how to find correlation coefficient for two images?

edit

I know that this thread is old but here is an answer for those who continuously browse the internet in search of answers.

The following code works with Opencv 3.0 and it should work with opencv 2.4 with few changes.

double correlation(cv::Mat &image_1, cv::Mat &image_2)   {

// convert data-type to "float"
cv::Mat im_float_1;
image_1.convertTo(im_float_1, CV_32F);
cv::Mat im_float_2;
image_2.convertTo(im_float_2, CV_32F);

int n_pixels = im_float_1.rows * im_float_1.cols;

// Compute mean and standard deviation of both images
cv::Scalar im1_Mean, im1_Std, im2_Mean, im2_Std;
meanStdDev(im_float_1, im1_Mean, im1_Std);
meanStdDev(im_float_2, im2_Mean, im2_Std);

// Compute covariance and correlation coefficient
double covar = (im_float_1 - im1_Mean).dot(im_float_2 - im2_Mean) / n_pixels;
double correl = covar / (im1_Std[0] * im2_Std[0]);

return correl;

}

Hi, you can use the template matching function of opencv with the method: TM_CCOEFFThis will give you the coeffcient you need. Just use the second image as a template. Here is an example: [http://docs.opencv.org/doc/tutorials/...]

Assuming both image1 and image2 are the same size:

float correlation(cv::Mat &image1, cv::Mat &image2) 
{
    cv::Mat corr;
    cv::matchTemplate(image1, image2, corr, cv::TM_CCORR_NORMED);
    return corr.at<float>(0,0);  // corr only has one pixel
}