POV-Ray : Newsgroups : povray.binaries.images : SSLT not working so well Server Time
23 Apr 2024 23:57:26 EDT (-0400)
  SSLT not working so well (Message 1 to 7 of 7)  
From: Mike Horvath
Subject: SSLT not working so well
Date: 5 Feb 2018 15:31:36
Message: <5a78bf28@news.povray.org>
Can anyone diagnose the cause of all the dirty marks on the materials? 
Lowering the translucency helped a lot, but I don't know if that's the 
actual cure or something else. Thanks.


Mike


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From: Mike Horvath
Subject: Re: SSLT not working so well
Date: 5 Feb 2018 15:36:52
Message: <5a78c064@news.povray.org>
On 2/5/2018 3:31 PM, Mike Horvath wrote:
> Can anyone diagnose the cause of all the dirty marks on the materials? 
> Lowering the translucency helped a lot, but I don't know if that's the 
> actual cure or something else. Thanks.
> 
> 
> Mike

Global settings:


	#if (Use_Radiosity = true)
		#include "rad_def.inc"
		global_settings
		{
			assumed_gamma	1
			adc_bailout		0.005
			max_trace_level	8
			ambient_light	0
			radiosity {Rad_Settings(Radiosity_Default, 1, 1)}
			#if (Use_SSLT = true)
				mm_per_unit		0.4
				subsurface
				{
					samples 5, 5
	//				samples 400, 40
					radiosity true
				}
			#end
		}
	#else
		global_settings
		{
			assumed_gamma	1
			adc_bailout		0.005
			max_trace_level 8
			ambient_light	1
		}
	#end


Surface finish:

   #declare lg_translucency = <0.01,0.01,0.01>;

   finish {
     ambient 0
     #if (lg_quality > 1)
       diffuse 1
       brilliance 1
       phong 1
       phong_size 40
       reflection { 0.025 falloff 1 exponent 1 }
       #if (Use_SSLT = true)
         subsurface { translucency lg_translucency }
       #end
     #end
     conserve_energy
   }


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From: Alain
Subject: Re: SSLT not working so well
Date: 5 Feb 2018 18:52:32
Message: <5a78ee40@news.povray.org>
Le 18-02-05 à 15:36, Mike Horvath a écrit :
> On 2/5/2018 3:31 PM, Mike Horvath wrote:
>> Can anyone diagnose the cause of all the dirty marks on the materials? 
>> Lowering the translucency helped a lot, but I don't know if that's the 
>> actual cure or something else. Thanks.
>>
>>
>> Mike

You need to increase the samples count.

> 
> Global settings:
> 
> 
>      #if (Use_Radiosity = true)
>          #include "rad_def.inc"
>          global_settings
>          {
>              assumed_gamma    1
>              adc_bailout        0.005
>              max_trace_level    8
>              ambient_light    0
>              radiosity {Rad_Settings(Radiosity_Default, 1, 1)}
>              #if (Use_SSLT = true)
>                  mm_per_unit        0.4
>                  subsurface
>                  {
>//                      samples 5, 5
// try this :
    samples 10, 10
// or this :
    samples 12, 8

>      //                samples 400, 40
>                      radiosity true
>                  }
>              #end
>          }
>      #else
>          global_settings
>          {
>              assumed_gamma    1
>              adc_bailout        0.005
>              max_trace_level 8
>              ambient_light    1
>          }
>      #end
> 
> 
> Surface finish:
> 
>    #declare lg_translucency = <0.01,0.01,0.01>;
> 
>    finish {
>      ambient 0
>      #if (lg_quality > 1)
>        diffuse 1
>        brilliance 1
>        phong 1
>        phong_size 40
>        reflection { 0.025 falloff 1 exponent 1 }
>        #if (Use_SSLT = true)
>          subsurface { translucency lg_translucency }
>        #end
>      #end
>      conserve_energy
>    }

You don't need "#if (Use_SSLT = true)". If SSLT is not enabled in the 
global_settings{...} block, then the subsurface{...} block have no 
effect and get ignored.

You should use reflection{0.025 fresnel}, or slightly higher, and set 
the IOR to around 1.5.
Just after the end of the finish block, add :
interior{ior 1.5}


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From: Mike Horvath
Subject: Re: SSLT not working so well
Date: 5 Feb 2018 19:57:40
Message: <5a78fd84$1@news.povray.org>
Good tips! Thanks!


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From: clipka
Subject: Re: SSLT not working so well
Date: 6 Feb 2018 04:40:22
Message: <5a797806$1@news.povray.org>
Am 05.02.2018 um 21:31 schrieb Mike Horvath:
> Can anyone diagnose the cause of all the dirty marks on the materials?
> Lowering the translucency helped a lot, but I don't know if that's the
> actual cure or something else. Thanks.

Due to its inner workings, SSLT /per se/ is prone to high-frequency
noise, that may sometimes exhibit a pattern. However, what I see in the
image appears block-ish (on the wide red wall) or blotch-ish (left sides
of the pieces making up the "DFC." writing), which strongly points
towards radiosity as the culprit.

Using more pretrace steps will probably help. Also, make sure to use
"always_sample off" (the default as of v3.7).


As for SSLT, at the size you're rendering, I doubt that subsurface
scattering will make much of a difference. Most LEGO bricks are not very
translucent. The lighting situation (comparatively strong diffuse
illumination from all sides, very few shadows visible) is also a
situation where SSLT would have little prominent effect.


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From: clipka
Subject: Re: SSLT not working so well
Date: 6 Feb 2018 08:57:38
Message: <5a79b452$1@news.povray.org>
Am 06.02.2018 um 00:52 schrieb Alain:

> You should use reflection{0.025 fresnel}, or slightly higher, and set
> the IOR to around 1.5.

For most LEGO materials, a refractive index of 1.6 is closer to the mark.


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From: Mike Horvath
Subject: Re: SSLT not working so well
Date: 6 Feb 2018 20:16:28
Message: <5a7a536c$1@news.povray.org>
On 2/6/2018 4:40 AM, clipka wrote:
> Am 05.02.2018 um 21:31 schrieb Mike Horvath:
>> Can anyone diagnose the cause of all the dirty marks on the materials?
>> Lowering the translucency helped a lot, but I don't know if that's the
>> actual cure or something else. Thanks.
> 
> Due to its inner workings, SSLT /per se/ is prone to high-frequency
> noise, that may sometimes exhibit a pattern. However, what I see in the
> image appears block-ish (on the wide red wall) or blotch-ish (left sides
> of the pieces making up the "DFC." writing), which strongly points
> towards radiosity as the culprit.
> 
> Using more pretrace steps will probably help. Also, make sure to use
> "always_sample off" (the default as of v3.7).
> 
> 
> As for SSLT, at the size you're rendering, I doubt that subsurface
> scattering will make much of a difference. Most LEGO bricks are not very
> translucent. The lighting situation (comparatively strong diffuse
> illumination from all sides, very few shadows visible) is also a
> situation where SSLT would have little prominent effect.
> 

Yeah, my mistake. I will turn it off.


Mike


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