[Bf-committers] Yafray export

[Arne Schmitz]

Am Freitag, 9. Juli 2004 22:02 schrieb Matthew H Plough:
> I disagree.  Wattage is a relatively useless way of specifying how much
> light is emitted.  It is a measure of the amount of energy (joules) used in
> a given amount of time (seconds).  It is not a measure of luminance,
> irradiance, or other interpretation of lighting intensity.  For example, a
> 25 watt incandescent bulb can barely be used for reading, while a 25 watt
> fluorescent is quite bright.  Since joules coming off of a black body of a
> given size is so far from intuitive that it prohibits further discussion, I
> suggest using lumens or another measure.  But that would require
> correlating the grid size with a real-life distance measurement, such as
> the meter.  I don't see a problem with that from a usability standpoint, so
> long as that distance can be user-set.

Ok, I can agree with this. Using some sort of lumen or such would be nice 
though. The real-life distances wouldn't be that much of a problem, I think, 
because the light power would have to scale with the size of the scene then, 
which is better than the current solution, in my opinion.

As Jonathan pointed out, there is a formula for converting blender's energy 
and distance term to a yafray value that produces the same lighting effects. 
So I think the best solution for now would be to incorporate this formula 
into the export code.

I'm thinking about this, because I'm currently implementing a (besides other 
hings) photon mapping renderer for my thesis which uses the same XML format 
as yafray for convenience. Calculating the power and number of photons to 
shoot is right now not straightforward given that blender only writes the 
distance value to the power attribute. Right now I assign the power manually 
in the XML file.

Arne

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