Display filters

Apply post-process colour-matrix transforms to each captured PNG — grayscale (Android’s “bedtime mode”), classic colour inversion, and colour-blindness simulations (deuteranopia, protanopia, tritanopia). Each enabled filter produces an additional PNG sibling alongside the base capture, so an agent can verify a UI still communicates without hue, holds up under inversion, or remains readable for colour-vision deficiencies.

At a glance

Kinds	displayfilter/variants
Schema version	1
Modules	:data-displayfilter-core (published) · :data-displayfilter-connector
Render mode	default — purely post-capture, no Compose changes
Cost	very low — one matrix multiply per pixel per enabled filter on the captured BufferedImage
Token usage	~10 tok inline (manifest is tiny — {filter, path} per variant); +~1.5 k per filtered PNG read.
Transport	inline (JSON manifest) · variant PNGs ride as extras
Platforms	Android, Desktop
Status	Wired across both render paths — the daemon (VS Code, MCP, CLI daemon mode) and the Gradle-plugin direct path (:samples:cmp:renderAllPreviews) both emit variants and the manifest after each capture.

What it answers

• Hue-only signalling — does this UI still distinguish error/success/warning when the display is grayscale? Run with grayscale and look at the variant PNG: if a red error pill collapses to the same grey as a green success pill, hue is carrying signal that contrast/iconography should.
• Inversion robustness — does the UI hold up when the user has Android’s “Color inversion” accessibility setting on? invert reveals hard-coded white/black assumptions and assets that don’t react to dark theme.
• Colour-vision deficiency — what does this design look like to a viewer with the most common forms of colour blindness? deuteranopia (~6% of males), protanopia, and tritanopia simulate cone-loss using the Machado / Oliveira / Fernandes 2009 LMS-cone-loss matrices at severity 1.0.

What it does NOT answer

• It is simulation, not correction. Android’s accessibility “Color correction” setting applies an error-shifted matrix that compensates for the deficiency; that’s a separate transform that belongs in the a11y bag.
• It does not perform contrast checks — for WCAG-style audits use a11y/atf.
• It does not understand image content (e.g. embedded photos), so smart-invert-style preservation of media is not modelled.

Use cases

• PR review: render any UI PR with grayscale enabled and skim the variant column — hue-only state is the most common reviewer-blind regression.
• Accessibility audit: sweep the design system once with deuteranopia to find palette pairs that collapse for the most common colour-vision deficiency.
• Bedtime / digital-wellbeing parity: confirm the app still looks deliberate when Android’s bedtime grayscale schedule kicks in, not just “all icons gone grey”.

Payload shape

DisplayFilterArtifact, DisplayFilterArtifacts — defined in :data-displayfilter-core. The manifest written to disk:

// build/compose-previews/data/<previewId>/displayfilter-variants.json
{
  "variants": [
    {
      "filter": "grayscale",
      "path": "<absolute>/build/compose-previews/data/<previewId>/render_displayfilter_grayscale.png",
      "mediaType": "image/png"
    },
    {
      "filter": "invert",
      "path": "<absolute>/.../render_displayfilter_invert.png",
      "mediaType": "image/png"
    }
  ]
}

data/fetch against displayfilter/variants returns the same JSON inline plus one DataProductExtra per variant pointing at the variant PNG, so a panel that subscribed to the manifest gets every PNG path without a follow-up fetch.

Filter catalogue

id	Matrix source	What it simulates
grayscale	setSaturation(0) with Rec.709 luma weights (R · 0.2126 + G · 0.7152 + B · 0.0722) — same weights android.graphics.ColorMatrix uses	Android Digital Wellbeing’s bedtime-mode grayscale
invert	RGB channel negation, alpha preserved	Android “Color inversion” accessibility setting (classic, not Smart Invert)
deuteranopia	Machado / Oliveira / Fernandes 2009, severity 1.0 — M-cone (green) loss	Most common colour-vision deficiency (~6% of males)
protanopia	Machado 2009, severity 1.0 — L-cone (red) loss	Red-blind
tritanopia	Machado 2009, severity 1.0 — S-cone (blue) loss	Rare blue/yellow deficiency

Enabling

A comma-separated list of filter ids enables the feature. Empty / unset disables it entirely (no manifest, no variant PNGs, no extension registration).

Gradle plugin / direct render path. Pass the Gradle property (matches the rest of the composePreview.* flag namespace):

./gradlew :samples:cmp:renderAllPreviews \
    -PcomposePreview.displayFilter.filters=grayscale,deuteranopia

The plugin forwards the value to the spawned renderer JVMs as -Dcomposeai.displayfilter.filters=..., where RobolectricRenderTest (Android) and DesktopRendererMain (CMP Desktop) read it after each PNG capture and run DisplayFilterDataProducer.writeArtifacts(...).

Daemon path. Same sysprop, set on the daemon JVM directly: -Dcomposeai.displayfilter.filters=....

Unknown filter ids are dropped with a warning so a typo doesn’t strand the rest. Duplicates collapse — grayscale,invert,grayscale runs each filter once.

Companion products

• Accessibility — a11y/atf for ATF audit, a11y/overlay for annotated PNG. Pair grayscale with a11y/atf contrast findings to triage the same palette from two angles.
• Theme — compose/theme to see which tokens drove the render before applying a filter to the result.