Appendix 2—figure 1. Example of morphological operations on images: ‘Erosion’.

Blue pixels denote on-pixels with color values greater than zero, white pixels are ‘off-pixels’ with a value equal to zero. A mask is moved across the original image, with its center (dot) being the focal pixel. A focal pixel is retained if all the on-pixels within the structure element/mask are on top of on-pixels in the original image. Otherwise the focal pixel is set to 0. The type of operation performed is entirely determined by the structure element.