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opencv3 EM.getCovs(covs)

asked 2015-07-24 13:40:37 -0500

l3an gravatar image

what type should covs be in getCovs(covs)?

From the 3.0-beta c++, "Returns vector std::vector<Mat>& covs of covariation matrices. Number of matrices is the number of gaussian mixtures, each matrix is a square floating-point matrix NxN, where N is the space dimensionality."

from this old opencv2 bug, I understand that "vector<mat> corresponds to a list of numpy arrays, not 3D numpy array (since matrices in vector can in general have different size.) "

from cv2 import ml
import numpy as np

def dictionary(descriptors, number_clusters=N):
    covs = [np.zeros(( N, N), np.float64)]
    em = ml.EM_create()
    em.setClustersNumber(N)
    em.trainEM(descriptors)
    means = em.getMeans()
    covs = em.getCovs(covs)
    weights = em.getWeights()
    return np.float32(means), np.float32(covs), np.float32(weights)[0]

printing out covs just prints out the original [np.zeros(( N, N), np.float64)]. Any body know how to get the covs?

Note that attempting to run this code will not work without fixing this bug and rebuilding.

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answered 2015-07-25 01:16:24 -0500

berak gravatar image

updated 2015-07-25 01:43:12 -0500

thanks a lot for reporting back. it was indeed missing a second tweak (a CV_OUT before vector<mat>) so it actually returns the covs array. (you do not have to pre-allocate or feed it in).

patch is updated, please try again !

from cv2 import ml
import numpy as np

data = np.ones((10,10), np.float32)

em = ml.EM_create()
em.setClustersNumber(5)
em.trainEM(data)
covs = em.getCovs()
print(covs)

[array([[  2.22044605e-16,   0.00000000e+00,   0.00000000e+00,
          0.00000000e+00,   0.00000000e+00,   0.00000000e+00,
          0.00000000e+00,   0.00000000e+00,   0.00000000e+00,
          0.00000000e+00],
       ....

(5 arrays a 10x10)

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you're the man. Thank you

l3an gravatar imagel3an ( 2015-07-25 07:54:23 -0500 )edit
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Asked: 2015-07-24 13:40:37 -0500

Seen: 283 times

Last updated: Jul 25 '15