How to measure a crack length (using skeleton function)?

2020 10 20
2 个回答
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更新时间：2022 1 16
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I am trying to calculate the length of the crack (attached) however I can't figure out a way to remove the extra sections of the skeleton that branch off from the main crack path - crackoverlay.png.
Does anyone have any advice as to how I could do this?
clc
clear variables
RGB = imread('crack2.jpg'); % Aquires original image
I = rgb2gray(RGB); % Creates greyscale image
BW = imbinarize(I,'global'); % Binarises it
BW2 = ~(bwmorph(BW,'majority',Inf)); % Fills in holes
BW3 = bwmorph(BW2,'skel',Inf); % Reduces image to center areas of the white sections
BW4 = bwmorph(BW3,'spur',Inf); % Removes spurs
Ov = imfuse(RGB,BW4); % Overlay of original image and skeleton
figure('Name','All_Steps')
subplot(3,2,1), imshow(RGB), title('Original Image')
subplot(3,2,2), imshow(BW) , title('Binarised Image')
subplot(3,2,3), imshow(BW2), title('Binarised Inverted')
subplot(3,2,4), imshow(BW3), title('Skeleton')
subplot(3,2,5), imshow(BW4), title('Simplified Skeleton')
subplot(3,2,6), imshow(Ov), title('Overlay')

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Adam Danz
Adam Danz 2020-10-20
This is the shortest path problem and there are several algorithms you can search for and learn about. You can apply it to the coordinates in BW4 which can be found using [y,x]=find(~BW4). You'll probably need to identify the starting and ending points manually which can be done using ginput() or something slimiar and then finding the closest coordinates to your selection.
Thomas Bainbridge
Thomas Bainbridge 2020-10-21
编辑：Thomas Bainbridge 2020-10-22
Thank you - I'll give that a go.
UPDATE: Thats worked - thank you for your help
Adam Danz
Adam Danz 2020-10-22
Well done! Perhaps you could share your solution as an answer. I'd be interested in seeing it.
Thomas Bainbridge
Thomas Bainbridge 2020-10-22
Thanks - Ive uploaded my code as an answer along with a hyperlink to a MATLAB blog that had a lot of useful information.

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 采纳的回答

Thomas Bainbridge
Thomas Bainbridge 2020-10-22

1 个投票

Here is my solution code.
Thanks to Adam Danz for the pointers.
Blog with useful code
clc
clear variables
RGB = imread('crack2.jpg'); % Aquires original image
I = rgb2gray(RGB); % Creates greyscale image
BW = imbinarize(I,'global'); % Binarises it
BW2 = ~(bwmorph(BW,'majority',Inf)); % Fills in holes
BW3 = bwmorph(BW2,'skel',Inf); % Reduces image to center areas of the white sections
BW4 = bwmorph(BW3,'spur',Inf); % Removes spurs
Ov = imfuse(RGB,BW4); % Overlay of original image and skeleton
imshow(BW4) % Displays the skeleton de spurred
y1 = 151; % Start of crack co-ordinates
x1 = 23;
y2 = 169; % End of crack co-ords
x2 = 307;
hold on
plot(x1, y1, 'g*', 'MarkerSize', 15) % Puts * at location of start and end of crack
plot(x2, y2, 'g*', 'MarkerSize', 15)
hold off
D1 = bwdistgeodesic(BW4, x1, y1, 'quasi-euclidean');
D2 = bwdistgeodesic(BW4, x2, y2, 'quasi-euclidean');
D = D1 + D2;
D = round(D * 8) / 8;
D(isnan(D)) = inf;
skeleton_path = imregionalmin(D); % Returns regional minima
P = imoverlay(BW4, imdilate(skeleton_path, ones(3,3)), [1 0 0]);
imshow(P, 'InitialMagnification', 200)
hold on
plot(x1, y1, 'g*', 'MarkerSize', 15) % Start position marker
plot(x2, y2, 'g*', 'MarkerSize', 15) % End poisition marker
hold off
path_length = D(skeleton_path); % Path length calculation
path_length = path_length(1)
figure('Name','Montaged') % Montage of stages
montage({RGB, BW, BW2, BW3,BW4, Ov})
figure('Name','All_Steps')
subplot(3,2,1), imshow(RGB), title('Original Image')
subplot(3,2,2), imshow(BW) , title('Binarised Image')
subplot(3,2,3), imshow(BW2), title('Binarised Inverted')
subplot(3,2,4), imshow(BW3), title('Skeleton')
subplot(3,2,5), imshow(BW4), title('Simplified Skeleton')
subplot(3,2,6), imshow(Ov), title('Overlay')
figure('Name','Reduced')
subplot(2,3,1), imshow(RGB), title('Original Image')
subplot(2,3,2), imshow(BW2), title('Binarised Inverted')
subplot(2,3,3), imshow(BW4), title('De-Spurred Skeleton')
subplot(2,3,4), imshow(Ov), title('Overlay')
subplot(2,3,6), imshow(P), title('Path on Skeleton')

更多回答（1 个）

0 个投票

the script was so helpfull for my program too thanks!!
one question, the units from the path length are pixels?

1 个评论
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Image Analyst
Image Analyst 2022-1-16
Yes, units are pixels. See attached spatial calibration demo and other demos.
Also, you might want to look at bwskel() - I think it has less spurs than bwmorph()

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