First get the shapes. You extract red, green, and blue. Then threshold them to find dark things. Then AND them all together. Now you have a binary image of the shapes. Then call bwboundaries() to get the (x,y) coordinates of the shape perimeters. Then use the FAQ to find kinks in the curve: http://matlab.wikia.com/wiki/FAQ?title=FAQ&cb=4698#How_do_I_find_.22kinks.22_in_a_curve.3F The triangles will have 3 kinks. Good luck.
% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Find binary images
redBinaryImage = redChannel < 250;
greenBinaryImage = greenChannel < 250;
blueBinaryImage = blueChannel < 250;
binaryImage = redBinaryImage & greenBinaryImage & blueBinaryImage;
boundaries = bwboundaries(binaryImage);
% Now use the FAQ to find kinks.
It might be easier if you knew all the triangles had the same aspect ratio because you could use regionprops and look at the perimeter squared to shape ratio.
