View Full Version : How to get Flicker Free Animated Cached GI with Dissolving Objects?

07-03-2013, 11:28 AM
Baked Scene GI at 5 frame interval for a 300-frame industrial machine illustration anim with very slow camera-only movement. Various layers/objects need to be dissolved out to show internal operation in cut away fashion. The problem is when the dissolves begin, GI starts flickering on objects in close proximity to the one(s) dissolving. Why?

I'm not a compositing guru, so I don't know how to render each object out as a separate image sequence (solid, not dissolving, so seq. could be dissolved out in AE) in order to capture their direct interactions with surrounding objects... GI, cast shadows, reflections, transparency etc. It would just be SO much easier to do this as a single, in-camera pass... sans the GI flickering.

Ideas or easier, less intensive work arounds?

07-03-2013, 12:12 PM
Anything that changes light/shadow will cause pop/flicker... only static things work with caching properly... as you can see demo'd in the last section of this vid... http://www.youtube.com/watch?v=0YFZ2av-BLg

The commercial extra part on animated rad has a few different methods... but the easiest one for you to use here is to forget caching, and instead just use really high rpe/sbr setting with interpolation still on. This can give you a solution that both renders quick and minimises flicker.

07-03-2013, 12:43 PM
Thanks for reminding me of your video. Watched it not too long ago. Using 2 bounce interp. MC @ 800 primary, 20 secondary. Will up a bunch. Only problem... need to render a second or two's worth to see if animation shows flicker as the temporal domain is 1000 times more sensitive to "invisible" sploching in a still image. BTW, this is an exterior, daylight shot with ground and sky objects. Sky is unseen by rad. to prevent unwanted coloration. A second, unseen by cam sphere is textured with desired color cast and illumination for GI only.

07-03-2013, 01:54 PM
Groovy... In case u forgot sections of it, I recomend you watch again for your test rendering needs... there's the vid that explains how to find the min rays a given scene needs before running to extra bounces, which'll help you test and check faster.

stiff paper
07-04-2013, 04:59 AM
Render with and without and do a simple crossfade in post?

07-04-2013, 11:50 AM
I have your tuturial on CMIVFX RebelHill, and you demonstrate that GI cache only works with none moving objects.
My experience is if you don't use cache, the render time will build up. I have started to render sequenses where the first frame render in five minutes, while the last render in 35 minutes. (Before I stop the whole thing).
Do you have any solution for that?


07-04-2013, 12:23 PM
Nope... that happens if you DO use cache, but dont LOCK it... causing additional generation and evaluation of new samples. Using the high rays method, no cache... no such occurrence.

07-04-2013, 12:44 PM
Ok. Thank you


07-05-2013, 10:45 AM

Since it's the intra-frame change in sample loci of interpolated mode that causes flicker if cache is not used, wouldn't lowering MaxPS significantly help, too? True, your render times go up because there are fewer pixels btwn samples, thus more samples = lots more primary and secondary rays flying all over the place, but it should be faster than non-interp mode (where non-interp = 1 px min and 1 px max sample spacing), yes?

07-05-2013, 11:01 AM
yes, ofc... as u bring maxPS down to 1 you approach effectively a brute force solution (though it IS still interpolated a lil as true brute force still "sub samples" pixels during AA passes). In truth, either method will reduce flicker, but I think ull tend to find in most situations using the high RPE/SBR with a wider maxPS will give u better results, or faster than pulling ur maxPS way down.

Only way to know is to test render a bit with each. (note, do it limited region cropped round a problem area to get fast test render)

07-05-2013, 09:58 PM
Only way to know is to test render a bit with each. (note, do it limited region cropped round a problem area to get fast test render)

Palm to forehead again and again...

I wonder how many hours I have wasted doing test renders of flickering foliage without rendering a limited region "cropped round a problem area"... :bangwall:

Thanks for the tip RebelHill! :thumbsup: