can any one correct me this code please??

Question

Pamela Paolo 2012-9-18

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Can you correct me this code to draw the 4 axis (major axe, minor axe and the 2 diagonal and ortogonal axes) not the ellipse

bw = imread('13.jpg');
bw = bwlabel(bw);
imshow(bw)
s = regionprops(bw, 'Orientation', 'MajorAxisLength', ...
    'MinorAxisLength', 'Eccentricity', 'Centroid');
phi = linspace(0,2*pi,50);
cosphi = cos(phi);
sinphi = sin(phi);
      xbar = s.Centroid(1);
      ybar = s.Centroid(2);
      a = s.MajorAxisLength/2;
      b = s.MinorAxisLength/2;
      theta = pi*s.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);
  hold off

thanks

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Azzi Abdelmalek 2012-9-18

what is k? have you read errors messages?

Pamela Paolo 2012-9-18

I'm sorry I corrected it

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Answer 1

Thomas 2012-9-18

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编辑：Thomas 2012-9-18

在 MATLAB Online 中打开

bwlabel works on a 2D matrix, Your 13.jpg image is probably a color (rgb) image and hence is a 3 dimensional matrix. You could convert it to grayscale ( which is a 2d matrix)

bw2 = imread('13.jpg');
% bw2= rgb2gray(bw2);  If image is binary
bw2 = bwlabel(bw2);
imshow(bw2)
s = regionprops(bw2, 'Orientation', 'MajorAxisLength', ...
    'MinorAxisLength', 'Eccentricity', 'Centroid');
phi = linspace(0,2*pi,50);
cosphi = cos(phi);
sinphi = sin(phi);
        xbar = s.Centroid(1);
        ybar = s.Centroid(2);
        a = s.MajorAxisLength/2;
        b = s.MinorAxisLength/2;
        theta = pi*s.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);
    hold off
 % ADDED EDIT
  plot(s.Centroid(1),s.Centroid(2),'*')
  line(s.Centroid(1)-a:s.Centroid(1)+a,s.Centroid(2));
  line(s.Centroid(1),s.Centroid(2)-b:s.Centroid(2)+b);

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Pamela Paolo 2012-9-18

i can't understand what do you mean :(

Image Analyst 2012-9-19

I think it's because you asked for major and minor axis when what you want does not match regionprops definition of those. See my answer.

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Answer 2

Azzi Abdelmalek 2012-9-18

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编辑：Azzi Abdelmalek 2012-9-18

在 MATLAB Online 中打开

The corrected code

bw = imread('13.jpg');
bw = bwlabel(bw);
imshow(bw)
s = regionprops(bw, 'Orientation', 'MajorAxisLength', ...
  'MinorAxisLength', 'Eccentricity', 'Centroid');
phi = linspace(0,2*pi,50);
cosphi = cos(phi);
sinphi = sin(phi);
xbar = s.Centroid(1);
ybar = s.Centroid(2);
a = s.MajorAxisLength/2;
b = s.MinorAxisLength/2;
theta = pi*s.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);
hold off

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Pamela Paolo 2012-9-18

This code also draw the ellipse not the 4 axis (major axe, minor axe and the 2 diagonal and ortogonal axes)

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Answer 3

Pamela Paolo 2012-9-18

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It seems that my question is not clear I will try to explain more. This code allows you to trace the ellipse while I do not need this ellipse, I only need to draw 4 axes (major axis, minor axis, and the two diagonal orthogonal axes)

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Thomas 2012-9-19

I have edited my code .. Please try it and see if it works..

Image Analyst 2012-9-19

Pamela, people are giving you what you asked for which I don't think is what you want. See my answer.

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Answer 4

Image Analyst 2012-9-19

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编辑：Image Analyst 2012-9-19

Pamela, My guess is that you really mean Feret Diameter ( http://www.sympatec.com/Science/Characterisation/05_ParticleShape.html) rather than the major and minor axis of an ellipse fitted to the shape. Am I correct? Feret diameter will touch at least two points on the perimeter of the object, like a caliper distance, while an ellipse's axes won't necessarily have the axis endpoints on the shape's perimeter.

MATLAB does not provide Feret diameters. You can calculate it yourself using bwboundaries. Let me know if you can't figure it out. I don't have any code all ready to give you though. However, you might take a look at this File Exchange submission: http://www.mathworks.com/matlabcentral/fileexchange/30402-feret-diameter-and-oriented-box

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Pamela Paolo 2012-9-19

编辑：Pamela Paolo 2012-9-19

The code in my first message can draw an ellipse and it can't draw the axis. So I should correct it. The segmentation had a good result (color image) but i uploaded just the binary masque because i can't use the regionprops with a color image. I will try later to use these axes with the color image. To study the asymmetry can I use the PCA?? I thik it's a good solution to study the asymmetry in a color image but i can't understand it very well. Have you please a matlab code because i couldn't implement it??