View Full Version : Global Illumination Flicker?

05-25-2003, 07:11 PM
Kind of a newb question but here goes..

I keep reading here and ther that: LW produces a flickering effects in animations that use GI? Is this right? Can someone explain this more or show me an example. I just rendered out a camera flyby animation of an object lit with GI (specifically HDRi imageworld map) and I don't see this. Can anyone explain more or link me to more info?

This seems like it would be a serious handicap for anyone wanting to light with GI. PLease tell me this isn't true


05-25-2003, 08:02 PM
You usually get a flicker when moving lights around.

05-25-2003, 08:10 PM
The radiosity sampling will shimmer very noticeably if you have the settings turned down. Generally Noise Reduction and/or having dithered motion blur gets rid of most of it.

If it's a still scene and nothing is moving then you can turn on "cache radiosity". That will also get rid of any flicker.

If you are not getting flicker then I wouldn't worry as long as you can handle the render times.

05-25-2003, 10:42 PM
thanks much for the info guys. Just good to know that it's not an unavoidable problem. btw-just for knowledge sake, does the flickering appear as a quick changes in overall light level or is it localized somewhere. Can you think of a quick way to replicate it? move the lights?

05-26-2003, 08:05 AM
That's possible. I've only had that when the radiosity settings very low, so that on one frame the sampling finds a very bright spot in your geometry that illuminates the surroundings, and then the following frame it misses this bright spot.

You might also get the lights on - lights off effect from using HDRI image world for the same reason. Generaly they are ok but a few images that are very hi res or just very noisy you might want to blur the image in the Image Editor with an FPblur.
This also cures the speckles that are sometimes apparent when using HDRI images with Image World.

05-26-2003, 09:36 AM
Thanks again for the info and help Mattoo.

05-27-2003, 05:33 AM
Originally posted by Mattoo
. . . you might want to blur the image in the Image Editor with an FPblur.
This also cures the speckles that are sometimes apparent when using HDRI images with Image World.

ahhhh, that really bugged me and stopped me using HDRI, might give it a go again!


05-27-2003, 09:33 AM
Reminds me of another q:
Besides the excessive render times, is that why people don't use radiosity (and/or hdri lit) in animation? Does anyone? If so, any good examples?

Meni's anim "the freak" looks great. What did he light with?

05-27-2003, 02:08 PM
People do use radiosity in production. Although I can't think of any examples off the top of my head that you might have seen.

To speed up production time Meni used surface baking to the best of my knowledge.
Another way is to render in passes (what I normally do), for instance. Much of the background might be quite complicated and render intensive, especally with radiosity. It's often best to render just a still of the background and composite in any moving elements afterwards, such as characters, or the leaves of a tree blowing in the wind.... etc

The other thing I've found is that plain surfaces show up the radiosity noise much more than textured surfaces. Try to avoid plain surfaces and that way you get away with having your radiosity sampling set lower than you might otherwise have to.

05-27-2003, 05:30 PM
Using motion blur (even if there's no fast motion) smoothes the flickering quite well. And then there's always the possibility to fake GI with i.e. spinning lights trick...

05-27-2003, 06:22 PM
Does motion blur really fix it that well? IF so, does everyone know about this? Or is it that the time hit is just as long as higher ray samples?

Hey as long as I got your ear, I haven't tried your pak yet, but I've seen great stills, which leads me to this Q:

How well does your pak (overcaster and other variants on the spinning light trick) work with animation? Got or can you point me to any good examples?


05-28-2003, 03:37 AM
Using AA with radiosity works quite well - you can use lower ray settings for better render times.

Here's a comparision image -


Spinnning lights work perfectly with animation - no flickering whatsoever. They *need* to have motion blur to work, but as more or less all animations (should) use MB, they don't add much to the render times (compared to same amount of "normal" lights).

For examples - i.e. this


uses an early nersion of overcaster / spinning lights. All the driving, modern F1 cars are 3D.

