Rendering Workflow - Background as a Single Frame over Multiple Shots?

[tharrell]

Generally, you handle this in comp. Render out a background plate (or collection of passes) then use some sort of matte workflow to get your shadows and knockouts. The less pixels you have to consider, the faster your frames will get rendered out.

useBackground kinda sorta works in both RFM and MR. You can collect shadows and reflections with it, although the quality and usablity of the shadow pass will vary greatly depending on your lighting setups. MR has trouble when you turn on final gather, RFM has trouble with environment lights and raytraced shadows.

In MR, you have the option of using the production shaders (like mip_matteshadow)... while a pain to set up, they allow for your not-actually-there background to emit bounce light and correct reflections. You can cheat the bouncelight and reflections with useBackground though.

DJX has a really awesome primer on how to get matteshadow working here:

http://www.djx.com.au/blog/2008/04/08/mip_matteshadow-and-how-i-have-used-it/

...and he links to a Zap blog entry about how to use it as well.

I can't really imagine doing a short in MR without using some degree of final gather, so this is likely your best option, although you can grab shadow passes, and cut them out with an alpha mattte of your main objects in a pinch. Lots of folks run RGB object ID passes so they can use them to matte out objects within a frame at-will, and the inverse alpha works for reflections and shadows.

In Renderman/3DL you generally collect your shadows as direct, indirect and occlusion AOV passes and flag your floor as a matte object, because useBackground results in 100% black ugly shadows without indirect contribution.

Hope this helps,

--T

[mixermanic]

Thanks for the detailed answer Trey.

It's always a matter of working around the bugs isn't it? :D It's the same with music sequencing and DAW software (my background)...

Out of interest - and slightly OT - what render passes would you recommend for a background plate to maintain a decent level of control whilst not drowning in files...?

M

[tharrell]

Well, the very nature of render passes means that you'll be drowning in files :)

In general, you run beauty plus a collection of basic passes: diffuse, specular, reflection, shadow, ambient, irradiance, occlusion, reflection occlusion... the list goes on and on. I prefer breaking out my shading from my raw color plates -- so I do a diffuse, then a diffuse direct shading, diffuse indirect shading... and diffuse environment shading. You can even break it down per-light if you're feeling particularly control-freaky about the whole thing.

Here's a basic rundown from Alex Alvarez at Gnomon... he hits up the basic passes that you need to add up to your beauty result.

http://www.thegnomonworkshop.com/tutorials/passes_layers/passes_layers.html

On top of the basic passes a lot of folks run utility passes on top of them. A few examples: Z-depth (for depth of field & compositing), Object ID (flat color mattes, usually RGB, so help break down your overall alpha per-object in a pass), normals (for relighting in comp), uv pass (for retexturing in comp), motion vectors (to do motion blur in post), per-light RGB contributions (so you can adjust lights interactively in comp... even on a still background)... the list goes on and on.

It's a really extensive topic that I can only really gloss the surface of in a post. The best advice I can give you is to figure out what you're going to be using for composites, then start googling what utility passes are supported without extra plug-ins, and how you assemble your average shot.

Two biggish pieces of advice:

1. Get in the habit of rendering to 32-bit EXR or TIFF... it'll allow you much much finer control in comp over your look, and you can push levels & adjustments around like rubber with a 32-bit file meaning you can often salvage renders that didn't come out perfect -- but more importantly you don't have to do all of your look tuning in Maya... get 90% of the way there and do the rest in comp. With a normal 8-bit file there's only so far you can go before colors start clipping. The files are big, but it's worth it. Of course, that opens the door to start studying linear workflow which is an entirely other can of worms.

2. In the general tab of your render globals, you can right click in the filename block to add variables. So instead of having 50,000 files dumped into the same folder for a shot, you can organize everything into /<scene>/<layer>/pass.<#>.<ext>

Hope it helps. You've got a lot of R&D ahead of you :)

--T

[mixermanic]

In general, you run beauty plus a collection of basic passes: diffuse, specular, reflection, shadow, ambient, irradiance, occlusion, reflection occlusion... the list goes on and on. I prefer breaking out my shading from my raw color plates -- so I do a diffuse, then a diffuse direct shading, diffuse indirect shading... and diffuse environment shading. You can even break it down per-light if you're feeling particularly control-freaky about the whole thing.

