Add saturation, value, brightness and color blind views

README.md

@@ -28,11 +28,52 @@ cargo run --release -- /path/to/screenshot.png
 5. **Save crop PNG** writes a uniquely named PNG in the system temporary directory
    and displays its path. Drop an image or click **Open image…** to browse for a file in KDE's file picker.
 
-The HSV histogram has 36 ten-degree bins. Switch between pixel counts and equal
-weight per distinct RGB color. Colors with saturation below 5% are counted
-separately as neutrals. The palette is exact (no quantization), ordered by count,
-then RGB for deterministic ties. Fully transparent pixels are excluded; partially
-transparent pixels retain their stored RGB values and count once.
+## Color analysis and vision checks
+
+The **Color analysis** tab has four distributions:
+
+- **Hue**: HSV hue in 36 ten-degree bins; saturation below 5% counts as neutral.
+- **Saturation**: HSV saturation, from neutral to fully saturated.
+- **Brightness (V)**: HSV value, the maximum RGB channel. This is not perceived
+  lightness: fully saturated red and green both have 100% value.
+- **Luminance**: relative luminance in linear sRGB, weighted for contrast.
+
+Saturation, value, and luminance use 20 five-percentage-point bins, including
+100% in the final bin. Each has a mean. Switch between pixel frequency and equal
+weight per distinct RGB color; hover bars for counts and percentages. The exact
+palette is ordered by count, then RGB for deterministic ties. Fully transparent
+pixels are excluded; partially transparent pixels retain their stored RGB values
+and count once. Pixel inspection includes HSV and relative luminance.
+
+Use **Compare vision** below the selection to show the original crop alongside
+protanopia, deuteranopia, tritanopia, or grayscale. The first three use the
+Machado–Oliveira–Fernandes full-severity model, applied in linear RGB and then
+encoded back to sRGB. Grayscale uses relative luminance and tests removal of color
+cues; it does not model all aspects of achromatopsia. Preview mode does not change
+histograms, copied pixel values, or the exported PNG: those always use the original.
+
+**Vision check** automatically checks all four scenarios. It flags pairs whose
+OKLab distance falls from at least 0.08 to at most 0.04, losing at least 50% of the
+original separation. These are project-specific screening heuristics, not
+validated visibility thresholds or WCAG criteria. Each scenario shows original
+and simulated swatches, numeric hex values, and up to six closest candidate pairs.
+The preview button opens the corresponding simulation for the current crop.
+
+The check is bounded to the 64 most frequent **opaque** colors and reports both
+color and pixel coverage. Partially/fully transparent pixels have no known
+backdrop and are excluded from this check. No findings does **not** establish
+accessibility. The check cannot infer adjacency, text/background relationships,
+or the gameplay meaning of a color. Review important cues in context and combine
+color with shapes, labels, or differences in lightness. Select a smaller region
+when an important detail is outside the reported palette coverage.
+
+References:
+
+- [Chrome's contrast audits and vision simulations](https://developer.chrome.com/docs/chromium/cvd)
+- [Machado, Oliveira & Fernandes simulation model](https://www.inf.ufrgs.br/~oliveira/pubs_files/CVD_Simulation/CVD_Simulation.html)
+- [Published matrix coefficients in QGIS](https://api.qgis.org/api/qgsprevieweffect_8cpp_source.html)
+- [OKLab color space](https://bottosson.github.io/posts/oklab/)
+- [W3C: use of color](https://www.w3.org/WAI/WCAG22/Understanding/use-of-color.html)
 
 Choosing a source always opens KDE's picker. The last portal token is saved at
 `$XDG_CONFIG_HOME/whoshue/config.toml` (normally `~/.config/whoshue/config.toml`)
@@ -55,7 +96,7 @@ cannot strand the cached D-Bus connection on a stopped executor.
   many unique colors are more expensive; release builds are recommended.
 - Game-specific behavior on focus loss/minimization needs desktop testing.
 - Perceptual OKLCH views, color/hue highlighting, and comparing saved selections
-  are future features; this first version uses HSV.
+  are future features; the distributions currently use HSV and relative luminance.
 
 ## Validation
 
@@ -67,10 +108,13 @@ cargo fmt --check
 
 Tests cover hue boundaries, neutral/transparent pixel handling, weighting,
 cropping, selection coordinates, pixel-format conversion, frozen-frame behavior,
-resize handling, headless UI rendering, file-picker cancellation/reopening, and
+resize handling, all histogram/vision UI views, file-picker cancellation/reopening, and
 repeated portal requests during/after capture. The portal regression test requires
 `dbus-run-session` and permission to create a local socket; it uses its own private
-bus and does not open desktop dialogs. Actual portal capture requires a running
+bus and does not open desktop dialogs. Color tests cover histogram endpoints and
+weighting, sRGB gamma, simulation reference colors, alpha handling, warning
+positives/negatives, palette coverage, and preserving source pixels.
+Actual portal capture requires a running
 Wayland desktop and permission through KDE's picker.
 
 For a capture-only diagnostic (saves the first full source frame):