Physical render random color shifts...

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  03 March 2012
Originally Posted by vid2k2: FWIW,
I rendered out frames 470 to 490 without any problems ...
v12 (without Physical renderer).

Right. It is a physical render issue
  03 March 2012
Originally Posted by HolgerBiebrach: 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 I allways usea "dead-particle"-Group.

How does one do this? I'm using the standard particle emitter. This is not thinking particles.
  03 March 2012

this is only possible with Thinking particles. Standardparticle can not be assigned to a particle group. You need to redo your particle-setup with TP I guess.
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  03 March 2012
Originally Posted by interactiveBoy: 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.

I guess from the information I had.
Flickers in the render, a frame range when they happen and then the tech support mention of the emitter I stripped the scene down to just those a cube so I could see brightness.

Then I tried a render with the visible light off...everything worked.

so it was a visible light in an emitter.

so I rebuilt the emitter in a new scene so that I could look at what was happening to only a few particles.

Then I rendered again.

When a particle/light dies I noticed that there is a blur between the light/particle that just died and another particle/light that was still living.

So this showed a shift in object IDs that it didn't know how to deal with.

so from there I started working toward towards a solution.

This isn't so much a bug as a limitation, I don't think they ever thought that the standard particles needed to have unique IDs when they were written 10+ years ago or however old the standard particles are.

As far as creating a particle that will likely need to stretch the brain and start delving into TP.

@ holger - I would be interested to see a screen of a "dead" group.
The views expressed in this post are by no means the opinion of those making the post or of any one person in particular.
  03 March 2012
Man Chi - Thanks for your breakdown. While I agree that it is a limitation in regards to the particle emitter...I still am dumbfounded as to why it is happening like it is when those emitted lights are so far away from where the blow out is happening in my original scene. Also, the problem goes away if you disable the square spotlight in my scene (the one called computerLight) You can leave the particles completely alone (don't change anything from the settings I have in the example file), and just disable the computerLight. The problem goes away. That's why I believe there is much more going on here.

Your research and solution will indeed get me a work-around for this exact issue, in this exact scene. Unfortunately this same type of issue happens in scenes that don't even have an emitter.

I'm on the verge of abandoning the physical renderer because of this.

I'm very thankful for your help.

  03 March 2012
so I just tried making a new scene with nothing but an emitter, visible lights and a cube as you did Chi. Indeed that shows a streak between two lights as a particle dies.

(nice find!)

However, the same does not happen if I change the particle to be a sphere with a luminous texture. (See attached images)

This limitation seems to only affect visible lights? Sorry to sound like I'm repeating myself here, but it is a bigger issue. Again, I'm thankful for the insight and the way you found a work-around...but there are more problems lurking under the hood.

Tech support gave me a response that only touched the surface.
Attached Images
File Type: png visibleLights.png (30.3 KB, 17 views)
File Type: png luminousSpheres.png (27.8 KB, 15 views)
  03 March 2012

looks like it is an issue with the lights in general.
killing a light causes all lights in the scene to shuffle around.

another workaround then might be to use a luminant disc for visibility + a light for illumination.

either way looks like an issue that couldn't really have been foreseen...but is unfortunate.

Phys. render is a growing beast and I still love it...even with it's quirks.
The views expressed in this post are by no means the opinion of those making the post or of any one person in particular.

Last edited by chi : 03 March 2012 at 09:38 PM.
  03 March 2012
If you did want to convert the solution to TP yuou coudl use a matric object set to generate thinking particles, turn off the dying and then use the die group
Quote: "Until you do what you believe in, how do you know whether you believe in it or not?" -Leo Tolstoy
Kai Pedersen
  03 March 2012
You guys rock. Thanks for your time looking into this.

I got comfirmation from tech support that this is a bug. I've offered to send them 2 other files that have similar/but different problems with color shifting on random frames with no emitters at all in the scene.

I'll start a new thread for that.
  03 March 2012
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