A raw whose camera look fails the acceptance gates fell back to the neutral
rendering: dark (9-22 L* below the camera JPEG), about a third of its
colourfulness, hues from the generic camera = sRGB matrix. Before falling
back, fit a partial look: the quantile tone curve (registration-free), the
chroma curve and, on a scene with enough colour, the photo's own matrix at
half weight (no hue/saturation table). It is used only when it cuts the
held-out error to below 0.7 of the neutral fallback's (linear and encoded)
and the JPEG's luminance ranks the pixels like the scene's (Spearman >= 0.5).
The full look's gates and search are unchanged. Render cache version 24.