Physical render random color shifts...

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Old 03 March 2012   #1
Physical render random color shifts...

We've done several projects using physical renderer in C4D, and in every one of them there have been random frames that have a completely different color range. For example, in most frames the mood is dark and contrasty as it should be, but then for one random frame, everything looks blown out. I thought it had to do with a net render glitch, but last night I ran a render on just my station.

In this animation the only animated object is the camera.

Notice how one of the frames is completely blown out and grainy.

What gives? We've had this issue on every project that has used physical renderer, costing us many hours of trouble shooting.
Attached Images
File Type: jpg correctColorRange.jpg (14.0 KB, 132 views)
File Type: jpg incorrectColorRange.jpg (22.9 KB, 123 views)
 
Old 03 March 2012   #2
So we've been running some tests, and it appears that motion blur in the physical renderer is causing this. Motion blur is the number one reason we are using the physical renderer.

This is really frustrating. Has anyone else had this issue? What are the work-arounds?
 
Old 03 March 2012   #3
Have you sent the file to Maxon tech support? They are very helpful and responsive in my experience.
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Old 03 March 2012   #4
is it possible to post a stripped down version of the file?
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Old 03 March 2012   #5
I have sent the file to tech support. We'll see what happens. Previously, on other projects, it was too difficult to strip it down.

I'll update this thread when I hear back from them.

Thanks!
 
Old 03 March 2012   #6
my initial suspicion was a computer on the farm with a weird LUT, but if your sure it's the motion blur causing it I'd look at when it happens, is is the first frame a specific computer renders? Which physical sampling mode is being used, fixed, adaptive, does baking animation help etc.
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Old 03 March 2012   #7
As I mentioned, this was rendered on a single station. I suspected net render at first also, but last night I rendered overnight on my station only, and the problem persists.

I'm gonna wait and have tech support look at it.
 
Old 03 March 2012   #8
Well I got a response from tech support, but they didn't really look thoroughly into the issue, as their answer does not make sense. Anyone here care to have a look at the file?


One of the frames that blows out is 488. Please render to picture viewer - frames 487 and 488 in the least, so you can see the difference.

Things I've tried: Turning motion blur off prevents the blow out.
Turning off the square spot light prevents the blow out.

If it were happening on every frame I would be able to blame it on one or the other...but it is randomly happening. (Well, random in the sense that I can't figure out why some frames are fine and others are not)

Tech support said it was the emitter with the lights in it blowing out the scene. I disagree. It may be contributing, but why only on certain frames?

Very frustrating to say the least. I think physical renderer has some major issues with color shifting and lights blowing out randomly. This has happened on other projects as well.
Attached Files
File Type: zip house_stripped.c4d.zip (55.9 KB, 22 views)
 
Old 03 March 2012   #9
Don't know yet what's causing it, but on my computer, your scene exhibits the same flash that you descibes on frame 488 with MB on.
 
Old 03 March 2012   #10
Thank you Eric for checking it out. I'm hoping to get several sets of eyes on this file and maybe at least be able to come up with a reproduceable bug that can be done in another file following certain steps.

We recently did another project that did not have emitted lights or anything out of the ordinary and there are several frames that shift color for no apparent reason. (Notice I say "apparent") I'm not totally ruling out user error here, but even so, it seems that there's more to using physical render than meets the eye...and certain things will just not play well together.
 
Old 03 March 2012   #11
I don't think tech support was totally wrong on this one.
when the light/particles are born/die they are getting a crazy movement...as if the particle ID changes...this would make the renderer think that the particle has traveled a great distance over 1 frame.

and if you look at when errors start cropping up, it seems to happen where most of your particle/lights are dying, around the 480 mark.

Try setting the particle life to be as long as the project.

I tested this over a trouble area and it seems to work fine.
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Last edited by chi : 03 March 2012 at 03:22 AM.
 
Old 03 March 2012   #12
I have noticed that brigtness values over a couple of hundred percent generate black clipping like spots. I had the same problem with a Sun reflection in water.

Don't know a fix for this, maybe dial down the brightness?
 
Old 03 March 2012   #13
Chi - Thanks so much for your time and for explaining what's going on here. So tech support was right only in that it involves the emitter in some way. However, why does the problem go away if you kill the square spotlight? If you leave the file as is (no change to the particle lifetime) but disable the square spotlight, the scene no longer gets blown out on frame 488. There seems to be more to the problem than meets the eye.

So, anyway, I think what you're saying is that the renderer thinks the particles are moving a great distance, and therefore the motionblur is randomly blowing out frames? Is that correct? I'd call this a bug. How do you have that information? How are you able to determine that the particle IDs are changing? I didn't realize you could do that with the standard emitter.

This color shift has happened in projects where there are no emitters at all. In one particular project, it is a COLOR shift, not just a brightness change in the lighting.

Physical renderer is BUGGY. Plain and simple.

Thanks for the work-around. I have extended the lifetime of my particles to compensate for this buggy behavior. However, what am I gonna do when I need to have a scene where my particles die DURING the scene?

By the way - if I sound negative...it's unintentional. I'm just trying to get to the bottom of this. I appreciate your insight!!


Last edited by interactiveBoy : 03 March 2012 at 01:37 PM.
 
Old 03 March 2012   #14
Originally Posted by chi: I don't think tech support was totally wrong on this one.
when the light/particles are born/die they are getting a crazy movement...as if the particle ID changes...this would make the renderer think that the particle has traveled a great distance over 1 frame.

and if you look at when errors start cropping up, it seems to happen where most of your particle/lights are dying, around the 480 mark.

Try setting the particle life to be as long as the project.

I tested this over a trouble area and it seems to work fine.


Yes, its certainly because of the ID-change of the particles. When particles die all other paticles get a new ID. Instead of letting the particle die you can assign them to another Paticle-group.
I used to have similar problems....now I allways usea "dead-particle"-Group.
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Old 03 March 2012   #15
Originally Posted by interactiveBoy:
Physical renderer is BUGGY. Plain and simple.



FWIW,
I rendered out frames 470 to 490 without any problems ...
v12 (without Physical renderer).
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