@techreport{murrell-masks-2021,
  title="Luminance Masks in R Graphics",
  author = {Paul Murrell},
  year={2021},
  note={version 1},
  institution={Department of Statistics, The University of Auckland},
  number={2021-04},
  url={https://stattech.blogs.auckland.ac.nz/2021/12/01/2021-04-luminance-masks-in-r-graphics},
  doi={10.17608/k6.auckland.17102657}
}