*4.3.2. Search*

The actual search is performed using a resolution of 192 × 144 pixels. This allows quick processing while still preserving all the information necessary for a successful detection.

After taking a picture it is converted into a greyscale image and the Hough detection is performed. The number and quality of detected circles heavily depend on the threshold used during the Hough circle detection. A good value for the required number of votes is 30% of the circumference of the smallest radius. With significantly higher values, target objects tend to get missed far too often because the constant movement of the quadrocopter tends to prevent the camera from taking sharp pictures.

All detected circles, i.e., all target candidates, are then analysed for their colour. For each pixel inside a candidate's enclosing circle, it is checked if its RGB values lie within a certain range. The range is determined during the initial scan. For a candidate to get confirmed as a target, a certain percentage of its pixels has to be target pixels. Setting this threshold to about 40% was a good value here.
