"Ard" <ard### [at] waikatoacnz> wrote:
> if (! horse->dead)
>  flog(it)
> else
>  flog(it)
>
> So tweaking RGB values in pigments brings them back into line, if they are
> fully lit.  But adding {assumed_gamma 1} makes the edges of soft shadows
> and spotlights sharper and faces oblique to incident light brighter...
>
 YES! Very true indeed. (BTW, I did get around to running my grey_band test
scene with an overall system gamma/display_gamma of 2.2, altering the
gray-band values by raising them to the power of 2.2, and the scene did
render just as beautifully and realistically as before.)

OK. So here are the facts so far: to make my POV "linear" grey band test
reproduce in POV's preview window with a correct , real-world appearance,
and using the recommended assumed_gamma of 1.0, then my grey values need to
be specified in a NON-linear way--i.e., instead of <.5,.5,.5> being used to
represent "half as perceptually white" as <1,1,1>, the values instead need
to be raised to the power of [whatever system gamma I've chosen.]
Apparently for the sole purpose of letting POV work in its ideal "linear"
gamma-of-1.0 color space

Ugh. Well, it works, and I accept it...I'M NOT HAPPY... but I'll accept it.
For the moment anyway.

Ah, but what about lighting? As you've mentioned, strange things happen. My
test scene made no use of lights.  The gray bands were
"self-illuminated"--{ambient 1 diffuse 0}. When light sources ARE included,
things turn...ugly! Your test images over at p.b.i. show very clearly what
happens.

Funny thing. I was JUST getting ready to post my own example scene to show
these effects (and discuss them), but happened to see your examples first,
and found that your test is EXACTLY the same as mine!!! Even down to the
direction of the light source!   Adventurous minds think similarly. ;-) But
I'd like to explore this little test, as it goes to the very HEART of my
initial "perceptual" argument and discussion.  (For the edification of
others: It's just a white sphere, illuminated by a single white
point-source light placed very far away, and with no ambient lighting to
muddle things.  You can't get much simpler than that!!) But in its very
simplicity, it clearly and "honestly" shows the effect of lighting on an
object...and the fundamental difference in "render realism" between using
assumed_gamma of 1.0 as opposed to my use of 2.0 (or 1.8 or 2.2). And it
duplicates, though in a completely different way, the "distorted"
brightness levels I was seeing in my original "linear" gray band test
scene.

Everyone, take a look at Ard's assumed_gamma of 1 image--that's an order!!--
or just run such a test.  I'd really like to know how each of us perceives
the illumined sphere...how the light reacts with the curving surface. And
what we each do to correct for it...if in fact we DO correct for it. (I
do...by using assumed_gamma of 2.0! Ard uses a different method.) But
others may not do so at all...??? I'm actually going somewhere with this
argument, though it may not seem so right now; kind of like a chess game!

It's important to note that with this test, there is obviously no way within
POV to alter any of the gray values OR the lighting to be "non-linear" (as
I did to my original gray-band test scene per Ard's suggestion.) An absurd
idea anyway.

More later!

Ken

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