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Fess
07-13-2009, 10:47 PM
Hello everyone,


I'm yet again solving another production problem, need some help regarding FG flicker:

Animation here (http://www.mohan-conceptual.com/lglass_flicker_problem.mov)

http://www.mohan-conceptual.com/lglass_flicker_screenS.jpg



MR Settings & lGlass Settings:

http://www.mohan-conceptual.com/lglass_flicker_problem.jpg


The ground had tons of FG flicker but was curb with the below workflow..

FG tuning done:

-Enabled the Optimize for Animations option
-Set the Render Mode to render final gather maps ONLY. (FG map "rebuild" is "off")
-Set the scene to render every 4 frames of animation.
-Render....
-Set "Rebuild" to Freeze
-Set Render Mode to full
-Fully render the scene.

This helped with the ground, but the ice is a no go. Using the l_glass-v2-beta2

EDIT: also using a spot light with "Linear" falloff and raytraced shadows with a ray depth limit of 2.

Any input on how to make that ice/glass stop FLICKERING :banghead:

Appreicate any help..
-J

techmage
07-14-2009, 04:14 AM
kinda hard to tell without seeing a video

But I would assume that your glass shader is refracting portions of your scene in which final gather rays are not touching. Because the final gather rays actually will shoot trough your refraction and land upon the surface that is being refracted. If you check the 'enable map visualizer' in final gathering map options, then do a render, it will show you dots in your viewport for the FG points and you can see how the FG points refract through your object and land all over the place.

So if your rendering every 4th frame, these rays are shooting through your object and flying out every which angle. Which when your inbetween those 4th frames, there might be no FG points on the surfaces your ice is refracting since the angle of refraction can be going every which way. Then you get uneven lighting.

What I would do is, after you comptue FG for every 4th frame, set the rebuild mode to off. This will make it append new FG points onto your FG file from your new renderings. Then fly over to your ice, and do a render pointing each direction away from your your ice. So that you get FG points on all the terrain surrounding your ice, from the point of view of the ice, so then FG points are on all the surface it could be refracting. Set it back to freeze and render your animation.

If you turn on enable map visualizer, it will help you see this and understand it and lay out your FG points where necessary. Usually when you do this type of thing, you do have to set rebuild mode to off and do a few extra, manually placed, renders here and there to get FG points where the every nth pass missed.


Either that or, the refractive samples on your ice themselves are flickering. In which case you either gotta turn up the AA samples, or slightly blur your refraction.

Fess
07-14-2009, 05:03 PM
What I would do is, after you comptue FG for every 4th frame, set the rebuild mode to off. This will make it append new FG points onto your FG file from your new renderings. Then fly over to your ice, and do a render pointing each direction away from your your ice. So that you get FG points on all the terrain surrounding your ice, from the point of view of the ice, so then FG points are on all the surface it could be refracting. Set it back to freeze and render your animation.


Ryan, thanks for responding.
Interesting way to manipulate FG in your suggestion. :applause:

I will give it a shot & keep you updated.

-J

mhartle1
07-15-2009, 05:13 AM
I don't think you are seeing FG issues in this...

If it was an issue, the first thing to look at is what the scene scale is set to... People tend to create their entire scene inside of the default grid, in the default scale setting, which is centimeters. FG is a physically based calculation, so your scene needs to have at-least some relativity to the real-world scale you are approximating. If you did create the scene inside the grid, and you could not scale it, then you would just have to use a ton of fg points to get ride of the flicker, or you would have to bake it, ect.

However, you not having FG issues I don't think. Outside of general flickering over all surfaces, which you don't have, you would see flickering at the points of contact between neighboring pieces of geometry, which you also don't have.

You issue is aliasing. The ground itself if swimming all over the place. This is most likely correctable by using a lower contrast threshold. Right now you have it set to .1 in your pictures, and that's way high for a final production level render with textures that have a lot of noise, which yours do. So try to lower this setting to .025 or .01 and see if that does not help the ground. If it doesn't, you may have to do some texture filtering to solve it. You can use elliptical filtering by setting your file texture to mipmap, then under the mental ray tab on the file texture, turn on filtering. Try the default settings first. This will make your render take much longer, but it will eliminate the type of swimming that you have.

As for the glass. That is mostly likely an issue with the min/max sample level setting. A setting of 0 and 2 is high unless you have highly reflection/refractive surfaces in your scene, which you do. So you need to set this setting much higher to solve this issue. I would try setting max to 3 or 4. If you don't want to do crazy super sampling on the entire scene, then you can do it on a per object level by adjusting the min/max sample levels on the object itself.

Hope this helps.

-m

Hamburger
07-15-2009, 02:22 PM
your final gather is fine, it's not fg thats causing the flicker. it's just the sampling.

try the gauss filter. Mitchell is sharp and great for stills but guass is nice and smooth and helps alot in these situations.

yes, it will be more "blurry" but if you render it out in 16bit you can apply a nice unsharp mask filter in your compositing program that'll get you a sharper pic. your audience will notice flickers more so than "blur".

Fess
07-20-2009, 03:32 AM
@ HamburgerTrain:
Interesting technique. I did not have to apply it, but will archive your suggestion in case.


@mhartle1:
I applied the higher contrast threshold as well as the elliptical filtering and the swimming has been resolved. The sampling increase for the flicker was not as successful, I'll give rygoody's suggestion a go to this scene.
animation here (http://www.mohan-conceptual.com/noSwimming.mov)


@rygoody:
The suggested method for manipulating the FG by doing some rogue shots pointing in various directions seemed interesting, I tried it on another "Hero" shot scene and the flicker was gone.

Thanks again everyone!! :beer:

-J

Fess
12-31-2009, 09:49 PM
lGlass was a pleasure to work with, thank you:

http://forums.cgsociety.org/showthread.php?p=6275932

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