MATLAB: How to detect the shape in matlab

Question

I can't understand the technique how to analyse the shape. So any please help me to understand this concept.

 Code is below
function W = Classify(ImageRead)
RGB = imread('test.bmp');
figure,
imshow(RGB),
title('Original Image');
GRAY = rgb2gray(RGB);
figure,
imshow(GRAY),
title('Gray Image');
threshold = graythresh(GRAY);
BW = im2bw(GRAY, threshold);
figure,
imshow(BW),
title('Binary Image');
BW = ~ BW;
figure,
imshow(BW),
title('Inverted Binary Image');
[B,L] = bwboundaries(BW, 'noholes');
STATS = regionprops(L, 'all'); % we need 'BoundingBox' and 'Extent'
% Step 7: Classify Shapes according to properties
% Square = 3 = (1 + 2) = (X=Y + Extent = 1)
% Rectangular = 2 = (0 + 2) = (only Extent = 1)
% Circle = 1 = (1 + 0) = (X=Y , Extent < 1)
% UNKNOWN = 0
figure,
imshow(RGB),
title('Results');
hold on
for i = 1 : length(STATS)
  W(i) = uint8(abs(STATS(i).BoundingBox(3)-STATS(i).BoundingBox(4)) < 0.1);
  W(i) = W(i) + 2 * uint8((STATS(i).Extent - 1) == 0 );
  centroid = STATS(i).Centroid;
  switch W(i)
      case 1
          plot(centroid(1),centroid(2),'wO');
      case 2
          plot(centroid(1),centroid(2),'wX');
      case 3
          plot(centroid(1),centroid(2),'wS');
  end
end
return

Answer 1

What are the kinds of shapes you have there?

1. polygons (everything is a polygon)
2. quadrilaterals, polygons, and ellipsoids
3. quadrilaterals, rectangles, polygons, and ellipsoids
4. quadrilaterals, rectangles, polygons, circles, and ellipsoids
5. quadrilaterals, rectangles, squares, polygons, circles, and ellipsoids

You might look at the solidity, area, and perimeter. And the circularity = perimeter.^2 ./ (4*pi*area).

You may also find this useful to determine how many sides a polygon has: http://matlab.wikia.com/wiki/FAQ#How_do_I_find_.22kinks.22_in_a_curve.3F