Thanks for yours answers! it is very nice to meet helpfull people!

I was thinking to use the method proposed by Chris. THere are still
technical problem that I have to overcome, but it is playable! I guess It
would be faster to create the image in povray and to analyse each pixel in
matlab.

It looks very strange to me, that it is not possible to re-create a virtual
goniometre. As I am working on textile texture and gloss, I want to compare
measurements to a simulated surface. I hope it is gonna be possible using
povray.

->to Trevor
I have no clue on Megapov. I am gonna look at it. But perhaps you could
explain the main advantage to use HDR image output/input?

Anyway, I will try to find something and I will let you know the result.
Greetings
Pierre


"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> "Chris B" <c_b### [at] btconnectcomnospam> wrote:
> > I don't know of any way of measuring the light that would be recorded by the
> > camera during the render.
> > However, once you have the rendered bitmap you could read the values for
> > each pixel and average them, which would give you an approximation of the
> > amount of light that the camera captured.
> >
> > You could probably do this post-rendering step using POV-Ray, by defining
> > the image as a pigment and using the eval_pigment function to find the
> > values of each pixel. You could then display the total or average value in
> > the message stream or you could use the value on a second pass at rendering
> > the scene (e.g. turn on another light if the first pass was too dull).
> >
> > Regards,
> > Chris B.
>
> This may be the best approach, however, the resulting image will be
> low-dynamic range, i.e., values greater than 1 will be clipped, giving you
> a false result.  Perhaps use this approach, but using HDR image
> output/input feature of megaPOV.  (I do something along the lines of this
> somewhat successfully for the HDRI environment lighting macro I've been
> working on for a while.)
>
> -tgq

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