CV-workshop7

Workshop 7 Tracking

Colourful ball bouncing off walls Using the pygame library, the following video clip can be generated

Step1: Identification

• Before being able to track the ball, we must identify it • This mean learning its appearance • Use (r, g) in the normalised RGB colour space

• The PNG image for the colourful ball is on Blackboard • Read the image, create an array for the (r, g) space • For each pixel of the ball, populate the array • Normalise the (r, g) space to make it a probability density function (PDF) • The PDF will be the colour model for your ball

Step 2: extracting frames

• You are given a video clip for the ball bouncing in the constraint environment • Extract all frames and save them in a FRAMES folder

Step 3: tracking

• Using the alpha-beta tracker, track the ball throughout the video • What you need to do is to detect where the ball is in the first frame • The ball in the image should be the same size of the ball in the video and the frames • So, you can use template matching to search for its first position • You then define a bounding rectangle for the ball • In the minimal alpha-beta tracker, you can use a fixed bounding rectangle, its position and a constant velocity