CODEWITHSUNDEEP
opencvcovariance
Armin Meisterhirn
Armin Meisterhirn

Reputation: 801

opencv2 covariance matrix strange results

The following code gives inconsistent covariance matrix sizes. 

cv::Mat A = (cv::Mat_<float>(3,2) << -1, 1, -2, 3, 4, 0);
cv::Mat covar1, covar2, covar3, covar4, mean;
calcCovarMatrix(A, covar1, mean, CV_COVAR_NORMAL | CV_COVAR_ROWS);
calcCovarMatrix(A, covar2, mean, CV_COVAR_SCRAMBLED | CV_COVAR_ROWS);
calcCovarMatrix(A, covar3, mean, CV_COVAR_NORMAL | CV_COVAR_COLS);
calcCovarMatrix(A, covar4, mean, CV_COVAR_SCRAMBLED | CV_COVAR_COLS);

std::cout << "size: " << covar1.size() << "\n";
std::cout << "size: " << covar2.size() << "\n";
std::cout << "size: " << covar3.size() << "\n";
std::cout << "size: " << covar4.size() << "\n";

covar1 and covar2 should have the same size because they both describe the covariance over the rows, and covar3 and covar4 should have the same size because they both describe the covariance over the columns, respectively. However, the output is:

size: [2 x 2]
size: [3 x 3]
size: [3 x 3]
size: [2 x 2]

Upvotes: 0

Views: 168

Answers (1)

Adi Shavit
Adi Shavit

Reputation: 17265

The calcCovarMatrix() docs, specifically say that when using CV_COVAR_SCRAMBLED "The covariance matrix will be nsamples x nsamples."

Upvotes: 1

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