Forest Pack > Forest Pro (*)

problems with flickering

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Kai:
I have been using billboard trees with forest pro but would like to make the change to 3d trees. In my initial tests I've been having a lot of trouble. Fist of all, backburner consistently crashes on every other frame. Thankfully it keeps restarting and the render eventually gets done.

My main concern is how to eliminate flickering. I'm using 3dsmax 2012 with mental ray and Forest Pro 3.6. I'm using forest color to create variation on the leaves. I've followed the guidlines on the best practices chapter of the reference manual. Are there other recommended settings in mental ray to avoid flickering?

Thanks,
Kai

iToo:

I'm not a Mental Ray expert, because for our scenes we use mainly VRay, but most of times the flickering is caused by Final Gather or by using low antialiasing values.

Here there are some links about this issue:

http://forums.cgarchitect.com/64329-mental-ray-onyxtree-flickering.html
http://forums.cgsociety.org/showthread.php?t=345991
http://www.mymentalray.com/wiki/index.php/Flicker-free_global_illumination

Also for VRay:

http://www.chaosgroup.com/forums/vbulletin/showthread.php?49584-VrayAmbientLight-to-reduce-GI-flicker&highlight=flicker
http://www.chaosgroup.com/forums/vbulletin/showthread.php?47561-Rendering-large-exterior-animation&highlight=flicker
http://www.chaosgroup.com/forums/vbulletin/showthread.php?45699-Antialiasing-for-Animations-with-Proxy-Trees
http://www.chaosgroup.com/forums/vbulletin/showthread.php?64193-Flickering-Shimmering-trees-in-animation&highlight=flicker

Sometimes it is very difficult to remove completely the flickering, even using high AA values. If you have After Effects, it is very helpful to apply a "Noise & Grain -> Remove Grain" filter.

jonavark:
If you will post your Mental Ray settings I think I may be able to help. I use MR and have conquered the flicker problem. Once under control it is a very nice render engine.

Kai:
hey, thanks for jumping in, I was pretty sure I'm not the only one to run into this problem. I've been playing around with the sampling and final gather settings but there must be something I'm missing. I attached an image with my mental ray settings.

I'm rendering a forest with just one 3d tree model created in onyx and converted to an editable mesh. I'm using arch and design materials on the tree and forest color in the diffuse channel of the leaves.

The surface terrain is using a mr matte/shadow/reflection material.

I appreciate any advice you may offer.

jonavark:
hmmm.. first thoughts..

You have soft shadows precision multiplier at 8. That's gotta hurt your render time and may be overkill.
I get great results with it set at 1.0

Sample setting of 4-64 might be a bit high as well. I get good results with 4/16. 64 is the highest I would usually go.

Instead of Triangle I use the Mitchell filter.

In "Project Points form Camera Position" the FG points actually move along the geometry as the camera moves. Think of it as a spray paint can moving across objects. Paint particles fall on whatever the camera is pointing to.

In "Project Points along camera path" the points are kind of stuck to the geometry at specific sections along the camera path. this works much better for animated cameras but

Moving trees, or other animated objects will flicker because Mental Ray is only projecting points for "n" segments in your camera move (9 is the default). You can increase that value if you are rendering a lot of frames but if your camera moves a lot it isn't necessarily true that FG points will fall on the geometry at the right places.

If you are rendering a complex scene it is helpful to render the environment and objects that are not moving with the "Project points along camera path" method and render the animation passes with "Project points form camera position". Then, in order to reduce flicker you have a few options, like interpolating between "n" frames from pre-calculated FG map files, which you can do using the "Reuse" rollout of the render setup | Indirect Illumination dialog.

If you want to get a better idea of what I am saying here google for Master Zap's Mental Ray tutorials. There is a set of videos that he has created available at some of those links that will really help.

Happy to try and answer any more questions you might have.

jona

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