Scattered Trees: Forced bitmap filter= none.....*massive* aliasing/shimmering. Help!

[JohnW3D]

Hi guys,

 

I posted this in the Vray forum too but thought it might be more at home here in reality. I have a bit of an issue with trees. I recently dumped using Vue for my trees when I realised the program was just a massive pain to use and doesn't integrate well at all with max (particularly vray).

 

I am now trying to scatter tree models (with a plugin called MultiScatter), which seems to be working well to get large amounts of low-medium quality (50-400k poly) trees rendering quickly. I am using trees that have alpha mapped leaves, and because of this I am forced to set the bitmap filtering from pyramid to none (if I leave this filtering on, my render times are something like 30 times longer and unsupportable).

 

Because this filtering is off, my trees go from being quite soft and pretty, to quite harsh and sharp. The result of a quick test render is huge huge shimmering/crawling.

 

My normal tactics for avoiding this kind of thing in animation would be to apply a bit of a softening filter, boost the AA a bit, and perhaps do a little DoF/motionBlur or something in post. In my test render I already had a slightly soften filter applied, and -1/2 Vray AA settings on Adaptive Subdivision (Vray), so I guess for production I would normally use more like 0/3 which may help a little.

 

My point is that there are only so many extra tricks I would normally apply, and my shimmering effect is just massive at the moment.....I see lots of animations with scattered trees where the trees look just perfect......any ideas on how I might start to achieve this?

 

I have uploaded the clip to youTube although I have to say the effect is far far less noticeable here than on the uncompressed video on my side.

 

http://www.youtube.com/watch?v=RhqMMNxEDRo

[Devin Johnston]

I can't tell without a closer view but could your alpha maps be inverted or not mapped properley onto the leaves? You need to make sure that all of the map filtering in your tree materials is set to none, that might be what's wrong.

[Tommy L]

I think the best way to do this is avoid transparency altogether. You say the trees are up to around 400k poly. As you are already up there with the polycount, just have the leaves as a mapped poly without transparency. Vray with multiscatter will be fine. I put a million x 20k poly trees in one animation and it was fine:

http://4.bp.blogspot.com/_0GCIc31NK6E/TG8F8S4F0xI/AAAAAAAAAOs/hPmVmTVHx2o/s1600/3d_map_005.jpg

 

Oh, avoiding transparency can really help in post as well with depth passes etc as they calculate correctly.

[beestee]

After viewing the video again, I am getting the impression that the indirect light solution may be part of the problem since the noise issue appears larger than the pixel level. Once you get such small geometry at this distance and then add to the equation the averaging properties of VRay's more efficient indirect lighting methods that will be bouncing relatively few rays around all of those faces, it becomes quite random how a leaf at that scale will solve from one frame to the next.

 

If you are using the irradiance map for part of your indirect lighting, try turning off 'check sample visibility' if it is not already. You can also test without 'randomize samples' to see if it gets you closer to what you are after.

 

Going for more refined computations will also help if my assumption is correct, but this will also proportionally increase render time.

 

And even with all of this AA could still be an issue, albeit a smaller issue, but still an issue.

 

The perfect solution would be Brute Force Universal Settings, but you are looking at much, much higher render times per frame...but I would bet those animations that you are comparing to your own may have been solved this way.

[JohnW3D]

Tommy L: Do you have a sample of your animation? I'd be interested to see it if so....were your full-geometry (no transparency) trees free of all major shimmering/crawling then? Did you have to employ any special tactics? Did you make the 20k trees yourself or get them from somewhere you can recommend? (the trees that don't use opacity mapped leaves that I have are *much* higher poly count than this).

 

Thanks for the tips beestee - I have set a number of tests going on our render farm over the next 24 hours, which include a mixture of variables, such as full geometry trees, better GI solutions (for both full geometry and opacity mapped trees), some better AA solutions and so on.

 

I will see how those come out, and certainly look into the IR map tweaks you suggest on my next round of tests.

 

I would imagine with the kind of full geometry trees I am using in some of these new tests (from iCube, probably average 700k polygons each), the kind of GI solutions I would need to bounce enough light around this number of leaves would be insane.....