POV-Ray : Newsgroups : povray.beta-test : Subsurface scattering Server Time: 30 Mar 2020 14:00:51 GMT
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From: Stephen
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 10:03:45
Message: <5a782c01$1@news.povray.org>
On 05/02/2018 08:57, Mike Horvath wrote:
> On 2/4/2018 3:03 AM, Stephen wrote:
>> On 04/02/2018 06:59, Mike Horvath wrote:
>>> Does POV have this feature yet, or is it still just an Uberpov thing?
>>>
>>>
>> Yes in Ver 3.7
>>
>>
> 
> Do you mean 3.7.1? Because that's what it says in my old uberpov scenes.
> 
> 

3.7.0 on my machine. I've not used it much recently.

-- 

Regards
     Stephen


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From: William F Pokorny
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 11:16:13
Message: <5a783cfd$1@news.povray.org>
On 02/05/2018 04:20 AM, Mike Horvath wrote:
> I tried an old scene that worked properly in uberpov, but I see no 
> effect in 3.7.0 or 3.8.0 alpha.
> 
> Here are my global_settings:
> 
> 
> global_settings
> {
>      assumed_gamma    1
>      #if (Use_Radiosity = 1)
>          radiosity
>          {
>              pretrace_start    0.1
>              pretrace_end    0.001
>              recursion_limit    2
>              count            3
>              nearest_count    20,10
>              always_sample    off
>              maximum_reuse    0.1
>              minimum_reuse    0.001
> //            no_cache
>          }
>      #end
>      ambient_light    0
> //    mm_per_unit        0.4
>      mm_per_unit        1/4000
>      adc_bailout        0.001
>      max_trace_level    8
>      subsurface
>      {
>          samples 5, 5
>          radiosity true
>      }
> }
> 
> 
> Here is my finish:
> 
>      #declare lg_solid_finish = finish
>      {
>          ambient    0
>          #if (lg_quality >= 2)
>              diffuse albedo    0.9
>              specular albedo    PlasticSpecularity
>              roughness PlasticRoughness
>              fresnel on
>              reflection
>              {
>                  PlasticSpecularity
> //                roughness PlasticRoughness
>                  fresnel on
>              }
>          #end
>          conserve_energy
>      }
> 
> 
> Are there additional settings I am missing?
> 
> 
> Mike

You need a subsurface {} block in your finish {} block in addition too 
the one in global_settings {}.

Remember there are almost always example scenes for features. A 
subsurface.pov sample scene ships with POV-Ray. It can also be found 
online at:

https://github.com/POV-Ray/povray/tree/master/distribution/scenes/subsurface

Bill P.


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From: Mike Horvath
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 12:56:30
Message: <5a78547e@news.povray.org>
On 2/5/2018 6:16 AM, William F Pokorny wrote:
> On 02/05/2018 04:20 AM, Mike Horvath wrote:
>> I tried an old scene that worked properly in uberpov, but I see no 
>> effect in 3.7.0 or 3.8.0 alpha.
>>
>> Here are my global_settings:
>>
>>
>> global_settings
>> {
>>      assumed_gamma    1
>>      #if (Use_Radiosity = 1)
>>          radiosity
>>          {
>>              pretrace_start    0.1
>>              pretrace_end    0.001
>>              recursion_limit    2
>>              count            3
>>              nearest_count    20,10
>>              always_sample    off
>>              maximum_reuse    0.1
>>              minimum_reuse    0.001
>> //            no_cache
>>          }
>>      #end
>>      ambient_light    0
>> //    mm_per_unit        0.4
>>      mm_per_unit        1/4000
>>      adc_bailout        0.001
>>      max_trace_level    8
>>      subsurface
>>      {
>>          samples 5, 5
>>          radiosity true
>>      }
>> }
>>
>>
>> Here is my finish:
>>
>>      #declare lg_solid_finish = finish
>>      {
>>          ambient    0
>>          #if (lg_quality >= 2)
>>              diffuse albedo    0.9
>>              specular albedo    PlasticSpecularity
>>              roughness PlasticRoughness
>>              fresnel on
>>              reflection
>>              {
>>                  PlasticSpecularity
>> //                roughness PlasticRoughness
>>                  fresnel on
>>              }
>>          #end
>>          conserve_energy
>>      }
>>
>>
>> Are there additional settings I am missing?
>>
>>
>> Mike
> 
> You need a subsurface {} block in your finish {} block in addition too 
> the one in global_settings {}.
> 
> Remember there are almost always example scenes for features. A 
> subsurface.pov sample scene ships with POV-Ray. It can also be found 
> online at:
> 
> https://github.com/POV-Ray/povray/tree/master/distribution/scenes/subsurface 
> 
> 
> Bill P.


Thanks!!

For LEGO, should I just reuse the surface color for the transparency? Or 
something else, like white or black?


Mike


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From: clipka
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 16:43:31
Message: <5a7889b3@news.povray.org>
Am 04.02.2018 um 07:59 schrieb Mike Horvath:
> Does POV have this feature yet, or is it still just an Uberpov thing?

