We're supposed to output linear values there, as sRGB transfer function
gets applied either by GL framebuffer or FBOUT later on.
min_ev and max_ev also need to be adjusted, as they're tweaked for
a pipeline with exposure compensation. The current values lead to a very
washed-out image, which was "hidden" by subsequently applying gamma twice.
It may make sense to revisit these values in the future to better match
the rendering pipeline.
