Minor and major axis inside elipse

Hi. I want to plot axis inside elipse in front of my 7 figures, for checking the Orientation angle like that:

Code:

A = imread('4.png');

level = graythresh(A); 
if level < 1
level = level +0.20 
end

BW = im2bw(A,level);
figure(1), imshow(BW)

BW2 = imcomplement(BW);
figure(2), imshow(BW2)

s = regionprops(BW2, 'Orientation', 'MajorAxisLength', ...
                'MinorAxisLength', 'Eccentricity', 'Centroid', 'Area');

imshow(BW2)
hold on

minArea=5000;
maxArea=40000;
list = find([s.Area] > minArea & [s.Area] < maxArea);
assignin('base','list',list);
display('Index list: ');
display(list);

for k = 1:numel(list)
k_iter = list(k); 
c = s(k_iter).Centroid;
text(c(1), c(2)+20, sprintf('%d', k_iter),'HorizontalAlignment', 'center','VerticalAlignment', 'middle');
plot(c(1),c(2),'b*');
end

phi = linspace(0,2*pi,50);
cosphi = cos(phi);
sinphi = sin(phi);

for k = 1:length(s)
    xbar = s(k).Centroid(1);
    ybar = s(k).Centroid(2);

      a = s(k).MajorAxisLength/2;
      b = s(k).MinorAxisLength/2;

      theta = pi*s(k).Orientation/180;
      R = [ cos(theta)   sin(theta)
      -sin(theta)   cos(theta)];

      xy = [a*cosphi; b*sinphi];
      xy = R*xy;

       x = xy(1,:) + xbar;
       y = xy(2,:) + ybar;

       plot(x,y,'r','LineWidth',2);
       end
       hold off

Results:

Answer 1

[Image Analyst]

It's not so easy to find the largest ellipse than can fit inside the shapes. Why do you think you need this?

[Damian]

The largest? I didn't say that i need the largest. I just want to plot ellipse that measures regionprops's orientation in this figures. Ok so... is it feasible? If not ellipse that can fit, it can be smaller ellipse but with axis.

[Image Analyst]

You said "inside" - well there are lots of ellipses that can fit inside. You are already plotting the ellipses that match what regionprops gave you and you can see that they are NOT inside the shapes. If you want to plot at the centroid but without being as large, you can find the distance from the centroid to the nearest edge with either bwdist() or bwboundaries(). Then make that your major axis and make the minor axis the same ratio smaller and plot this smaller ellipse.

[Damian]

Of course that NOT INSIDE, i was wrong. I want something like this ( i made it in Photoshop ).

[Image Analyst]

5 points are needed to define an ellipse. If you have less than that you'll have to determine the missing ones. You can perhaps take the "missing" ones as the ends of the major axis with the same major axis length as regionprops gives you. So take the convex hull with convhull(). Then if there are less than 5, use the orientation and major axis length to define points out on the tip of the long axis of the ellipse. Then you'll have 5 points and you can determine the ellipse. The attached paper may help.

[Monica Vazquez]

Thank you for share with us the paper