It never was an UberPOV-only thing in the first place ;)


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From: clipka
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 17:18:13
Message: <5a7891d5$1@news.povray.org>
Am 05.02.2018 um 03:10 schrieb Mike Horvath:
> On 2/4/2018 3:03 AM, Stephen wrote:
>> On 04/02/2018 06:59, Mike Horvath wrote:
>>> Does POV have this feature yet, or is it still just an Uberpov thing?
>>>
>>>
>> Yes in Ver 3.7
>>
>>
> 
> Does anyone know what appropriate values might be for LEGO (Ldraw) models?
> 
> Here are the mm and ldu units:
> 
> http://www.brickwiki.info/wiki/LDraw_unit

According to that table, and presuming that POV-Ray export of LDraw
models uses 1 LDU = 1 unit in POV-Ray, you should use

    global_settings {
      mm_per_unit 0.4
    }

and either of:

    // opaque (ABS, acrylnitrile butadien styrene)
    interior { ior 1.6 }

    // transparent (Makrolon(R), a polycarbonate)
    interior { ior 1.585 dispersion 1.02 }

    // axles (polyamide, maybe Nylon)
    interior { ior 1.53 }

(The `ior.inc` in the master branch contains values for ABS and PC,
named `iorABS`, `iorPC` and `dispPC`, respectively, but not for PC yet;
it also needs a POV-Ray version newer than v3.7.0.)

As for the subsurface translucency values, you'll have to tinker. I know
of no measured values, and the properties may differ from colour to colour.


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From: clipka
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 17:34:04
Message: <5a78958c$1@news.povray.org>
Am 05.02.2018 um 13:56 schrieb Mike Horvath:
> For LEGO, should I just reuse the surface color for the transparency? Or
> something else, like white or black?

I guess you mean the `translucency` setting.

No, use neither the pigment colour nor black.

This is actually not a colour /per se/, but rather a value related to
the average distance a photon will travel inside the material before
being absorbed/scattered/both (can't remember the exact interpretation
off the top of my head), which can be specified differently for the
three colour channels (R,G,B).

There are no limits to the setting -- particularly translucent materials
might have values like <10,10,10> or even higher, while "dense"
materials might have values like <0.1,0.1,0.1> or even lower.

I'd start at <1,1,1> and see how it looks. If the material appears too
waxy, reduce the value. If it appears too "hard", increase the value.


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From: Mike Horvath
Subject: Re: Subsurface scattering
Date: 5 Feb 2018 22:33:30
Message: <5a78dbba$1@news.povray.org>
On 2/5/2018 11:43 AM, clipka wrote:
> Am 04.02.2018 um 07:59 schrieb Mike Horvath:
>> Does POV have this feature yet, or is it still just an Uberpov thing?
> 
> It never was an UberPOV-only thing in the first place ;)
> 

I think I've been confusing two entirely different features. What I've 
been trying to achieve is *blurred reflections*, not SSLT. Are they 
related? I got confused because my old Uberpov scenes tried to do both. 
But blurred reflections are still an Uberpov-only thing right?

Mike


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From: clipka
Subject: Re: Subsurface scattering
Date: 6 Feb 2018 13:53:13
Message: <5a79b349$1@news.povray.org>
Am 05.02.2018 um 23:33 schrieb Mike Horvath:

> I think I've been confusing two entirely different features. What I've
> been trying to achieve is *blurred reflections*, not SSLT. Are they
> related?

No, not at all. Essentially the only thing they have in common is that
they both are stochastic algorithms and as such create a bit of pixel noise.

> But blurred reflections are still an Uberpov-only thing right?

Yup.


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From: Kenneth
Subject: Re: Subsurface scattering
Date: 7 Feb 2018 02:00:00
Message: <web.5a7a5cacff8943e7a47873e10@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:
>
> Here are my global_settings:
>
> global_settings
> {
> [snip]
>
>  subsurface
>  {
>   samples 5, 5
>   radiosity true
>  }
> }
>

I have only limited experience with SSLT so far, but your samples count should
be much higher (try 100,100); otherwise you'll still see some linear-like
stochastic noise or blotches. I *think* the noise appearance has no relation to
the size of the object or its distance from the camera; it shows up as the same
'size' in the render no matter what.


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From: Alain
Subject: Re: Subsurface scattering
Date: 8 Feb 2018 21:15:48
Message: <5a7cbe04$1@news.povray.org>
Le 18-02-06 à 20:55, Kenneth a écrit :
> Mike Horvath <mik### [at] gmailcom> wrote:
>>
>> Here are my global_settings:
>>
>> global_settings
>> {
>> [snip]
>>
>>   subsurface
>>   {
>>    samples 5, 5
>>    radiosity true
>>   }
>> }
>>
> 
> I have only limited experience with SSLT so far, but your samples count should
> be much higher (try 100,100); otherwise you'll still see some linear-like
> stochastic noise or blotches. I *think* the noise appearance has no relation to
> the size of the object or its distance from the camera; it shows up as the same
> 'size' in the render no matter what.
> 
> 
The dafault values are 20, 20. You can reduce that if you can live with 
some graininess. In my experience, something around 10 to 15 tend to 
give acceptable results.
If you have very low translucency, or very large relative to the size of 
the object, you may be able to get away with smaller values.
Also, when taking radiosity into account, you probably need to take more 
samples.


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