Le 18-04-06 à 13:27, IGM a écrit :
> clipka <ano### [at] anonymousorg> wrote:
>> You can model an ideal diffuser sheet using a patch primitive (such as a
>> triangle, an open mesh or a bezier patch*), and using the two-value
>> `diffuse` syntax, aka backside illumination, like so:
> 
> Is it possible also with simple objects like boxes? If not, why?

Not directly.
It can work in a radiosity scene where the second surface can get 
illuminated by the backside illumination.
It takes MUCH longer to render. You may need to increase the back part 
so that both components add up to more than 1.

> 
>> This tells POV-Ray that from all the light shining onto the surface of
>> the object, 60% should be reflected in a lambertian manner, i.e.
>> independent of the incident light angle and with a cos-law distribution,
>> while another 30% should be emitted on the other side, also independent
>> of the incident light angle and with a cos-law distribution.
> 
> Are photons needed for this effect?
Not at all
> 
>> Of course real-life diffuser sheets aren't ideal, as transmitted light
>> /is/ dependent on incident light angle, so if you need to model the
>> material more precisely, in its current form the backside illumination
>> is probably of little use to you.
> 
> May "fresnel" keyword help?
> 
> Thank you!!
> igmar
> 
> 

fresnel is for specular reflection that obey the fresnel equation/law, 
where the reflection depend on the angle of incidence and difference of 
IORs between the outside and inside of the object.

One way that /may/ possibly work could be to abuse the brilliance 
parameter in a way that was not intended.
Setting a large brilliance value may affect the backside illumination in 
some way. Do your experiment as I never tried that trick.
The default for brilliance is 1.

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