wcag_vision 0.0.2

Check color contrast, simulate color blindness, and extract dominant colors from images — accessibility tools for Flutter, no expertise required.

Changelog

All notable changes to this package will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

0.0.2 - 2026-07-05

• Housekeeping release: no functional changes. Re-published after making the GitHub repository public so pub.dev's analysis can verify the repository URL (it was private during the 0.0.1 analysis).

0.0.1 - 2026-07-05

Added

• K-means dominant-colour extraction:

  • extractDominantColors — pure, synchronous, deterministic Lloyd's k-means over sRGB with seeded k-means++ initialisation (Arthur & Vassilvitskii 2007). Configurable k (default 6), seed, maxIterations (default 25), convergenceThreshold (default 1/255) and maxSamples (default 4096) stratified random downsampling — one seeded draw per grid cell, immune to the aliasing stride sampling suffers on periodic patterns, and fully reproducible via seed.
  • extractDominantColorsAsync — one-shot, single-capture entry point running the same extraction off the main isolate via Isolate.run (no Flutter dependency); continuous per-frame streaming is explicitly out of scope.
  • ExtractedColor — centroid colour plus population share, sorted largest-first.

• Unit tests for extraction: solid/two-colour images, degenerate k > distinct colours, convergence within the iteration cap, seeded determinism, downsampling proportions, and sync/async equivalence.

• CVD (colour vision deficiency) simulation:

  • CvdType — none, protanopia, deuteranopia, tritanopia.
  • simulateCvd — applies the Machado, Oliveira & Fairchild (2009) physiologically-based model (severity-1.0 matrices, applied in linear RGB with IEC 61966-2-1 sRGB decode/encode) to a Color. CvdType.none is the identity; achromatic colours are invariant; alpha passes through untouched.

• Unit tests for CVD simulation: identity, achromatic invariance, hand- computed reference values from the published matrices, red–green confusion behaviour, clamping, and alpha preservation.

• WCAG 2.x contrast engine:

  • relativeLuminance — relative luminance per the WCAG definition, including the sRGB linearization transfer function.
  • contrastRatio — the (L1 + 0.05) / (L2 + 0.05) contrast ratio for opaque colour pairs, with minContrastRatio / maxContrastRatio constants.
  • compositeOver — Porter–Duff source-over alpha compositing, so semi-transparent foregrounds are resolved to their effective colour before contrast is measured.
  • contrastRatioOver — contrast of a possibly translucent foreground against an opaque background.
  • WcagConformanceLevel (AA / AAA), WcagTextSize (normal / large) and wcagThreshold — the SC 1.4.3 / 1.4.6 minimum-ratio lookup.
  • ContrastReport and evaluateContrast — a single-call evaluation returning the ratio plus pass/fail against every level/size combination.

• Unit test suite covering luminance reference values, ratio bounds and symmetry, threshold boundaries, and alpha-blending edge cases.