GI Flicker on ground from clouds

Started by MrHooper, April 13, 2010, 10:19:52 am

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chris_x422

I do a lot of animation, and have come across this situation many times now.

For me it's invariably a balancing act with the GI quality settings and GI blur radius.
I usually run a couple of tests to establish it's smooth rendering before going for a final render.

As a rule of thumb, the larger the area visible to the camera, the higher the blur settings need to be for smooth animation.

Also, when I absolutely have no choice, and have to deliver, I have been known to put the sequence through after effects or Nuke and render back out with frame blending.
It's got me out of a few tight situations after seriously heavy renders.

Hope that helps

Chris

Kadri

Quote from: chris_422 on April 27, 2010, 09:43:08 am
...
Also, when I absolutely have no choice, and have to deliver, I have been known to put the sequence through after effects or Nuke and render back out with frame blending.
...


Interesting all what you said , Chris . Thanks!

This  frame blending does it look like kind of a blur efect ?

chris_x422

QuoteThis  frame blending does it look like kind of a blur efect ?


There is usually a slight softening, but nothing dramatic as its interpolating between frames not applying any form of blur. (My clients and art directors never notice ;)

One shot recently, went thought several iterations of blending that also helped reduce flicker on some very distant clouds.
Again, no one noticed between my test frames and the animation that it had been through this process.


Kadri

Quote from: chris_422 on April 27, 2010, 11:50:42 am
QuoteThis  frame blending does it look like kind of a blur efect ?


There is usually a slight softening, but nothing dramatic as its interpolating between frames not applying any form of blur. (My clients and art directors never notice ;)

One shot recently, went thought several iterations of blending that also helped reduce flicker on some very distant clouds.
Again, no one noticed between my test frames and the animation that it had been through this process.



Clever  ;)
Thanks , Chris.

Oshyan

Just so you don't think I've forgotten, I am still looking into this. I could give you advice about a few settings in general, but so far I haven't quite eliminated the problem (it already seemed fairly minor). But for future reference, GI Supersampling is a good thing to try. Also higher GI Blur Radius settings. I'm testing a few other options now and I'll let you know if I come up with a complete solution.

Given the extremely high cloud and atmosphere samples needed here, you might just want to render clouds and sky separately and composite. You could render the sky with Raytrace Everything and get better quality with faster render time (but the terrain would look terrible, so it's really only applicable if you render elements separately).

- Oshyan

Oshyan

Alright, so I think I've essentially concluded my tests. While you can eliminate this by increasing GI Sample Quality and GI Blur Radius (for Blur Radius to something fairly high like 100-200), this will increase render time and generally give you less detailed GI. Since the flicker seems to mostly be on the ground and not in the clouds, the simple solution I discoved is to turn down "Strength on Surfaces" in the Enviro Light to 0. This does mean that GI will no longer affect the ground, and likewise that the ground won't reflect light onto the sky (I think). So it does change the "tone" and lighting of your scene. However from what I saw it should be fairly easy to adjust this in post, particularly with some tone mapping on the original EXR. The major differences I saw were darker shadows on terrain and an overall more blue tint than the yellow of the original. Both of these should be adjustable from the EXR.

You could also use a Fill Light setup with no GI, or use just a single fill light of radius small enough to not affect the clouds, simply to light up the foreground a bit and still keep GI on the clouds.

- Oshyan

Kadri

May 01, 2010, 07:28:46 am #21 Last Edit: May 01, 2010, 08:31:54 am by Kadri
Oshyan i doubt that what i am going to say will help in this position but...

Did you or anyone tried to render 2 times the size  you want to use and then shrink it ?

Of course you have to use some lower settings otherwise render times will be too long .
You have to choose a optimal level of settings for a 2X image.

In the past i heard that some users used this method for faster and better(?) anti aliasing in Lightwave .
As i said i am not sure if this would help on flickering in images or would be practical ,  just a thought !

Oshyan

I don't think that would resolve the GI flickering, although perhaps with a larger sampling area it would help? I doubt the render time cost would be worth it though. With having to reduce the GI detail (and overall detail) to save render time with the larger size, any improvement in GI would probably be a "wash" anyway.

- Oshyan

Kadri

Quote from: Oshyan on May 02, 2010, 12:38:02 am
I don't think that would resolve the GI flickering, although perhaps with a larger sampling area it would help?
I doubt the render time cost would be worth it though. With having to reduce the GI detail (and overall detail)
to save render time with the larger size, any improvement in GI would probably be a "wash" anyway.
- Oshyan


I think you might be right on this , Oshyan  . As i said i doubt it too, but it would be nice to have a test on this  :)

MrHooper

Thanks Oshyan, Chris and all,

I'm testing the new suggested settings now.  Thanks for all the info.  Very helpful.  I'm trying first, to mix a bit of all.  Increasing the blur radius and reducing (but not eliminating) the enviroLight's effect on surfaces to .5.  (also tuned the memory settings to be more reasonable.  We have a lot of ram here, so I suppose it never crashed for that reason?  Though even with the higher settings, it never went that high.  Anyway, I'll let you know what happens.  Also, I tried some frame blending, and that certainly helps... given there is so little motion in the scene, it may be the answer in the short term... but the scientist in me cant help but do some more tests.  We have a farm here after all!