Add contrast_map: grade on-screen text contrast by sampling its colours#444
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a11y_audit.contrast_ratio grades a known foreground/background pair, but a button or label on screen is a patch of pixels, not two known colours. dominant_pair splits sampled pixels at the mean luminance into the dominant text (minority) and background (majority); grade_contrast grades a pair against WCAG AA/AAA; region_contrast samples a region (injectable sampler) and grades it. Grade + split are pure, reuse contrast_ratio.
Up to standards ✅🟢 Issues
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| Metric | Results |
|---|---|
| Complexity | 37 |
| Duplication | 0 |
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Summary
Third feature of the ROUND-15 perception lane.
a11y_audit.contrast_ratiogrades a foreground/background pair you already know — but a button or label on screen is a patch of pixels, not two known colours.utils/contrast_map/:dominant_pair(split sampled pixels at the mean luminance into the dominant foreground = minority/text and background = majority; uniform patch → same colour, no contrast),grade_contrast(grade a pair against WCAG 2.x AA/AAA for normal + large text →{ratio, aa, aaa, aa_large, aaa_large}),region_contrast(sample a screen region through an injectablesamplerand grade it). Grade + split are pure and reusea11y_audit.contrast_ratio, fully testable without a screen.__all__;AC_grade_contrast/AC_dominant_pair(pure) +AC_region_contrast(device) executor commands; matching read-onlyac_*MCP tools; Script Builder under Image.v216_features_doc.rst+WHATS_NEW.md.Test
test/unit_test/headless/test_contrast_map_batch.py— grade black/white passes all, low-contrast fails AAA, symmetry; dominant_pair text-on-bg / uniform / empty; region_contrast with injected sampler + region passthrough; plus JSON executor coercion and facade + executor/MCP/builder wiring. All 11 green;ruff+bandit+radonclean (extracted_partition_by_luminanceto keep CC < C); no float==; package stays Qt-free.