05-29-2003, 06:10 AM
Well, I'm now a victim of the flickering GI annoyance!

Just done an small animation using these settings:

Radiosity Type Backdrop
Rays Per Evaluation 6x8
Intensity 75%
Shading Noise Reduction On
Anti-Aliasing Enhanced Low

http://www.creactive-design.co.uk/temp/waterra.jpg (http://www.creactive-design.co.uk/temp/waterra.mpg)
click image to download mpg movie (980kb)

It was rendered using ScreamerNet over 3 Dual Xeon machines (total of 6 processors) would this have any effect on the flickering?

No lights move in the scene, the only things that move are the parts, so would upping the 'Rays Per Evaluation' solve this flickering?

I have to say, this flickering is a MAJOR drawback, I really hope NewTek do something about it on lower Rays Per Evaluation settings OR speed it up so you CAN use higher settings to solve it.

Otherwise it's useless.

05-29-2003, 08:54 AM
OK that is a perfect example of something we should be able to fix if the above suggestions are correct.

Damn, that animation look great except for the flickering of the shadows eh?

This does seem like a major drawback of LW. Someone please tell me this is fixable so I can sleep at night.

Matt, how about an example with motion blur on per Eki's advice (see above)?
Just a 1/2 a seconds worth will tell us.

How about another 1/2 sec test render with higher rays?

Crossing my fingers,

05-29-2003, 09:27 AM
Originally posted by Matt

It was rendered using ScreamerNet over 3 Dual Xeon machines (total of 6 processors) would this have any effect on the flickering?

To me it looks like one of the machines has rendered the scene differently from the others, rather than being the "regular" radiosity flicker problem. It looks like the "fuzziness" of the shadow fluctuates - just as if one of the machines has somewhat different settings on i.e. noise reduction.

Try rendering i.e. one second of the animation with just one machine - does the problem still occur??

If not, the problem is with your screamernet setup, i guess -

05-29-2003, 09:28 AM
Oh, great work, BTW.

05-29-2003, 09:34 AM
That's a good point Eki. I've seen the GI flickering first hand on my friends recent animation and it looks a little more like someone turning a light switch on and off again (if I remember correctly).

If it were the dreaded "GI flicker", wouldn't we see it as a quick and repetitive change in the brightness of the model's diffuse channel also (in matt's animation)?


05-29-2003, 10:36 AM
Thx! :)

I've not finished texturing this scene yet, and the motor on the back needs switching with a more detailed version.

(All modelling done in SolidWorks btw, not LightWave, clearly the rendering is!)

I was wondering if screamernet might have caused some problems; the machines are all Dell dual xeon processors, apart from the fact that two of the three machines are 2.4ghz and the other 2.0ghz they are all identical.

I HOPE that isn't the cause of the flickering, otherwise I can never use GI with our render setup, how totally crap is that!!!

Besides, look at the front casting, there's a few procedural textures on that and they're rock solid.

I thought the issue with textures etc changing on different processors was down to how the processor math calculated random numbers and the like, GI surely is just straight normal math?

I'll try the anim again with:

1) higher rays

2) Motion blur

3) Single machine

I'll post the results as soon as I have them!

We'll nail this yet!!!


05-29-2003, 10:46 AM
It could be one of the machine on the screamernet hasn't got it's configs, or that its configs are slightly different?

Dithered (it has to be dithered) Motion blur will make a huge difference. I never render an animation with GI without it.
6x8 rays should easily be fine aslong as you had dithered motion blur on. I frequently go much lower than that with Monte Carlo and it's fine.

05-29-2003, 11:20 AM
hmmmm, motion blur wasn't on, just to blow the different machine theory out of the water check this . . .

http://www.creactive-design.co.uk/temp/gi_flicker_small.jpg (http://www.creactive-design.co.uk/temp/gi_flicker_big.jpg)
click for large version

will continue with testing . . .

Arnie Cachelin
05-29-2003, 11:34 AM
I think you should make sure "Cache Radiosity" is off.

