Segment an image using python and PIL to calculate centroid and rotations of multiple rectangular objects

Question

I am using python and PIL to find the centroid and rotation of various rectangles (and squares) in a 640x480 image, similar to this one

Answer 1

Here is an example of how you can do this by labelling the image, and then taking the centroid for the centers, this is all built in to ndimage in scipy (along with a bunch of other cool image things). For the angles, I've used the rectangle corner intercepts with the edges of the bounding slices.

import numpy as np
import scipy
from scipy import ndimage

im = scipy.misc.imread('6JYjd.png',flatten=1)
im = np.where(im > 128, 0, 1)
label_im, num = ndimage.label(im)
slices = ndimage.find_objects(label_im)
centroids = ndimage.measurements.center_of_mass(im, label_im, xrange(1,num+1))

angles = []
for s in slices:
    height, width = label_im[s].shape
    opp = height - np.where(im[s][:,-1]==1)[0][-1] - 1
    adj = width - np.where(im[s][-1,:]==1)[0][0] - 1
    angles.append(np.degrees(np.arctan2(opp,adj)))
print 'centers:', centroids
print 'angles:', angles

Output:

centers: [(157.17299748926865, 214.20652790151453), (219.91948280928594, 442.7146635321775), (363.06183745583041, 288.57169725293517)]
angles: [7.864024795499545, 26.306963825741803, 7.937188000622946]