I want to find end to end distance of this skeleton image

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filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/1045155/insect.jpg';
k = imread(filename);
k = rgb2gray(k);
%imshow(insect);
%applyig threshold to convert the image into binary so that backgroung can
%be separated
BI = k < 160;
%imshow(BI)
BI = bwareaopen(BI,40);
%imshow(BI)
%finding the skeleton of image
k = bwskel(BI);
%imshow(k);
[a b]=size(k);
output=zeros(a,b);
for i=2:a-1
for j=2:b-1
ws=[k(i-1,j-1),k(i-1,j),k(i-1,j+1),k(i,j-1),k(i,j)...
,k(i,j+1),k(i+1,j-1),k(i+1,j),k(i+1,j+1)];
kg=sum(ws);
if(k(i,j)==1 && kg==2)
output(i,j)=1;
end
end
end
figure;
output=imdilate(output,strel('diamond',5));
imshow(output+k);
i have this code with which i highlighted the end points but dont know how to go further
  2 Comments
Adarsh Tripathi
Adarsh Tripathi on 25 Jun 2022
Edited: Adarsh Tripathi on 25 Jun 2022
Thanks for your reply @walter Roberson Actually I attached the image before the code named insect in which end points are clearly specified i don't know how this below image is visible. And also just after sometime of posting i solved it myself but again thanks for your early reply.

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Answers (1)

Image Analyst
Image Analyst on 25 Jun 2022
What exactly is the end to end distance? Do you mean the Feret diameter bwferet?
Do you mean the sum of all white pixels to the neighbor pixels? Have you tried pdist2, and extract all pairs just 1 or sqrt(2) pixels apart, sum them, and divide by 2? Something like (untested):
[y, x] = find(k); % Find coordinates.
xy = [x(:), y(:)]; % Combine into matrix.
distances = pdist2(xy, xy); % Find distance of every point to every other point.
mask = distances < mean([sqrt(2), sqrt(3)]); % Find pixels that are adjacent or on nearest diagonal ONLY.
sumOfDistances = sum(distances(mask)) / 2 % Divide by 2 since we get the sum for each endpoint so it's counted twice.
  9 Comments
Adarsh Tripathi
Adarsh Tripathi on 26 Jun 2022
@walter Roberson That is significant because changing of that distance will give the activity of the worm with time.

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