Hi Andrei,
Chris has good advice regarding convergence testing, and the appropriate
parameter settings are really dependent on your scene and lighting
conditions. That said, there is a table that discusses various rendering
parameters and is a good place to start. Unfortunately, it is badly in
need of an update:
http://radsite.lbl.gov/radiance/refer/Notes/rpict_options.html
This same out-of-date text file sits in the ray/doc/notes directory of the
standard distribution.
The main thing to be aware of is that changing the -aa setting alone is no
guarantee of overall accuracy, since this parameter *only* controls the
indirect irradiance interpolation accuracy. If the indirect irradiance
values themselves are wrong due to a too-low setting of the -ad parameter
(for example), then improving the interpolation won't help you. This goes
for the other parameters as well. You can think of each as a link in a
chain. It would be great to have an overall accuracy setting, but that
would require a much more basic (and necessarily slower) calculation
method, such as naive Monte Carlo, to work.
Cheers,
-Greg
*From: *Christopher Rush <[email protected]>
*Subject: *Re: [Radiance-general] Effect of -aa parameter on Rpict
Rendering Accuracy
*Date: *August 6, 2015 8:12:46 AM PDT
Someone with better understanding of the math of it might hopefully chime
in, but my understanding has been that the phrase “and approximately
represents the error that is associated with it” – which I think is from
the manual page – may cause some undue concern. Similar to recommendations
for setting the other parameters, if you want test for stable results,
instead of jumping from 0.2 all the way to the extreme 0.01, you might try
0.15, 0.125, 0.1, 0.075 until you don’t notice any difference in your
results from one to the next. I think you mentioned testing various values
for –aa, and what change in results did you see? –aa will sometimes have a
stronger impact on rendering time than it does on your results depending on
the geometric scale of pixels/points you’re trying to discern accurately
from your image.
A second note, if you’re running –aa 0 you probably want –ps 1 and you
want to render an image several times larger than your intended result and
filter it down to reduce noise. I’m not sure of the numerical accuracy of
this technique but I think this is the usual recommendation. If you were
using rtrace for point calculations I suppose the noise introduced in –aa 0
is more visual and should be averaged out in the contributions as measured
at the point (if I’m thinking about it clearly), but maybe not if using
rtrace without the –I parameter?
Hopefully I’m not oversimplifying, and I make my comments hoping someone
will correct my misunderstandings and further expand on it.
-Chris
*From:* Kolomenski, Andrei (JSC-SF311)[WYLE INTEG. SCI. & ENG.] [mailto:
[email protected]]
*Sent:* Thursday, August 06, 2015 10:35 AM
*To:* [email protected]
*Subject:* [Radiance-general] Effect of -aa parameter on Rpict Rendering
Accuracy
Hello Radiance Community,
The –aa input argument to rpict controls the ambient accuracy of the
rendering and approximately represents the error that is associated with
it. I ran some tests varying the –aa parameter while holding all other
input parameters constant. To my surprise, the execution of a rendering
with –aa 0 took 1.6 hours and the a rendering with –aa 0.01 has taken 15
hours and has only finished 28%.
What is considered to be the most accurate rendering? One with no ambient
interpolation (-aa 0) or a low error interpolation (-aa 0.01) ?
Overall, what rpict input parameters that will produce the most accurate
rendering? Currently, I’m using the following parameter settings, for my
“truth” renderings that I’m assuming are as accurate as reasonably possible.
General Parameters: -lr 9 -lw 0.0005 -ps 4 -pt 0.05
Specular Parameters: -ss 2 -st 0 -as 256
Direct Parameters: -dr 3 -dp 1024 -ds 0 -dt 0 -dc 1
Ambient Parameters: -ab 11 -aa 0 -ar 256 -ad 2048
Please let me know if you think I’m missing some important parameters that
affect the rendering accuracy.
Thank you for your input,
Andrei Kolomenski
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