Increasing Accessibility for Map Readers with Acquired and Inherited Colour Vision Deficiencies: A Re-Colouring Algorithm for Maps

Approximately 8% of the male population suffers from an inherited form of colour vision deficiency (CVD). Age, diabetes, macular degeneration, cataracts and glaucoma result in eye defects including an acquired form of CVD. Inherited CVD is marked by a difficulty in discerning red from green, while acquired CVD is marked by a difficulty in discerning blue from green. A recent review of the cartographic literature revealed a deficit in studies on accessible maps for readers with the acquired form of CVD. In addition, research on accessible maps for readers with the inherited form of CVD was restricted to the design or pre-publication stage. An approach is needed to render maps already in circulation accessible to an audience with CVD. The purpose of this paper is twofold: first, to provide the reader with some background on acquired and inherited CVD; second, to introduce a potential approach to improve the accessibility of maps post-publication. Image re-colouring is a method of altering an image’s colour composition in such a way as to make it accessible to a colour vision deficient audience. An innovative algorithm is presented that produces a re-coloured map that can be perceived by both red-green (inherited) and blue-green (acquired) deficiencies. Although the algorithm has yet to be tested on human subjects, it performed well on an edge detection analysis.