Christian Walther <cwa### [at] gmxch> wrote:

> ...I have to say that Ard's first sample image
> doesn't look nearly as wrong to me as it seems to look to you... consider the
> first-quarter moon. It's approximately a diffusely reflecting sphere
> illuminated from a single direction in an otherwise dark space - and
> doesn't it look more like the upper image than the lower one?

Yes, I do have to agree with you there. I was thinking of the same example:
a half-moon in a dark sky DOES appear to be like Ard's assumed_gamma of 1
image. Which has caused me some head-scratching. But I wonder...is it
*possible* that that's because the BRIGHTEST part of the moon--coupled with
the dark-to-black night sky background-- presents too MUCH brightness and
contrast (contrast with the background)  for our eyes to "make sense" of?
Just a conjecture.  But your argument is definitely worth thinking about.
I suppose a conclusive "proof" for me would be to set up a white sphere
against my Kodak neutral-gray card...to lessen the contrast... and just
LOOK at what a single, far-away light source does to it. Who knows, I may
be surprised!

> > I wonder--is the POV community equally divided on this particular
> > issue, or am I one of the few wandering madmen??
>
> I'd be interested in that too - I'd guess the latter, not because I
> consider you a madman :), but because I think POV-Ray's "numerical" user
> interface (as opposed to the "graphical" way other 3D applications work)
> appeals more to "scientist" types than to "artist" types.

You may very well be correct, from what I read not only in this discussion
but others in the newsgroup. Yes, I suppose I would be squarely in the
"graphical" camp---and sometimes I do find it odd MYSELF that I actually
like the numerical way of working in POV!!  Yet it definitely appeals to
me. That left brain/right brain thing, I suppose.
> f
>
> >>>...and then re-massaged THOSE values before spitting them back to the
> >>>monitor, so that they appeared perceptually correct in the user's
> >>>chosen gamma environment?
> >>
> >>POV-Ray already does that (if you use assumed_gamma 1).
> >
> > ...I disagree, using my "linear-value" grey-band test scene as a prime
> > example.
>
> I think you're misunderstanding me. I'm talking about what POV-Ray does
> at the output end, assuming that you feed it what it expects at the
> input end...
>
> POV-Ray interprets the 0.5 in the middle of your gray-band as "half the
> intensity" (that's not what you meant it to be, but that's just the way
> POV-Ray works)... When the file is displayed,
> that value is copied into video memory and makes your screen pixels glow
> with (186/255)^2.2 = 0.5 of full intensity (assuming your display is
> properly calibrated to a gamma of 2.2). That's the correct value, given
> what was input at the beginning, even though it's not "half the
> perceptual brightness".
>
Ah, I do now understand what you meant. (And nicely-explained, too!) Yes, we
are in agreement.

Many, many thanks, both to you and to the others who've contributed, for
taking the time to go into this topic in such detail. I've learned a great
deal.

 Ken

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