clipka wrote:
> Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
>> In these discussions it would be nice to know how the "reference
>> renderer" handles this. Reference being MC-Pov.
> 
> Why would MC-Pov be qualified as a "reference renderer" in this case?

Cause it doesn't exhibit radiosity artifacts - only noise. I just meant
that I'd love to see POV-ray support unbiased rendering as opposed to
radiosity with all its shortcomings. The argument against path tracing
and similar methods is usually speed so I wonder how would a properly
implemented path Monte Carlo renderer do in this scene.

Post a reply to this message

"clipka" <nomail@nomail> wrote:
> Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
> > In these discussions it would be nice to know how the "reference
> > renderer" handles this. Reference being MC-Pov.
>
> Why would MC-Pov be qualified as a "reference renderer" in this case?

http://pagesperso-orange.fr/fidos/MCPov/MCPov.html

It's a megapov patch based on path-tracing and reportedly very accurate.  Very
slow too, but more accurate no doubt than current radiosity.

fidos developed it last year and I remember there were many interesting posts
with comparisons between path-tracing and radiosity, path-tracing giving very
accurate results, despite the noise still left and render times.  Here's the
relevant links, very interesting read anyway:

http://news.povray.org/povray.binaries.images/thread/%3Cweb.47a4a907a327f677ce311500%40news.povray.org%3E/?ttop=294498&
toff=500
http://news.povray.org/povray.binaries.images/thread/%3C47bde8f9%40news.povray.org%3E/?ttop=294498&toff=450
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4838403f151ae76dd309f1e00%40news.povray.org%3E/?ttop=294498
&toff=300
http://news.povray.org/povray.binaries.images/thread/%3Cweb.48429c2754fc510a2b3143ed0%40news.povray.org%3E/?ttop=294498
&toff=300
http://news.povray.org/povray.binaries.images/thread/%3Cweb.484d6237b20e507399bf01250%40news.povray.org%3E/?ttop=294498
&toff=300

Post a reply to this message

clipka wrote:
> Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
>> In these discussions it would be nice to know how the "reference
>> renderer" handles this. Reference being MC-Pov.
> 
> Why would MC-Pov be qualified as a "reference renderer" in this case?

Because it's closer to reality, at the cost of insane render times.

Post a reply to this message

Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
> In these discussions it would be nice to know how the "reference
> renderer" handles this. Reference being MC-Pov. In 1 hour the result
> might be quite good with a path tracer. At least if MC-POV implemented
> all known techniques to speed up the convergence.
>
> Severi S.

I am going to try it.  I am new to MC-Pov, but it *seems* to be working
correctly (i.e. black image with random white speckles after 2 minutes).  It'll
take me a while to know for sure, though...

I modified the scene a bit, though.  The version I grabbed from the other thread
had the reflective finishes commented out and some other alternative values
commented out for the specular components.  I put the reflection back into the
finishes, changed the global ambient_light to 1, and changed all textures to a
plain white pigment with diffuse of 1.00.  The normal statements are unchanged.

I am now sort of intrigued by MC Pov, particularly by the fact that the
algorithm could take advantage of multiple cores or machines.  It also makes me
think that, in the future, it might not be a bad idea for Pov to support more
than one possible global illumination method or light model that would be
specified in the ini file or global_settings block.



-Reactor

Post a reply to this message

Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
> In these discussions it would be nice to know how the "reference
> renderer" handles this. Reference being MC-Pov. In 1 hour the result
> might be quite good with a path tracer. At least if MC-POV implemented
> all known techniques to speed up the convergence.

Trying out a very similar scene in MC-POV, but at 1:30, I can tell you that the
1 hour result won't be worth posting.  Of course I can be very patient if I
need to, so no complaints here!  Speaking of MC-POV though, are there any plans
to include the montecarlo subsurface scattering?

 - Ricky

Post a reply to this message

"triple_r" <nomail@nomail> wrote:
> Trying out a very similar scene in MC-POV, but at 1:30, I can tell you that the
> 1 hour result won't be worth posting.  Of course I can be very patient if I
> need to, so no complaints here!  Speaking of MC-POV though, are there any plans
> to include the montecarlo subsurface scattering?

Well, here's the MC-POV version I did last night anyway.  It's about twenty
hours of serial time (divided by two cores) with a single point source behind
the wall, and a blue source inside the room.  The problem with MC-POV seems to
be that some effects end up over-sampled while others are very noisy.  I
haven't figured out how to control this well, yet.  Perhaps better portal setup
would fix the problem, but at the moment I think radiosity is the horse to bet
on for most scenes.  You do get nice sharp shadows with path-tracing, though.

 - Ricky

Post a reply to this message

Attachments:
Download 'test1.jpg' (66 KB)

Preview of image 'test1.jpg'

Very noisy, yes, but undoubtfully much more acurate.

So, we have 2 options so far:  noise and insane rendertimes or splotches and
high rendertimes.  Pick your poison.  :)

Post a reply to this message

"nemesis" <nam### [at] gmailcom> wrote:
> It's a megapov patch based on path-tracing and reportedly very accurate.  Very
> slow too, but more accurate no doubt than current radiosity.

Hehe - *current* radiosity is flawed, no doubt :)

Anyway: I guess I'll have a close look at that one, because it seems to be very
well suited to assess how a scene *should* look with radiosity.

I also think that some of the ideas may work well in radiosity, too.

Post a reply to this message

"triple_r" <nomail@nomail> wrote:
> The problem with MC-POV seems to
> be that some effects end up over-sampled while others are very noisy.  I
> haven't figured out how to control this well, yet.  Perhaps better portal setup
> would fix the problem, but at the moment I think radiosity is the horse to bet
> on for most scenes.  You do get nice sharp shadows with path-tracing, though.

To get my eyes off radiosity for a moment:

The over-sampling of some areas vs. remaining noise in others might be not too
difficult to control. The key would be to stop using a uniform number of trace
iterations, and instead stop tracing a pixel as soon as you are confident that
it is good enough. Or, to stay in the MCPov paradigm, instead of shooting a
fixed number of rays per pixels in each pass, modulate the number depending on
how confident you are about them.

As a confidence indicator, you can keep track of a statistical parameter like
the standard deviation for each pixel. If it has been low so far, chances are
it will continue to remain low, so a lower sample count should suffice for
them.

A less memory-consuming approach to drive this would be the standard deviation
of a "pixel neighborhood": If the pixels in some area currently deviate a lot,
chances are this is due to noise, so you may want to spend more computing power
on this area.


This might also make an interesting concept for the collection of radiosity
samples: Ditch the fixed count, and instead modulate the number of rays based
on the standard deviation encountered in nearby samples. A first coarse pass
could do an extremely high number of sample rays, which might allow it to pick
up small light sources.

Keeping track of the standard deviation for different directions could refine
this approach.

Post a reply to this message

"nemesis" <nam### [at] gmailcom> wrote:
> Very noisy, yes, but undoubtfully much more acurate.
>
> So, we have 2 options so far:  noise and insane rendertimes or splotches and
> high rendertimes.  Pick your poison.  :)

No splotches and moderate render times, that's what I'm aiming at :)

Post a reply to this message