Evolving CAM16-UCS for Modular Accessible Perceptibility and Simultaneous Contrast Detection Tool for Geovisualization

Keywords

accessibility, perception, cartography, design, WCAG, CIE, color appearance model

Abstract

Accessibility is a foundational principle of effective visualization design, yet achieving perceptual accessibility remains a challenge for both experts and non-experts. Standards like the WCAG2 contrast ratio are intended to guide designers toward accessible color use but are increasingly misapplied as oversimplified and misunderstood shortcuts for achieving perceptual accessibility. This misuse highlights the need for more nuanced, perceptually grounded evaluation tools. In response, we present our Modular Accessible Perceptibility (MAP) contrast model and tool, which integrates advanced color appearance models to assess perceptibility and flag risks associated with simultaneous contrast. By augmenting the CAM16-UCS model with a CAM16 CCz simultaneous chromatic contrast calculation, our model can isolate and measure the predicted shift resulting from simultaneous contrast along the chroma axis. This enables a more refined evaluation of visual contrast that better reflects the complexities of human color perception. Additionally, our tool performs modularly segmented automated checks to assign MAP contrast index scores, offering a holistic assessment of a map’s visual accessibility. This paper details the development and validation of the MAP model and tool, underscoring accessibility and inclusive design as fundamental rights, and demonstrating their utility in advancing perceptual accessibility in geovisualization.