Removing speckle on animated displacement grass?

[squeakybadger]

Hi all,

Anyone know how to control the moving speckle I am getting when using displacement grass in an animation?

Example here:

http://www.vimeo.com/20371175

Irr map has been calculated on 1 machine, and brute force for the rest. I have tried using a precalculated light cache as well, but just the same.

Adaptive Dmc as the image sampler
Mitchell-Netravali as the AA

Any ideas how I can calm that badboy down?

Cheers!

-j

[joconnell]

It could be the brute force for starters since it's a per pixel, grainy gi solution. Otherwise it's probably your aa. I find using render elements can track this down a fair bit - you get to see the level of sampling being done in different parts of the image be it GI, specular or normal anti aliasing. Mitchell is a sharpening filter so it'll enhance the contrast of pixels in your grass texture, and thus make the grain more obvious. Try using something like quadratic which is a bit softer, and also if you can afford the time, render with motion blur. At very least render a velocity element so you can add some post motion blur. If you've got either a texture or model with lots of tiny details and you're doing quite slow camera moves, the details can often be smaller than one pixel in size in your final render. With slow animations, the small details can end up falling between lines of pixels in your final image and it's often this moving in and out of tiny details that give the shimmery look. Either a higher max aa value or motion blur.

[stevesideas]

Have you tried calculating the irr map and lightcache without displacement and then turning it on for render. That worked for me when doing carpets...grass is longer so it may not work.

[percydaman]

As joconnell said, it could very well be your AA. Take a rock solid GI solution, add poor AA, and viola, crappy looking grass. If you can render out your grass as a separate matte pass, then you can choose an AA filter thats going to do a better job with the grass, with added benefit of extra control in post.

EDIT: Didn't watch the video until after posting. I see your already rendering as separate pass. With the camera that far away, why do you need anything more then a texture? As a troubleshooting technique, I'd render it with no GI and just a direct light. That'll let you know if AA is causing the issue .