Image Processing Reference
In-Depth Information
Function edges=sobel33(image)
%derive edges by 3*3 Sobel operator
%
% Usage: [new image]=sobel33(image)
%
% Parameters: image-array of points
%
% Author: Mark S. Nixon
%get dimensions
[rows, cols]=size(image);
%set the output image to black(0)
edges (1:rows, 1:cols)= 0;
%it's like Prewitt, but the central
weights are doubled
for x=2:cols-1 %address all columns
except border
for y=2: rows-1 %address all rows
except border
%apply Mx template
x_mag=image(y-1, x-1)+2*image(y-1,x)...
+image(y+1, x-1)-image(y+1,x-1)-...
2*image(y+1, x)-image(y+1, x+1);
%apply My template
y_mag=image(y-1,x-1)+image(y,x-1)...
+image(y+1,x-1)-image(y-1, x+1)-...
2*image(y,x+1)-image(y+1,x+1);
%evaluate edge magnitude
edges(y,x,1)=sqrt((x_mag*x_mag)
+(y_mag*y_mag));
%evaluate edge direction
if x_mag==0
edges(y,x,2)=sign(y_mag)*1.5708;
else edges(y,x,2)=atan(y_mag/x_mag);
end
end
end
Magnitude of eye edges
by Prewitt
Magnitude of eye edges
by Sobel
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Magnitude of Sobel edges (in comparison with Prewitt)
disp ('The direction is still much less easy to see!')
subplot(1,1,1), direction=sobel_edges(:,:,2);
imagesc(direction);
plotedit on, title ('Direction of eye edges by Sobel'), plotedit off
pause;
Title:
/a/gaia/export/ecs/isis/users/msn/mlab/chapter4/f949.eps
Creator:
MATLAB, The Mathworks, Inc.
Preview:
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with a preview included in it.
Comment:
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Direction of eye edges by Sobel
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Direction of Sobel edges
