"Jim Holsenback" <jho### [at] hotmailcom> wrote:
>     I'm running v3.6 and using the example in docs I've arrived at
> Display_Gamma = 2.5 for my display and using that value forever. I
> understand how this works just by simple empirical testing .... lower value
> for D_G makes image darker .... higher lighter.

Well, to be precise, it only does that for the midtones. (That's why comparing a
black & white checkerboard pattern with uniform 50% grey shows you whether your
gamma settings are ok.)

> It used to be that some
> folks have crt some lcd .... now a days it's pretty much lcd .... does that
> make a diff?

Not in practice. The LCD are designed so that they behave quite similar to a CRT
when it comes to gamma. After all, people not knowing about these issues expect
colors on the LCD to look similar to their old CRT.

> I'm using the color profile that came with the display, my vid
> card (nvidia) has an applet that allows to adjust gamma curve, I've left
> that alone (default says gamma=1.0).

Yeah, that's another point to tweak. I'd recommend lowering that value a bit, to
get your total display gamma (operating system + graphics card + LCD) to a gamma
of 2.2, so that what you see is what other people (on average) get. The majority
of images out there on the net is probably tuned for a gamma of 2.2.

> You know with all the variables it's no wonder that (gamma correction) is a
> frustrating excerise to say the least.

Definitely so. And we haven't even mentioned white point and black point yet.

Theoretically, to optimize your display gamma (if you don't have expensive
calibration hard- and software), you should start something like this:

- Set your operating system's display settings to use the display profile that
came with your hardware, to (hopefully) get the R/G/B "phosphor" colors right.

- Using your graphics card tools, tune your graphics card output so that it uses
the greatest "swing" for the voltages (or digital values) sent to the display
hardware, to make sure you get the best "resolution". (I presume that this is
usually the standard setting, but I might be mistaken.)

- Tune your display hardware (CRT or LCD) so that 0% black is as dark as your
display can possibly get but 5% grey is still looks slightly brighter, and 100%
white is as bright as your display can possibly get but 95% still looks slightly
darker (black & white point calibration), and white is some "standard" white
(whatever that may be; speaking of color "temperature" here)

- If you couldn't get the black and/or white point properly with the display
hardware settings, use your graphics card tools to do the rest.

(Instead of up to now, you might alternatively want to keep your display
hardware set to standard values so you can easily reset them in case you or
someone else accidently mess them up, and just use graphics card tools to set
black and white point, respectively.)

- Using your graphics card tools, tune your display system (operating system +
graphics card + display hardware) for a total gamma of 2.2 (using e.g. the
"tuning chart" in the POV manual), to best match what other people use on
average.

- Set your POV .ini settings (Display_Gamma and - in case of 3.7 - File_Gamma)
to 2.2 to match your newly optimized display setting of 2.2, and the expected
"other people's displays" setting of 2.2 for the file output.

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