Am 18.03.2018 um 21:31 schrieb Kenneth:

> Otherwise, it seems that using a LOW-dynamic-range sky + light_source(s)
> requires *some* kind of tweaking (of one subtle thing or another).. yet which
> still works against the radiosity mechanism, if only in a technical sense.

No, it shouldn't require tweaking.

(In v3.7 there's still /some/ tweaking to be done to balance reflections
vs. highlights. But stuff is improving.)


> My desire to increase the contrast of a rad scene-- if I feel that it's
> necessary-- looks like a no-win situation (except in the HDR light probe case).
> Unless I simply postpone that step, and do it later as a post-processing effect
> in another graphics app.

If you want realism, take what the proper settings give you.

If you want pure art, tweak as tweak can.

If you want art based on realism, render with proper settings, then
post-process to taste. (Inbuilt tonemapping featureas are on the agenda,
BTW.)


>> Radiosity and diffuse are mutually balanced automatically (if you don't
>> tamper with radiosity brightness...
> 
> *That* is a key insight that I've been wondering about. I hope I understand it
> (as it relates to a LOW-dynamic-range sky set-up):
> 
> Given:
> radiosity{brightness 1.0}
> light_source{rgb .7}
> object{... pigment{rgb <.3,.5,.7> finish{diffuse 1.0}}
> 
> Does the 'automatic balancing' keep the object surface color at <.3,.5,.7>
> (depending of course on the angle-of-incidence of the light source hitting it)?
> Or does my diffuse setting need to be manually reduced, to keep the color from
> washing out to, say, <.6,1.0,1.2> (just as a conceptual idea, not real math). Or
> am I still clueless about what 'automatic balancing means? :-O

`pigment { rgb Cp } finish { diffuse D }` means that /any/ incoming
light of brightness/colour Ci will be diffusely reflected for an
effective brightness/colour of Ci*Cp*D*F, where F is a factor that
solely depends on geometry (surface normal, incoming light direction and
outgoing light direction) and (if finish-level fresnel is enabled) the
refractive index of the material.

Point light sources, photon mapping and radiosity are all just methods
of computing which point on an object surface receives how much incoming
light from which direction, and they complement each other: The point
light source algorithm only takes into account light paths directly from
classic light sources to the observed surface (and not traversing photon
targets); the photon algorithm only takes into account light paths
refracted by photon targets; and the radiosity algorithm only takes into
account light paths where the light is bounced off other objects, or
where the light is emitted by another object (or a sky sphere) rather
than a classic light source.

There is no "washing out" caused by the radiosity algorithm itself: If
you replaced the sky sphere with a gazillion point light sources all
coloured in accordance with the image, you'd get pretty much exactly the
same result.


The surface of an object with pigment rgb <.3,.5,.7> will always have an
effective apparent colour of <.3,.5,.7>*Brightness, provided all the
light sources are "white" (R=G=B) and there is no specular reflection
nor specular highlights, nor "ambient" nor emission. (And no intervening
media or some such, of course.)

Note however that sky tends to be blue in hue, which might cause red and
yellow hues to appear more washed out; on the other hand, blue hues will
get more pronounced. To counteract this, make sure to tune your "sun"
light source to a yellowish hue, which by the way is also realistic.
(HDR sky spheres should normally already account for this effect.)

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