How to find coordinates of two corner points in an image without using ginput?

I have two corner points (I marked them in red so you can see it) in black and white image. I want to find coordinates of the points automatically without using 'ginput'.

I used the 'bwlabel' and 'regionprops' functions to crop an original image to find my region of interest (ROI).

          im = imread('LA_shape1.jpg');    
          LA = im2bw(im, graythresh(im));
          [Clab num] = bwlabel(LA);
          props = regionprops(Clab); 
          LABox = imcrop(LA,[props.BoundingBox]);
          figure; imshow(LABox);

Here is the result after cropping:

Is there any one who can kindly help me to find the coordinates of two corner points without using ginput? Thanks so much!

Answer 1

[Image Analyst]

No need to crop, label, call regionprops. Why bother if all you want are the endpoints? Simply use bwmorph()

skelImage = bwmorph(binaryImage, 'skel', inf);
endPoints = bwmorph(skelImage, 'Endpoints');
[rows, columns] = find(endPoints);

[Ivan Shorokhov]

Thanks a lot, it does work!

Here is the result:

[Image Analyst]

It looks like there are actually 2 endpoints per endpoint. That's because when you skeletonize a rectangle, you get s branch going into each corner. Zoom in and you'll see what I mean. I think it would be fine to just average the x and y points to get one point that is halfway in between the two points.

[Ivan Shorokhov]

Thank you, I did as you suggested!

But what if I have a lot of endpoints, as in the following case, what can I do to find coordinates of two corner points?

Code:

clear all; clc; close all; workspace; format long g; format compact;

im = imread('LA.jpg'); 
figure; imshow(im,[]);
LA= im2bw(im, graythresh(im));

% Filtering from noize by measuring blow 
[Clab num] = bwlabel(LA);
props = regionprops(Clab); 
% [maxValue,index] = max([props.Area]);

CC = bwconncomp(LA);
[~,idx] = max(cellfun(@numel,CC.PixelIdxList));
L=labelmatrix(CC);
LA=L==idx;

figure; imshow(LA);

skelImage = bwmorph(LA, 'skel', inf);           %
endPoints = bwmorph(skelImage, 'Endpoints');    % 
[rows, columns] = find(endPoints);              % Find coordinates of the End Points
figure; imshow(LA); hold on;
plot(columns,rows,'g*');