H.A. van der Meiden wrote:
> 
> Whilst expirimenting with the media feature, I've noticed something odd.
> 
> A media with absorption 1.0 blocks all passing light, given that the way
> of the light through the object is 1 unit long.

Actually, this isn't true.  There is an exponential fall-off of light
as it passes through the object : in a given distance, a given fraction
of the light is absorbed.  But over any finite distance, a finite
fraction of the light survives, subject to ADC bailout and color
quantization.

To see what I mean, increase the absorption to 100.  Now it comes
a lot closer to blocking all of the light.


> That makes sense.
> When adding emission rgb <0,0,1> one would expect the obstacle to appear
> uniformly blue.
> However, I've noticed that where the background contains more blue, the
> intensity of the obstacle is higher too. But the absorption 1.0 should
> have blocked all background light, no ?

No.  Note, as well, that the media INTERIOR is emitting as well as
absorbing.... so absorption 10 emission 100 will look different
than absorption 100 emission 10 -- in the former the emitter will
dominate while in the latter the absorber will dominate.
 
> I've created a small sample scene that shows this. It renders a
> background of red, blue and green hexagons, and a box with the described
> media.
> Comment away the emission value and the object will appear completely
> black (except for the edges). With emission, the blue hexgons in the
> scene appear brighter through the object.

This file is an excellent "intro" to media!  (I am a relative
newbie at them, myself.)  But commenting out the absorption
on my 3.1b6b results in a gray translucence, not black opaqueness.


-- 
http://www.flash.net/~djconnel/

Post a reply to this message