05-29-2003, 12:15 PM
My word the legend that is Arnie! Hi Arnie! :)

It is off, 'Backdrop Only' radiosity doesn't even activate that function, it's greyed out, it only comes into play when using 'Interpolated'.

05-29-2003, 02:04 PM
okay, done a quickie test rendering on the same machine:

http://www.creactive-design.co.uk/temp/waterra_anim_gi.jpg (http://www.creactive-design.co.uk/temp/gi_same_machine.mpg)
click for mpg movie (131KB)

It appears to be okay.

Please don't tell GI and ScreamerNet don't work together!!!

It can't be the scene file because all machines are loading the SAME one, the plugins are all the same because I copied them all from the source machine, they're all using the same config file (otherwise it wouldn't work at all).

The machines are:

1 x Dell Precision 530 (2.0ghz) Dual Xeon 1GB RAM

2 x Dell Precision 650 (2.4ghz) Dual Xeon 1GB RAM

It can't be the fact they they have different speed processors can it?

I could understand if one was a Pentium II and the others Xeon processors, but they're all pretty new machines, and all Xeon processors.

Has anyone else had GI flicker on renderings done over ScreamerNet?


05-29-2003, 02:25 PM
So Matt, those are the same settings as the orignal anim you post, except that you are just rendering on one machine?

You've haven't added more rays or dithered motion blur etc?

05-29-2003, 02:47 PM
It certainly sounds like you have something fishy going on with your screamernet setup. Radiosity should render across network just fine, if everything is set up correctly.

I suspect either bad config, or missing plugins on one of the nodes...

05-29-2003, 05:18 PM
Well I've been doing quite a bit of radiosity and spinning light stuff over screamernet recently and I haven't noticed any differences between machines.

But then, as I said, I usually do a few test (allways with dithered motion blur) until I can crank the radiosity down as far as it'll go before I get the noise crawling, then notch it up one for safety.

For instance, I rarely have to have the rays per evaluation above 6x18 (often 4x12) and tolerance set any lower than 2 - with Enhanced Low antialiasing and dithered motion blur. Noise reduction usually tops that off no problems.

05-30-2003, 03:22 AM
<original message modified due to user incompetence and now total irrelevance!!!>


05-30-2003, 03:41 AM
NO NO NO Noooooooooooooooooooooooooooooooooo!!!!


I can't believe I missed this!!!!

I copied the program files from my machine (7.5c) to one of the new machines,
but the other 'new' one I installed LW (7.5b) to check fast it was, totally forgot to update it to 7.5c!!!

Not checked this yet, but that's gotta be it!!!!!!

I dunno, didn't see the wood for the trees!!!

How can you ever forgive me? :)


05-30-2003, 08:15 AM
Give it a test and see for sure if that was it. I just want to know what the culprit was. I love to see problems go away, especially ones that keep us from making cool stuff. ;)

05-31-2003, 03:06 AM
will do, re-rendering over screamernet with 7 xeons!

will post when done . . . (just checking progress . . . on frame 120 of 299, knew I shouldn't have upped the rays and output size! It's taking ages!!!)

Hope they speed up GI in v8!

05-31-2003, 07:37 AM
I just noticed that you have some reflective stuff in there. Are you rendering with Raytrace Reflections on? I've found that they massively effect the speed of rendering.

Either turn that off and just use an environment map - or turn down the Ray Recursions in the Render Options to something like 4 or 5 (or less). That makes a huge difference especially with radiosity.

Apologies if any of that is obvious.

06-02-2003, 03:50 AM
yup, raytraced reflections is on (already turned down recursion limit) left it going over the weekend!!!

anyway, I can conclusively say that screamernet is okay with GI!

http://www.creactive-design.co.uk/temp/waterra_anim_gi.jpg (http://www.creactive-design.co.uk/temp/waterra2.mpg)
click for anim (1.7mb mpeg)

Phew, thank the Lord for that!