Katsuhiro Narikiyo and  Naoto Kobayakawa,  A Way of Converting Color Images to Gray Scale Ones for the Color Blinds -Reducing the Colors for Tokyo Subway Map-.   journal   = {International Journal of Electrical and Computer Engineering}, [online]. World Academy of Science, Engineering and Technology.
    December 2012, vol. 72(12). 1467 - 1471
    [viewed 09 May 2024]. Available from: https://publications.waset.org/pdf/4529.