POV-Ray : Newsgroups : povray.advanced-users : Why don't shadows get blurry after a certain distance? ("Distance Field Sha= Server Time
17 Aug 2022 04:11:22 EDT (-0400)
  Why don't shadows get blurry after a certain distance? ("Distance Field Sha= (Message 11 to 12 of 12)  
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From: Alain Martel
Subject: Re: Why don't shadows get blurry after a certain distance? ("Distance Field=
Date: 6 Jun 2022 10:50:11
Message: <629e1423$1@news.povray.org>
Le 2022-06-06 à 03:46, And a écrit :
> "HackerDaGreat57" <Hac### [at] gmailcom> wrote:
>> "Bald Eagle" <cre### [at] netscapenet> wrote:
>>> "HackerDaGreat57" <Hac### [at] gmailcom> wrote:
>>>
>>>> Is it possible to change the 'Radius' of the point light? Like in Blender's
>>>> Cycles for example, there is an option to change the point light's radius which
>>>> increases the 'amount' of penumbra on my shadows.
>>>>
>>>> Thanks anyway for the useful reference though.
>>>
>>> Not in the way you're asking.
>>> But maybe another way.
>>>
>>> If you create a sphere with an emissive finish, then you could make a scene
>>> using radiosity, and that might work in the way you want it to.
>>>
>>> You can also add no_image to the object definition so that it doesn't show up in
>>> the scene, if it's in the camera's view frustum.
>>
>> That would, in fact, work like a charm.
>>
>> Do emissive materials count as light sources? (I'm concerned about the 127 light
>> limit)
> 
> You can use an object with texture{ finish{emission 1.0}} instead of regular
> light_source, when the radiosity turn on.
> But, you need very high radiosity quality settings, especially "error_bound", or
> you will get a very blurred shadow without accuracy created by radiosity.
> 
> The accuracy will establish when error_bound is very small. But at this time you
> need high "count" to eliminate spotted result.
> 
> 
> 
> radiosity{
>   pretrace_start 64/image_width
>   pretrace_end   4/image_width
> 
>   count 160
>   nearest_count 2
>   error_bound 0.28      // this should be smaller
>                         // if you use radiosity emission
>                         // as a light source
>   recursion_limit 4
>   low_error_factor 0.5
>   gray_threshold 0.0
>   brightness 1.0         // brightness 1 is natural correct
>   media off
> 
> }
> 
> 
> radiosity {} block place in the global_settings{}
> 

In a case like that, it's very interesting to use the importance feature 
of the latest versions.

It's used as follow :
You start by assigning a default importance weight to everything with a 
#default statement :
#declare HighSamples = 50000;
#declare AverageSamples = 75;
#default{rediosity{ importance AverageSamples /HighSamples }}

Then, for the objects to be used as light sources, you add :
radiosity{ importance 1 }
usually just before the closing brace or just before the texture definition.

In cases like this, I tend to also use the adaptive nearest_count :
nearest_count 20 3

#declare HighSamples = 50000;
#declare AverageSamples = 75;
#default{radiosity{ importance AverageSamples/HighSamples }}

global_settings{ assumed_gamma 1
radiosity{
  pretrace_start 64/image_width
  pretrace_end   4/image_width
  minimum_reuse 4/image_width-0.05

  count HighSamples
  nearest_count 20 2
  error_bound 0.2      // this should be smaller
                        // if you use radiosity emission
                        // as a light source
  recursion_limit 4
  low_error_factor 0.35
  media off

}
<other optional global_settings stuff>}

That cause the average number of samples used to be about 75 for most f 
the scene, but to be up to 50000 when sampling the area near the high 
emission objects.


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From: Thomas de Groot
Subject: Re: Why don't shadows get blurry after a certain distance? ("DistanceField=
Date: 7 Jun 2022 07:44:31
Message: <629f3a1f$1@news.povray.org>
Op 6-6-2022 om 16:50 schreef Alain Martel:
> 
> In a case like that, it's very interesting to use the importance feature 
> of the latest versions.
> 
> It's used as follow :
> You start by assigning a default importance weight to everything with a 
> #default statement :
> #declare HighSamples = 50000;
> #declare AverageSamples = 75;
> #default{rediosity{ importance AverageSamples /HighSamples }}
> 
> Then, for the objects to be used as light sources, you add :
> radiosity{ importance 1 }
> usually just before the closing brace or just before the texture 
> definition.
> 
> In cases like this, I tend to also use the adaptive nearest_count :
> nearest_count 20 3
> 
> #declare HighSamples = 50000;
> #declare AverageSamples = 75;
> #default{radiosity{ importance AverageSamples/HighSamples }}
> 
> global_settings{ assumed_gamma 1
> radiosity{
>   pretrace_start 64/image_width
>   pretrace_end   4/image_width
>   minimum_reuse 4/image_width-0.05
> 
>   count HighSamples
>   nearest_count 20 2
>   error_bound 0.2      // this should be smaller
>                         // if you use radiosity emission
>                         // as a light source
>   recursion_limit 4
>   low_error_factor 0.35
>   media off
> 
> }
> <other optional global_settings stuff>}
> 
> That cause the average number of samples used to be about 75 for most f 
> the scene, but to be up to 50000 when sampling the area near the high 
> emission objects.

This is very good advise! Note that you may have to crank-up your 
emission value way beyond 1. For a rapid test, I used emission 1000 
together with diffuse 1, for instance.

-- 
Thomas


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