Contrast, Distance, and Color Vision

Evaluate contrast, perceptual difference, and color-dependent meaning.

In this chapter

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  1. Measure WCAG contrast

    Calculate contrast ratios and test AA and AAA thresholds.

  2. Measure APCA contrast

    Interpret signed APCA lightness contrast without discarding foreground-background polarity or inventing a universal pass threshold.

  3. Find accessible foregrounds

    Select or adjust foreground colors toward a target contrast ratio.

  4. Measure color distance

    Compare colors with an appropriate perceptual distance algorithm.

  5. Simulate color vision deficiencies

    Use color-vision simulation to review a complete semantic system without treating the transformed colors as a person's exact experience.

  6. Check color distinguishability

    Use simulated color distance as a screening signal while preserving redundant cues for every critical distinction.