POV-Ray : Newsgroups : povray.general : Highlight vs. reflected lamp dilemma : Re: Highlight vs. reflected lamp dilemma Server Time
17 May 2021 18:42:52 EDT (-0400)
  Re: Highlight vs. reflected lamp dilemma  
From: Alain Martel
Date: 2 May 2021 13:21:45
Message: <608edfa9$1@news.povray.org>
Le 2021-05-01 à 11:43, Cousin Ricky a écrit :
> What are highlights?  They are specular reflections, often blurred, of
> light sources.  So it dawned on me circa 2013 August 25 that if my
> objects have both reflection and specular/phong in their finish, they
> shouldn't also be reflecting the Sun or light bulb.  No prob, just set
> no_reflection on the looks_like for the time being.  For my desk lamp
> project, my idea has been to have a flag for whether or not the light
> bulb should reflect, thereby allowing the user to choose between
> highlights and a reflected bulb.
> Enter radiosity artifacts from lamp fixtures.  (See "Hooded lamp
> occlusion" in p.b.i.)  The inner surface of a lamp hood is so bright
> that radiosity leaves bright spots all over the scene unless an insanely
> high radiosity count is used.  Setting no_radiosity on the hood interior
> eliminates the artifacts, but now the light from that radiosity must be
> replaced.  A 180 degree cosine falloff spotlight does the trick.
> But now, this means that objects with both reflection and highlights
> will now reflect double the light from the hood interior!  I cannot set
> no_reflection on the hood interior, because then the texture of the hood
> exterior would show through in the reflection.  Besides, the hood is
> larger than the bulb, and the more extended an object, the bigger the
> morphological discrepancy between its reflection and the equivalent
> point highlight.  What was easy for the light bulb doesn't work for the
> fixture.
> So how should this dilemma be resolved?  Have the user refrain from
> setting specular or phong in finishes that have a reflection?  Just live
> with the double light, since it would most often exceed the image
> format's dynamic range anyway?  The former solution would require high
> quality (i.e, slow) blurred reflection for realistic highlights, and
> latter solution would be unsuitable for HDR and EXR images.  Is there a
> third way that doesn't involve the user in these complications?
> Or should I just go ahead with the reflection flag, and warn the user
> that the flag won't affect the hood interior?

For the radiosity case, you should use the latest version and benefit 
from the importance setting.
Do something similar to this :

#declare MXCount = 60000;
#declare AVCount = 100;

#default{radiosity{importance AVCount/MXCount}}

	radiosity{<some radiosity stuff>
		count MXCount, MXCount*1.5

For the object acting as your light sources, add :
radiosity{importance 1}

That way, the sampling count will average about 100 for most of the 
scene, but, those bright object will receive a lot of needed attention.

Also, using radiosity, you can add «brilliance on».
That way, objects with high brilliance will become reflective. That 
reflection will be blurred in a way similar to phong highlights.

When using blurred reflection, it's advantageous to have two copy of 
those objects :
Copy 1 have high quality, averaged, blurring. That copy need the 
no_reflection attribute. Also add no_radiosity to that one. Only one of 
the copies need to be taken into account when evaluating radiosity.

Copy 2 have rough, micro-normals blurring and have the no_image attribute.
Also adding no_shadow to one of the copy can help when evaluating the 

That solves the issue of self reflection causing an exponential 
explosion in the sampling.

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