So far we have seen how to install OpenCV and capture images from a video stream. Today we'll see how we can detect circles (or balls) in an image. Last year, the biggest challenge of PiWars was to be able to detect coloured balls kept on four corners of an arena and drive a robot towards it. Now I don't know if they will have the same challenge this year, however we can use this as a starting point to use a few more OpenCV tricks. Today we'll learn about how to use Hough transforms in OpenCV and how we can use it to detect balls in an image.