Hi folks,

I recently came across this post on the LDraw forums:
http://forums.ldraw.org/read.php?20,12928

The Lego renders here are pretty awesome. I'm always looking for ways to 
acheive better Lego renders in POV-Ray, so would appreciate any advice/code 
snippets on how to achieve more realistic renders. Maybe there is some 
general "rendering plastic materials" type stuff that I could benefit from?

I think my Lego models always look a bit too shiny:
http://news.povray.org/povray.binaries.images/attachment/%3C51a7b9c2%40news.povray.org%3E/lego_minifigures_3d.png


Thanks in advance.

Reuben
=====================================
Download 3D Lego models and other resources from:
http://www.pearse.co.uk/lego
=====================================

Post a reply to this message

"Reuben Pearse" <reu### [at] pearsecouk> wrote:
> Hi folks,
>
> I recently came across this post on the LDraw forums:
> http://forums.ldraw.org/read.php?20,12928
>
> The Lego renders here are pretty awesome. I'm always looking for ways to
> acheive better Lego renders in POV-Ray, so would appreciate any advice/code
> snippets on how to achieve more realistic renders. Maybe there is some
> general "rendering plastic materials" type stuff that I could benefit from?
>
> I think my Lego models always look a bit too shiny:
>
http://news.povray.org/povray.binaries.images/attachment/%3C51a7b9c2%40news.povray.org%3E/lego_minifigures_3d.png
>
>
> Thanks in advance.
>
> Reuben
> =====================================
> Download 3D Lego models and other resources from:
> http://www.pearse.co.uk/lego
> =====================================

Hi Reuben,

yes the renderings at the LDraw forum looks really nice. I'm not sure, but I
think first subsurface scattering is in use there to a small amount and second
blurred reflection. The first is implemented in POV 3.7 now, the latter can be
simulated in POV with averaged textures or parametrized with the unofficial
version UberPOV. May be you look at this new features. Unfortunatelly I'm not an
expert at this issues to give further guidance. I can only give you this poor
hints.

Best regards,
Michael

Post a reply to this message

Am 24.02.2015 um 21:42 schrieb MichaelJF:
> "Reuben Pearse" <reu### [at] pearsecouk> wrote:
>> Hi folks,
>>
>> I recently came across this post on the LDraw forums:
>> http://forums.ldraw.org/read.php?20,12928
>>
>> The Lego renders here are pretty awesome. I'm always looking for ways to
>> acheive better Lego renders in POV-Ray, so would appreciate any advice/code
>> snippets on how to achieve more realistic renders. Maybe there is some
>> general "rendering plastic materials" type stuff that I could benefit from?
>>
>> I think my Lego models always look a bit too shiny:
>>
http://news.povray.org/povray.binaries.images/attachment/%3C51a7b9c2%40news.povray.org%3E/lego_minifigures_3d.png
...
> yes the renderings at the LDraw forum looks really nice. I'm not sure, but I
> think first subsurface scattering is in use there to a small amount and second
> blurred reflection. The first is implemented in POV 3.7 now, the latter can be
> simulated in POV with averaged textures or parametrized with the unofficial
> version UberPOV. May be you look at this new features. Unfortunatelly I'm not an
> expert at this issues to give further guidance. I can only give you this poor
> hints.

Those hints are fare from poor - that's exactly what I think I see in 
the MODO renders, too (and I guess I have a keen eye for it): Subsurface 
scattering and blurred reflections.


Also, as far as specular highlights are concerned, a common 
misconception is that "specular 1.0" would correspond to a totally 
reflective surface - it does not, except for the hypothetical case of 
"roghtness 0.0"; with the traditional "specular FLOAT" parameterization, 
any increase in roughness also increases the total amount of reflected 
light. For a physically more straightforward parameterization, use the 
new "specular albedo FLOAT" syntax, where "specular albedo 1.0" indeed 
corresponds to a totally reflective surface, regardless of the 
roughness. (Same goes for "phong FLOAT" vs. "phong albedo FLOAT" with 
respect to phong_size, and "diffuse FLOAT" vs. "diffuse albedo FLOAT" 
with respect to brilliance.)

Another thing that can really add to the credibility of a material is 
the simulation of fresnelian effects, not only for specular reflection 
(which gets brighter at shallow angles) but also for highlights (which 
should do the same) and diffuse reflection (which should get less bright 
at shallow angles). POV-Ray 3.7.0 only supports fresnelian effects for 
specular reflection (via the "fresnel on" statement in the reflection 
block), but not on highlights, and for diffuse reflections it only 
supports them when using subsurface scattering (in which case they 
actually can't be turned off). POV-Ray 3.7.1 adds full support for the 
latter two (by specifying "fresnel on" directly in the finish block as 
well; note that "fresnel on" in the reflection block is still required 
as well); UberPOV 1.37.1.X supports this new syntax as well.


