[Radiance-general] ambient value and ambient cache interaction

[Charles Ehrlich]

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I just wanted to respond to this statement...

> Only computed ambient values live in the ambient cache, ...
 
This is somewhat true, but misses an important point.  
 
You can think about the -av ambient value as an estimated value for all of the ambient light in your scene that the ambient interreflection calculation can not "find."  It is applied to the "last bounce" of light during the ambient interreflection calculation.  The more -ab ambient bounces you have, the smaller its effect on the final value.  This is because the -av value is multiplied by the surface reflectance of each intervening surface beteen the "eye" and the "last bounce."  (If av=1.0, surface reflectance =0.5 and -ab 4, then effective  av=1.0*0.5*0.5*0.5*0.5=0.0625)
 
This has the effect of "seeding" the ambient value cache with the -av ambient value.  If the estimate of the ambient value is way off, then it will affect the ambient values stored in the cache.
 
-Chas

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<DIV>I just wanted to respond to this statement...<BR><BR>&gt; Only computed ambient values live in the ambient cache, ...</DIV>
<DIV>&nbsp;</DIV>
<DIV>This is somewhat true, but misses an important point.&nbsp; </DIV>
<DIV>&nbsp;</DIV>
<DIV>You can think about the -av ambient value as&nbsp;an estimated&nbsp;value for all&nbsp;of the ambient light in your&nbsp;scene that the ambient interreflection calculation can not "find."&nbsp; It is&nbsp;applied to the "last bounce" of light during the ambient interreflection calculation.&nbsp; The more -ab ambient bounces you have, the smaller its effect on the final value.&nbsp; This is because the -av value is multiplied by the surface reflectance of each intervening surface beteen the "eye" and the "last bounce."&nbsp; (If av=1.0, surface reflectance =0.5 and -ab 4, then&nbsp;effective &nbsp;av=1.0*0.5*0.5*0.5*0.5=0.0625)</DIV>
<DIV>&nbsp;</DIV>
<DIV>This has the effect of "seeding" the ambient value cache with the -av ambient value.&nbsp; If the estimate of the ambient value is way off, then it will affect the ambient values&nbsp;stored in the&nbsp;cache.</DIV>
<DIV>&nbsp;</DIV>
<DIV>-Chas</DIV>
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