How does Matlab produce thin edges?

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Ivan Matala
Ivan Matala 2014-8-21
评论： Royi Avital 2019-9-3
Im using sobel edge detection.
Here is the original image file if you have Matlab so you can take a look
How does Matlab, by itself manage to achieve very thin edges like this one (using just the Matlab's edge function with 'sobel' as parameter)
matlabsobel = edge(originalImage,'sobel')
imshow(matlabsobel)
but when I try to do sobel algorithm my own way, assuming the process is just the same..
originalImage = gaussianizedimage;
threshold = 60.5;
k = [1 2 1; 0 0 0; -1 -2 -1];
H = conv2(double(originalImage),k, 'same');
V = conv2(double(originalImage),k','same');
E = sqrt(H.*H + V.*V);
edgeImage = uint8((E > threshold) * 255);
imshow(edgeImage);
title('sobel algorithm')
Why is that its different? What is still lacking in my implementation to achieve Matlab's thin edges? Can anyone provide code to make it look/similar to Matlab native sobel edge detection?
Thanks

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采纳的回答

Image Analyst
Image Analyst 2014-8-21
edge() takes a grayscale edge image like you'd get with imgradient(), and then thresholds it and skeletonizes the thresholded image, like you'd get with bwmorph(BW, 'Skel', inf).
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Miroslav Hagara
Miroslav Hagara 2018-9-19
编辑：Miroslav Hagara 2018-9-19
according this, if I use this code:
BW1 = edge(I,'Prewitt');
BW2NT = edge(I,'Prewitt','nothinning');
BW2 = bwmorph(BW2NT, 'Skel',Inf);
I should get the same pictures. But this is not true.
I have get better result with
BW2 = bwmorph(BW2NT, 'thin', Inf)
but still without same pictures.
Royi Avital
Royi Avital 2019-9-3
If you look inside edge() you will see:
if thinning
e = computeedge(b,bx,by,kx,ky,int8(offset),100*eps,cutoff);
else
Which does the magic.
MathWorks doesn't specify what's done there.

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