[Radiance-general] Effect of -aa parameter on Rpict Rendering Accuracy

[Nathaniel Jones]

Hi Andrei,

I'd add one more thing to Chris and Greg's comments. When you use a
non-zero -aa value, your ray paths that have gone through differing numbers
of bounces to affect the ambient lighting calculation. Thus, it may not be
a fair comparison to use the same -lr and -lw values for comparing -aa 0 to
-aa 0.01. Instead, you might need to choose a smaller -lw or possibly a
larger -lr for your -aa 0 simulation. I've tested a few scenes where I get
significantly more illumination by using a non-zero -aa value, all other
settings being equal, and I generally believe the non-zero -aa simulations
to give closer results to physically measured values.

Also, perhaps Greg can correct me on this, but I'm not sure if there's
anything to be gained by setting -ab larger than -lr when -lr is positive.

Cheers,

Nathaniel

On Thu, Aug 6, 2015 at 12:24 PM, Greg Ward <gregoryjward at gmail.com> wrote:

> 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 This same out-of-date text file sits in the ray/doc/notes directory of the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 <Christopher.Rush at arup.com>
>
> *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:
> andrei.kolomenski at nasa.gov]
> *Sent:* Thursday, August 06, 2015 10:35 AM
> *To:* Radiance-general at radiance-online.org
> *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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