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DarkRoom/core/dr-decode
dtourolleandClaude Opus 5 f1f528fc42
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Stop rendering a missing white balance as neutral, which came out pink
`sane_wb` replaced any coefficient it could not use with 1.0. That reads as a
safe default and is not one. A Bayer sensor's green photosites collect roughly
twice the signal of its red and blue, so unbalanced data is strongly green —
and the camera matrix is built assuming the data reaching it has already been
balanced. Fed green-heavy input it subtracts green as designed, overshoots,
and the frame lands in magenta. Bodies whose as-shot coefficients rawler does
not report came out pink, and nothing anywhere said why.

The fallback is now the camera's own response to daylight, which
`cam_to_srgb_from` was already computing on its way to balancing the matrix
and then discarding. `daylight_wb` exposes it, and both callers read the same
matrix through the same illuminant preference — so the multipliers neutralise
exactly the white the matrix expects to be neutral, by construction rather
than by coincidence. With no matrix either, the body is unknown and neutral is
the honest answer: uncalibrated beats wrong in a specific direction.

A test caught me returning the response rather than its reciprocal, which
inverts the correction — a sensor is *least* sensitive to the channel needing
the largest multiplier, so that version boosted precisely the wrong one. The
doc comment now says which of the two it returns, because they differ by an
inversion and look alike.

Four tests, on a real matrix (Canon 6D, D65) rather than a contrived one: the
fallback is nowhere near neutral, lifts both red and blue against green, stays
green-normalised, and — the property that makes it consistent rather than
merely plausible — balancing by it and then applying the matrix maps the
camera's white to a neutral sRGB.

`daylight_wb` is also the anchor the white-balance presets need: a preset in
kelvin requires an absolute illuminant to be a preset *of*, and the temperature
control is currently a relative offset from whatever the camera chose.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-08-17 13:03:03 +02:00
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