How do I find the topmost, bottomost, leftmost and rightmost endpoints of a skeleton of a binary image? Please help.

skltn = bwmorph(binaryImage, 'skel', Inf);  %getting skeleton of binary image
endpts = bwmorph(skltn, 'endpoints');       %getting enpoints of 'skltn'
[node_x, node_y] = find(endpoints==1);      %getting the x and y coordinates of the endpoints in
                                            %node_x and node_y respectively

%Now, how do I find the topmost, bottomost, leftmost and rightmost endpoints? Please help.

Answer 1

[Image Analyst]

You really messed on on find. find() does not return x and y in that order -- it returns row and column (y and x) in that order. After that, just use min and max

[node_y, node_x] = find(endpoints==1);      %getting the x and y coordinates of the endpoints in
                                            %node_x and node_y respectively
% Get top row which is the smallest y value
yTopRow = min(node_y);
% Get bottom row which is the largest y value
yBottomRow = max(node_y);
% Get left column which is the smallest x value
xLeftColumn = min(node_x);
% Get right column which is the largest x value
xRightColumn = max(node_x);

[Soumyajit Pal]

First of all, thank you so much for rectifying me. One last thing, for topmost endpoint, yTopRow is giving me the y co-ordinate for the topmost endpoint, but what about the x co-ordinate for the topmost endpoint? Similarly, what about the x co-ordinate for the bottommost endpoint, and the y co-ordinates for the leftmost and rightmost endpoints? Thanks again for all the help.

[Image Analyst]

If you look at the help for min() and max(), you'll see that it returns a second argument, which is the index of where it found the element. So to get the x of the top most endpoint, you'd do

[yTopRow, index] = min(node_y);
xTopRow = node_x(index);

Similarly for the other 4 points.

[Soumyajit Pal]

thank you so very much