle_high)
    Result = gmag >= mag_min & angle_low <= gdir & gdir <= angle_high;
endfunction