Am 07.03.2013 15:03, schrieb s.day:

> I am trying out some HRD renders in Pov 3.7 RC7 and having some difficulty
> finding good settings. After a lot of adjusting (mostly guesswork) I have the
> following:

I have made the experience that with 3.7 the most straightforward 
settings also yield the most realistic results:

> global_settings {

"assumed_gamma 1.0" should go somewhere here.

>    radiosity {
>      pretrace_start 0.08
>      pretrace_end   0.01

That's a pretty low-quality pretrace. I'd suggest a lower pretrace_end. 
Shouldn't affect the overall brightness though.

>      count 500
>      nearest_count 10
>      error_bound 2.5

I usually use a setting below 1.0, e.g. 0.8 or 0.5.

>      recursion_limit 4

Recursion limit 2 is usually enough.

>      low_error_factor .5
>      gray_threshold 0.0
>      minimum_reuse 0.015
>      brightness 0.3

Whoa - stop there! For realism, you /do/ want brightness 1.0 (*). This 
will significantly boost the effective diffuse brightness of your 
object, and may already be enough to fit the brightness of the 
highlights, so that all you might need to do is reduce the overall 
brightness of the scene (we'll come to that in a moment).

(* There are actually some situations where a /higher/ brightness 
setting may give you more realistic results, but don't bother about them 
for now.)


>      adc_bailout 0.01/2
>
>    }
> }
>
> For HDR sky_sphere:
>
> sky_sphere {
>    pigment{
>      image_map{ hdr "galileo_probe.hdr"
>                 gamma 1.1

That should be 1.0 - or left out entirely. If you're going for realism, 
don't tinker with it unless you know exactly what you're doing there: If 
the author of the light probe did his homework, then by default POV-Ray 
3.7 will give you exactly the right thing.

>                 map_type 1 interpolate 2}
>        }
> emission rgb 0.6

THIS is where you're doing your overall scene brightness tweaking.

> rotate <0,40,0>
> }
>
>
> For finish on the main lantern (red painted finish):
>
> finish {
> specular 0.4
> roughness 0.01

As you have no conventional light sources (or do you?), you could just 
as well set this to "specular 0.0".

> brilliance 2

Most diffuse surfaces have a brilliance quite close to 1.0. (Aside from 
that, radiosity doesn't currently support brilliance settings other than 
1.0 anyway.)

> diffuse 1
> reflection 0.1

Hold it right there again: What you're effectively saying here is that 
100% of the incoming light is reflected diffusely, and another 10% is 
reflected specularly, i.e. the object reflects a total of 110% of the 
incoming light ;-)

A total reflection (diffuse + specular) of 80% is a lot more realistic.

By the way, when defining new materials it is good practice to use the 
"albedo" keyword for all diffuse, specular and phong, as this allows to 
employ a few rules that help you get realistic results (not only in 
HDR-lit scenes):

   diffuse albedo D
   specular albedo S
   phong albedo P
   reflection { R fresnel }

For realism, you usually want D+R<1 and S+P<R, with S+P=R/2 being a good 
guesstimate.

> conserve_energy

This setting has no effect unless you also use variable reflection, i.e. 
either of:

   reflection { 0.0 0.1 }
   reflection { 0.0 0.1 fresnel }
   reflection { 0.1 fresnel }

Using fresnel is a good idea anyway, not only for transparent but also 
for opaque materials, even if that may seem counter-intuitive: Real-life 
materials /all/ have an ior, and follow the fresnel law when polished. 
(ior 1.6 is a good bet for opaque materials.)

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