[Bf-committers] Realistic materials question (Farsthary)
Yves Poissant
ypoissant2 at videotron.ca
Mon Feb 23 23:55:46 CET 2009
From: <echelon at infomail.upr.edu.cu>
Sent: Monday, February 23, 2009 3:18 PM
> Modified Blinn-Phong model---> kd/PI + ks*(n+2)*(nor,H)^n/(2*PI) also
> have 3 parameters
This modified model already includes the normalizing of the specular
component. Now, all you need, is make sure ks+ks <= 1.0 the the equivalent
raytracing render. The path tracer will take care of that by itself with the
Russian roulette.
> what I mean is what are the ever needed material properties for a BxDF
> model? here I'm very open to ideas, suggestions,papers,links and so :)
For a BRDF, the ever needed material property would be roughness (two
roughnesses for anisotropy). From roughness (which is roughly the reciprocal
of the specular exponent), you would derive kd and ks for your russian
roulette. One simple way of deriving that would be Schlick "An Inexpensive
BRDF Model for Physically-Based Rendering".
> also I need good formulas for implementing tone mappers because path
> tracer images fall outside the (0,1) range.
While it is nice to have a tone mapping algo, you can run quite some mileage
with a very simple multiplier (for controling the exposure) followed by a
simple gamma correction. This simple scheme has the added advantage that you
don't have to wonder at the (sometime quite weird) idiosyncrasies of the
tone mapping algo. Whatever you choose, I would suggest you save your
renders to a floating point file format such as OpenEXR. Then, you can
experiment with different tone mapping algos. For the algos, here is a good
place to start:
http://www.mpi-inf.mpg.de/resources/tmo/
Yves
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