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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}}
global_settings{
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
shadows.
That solves the issue of self reflection causing an exponential
explosion in the sampling.
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