I posted a little part of my code, cause i keep getting a strange error that I can\'t seem to get rid of. The problem can be found on this line: Imgproc.GaussianBlur
This code works fine. Just reorder the parameters as you need.
Imgproc.GaussianBlur(mGray, mGray, new Size(15,15),50);
Size means that you will use it as kernel size. Also kernel size must be odd! 50 shows the kernel standard deviation in the X direction.
Formula : sigma = 0.3 * ((kSize-1)*0.5 - 1) + 0.8
Here sigma is passed 50 so sigmaX = sigmaY = 50