The new tone mapper, dubbed "GT7" in the code, is based on
the Gran Turismo 7 tone mapper, as described in the SIGGRAPH
2025 presentation called "Driving Toward Reality: Physically
Based Tone Mapping and Perceptual Fidelity in Gran Turismo 7".
This tone mapper exhibits fewer hue skews than the other tone
mappers, at the exception of PBR Neutral. The GT7 tone mapper
is however better at preserving the perception of high
dynamic range.
The tone mapper, as implemented, targets an SDR paper white
of 250 nits, using 100 cd/m^2 as the reference luminance (for
values of 1.0 in the linear HDR framebuffer). This can result
in an overall darker image compared to the other tone mappers
but this can be controlled through camera settings, post-
processing exposure, or lighting intensity.
The GT7 tone mapper also allows to target HDR output, and
could be made customizable via APIs if desired. The current
implementation offers a fixed aesthetic solution.
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