clipka <ano### [at] anonymousorg> wrote:
> Am 15.02.2016 um 13:45 schrieb Kenneth:
> > The docs mention using srgb "everywhere that color literals are used"...
>
> I'm not sure where you got that quote from; I just searched the Wiki
> (which includes the text of the docs) and couldn't find it anywhere.
>
> I suspect you extrapolated that from statements saying something like:
>
> "When converting an old scene to assumed_gamma 1.0, replace rgb with
> srgb everywhere."

Yes, it was probably here (about migrating old scenes to v3.7)...
http://wiki.povray.org/content/HowTo:Fix_old_scenes_to_work_with_the_new_gamma_system

" 3. Gamma-adjust all colour literals, by raising the R,G,B components to the
power of 2.2 (or wait for the next beta, and use "srgb" instead of "rgb")."

I thought I had seen it elsewhere, in another context, but I can't find it.

>
> There is NO requirement whatsoever that a scene must use "srgb" instead
> of "rgb" for physical realism.
>
> The "srgb" keyword is just for convenience of entering colours that you
> get from somewhere else: PhotoShop's colour picker, the World Wide Web,
> or even a 3.6 POV-Ray scene without explicit assumed_gamma.
> (... etc.)

Yes, I've understood that for several years now, and that 'srgb' is optional.

>
> > So is my question really just a matter of 'visual or artistic preference'
> > rather than computational consistency? Or, are there some things in POV-Ray
> > that should *not* use srgb at all?
>
> I wouldn't call it "visual or artistic preference", but rather
> "technical preference" -- for each "srgb" colour there is a matching
> "rgb" colour (albeit with different values) and vice versa...
>
> For light sources I would typically recommend using "rgb"...
>

Hmm, I might disagree with that (but for reasons that aren't purely technical.)

Just to give some background: In the v3.61 and 3.62 days, I used assumed_gamma
2.2 for all my scenes (right or wrong), because it gave me the light-and-object
colors that I was used to seeing and using in Photoshop (and many other apps)
operating in their own 2.2 gamma-adjusted color space. (I don't think I was
alone in this.) Actually, I chose 2.2 *solely* because assumed_gamma 1.0
resulted in 'washed out' colors-- washed out according to what I was expecting.
(At the same time, I didn't really grasp the difference between 'physically
correct' lighting using assumed_gamma 1.0, vs. what I was doing.)

But I finally realized my *major* mistake: the COLORS I was choosing simply
needed to be re-worked for assumed_gamma 1.0, in order to get the 'same'
rendered colors I had seen before. To do that in a practical way, one of two
things was required: picking colors visually from a 'different kind' of color
palette-- a fanciful one, a 'linear' one, what I called a 'gamma 1.0 color
picker' at the time-- OR, adjusting the colors' vector components with a 2.2
power law. All of that seemed rather cumbersome, so I happily stuck with
assumed_gamma 2.2-- in the face of much contrary criticism. ;-)

Then along comes v3.7, with its optional 'srgb' colors (plus various gamma
corrections) to solve this problem. (And to help me understand how/why I had
been wrong about my previous dislike of assumed_gamma 1.0.)

However...
Creating new scenes in v3.7 and using RGB for all colors (along with
assumed_gamma 1.0) requires thinking purely in 'linear' color terms. The trouble
is, I still *think* about colors and color-mixing in terms of the gamma 2.2
world-- and that world covers just about every graphics application we know of.
(I envy anyone who can think in a 'linear color' way.)

I had a pretty good 'feel' for how to mix numerical colors in POV-Ray's vectors
prior to v3.7. Now, when using an object with srgb colors, but a light with rgb
(linear) colors, I need to think in terms of the light's 'linear' color palette,
which isn't easy; and chances are, the final color 'mix' in the preview will no
longer match my intuition.

OBJECT colors are easy to choose (using srgb). The LIGHT's color is not so easy,
because light isn't a physical thing to *see* (unless I attach a looks_like
object to it), and it *interacts* with the object's color, shadows, etc.

That was the real point of my question.

At this point-- and I could be wrong again-- I think I'll use srgb for BOTH
things (and for everything else where color is used), solely for visual and
intuitive understanding . At least, until I get a better feel for v3.7xx's many
new color and gamma features.

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