animation, bitmap textures flicker in shadows.

[plastic_]

well i have to do a flythrough of some horrible little private house and everything works surprisingly good, based on the flythrough tutorial, even displacement.
but my grass and other bit-mapped surfaces flicker in the shadow areas of the sun...
i attached a quicktime showing the problem...
anyone knows off-hand whats the problem with my grass, before i dig through all the settings?
one thing i cant afford is raising the render time...
current render times for 10 seconds animation are: 30min light cache prepass, 30 min irr-map prepass, 5min/frame rendering @ PAL 16:9 squeezed anamorph.

my settings: adaptive AA, -1, 3, rand, normals.
AA: area
GI, pre, cached irr.map, medium animation.
sec, cached lightcache, 5000 (flythrough), sample size 0.02, store direct, screen, nearest, pre filter off.
everything else quite default.

grass setting: vraymat with diffuse and bump, bitmap blur 0.5, summed area.

light settings, shadow subdivs 8.

http://www.angstraum.at/pics/grassflicker.mov

thanks for looking.
i also accept other tips for reducing my rendertime

[ene.xis]

hi,
dreadfull hose ur right!
i think that noise moving around in da shadowed areas as something to do with time independent check bos in rqmc sampler rollout....but i ve got no time to test it....
hope u sort that!

[plastic_]

hi,
thanks for your hint...unfortunately it's not the problem...it only gets worse with 'time independent' switched off.

[ene.xis]

well...then u just have too bump up the sud values for ur gi....

[Morbid Angel]

try filter quadratic. Also, why are you using adaptive subdivision? I would say that the flicker looks like gi issue, rather then anything else. But then it doesnt flicker in other places. Does the flickering goes away if you render this scene with grey material override?
I would recomend trying adaptive qmc 1/100 settings, from vlado's universal thread.

[studioDIM]

It doesn't look to me it has to do with GI...
It looks more of an AA problem, where the threshold it too high.
In fact the noise is also on the glasses, which should have a negligible amount of GI on them, as well as being visible, if barely, on the grass to the righthand side of the screen.

One quick solution is to revert back to a 1.0 blur with pyramidal filtering.
Up the bitmap blur, lose detail, but gain both in renderspeed and in cleaniness of the result.

Or you could pump up the AA settings, so to get cleaner results as it is, but with an added amount of time.

Another solution to get a sharper texture would just be to use a bigger one, or a sharpen filter in post.

Hope it helps

Lele

[ene.xis]

i DO think its a GI issue... vray needs more samples in the less lit areas....as the rest of the scene is ultra lit this is only visible in that shadowed zone....

[plastic_]

ok i sorted it out

first i also thought it was a GI issue, not enough skylight samples, but it happened without GI too.

it's in the image sampling.

using +1, +3 instead of -1, +3 for adaptive image sampling cured it, but that's way to slow.

i changed the image sampler to QMC, default settings, and noise treshold to 0.001...now the flickering is gone _and_ rendertimes are almost half from the previous ones with flickering adaptive AA.

i'm happy now...the reason i used adaptive AA before was that because with still images i do mostly, adaptive provides sharper edges and seems to be faster.
but then again, i hardly used displacement before, and adaptive crawls with displacement, compared to QMC.

thanks for all replies.

[plastic_]

try filter quadratic.

i'm a bit confused by the different AA filters...
for stills i usually use catmul-rom, because it's sharp and i like that.

i think mitchel-netravali is a popular filter, but it seems to be quite slower than the default area, and not too different.
i tried quadratic now, it seems softer than area and about the same speed.

would you recommend quadratic for all situations when rendering to dvd?
i realize that something like catmul-rom would be problematic for animations on tv screens, but is quadratic considered to be superiour to area, as an all-purpose filter?

[Morbid Angel]

well, I used to use mitchell a lot, until one point where I had some major flickering guess where...on displacement. In much conversations with vlado, he explained that for animations, with great amount of details, such as dispalced objects, sharpening filters make things only worse. In my opinion and from much experinece, quadratic produces very good results, as generally for tv you dont need super sharp image. It usually is softened by motion blur and post process. If the antialiasing is good enough then soften filtering will only help make the image more stable. Now I use nothing but quadratic. Some times soften with a low value.
Cutmull rom is good, but it probably wont work for complex animations.
And if you are really looking for sharpness for some textures for example you can turn off filtering for the texture or reduce the blur on it in 3ds max. That can help sharpen the texture, then softening filter will balance it out.

[plastic_]

great info, thanks!