Does a PQ-encoded image keep its headroom when composited over the board canvas?
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1. Plain white div SDR reference
2. PQ image, standalone must out-glow #1
3. Over a WebGL canvas GATE — must match #2
4. Over canvas, opacity .6 GATE — must still glow5. WebGPU extended reference (Chromium only)
Intensity rungs
The glow is steady, not a pulse, so intensity is picked from the baked
luminance ladder rather than modulated with alpha (alpha flattens HDR — see swatch 4).
Which rung should be the default? Each sits over a WebGL canvas, as it will in the app.