View Full Version : Suggestions on rendering SSS head with Teeth, Eyes, Hands & Clothes

07 July 2009, 01:12 AM
I plan on doing a short animation approx. 5 min. & I have finally resolved my workflow for rendering out a displacement head using driven blendshapes in Mental Ray/Maya 8.5***with SSS! (I'm rendering about 45 sec. a frame for just the head) But I'm now struggling with rendering the other components to the character to make up the entire character (eyes & mouth interior, cloth and hair). How can I get all this to render efficiently?

If I use render layers, mental ray jumps up my time to more than 30 min/frame when mixing the displaced head and the other non displacement objects. So far I've tried the eyes and teeth using a phong but my render is way too slow even for this! Do you guys split up these things using software render and then mental ray for special shaders? Mental ray will quit if I try to include it all in one shot. I have used a background shader on the face to mask out the eyes and mouth, but I still get slow render times. What do you master render artists do/ any advice from you wise generalists of the world?

Thanks in advance.

07 July 2009, 04:27 PM
The trick is in knowing what all the settings in your render globals do and how/when to turn off everything that isn't needed in your shot, and also learning where specific bugs lie in the version you're using. For instance, I've found in Maya 2009 that if I leave some lights hidden, mental ray will spew 2,000 error messages a second (eating up 100% of my CPU and overflowing gigs of disk space writing to the mayarender.log). Deleting the hidden lights was the only fix in that case... the bug caused the lights to not honor my render verbosity settings.

A brute-force, but quick workaround:

Create three new surface shaders: one pure red, one pure green, one pure blue and assign them on a new render layer to different pieces (say... eyes, skin and teeth). This will let you extract mattes for them in compositing. Now you can assign a straight-up blinn or phong to everything in your shot on another render layer and just grab the teeth, for instance (make sure you're only using reflection depth of 1 or 2). If the RGB pass renders slowly, check out your geometry and render globals settings... a straight up RGB pass should render almost instantly.

I'm a *huge* fan of using an RGB pass to mask out specific elements when I can't figure out what's causing specific mixes of shaders to skyrocket my render time (it's probably your reflection or trace depth in this case, also likely high shadow trace counts... possibly sub-d approximation settings, possibly a light linking bug... try deleting lights that aren't used in each of your layers).


08 August 2009, 03:11 AM
Thanks for the reply. Based on what you've said, I've been deleting extra lights, and deleted my extra layers. Somehow this has made it render in one layer but I am still looking to make it render faster. Outputting to RGB on a seperate matte is a great idea. I have also looked into acceleration and bsp settings...trying to find out more about max displace settings, and I've unchecked Maya's feature displacement on all objects. I'm getting there.

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08 August 2009, 03:11 AM
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