dp parameter is about resolution of voting space.
dp is larger, voting resolution is small compare to image size.
so dp is larger, circle detection accuracy is not exact.
but dp is smaller, voting resolution is higher and circle detection is more accurate but that sensitive with noise ex)other edge..
I increase dp from 1 to 5 step by 0.1..
refer to this source code on here.
< gist code >
< end gist >
and result image.
and other reference.
python opencv tutorial
GaussianBlur, HoughCircles, CV_HOUGH_GRADIENT,