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clipka nous illumina en ce 2008-12-17 19:29 -->
> "Colin" <nomail@nomail> wrote:
>> So what I'm looking for is if you were tracing photons, how many per unit area
>> strikes a particular position on a surface. We usually measure this in things
>> like W/m2 or lux (lumens/m2).
>
> That's basically what an orthographic shot of the surface with photon mapping
> will give you: A bitmap specifying how many photons have hit which point.
>
> If you crank up the number of photons high enough, you can probably get any
> precision you may need.
>
> (At least if you make sure that gamma correction is turned off, and your light
> brightness has a proper brightness to represented by the output image format
> you choose.)
>
> To my knowledge, the principle behind this is extremely simple: PoV will shoot
> photons, remember where they hit, and increase the brightness of the object
> accordingly.
>
>
> The only problematic thing with this might be if the light source itself is
> directly visible from your "test surface", as you want to eliminate the (most
> likely not really exact) conventional lighting. I don't know by heart whether
> you can turn off conventional lighting completely and just use photon mapping.
You can. Set ambient to zero. Make sure that the light_source never encounter
the target plane in the visible area. A way to do that is to have a transparent
object in front of the light_source, a whide and thin box with pigment{rgbt 1}
will do just fine.
>
>
> A more brute-force attempt would be to do the same thing with radiosity, which
> basically does the very same thing "backwards" and should lead to the same
> results given extremely high-quality settings), but is probably a waste of
> computing power for this application.
Radiosity would need a insane count, larger than the 1600 maximum.
>
> If it cannot be helped otherwise, it would always be possible to do something
> with the trace() function, but something built-in will most likely be a lot
> faster.
>
>
>
--
Alain
-------------------------------------------------
You know you've been raytracing too long when you think 80s movies have the
funniest special effects.
Aaron Gage a.k.a Slartibartfast
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Alain <ele### [at] netscape net> wrote:
> > The only problematic thing with this might be if the light source itself is
> > directly visible from your "test surface", as you want to eliminate the (most
> > likely not really exact) conventional lighting. I don't know by heart whether
> > you can turn off conventional lighting completely and just use photon mapping.
> You can. Set ambient to zero. Make sure that the light_source never encounter
> the target plane in the visible area. A way to do that is to have a transparent
> object in front of the light_source, a whide and thin box with pigment{rgbt 1}
> will do just fine.
I'm not sure how this will stop the classic lighting from the light_source, as
the object will not cast a shadow. And using an opaque "light block" will also
block photons.
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