Ideally, you would be using UberPOV 1.37.1.X with the following finish 
settings:

     finish {
       diffuse albedo D brilliance B
       specular albedo S roughness R
       phong off
       fresnel on
       reflection { S roughness R fresnel on }
       conserve_energy
       subsurface { ... } // (optional)
     }

where D+S < 1. (Don't forget to specify an interior block with ior to 
all your materials, even the opaque ones. If you don't know the 
refractive index of a material, 1.5 is a good bet.)

When using POV-Ray 3.7.1, for sufficiently shiny materials an acceptable 
approximation is to leave out the "roughness R" statement in the 
reflection block:

     finish {
       diffuse albedo D brilliance B
       specular albedo S roughness R
       phong off
       fresnel on
       reflection { S fresnel on }
       conserve_energy
       subsurface { ... } // (optional)
     }

For sufficiently dull materials, you can turn off reflections entirely:

     finish {
       diffuse albedo D brilliance B
       specular albedo S roughness R
       phong off
       fresnel on
       reflection { 0.0 fresnel on }
       conserve_energy
       subsurface { ... } // (optional)
     }

(Theoretically you would need to compensate by fudging D up a bit for 
the sake of radiosity but not for classic diffuse, but that's something 
POV-Ray doesn't support at present.)

For materials in between, there is no really good solution in official 
POV-Ray at present.

When using POV-Ray 3.7.0, you should fudge up the specular highlights 
and (unless you're using subsurface scattering) fudge down the diffuse 
reflection, to compensate for the fact that they don't honor fresnelian 
effects:

     finish {
       diffuse albedo D*(1-F) brilliance B
       specular albedo S*F roughness R
       phong off
       reflection { S fresnel on }
       conserve_energy
     }

or:

     finish {
       diffuse albedo D brilliance B
       specular albedo S*F roughness R
       phong off
       reflection { S fresnel on }
       conserve_energy
       subsurface { ... } // (mandatory)
     }

where F is some fudge factor very roughly around 2.0.


High-quality diffuse inter-reflections are of high importance for 
creadibility as well. If you're using POV-Ray, this means using 
high-quality radiosity settings; with UberPOV, I'd recommend using 
"no_cache" in the readiosity block instead.


Finally, some of the MODO renders also use focal blur, which can also 
add to credibility, provided you don't overdo it. Ideally, the aperture 
value for a POV-Ray focal blur camera should correspond to somewhere 
about 1mm to at most 1cm in scene units.

Post a reply to this message

Am 24.02.2015 um 20:14 schrieb Reuben Pearse:
> Hi folks,
>
> I recently came across this post on the LDraw forums:
> http://forums.ldraw.org/read.php?20,12928

On a related note, I just tested the LDD2POVRAY mentioned in that post: 
It really sucks hard, as it is artificially constrained to selected 
POV-Ray versions. No way to render those scenes with UberPOV, not even 
development versions of POV-Ray.

Post a reply to this message

Am 26.02.2015 um 21:58 schrieb clipka:

> (Don't forget to specify an interior block with ior to
> all your materials, even the opaque ones. If you don't know the
> refractive index of a material, 1.5 is a good bet.)

BTW, the material definitions that come with LDD2POVRAY specify the ior 
of opaque bricks as 1.57, and that of transparent bricks as 1.2.

Post a reply to this message

Some of the Sunflow renders look really good too.

http://slswww.free.fr/neo-6930.5b.png

Unfortunately, I can't get the LDraw converter to work on my PC.


Mike




On 2/24/2015 2:14 PM, Reuben Pearse wrote:
> Hi folks,
> 
> I recently came across this post on the LDraw forums:
> http://forums.ldraw.org/read.php?20,12928
> 
> The Lego renders here are pretty awesome. I'm always looking for ways to
> acheive better Lego renders in POV-Ray, so would appreciate any advice/code
> snippets on how to achieve more realistic renders. Maybe there is some
> general "rendering plastic materials" type stuff that I could benefit from?
> 
> I think my Lego models always look a bit too shiny:
>
http://news.povray.org/povray.binaries.images/attachment/%3C51a7b9c2%40news.povray.org%3E/lego_minifigures_3d.png
> 
> 
> Thanks in advance.
> 
> Reuben
> =====================================
> Download 3D Lego models and other resources from:
> http://www.pearse.co.uk/lego
> =====================================
> 
> 
> 
>

Post a reply to this message