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

[JohnW3D]

Hi guys,

 

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 (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 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, 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 VrayScatter/MultiScatter animations 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

[beestee]

You will need a chaosgroup account to read this, but there are some pointers on this here:

 

http://www.chaosgroup.com/forums/vbulletin/showthread.php?54083-vray-specific-AA-filters.&highlight=tree+shimmer

[Nic H]

i would use a combination of.....

softening aa (i always use a softening filter for animation quadratic/area/video- never use a sharpening one)

decent aa settings (DMC 1/8 0.0075 etc)

motion blur - either 3d in camera or post via velocity channel

distance blur - via zdepth in post

 

a combination of these should fix/lessen it.

[JohnW3D]

1/8 for Vray AA settings? I am fairly new to Vray, but whilst MR uses a number of samples, Vray expresses its sampling in subdivisions, so a 1/8 rate would be a huge number of samples.....my understanding is that the samples would increase like this:

 

0 1x1 - 1 sample per pixel

1 2x2 4

2 4x4 16

3 8x8 64

4 16x16 256

5 32x32 1024

6 64x64 4096

etc.....

 

Surely no one can support this rate of sampling for animations? or am I out on how rate relates to samples used?

Edited May 27, 2011 by JohnW3D

[Nic H]

hmm not familiar with the ins and outs of MR but this is a fairly standard decent vray aa setting for stills / animation - might be a tad high - but it all does depends on the scene, materials, complexity so is not a catch all setting but its not overkill by any means. its adaptive so it can take between 1 and 8 samples - this is linked back to the adaptive amount in the DMC sampler which by default is set at .85

 

think im on the right path!