Normalize active DPR relative to the current ceiling for perceptual
effect scaling (e.g. detector-noise grain density should stay
perceptually constant across DPR overrides).
Against the CEILING, not the native DPR: a scale of 1.0 must mean
"full quality for this viewer", which under a cap IS the cap.
Normalizing against native would peg the scale at 0.5 forever on a 2x
display and silently attenuate detector noise to half sigma / a
quarter photon gain in every capped session.
Normalize active DPR relative to the current ceiling for perceptual effect scaling (e.g. detector-noise grain density should stay perceptually constant across DPR overrides).
Against the CEILING, not the native DPR: a scale of 1.0 must mean "full quality for this viewer", which under a cap IS the cap. Normalizing against native would peg the scale at 0.5 forever on a 2x display and silently attenuate detector noise to half sigma / a quarter photon gain in every capped session.