Reducing contrast turned every black in a night photograph pink. The
fragment lifted each pixel's luminance to its target by multiplying the
colour by target/luma. For a pixel at 0.001 on the way to 0.09 that is
a gain of ninety, and in the deepest shadows the channels are sensor
noise: after white balance the red and blue noise sits above the green,
their multipliers being nearly twice its, so ninety times that noise is
magenta.
Flattening now mixes the colour toward middle grey, which gives the
same luminance and adds the lift as a neutral. A black goes to grey and
its noise stays the size it was.
The same fragment clamped luma/0.36 into the curve's 0..1 domain, which
scaled every tone above twice middle grey down to 0.36 in either
direction: contrast +10 took a 230 grey to 162. Those tones are now left
where they are, which is continuous with the curve's top (value 1,
slope 0).
dtourolle
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