View Full Version : How effective are FG files?

08 August 2010, 12:23 AM
I have been trying to reuse FG calculations and getting some interesting results. My first attempt was to render a few frames of an animation with rebuild off and write to a file. Then set rebuild to freeze. This method gave me a lot of noise and interesting patterns. I then tried writing an FG file every 5 frames. The noise didn't happen as often but when it did, it was bad. The next thing I tried was to set rebuild to off and render the first frame in Maya then render the rest on the render farm (with rebuild still set to off). This seemed to work, giving me much better render times and no noise. Trying that method again, on a different project, I now am getting noise again. I was wondering what is the best approach to reuse FG in an animated scene (with moving cameras)? I am currently rendering stereo cameras, so I figured that there must be some way to reuse these calculations.

My understanding of reusing FG with rebuild off, is that the FG files are read and then MR fills in what is needed and then writes that to the file for future use. Is this correct? Would I be saving time for stereo renders?

I would post renders of this noise but it is all under NDA so it is not possible. Hoping that people have seen this before and have an idea as to what I am refering.


08 August 2010, 06:50 AM
Hey greg,

I "think" what you need to do is this:

You need a FG map that covers your whole set. You can either do this by having a seperate bake camera, or render ever 5/10 frames and merge the point clouds together (there's utility for doing this in the maya bin folder, something like fgMerge).

Then just reuse that map, and hopfuly that noise should go away.

Good luck!


08 August 2010, 09:56 AM
well you definitely shouldn't be getting any noise since the map should be frozen... you may know this but to make sure you cannot do this for animated scenes. the only thing that may move or animate is the camera or it'll go funky on you (no animated lights, objects etc). if the fg map misses any spots they should come out black-ish maybe with a rough edge but any noise should be static. if the noise is moving then something else is wrong. just make sure to get everything that will be visible into the map with pre-renders with rebuild off.

08 August 2010, 12:21 AM
With the tests I have done, the noise is on animated characters. It is a weird blotchyness. My assumption was that with rebuild to off, MR would fill in the rest. Even animated objects. But it seems that is not the case. I am noticing with 2010 there arn't many ways to optimise renders (especially FG) for stereo.


08 August 2010, 01:34 AM
if you want to get really tricky, you should be able to reuse the fg data from the left camera on your right. Basicly, bake out all the fg to a file in the left camera, and then read that in as your fg in your right camera. You might need to bake it out a little wider to cover the disparity though.

08 August 2010, 07:01 AM
you almost certainly can't re-use fg maps on animated characters i'm afraid =\ they'll keep moving off the samples you've already calculated and when MR recalculates for that geometry (if it even does) it won't be exactly the same as the previous samples for that geometry which is probably the noise you're seeing. for animation it's just safer and easier to calculate every frame. with the amount MR would have to recalculate I don't know how much time you'd be saving anyways!

08 August 2010, 07:04 AM
As Nick suggested you can render fg points for every 5 to 10 frames, but I guess you need not do a fg merge for maya 2009 onwards. ( this is certainly not for animated characters)
I guess from Maya 2009 onwards you can use multiple fg maps from the render globals itself.
You need to add one primary map and then you can append more secondary maps in the render global itself.
Also I loved the idea of baking a wider fg map from the left camera and apply it to the right.. nice idea there ..

08 August 2010, 07:51 AM
using prman at the moment, and it has a nice feature where it dices a little more geo than it needs for the left camera, and uses the extra data to generate the r camera. So you get left and right from one render, nice.

08 August 2010, 09:19 AM
That seems to be a really cool feature....

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