Darkened Frames? - BMRT

Darkened Frames? - BMRT

Post by John Ferguso » Fri, 05 Nov 1999 04:00:00




>Hi All,

>I've encountered a wierd problem in an animation I'm trying to
>get rendered with rendrib. About 1 out of every 5 frames or so
>is approximately 20% "darker" than all the rest.

What method/script are you using to render the animation?  Try rendering the
frames 1 at a time, and don't say rendrib *.

John

 
 
 

Darkened Frames? - BMRT

Post by Larry Gri » Fri, 05 Nov 1999 04:00:00




>Hi All,

>I've encountered a wierd problem in an animation I'm trying to
>get rendered with rendrib. About 1 out of every 5 frames or so
>is approximately 20% "darker" than all the rest.

This has occasionally been reported for certain RIB files containing
many frames.  However, previously it's only been reported on Windoze,
which is very hard for me to debug since I never use it.

Quote:>I'm using the latest version of BMRT (2.4g), and I've tried it
>running under both Linux and Windoze, with similar results.

If this is really reproducable under Linux, can you tar up a complete
example (after reducing it to as small a scene as still exhibits the
problem) and send it to me?  I'd very much like to track this down
once and for all.

     -- lg

--
Larry Gritz                                     Pixar Animation Studios


 
 
 

Darkened Frames? - BMRT

Post by Michael B. Johnso » Fri, 05 Nov 1999 04:00:00



> Hi John,

> > >I've encountered a wierd problem in an animation I'm trying to
> > >get rendered with rendrib. About 1 out of every 5 frames or so
> > >is approximately 20% "darker" than all the rest.

> > What method/script are you using to render the animation?  Try rendering
> the
> > frames 1 at a time, and don't say rendrib *.

> Well, I had been just using "rendrib -safe anim.rib", but I'll
> try a frame-by-frame approach. If that works, what does it mean
> the problem was?  :-)

Someone sent me an example of this a few months ago, and at the time (which was mid-TS2, so my memory is fuzzy) I remember that I determined that it was a Windows only problem, or at least - happened on Win32, didn't happen on IRIX (the only two current BMRT platforms I have easy access to).  Due to schedule pressures, I'm afraid I let the bug drop and forgot to pick it back up.

What it might mean is that there is some variable initialization problem, where on IRIX things are getting zeroed out between frames, and they're not on Win32.  This could be an actual BMRT problem, or it could be a compiler bug.  

The smaller the example (i.e. simple geometry and minimal shader) the better chance we have of finding it.  Again, I know someone sent me such an example a few months ago, but I'm not sure what I did with it after I confirmed the existence of the problem.  If you're out there, feel free to drop me a line...

--

-->  Studio Tools, Pixar Animation Studios
-->  http://www.media.mit.edu/~wave

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Sat, 06 Nov 1999 04:00:00


Hi All,

I've encountered a wierd problem in an animation I'm trying to
get rendered with rendrib. About 1 out of every 5 frames or so
is approximately 20% "darker" than all the rest. By that, I mean
uniformly darkened, as though somebody has reduced the
intensity of every light source in the scene. It doesn't happen
periodically (say, to frames 1 6 11 ...), but apparently
sporadically, and I can't find a good reason for it.  :-(

I'm using the latest version of BMRT (2.4g), and I've tried it
running under both Linux and Windoze, with similar results.
The animation has a quite complicated file structure with
several different "ReadArchive"'s called, and it's also quite
large, so I can't post it to the list.

The scene uses mostly standard shaders from the BMRT
distribution, and spotlight light sources. I'm using radiosity,
3x2 pixel samples, and a 3x3 Gaussian pixel filter. The
radiosity calculations only distribute around 70% of the
light, but the amount distributed varies by less than 1% per
frame. I'm also "using" motion blur (there's a generic export
script + C utility I wrote for Blender that includes motion
blur), but the camera moves _very_ slowly, so I don't think
it should have noticable effects.

I can't think what's causing this. The light sources are the
same from frame to frame - they sit in a couple of files that
are read in for each frame. Has anyone else experienced this?
If so, what causes it, and how do I fix it?

Heeelllppp!!!  (BMRT crisis...)

--
Jonathan Merritt

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Sat, 06 Nov 1999 04:00:00


Hi John,

Quote:> >I've encountered a wierd problem in an animation I'm trying to
> >get rendered with rendrib. About 1 out of every 5 frames or so
> >is approximately 20% "darker" than all the rest.

> What method/script are you using to render the animation?  Try rendering
the
> frames 1 at a time, and don't say rendrib *.

Well, I had been just using "rendrib -safe anim.rib", but I'll
try a frame-by-frame approach. If that works, what does it mean
the problem was?  :-)

--
Jonathan Merritt

 
 
 

Darkened Frames? - BMRT

Post by jmo.. » Sat, 06 Nov 1999 04:00:00




Quote:> Hi All,

> I've encountered a wierd problem in an animation I'm trying to
> get rendered with rendrib. About 1 out of every 5 frames or so
> is approximately 20% "darker" than all the rest. By that, I mean
> uniformly darkened, as though somebody has reduced the
> intensity of every light source in the scene. It doesn't happen
> periodically (say, to frames 1 6 11 ...), but apparently
> sporadically, and I can't find a good reason for it.  :-(

> I'm using the latest version of BMRT (2.4g), and I've tried it
> running under both Linux and Windoze, with similar results.
> The animation has a quite complicated file structure with
> several different "ReadArchive"'s called, and it's also quite
> large, so I can't post it to the list.

