Fig 4. Counting flowers gone wrong.

Consider a simple algorithm counting the number of dandelions in digital images based on the number of yellow pixels in the image and the scale indicated by the black rod (actually a flashlight). After calibration, using the two images on the left, the algorithm happily reports that there are approximately five and ten dandelions in the middle and right image, respectively. The fact that the yellow patterns actually show different species of plants could relatively easily be detected by visual inspection of the data. Algorithmically distinguishing the plants could also be possible but would take substantially more effort than we spent here on simple pixel counting. The code and the original images are provided as S6 Data.