Alain <kua### [at] videotronca> wrote:

>
> >
> > I am wondering if this problem is solved? I am using double_illuminate scene and
> > found that the reflectance of the scene is underestimated (version 3.7.1).
> > Thanks in advance.
> >
> >
>
> double_illuminate is not physically acurate.
> Instead, I recomend using the new, as of version 3.7.0, back side
> illumination. It's activated by adding a second value for diffuse as follow:
> diffuse 0.5, 0.4
>
> In this case, 50% of the incomming light is diffused from the front side
> and 40% is diffused through the surface to the back side. Front and back
> been relative to where the light is comming from.
>
> Back side illumination is fully compatible with radiosity.
> It allow precise controll over the transmitted part of the incident light.
> Care should be made to ensure that the sum of the two components add to
> less than one if you want to get physically acurate, or at least
> plausible, results.

Thanks. I tested the back side illumination with radiosity. I am rendering a
scene with very dense leaves. The objective is to get the physically accurate
illuminace of each pixel. I set the assumed_gamma and file_gamma as 1.0. Then
this the pixel color is supposed proportional to the illuminace? However, it
seems the light does not propagate deep enough into the canopy (with radiosity
and side diffused light). When compared with the reference results achieved with
Monte Carlo method, the illuminace or reflectance is underestimated. I am
wondering this is because Pov-ray ignore some physical processes or I did not
set the right functions. Thanks again.

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