I had the same problem in the past. I did not have time to try to figure
out specifically what caused it.  However, I noticed that it usually
happened when I tried to use both processors on a dual processor machine
(I had it occur on NT, Linux, and IRIX mips4).  It happened less when I
only used one processor. It seems that when the machine gets overloaded,
it occurs.  Interestingly the whole image is darkened, including the
alpha. For me it occured with both radiosity on and off.

-j.monos

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Sun, 07 Nov 1999 04:00:00


Quote:> If this is really reproducable under Linux, can you tar up a complete
> example (after reducing it to as small a scene as still exhibits the
> problem) and send it to me?  I'd very much like to track this down
> once and for all.

OK, so it seems I'm not to only person to whom this has happened.
I'll start cutting down the animation, and then send it off as
soon as I can. It might take a while, though, since the thing's
pretty big, and my exams start in 2 days... :-(

If anyone else has a small, prepared example, I'd suggest that
they send it to Larry first - it really is going to take a bit of
work to cut all the rubbish out of my animation, and it will
presumably require doing it bit-by-bit until I arrive at the
minimum "thing" which still causes the bug. Maybe John Monos
has a small example?

--
Jonathan Merritt

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Sun, 07 Nov 1999 04:00:00


Quote:> > If this is really reproducable under Linux, can you tar up a complete
> > example (after reducing it to as small a scene as still exhibits the
> > problem) and send it to me?  I'd very much like to track this down
> > once and for all.

> OK, so it seems I'm not to only person to whom this has happened.
> I'll start cutting down the animation, and then send it off as
> soon as I can. It might take a while, though, since the thing's
> pretty big, and my exams start in 2 days... :-(

Just an update:

I can confirm that when I tried rendering the darkened frames
individually (using "rendrib -frames x x anim.rib") they
brightened up, almost as much as I did upon making that
discovery. :-)

It sounds like this lends credibility to Mr Johnson's (or should
that be "wave's" - I've got no idea about protocol :^) suggestion
of some kind of variable initialization problem. I'll work on
creating a small scene to demonstrate the bug as soon as I have
time. How does BMRT handle rendering when it's called to do a
single frame, and how does that vary from the procedure used for
a whole animation?

--
Jonathan Merritt

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Sun, 07 Nov 1999 04:00:00


Quote:> > If this is really reproducable under Linux, can you tar up a complete
> > example (after reducing it to as small a scene as still exhibits the
> > problem) and send it to me?  I'd very much like to track this down
> > once and for all.

> OK, so it seems I'm not to only person to whom this has happened.
> I'll start cutting down the animation, and then send it off as
> soon as I can. It might take a while, though, since the thing's
> pretty big, and my exams start in 2 days... :-(

Just an update:

I can confirm that when I tried rendering the darkened frames
individually (using "rendrib -frames x x anim.rib") they
brightened up, almost as much as I did upon making that
discovery. :-)

It sounds like this lends credibility to Mr Johnson's (or should
that be "wave's" - I've got no idea about protocol :^) suggestion
of some kind of variable initialization problem. I'll work on
creating a small scene to demonstrate the bug as soon as I have
time. How does BMRT handle rendering when it's called to do a
single frame, and how does that vary from the procedure used for
a whole animation?

--
Jonathan Merritt

 
 
 

Darkened Frames? - BMRT

Post by Larry Gri » Wed, 10 Nov 1999 04:00:00




>I've encountered a wierd problem in an animation I'm trying to
>get rendered with rendrib. About 1 out of every 5 frames or so
>is approximately 20% "darker" than all the rest.

Somebody finally sent me a *simple* test that fails on all
architectures.  

See www.bmrt.org for an update -- 2.4h -- which fixes the bug.
I'm sorry, all the Unix versions are ready now, but Win32 will be
a couple more days.

Incidentally, the bug only affected multi-frame RIB files (if you
rendered one frame per RIB file, you were fine), and only when
PixelSamples were not 1.

        -- lg

--
Larry Gritz                                     Pixar Animation Studios

 
 
 

Darkened Frames? - BMRT

Post by Jonathan Merrit » Wed, 10 Nov 1999 04:00:00





> >I've encountered a wierd problem in an animation I'm trying to
> >get rendered with rendrib. About 1 out of every 5 frames or so
> >is approximately 20% "darker" than all the rest.

> Somebody finally sent me a *simple* test that fails on all
> architectures.

> See www.bmrt.org for an update -- 2.4h -- which fixes the bug.
> I'm sorry, all the Unix versions are ready now, but Win32 will be
> a couple more days.

> Incidentally, the bug only affected multi-frame RIB files (if you
> rendered one frame per RIB file, you were fine), and only when
> PixelSamples were not 1.

Yipee!!!!!!

Thanks to whoever that was! I wasn't looking forward to trying
to cut down my animation at all!!!  We have such great tech
support connected with this newsgroup: a bug reported 1 week ->
fixed in a software update the next. AWESOME!!! :-) :-) :-)

--
Jonathan Merritt

 
 
 

1. Splitting a frame over several procssors in BMRT?



Did you look at the "farm" script that comes with BMRT?
It's rather simplistic -- I wrote it in about 2 hours.
It just divides into crop windows, sends different ones off
with rsh, then reassembles the results.  I'm sure that any
halfway decent Perl hacker could spend a couple days on the
problem and come up with a much spiffier solution.

     -- lg

--
Larry Gritz                                     Pixar Animation Studios

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