Mental Ray FGM file question



I’m having some trouble understanding the FGM system in Final Gather. I’ve ticked the box to keep the same FGM file rather than rebuild, but it seems to be rebuilding every frame. Am I missing something? At first I thought maybe it only stores the FG data for the current shot, but this can’t be the case! I’m doing an animation and my plan was to do a big FG at 1500 samples or so then store it…

Any help is appreciated.



Have you turned Rebuild Final Gather Freeze or Off?If not,MR would rebuild FG map even if you have generated it.


Hi! Thanks a lot for your reply. Unfortunately I can’t find this option anywhere :S. The window I’m looking at is as follows:

I’ve searched in other areas also, and searched in the help file but I can’t seem to find this freeze option! If you could tell me where it’s located I’d be very grateful.



Oh,Im using mentalray for maya.Im quite a newbie in max.Hope someone can help u.


Oh right! It all makes sense now, I thought I was going crazy :). Thanks anyway.

Well, if anyone else has any ideas, please let me know!



It will be using hte FG cache but there will always be some calculation per frame. At least that’s how I’ve understood it… Also, do you really need 1500 samples? I’ve done renders with as little as 20 samples. This of course depends on your scene and lighting but still, you might be able to use fewer.


Yea I suppose I can! I was getting a lot of dirtiness in corners and so on, but 1500 is unnecessary; it was a dream amount! I guess I’ll keep pushing it up until I have something I’m happy with, and hopefully this will be around 400-500 max.

Thanks for your advice,


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