The Fujifilm RAF this was reported on opened with magenta through every white
in the frame. The develop itself was the cast, not the tone curve fitted over
it: run flat — white balance, matrix, knee, encode, no curve at all — the
frame's bright neutral blocks came back 232,196,201 against the 223,232,236
the camera's own preview has there. The matrix is not it either; every row of
`rgb_cam` sums to one, so a neutral triple opens neutral. What was wrong is
the balance it was given.
Neither balance LibRaw hands over is the one the frame was rendered with.
`pre_mul` on that frame is R/G 2.296, B/G 1.307; `cam_mul` is 1.795, 1.626;
the balance the preview's own bright neutral blocks imply is 1.588, 1.266 —
and that one is readable: average the sensor triple behind each block the
camera left bright and near neutral, and the ratio that equalises those
blocks is the frame's white.
So the develop reads it there, before the first draw, from the same preview
map the tone curve is fitted on, and keeps LibRaw's tags only as the fallback
a frame with nothing neutral and bright to read (a clipped or dark frame)
falls back to. `cam_mul` is tried before `pre_mul` on that path: as-shot
before daylight, measured 6.73 -> 5.27 on this frame where the reverse gave
6.66.
Measured end to end through the real develop (LibRaw worker + CanvasKit,
64x64 block grid against the file's own preview), mean dE00 / mean dRGB:
HAGIANG-20170202-FUJIFILM-418.RAF 6.73 -> 4.89 +5.8,+0.9,+0.5 -> 0.7,-0.5,-0.7
_DSF3087.RAF 7.52 -> 6.78 +1.6,+0.1, 0.0 -> 0.5,-0.2,-0.7
DSCF1701.RAF 6.86 -> 6.54 ~0 -> -1.5,-1.7,-0.9
_DSF7273.RAF 5.13 -> 4.66 +2.4,+1.0,+1.5 -> 1.8,+0.9,+1.5
_3279791.ORF 5.81 -> 5.93 ~0 -> -0.4,-0.2,-0.5
P1010256.RW2 9.60 -> 9.56 +2.5,+0.6,+0.7 -> 1.6,+0.4,-0.1
The four Fujifilm frames lose the cast; the Olympus and Lumix frames hold.
The two that open as their preview (Nikon NEF, DNG) still do. The bright
neutral fifth of both Fujifilm frames now differs from the preview by the
same figure on all three channels — a difference in brightness, not in
colour, which is the tone curve's business and not this one's.
The read is on the frame, not on the brand or its tags, so the bodies with
no sample here (Sony, Canon, Ricoh, Leica) take the same path.
scripts/raw-develop-check.mjs had gone stale against the module and is back
in step with it — the highlight gate's threshold, the gain's divisor, the
preview-WB read and the tag order are pinned, and previewWhiteBalance now
carries a case that hands it a plane and a map and reads the balance back.
3dtours
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