> Hi all,
>
> I was wondering if it is possible to create a photographic plate in POV-Ray? You
> could use this plate to create a camera obscura with upside-down image on the
> plate, or visualize the typical upside-down candle when using a lens.
>
> I guess not, reading on how POV-Ray works by casting rays from the origin of the
> camera to every pixel in its viewport. What I ask requires the inverse: casting
> rays from the light sources, and see if they happen to fall on the sensor.
> Obviously, the former one is faster.
>
> If not possible out-of-the-box, are there techniques to achieve this? I was
> thinking along the lines of putting a 'milk-glass' plane where the photographic
> plate, or sensor, should be.
>
> I just read about photon mapping
> (http://wiki.povray.org/content/Knowledgebase:Language_Questions_and_Tips#Topic_27).
> Would that be of any help for what I like to do?
Absolutely!
>
> Keywords, to know at least what to google for, would be handy.
>
> Cheers!
>
> Bart
>
>
>
>

You can use the photons feature. It uses forward ray tracing.

All objects to be seen will need to have some good amount of reflection, 
and it will need to be diffuse reflection achieved using averaged 
normals. Make the objects no_reflection to prevent inter-reflection 
unless the object is to be seen in a mirror. That will improve the 
rendering time.
All those objects will need to be made photons target with reflection on.
The light_source will probably need to be prety strong.
Try to use a lense as whide as possible. The more photons you capture, 
the beter the result.
You will probably need a prety small spacing like 0.01 or less, or a 
prety large count, like over 20000000.
Only use spacing OR count, not both.

Another way is with radiosity.
There are some stringent limitations:
The focal lenght must be short: less that twice the diameter of the lense.
The radiosity count must be large. No less that 400 in the best case if 
you want acceptable results. The longer the focal lenght, the more 
samples are needed. In some cases, count 1600 (the maximum value) is to 
small...
The rendering time will be long to very long.
The plus side is that you don't need to make the objects reflective.


Alain

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