[Lcms-user] Display gamma

[Richard H. <hug...@gm...>]

Hey all,

I've had a chance to look more at the problem of display gamma
recently. It seems there is quite a lot of misinformation out there,
and very little in the way of standards that are actually applicable
to the technology we have now. Theory is diverging from practise in a
number of areas, for instance we calibrate to gamma 2.4 to adapt for
viewing conditions in Linux, and people are calibrating to gamma 2.2
in Windows when using the X-Rite tools.

I'm wondering about the basics of what gamma is and also how to
measure it. Some of the questions I'm asking myself:

* on real life hardware, can we assume gamma_red == gamma_blue == gamma_green?
* how do we measure gamma given there's an offset at zero for anything
other than LED displays - pretending the backlight is zero and
offsetting everything to that seems a giant hack given our perception
of light isn't linear.
* roughly how many points does it take to calculate the gamma assuming
the hardware is well behaved (e.g. monotonic) -- three seems the
obvious answer, but the backlight at 0,0,0 and measurement accuracy
makes that tricky.
* how does the 2.4 v.s. 2.2 gamma adaption for viewing conditions
work? Is that a function of the luminance of the room, in which case
we should probably measure ambient first and do something more
technical than += 0.2.

I can't find much up-to-date technical literature on display gamma
(anything written in the last 5 years) so if anybody can point me at
anything in Amazon or a research journal that a human being could
understand I'd appreciate it.

Thanks,

Richard.