Thanks Trey. You are being a bit of a star answering my ramblings on a couple of threads here :cool:

[/QUOTE]


Here's a basic rundown from Alex Alvarez at Gnomon... he hits up the basic passes that you need to add up to your beauty result.

http://www.thegnomonworkshop.com/tutorials/passes_layers/passes_layers.html



Thanks! I've just ordered a couple of Alex Alvarez titles from them. The 3Delight tutorials also mention passes in some detail.

It's a shame there aren't more training materials for RM...

1. Get in the habit of rendering to 32-bit EXR or TIFF... it'll allow you much much finer control in comp over your look, and you can push levels & adjustments around like rubber with a 32-bit file meaning you can often salvage renders that didn't come out perfect -- but more importantly you don't have to do all of your look tuning in Maya... get 90% of the way there and do the rest in comp. With a normal 8-bit file there's only so far you can go before colors start clipping. The files are big, but it's worth it. Of course, that opens the door to start studying linear workflow which is an entirely other can of worms.

2. In the general tab of your render globals, you can right click in the filename block to add variables. So instead of having 50,000 files dumped into the same folder for a shot, you can organize everything into /<scene>/<layer>/pass.<#>.<ext>

Yep - a very quick question regarding compositing. It would appear that I need to start really learning about more formal compositing techniques (a la Fusion, Combustion etc.) rather than After Effects. Would you reccommend this?

Hope it helps. You've got a lot of R&D ahead of you :)

Yep! I know. Well, I'm a full time carer for my dad at the moment, so I need *something* to concentrate on now I'm living out in France :beer: Even the cafés of Avignon get dull after 6 or 7 coffees (and I start bouncing off the walls!)...

This short I'm doing could quite easily take several years (not to mention the various iterations things will go through as my skills increase)... But I'm the knowledge I'll have at the end of it... (hopefully!)

Cheers!

Martin

[tharrell]

Yep - a very quick question regarding compositing. It would appear that I need to start really learning about more formal compositing techniques (a la Fusion, Combustion etc.) rather than After Effects. Would you reccommend this?

Without a doubt, learn a node-based compositor. When you're dealing with render passes and particularly utility passes, you'll start to go insane pretty quickly in AE. It's good & fast for not-terribly-complex stuff (I use it over other stuff when I'm just slapping beauty segments together or doing fast roto), but a node-based system is much more flexible and easier to make sense of when you're dealing with a ton of passes per shot -- and that's where AE falls apart. You end up having to have 50 precomp timelines to apply adjustments efficiently on complex composites.

Toxik comes with Maya 2010... and apparently it's decent. Haven't upgraded yet personally due to plug-ins, but it'll assemble your passes for you (export precomp from Maya). I've been in the Shake camp for years, but now that Apple's formally dumped it, I'm getting up to speed on Nuke. Other people are moving to Fusion.

I'm quite liking Nuke, for what it's worth, but it's kinda pricey. FXPHD has a pretty great set of intro courses that are reasonably priced... and Nuke can handle multichannel exrs -- dumping all of your passes into a single file -- which is unbelievably awesome.

Shame Apple dumped Shake... you could get a Mac AND Shake (and Final Cut Studio which rocks) for less than the price of most of the true competition.

But, I'm kinda biased there. I do all my post work on the Mac side of things, mostly because I prefer it... but also because the system stays usable during renders :)

The PLE of Nuke 5 feels nice and responsive on the Mac side of things -- plus its file format is just a straight up TCL script. You can do some pretty crazy MEL-based time saving glue to assemble things pretty easily (Shake was that way too).


--T

[mixermanic]

I'm still thinking about whether to go for Maya 2010 or not. At least, until 3Delight for Maya gets a 2010 compile it's definitely out, but even then I don't know whether I'm willing to shell out for the Maya upgrade - the addition of Toxik would be great (I can't believe 2009 isn't still available... in fact, I can believe it - Autodesk seems to cut support for its older products as soon as a new one is released!)

Hadn't heard of Nuke - thanks. Just grabbed the PLE, so will check it out.

and Nuke can handle multichannel exrs -- dumping all of your passes into a single file -- which is unbelievably awesome.

Again, speaking from ZERO experience, but I had read that multichannel EXRs can slow the system right down (as opposed to separate files for each pass). Is this not your experience?

Thanks,

M

[tharrell]

Well, as with most things when you're dealing with managing a crapton of files in a production workflow, there's tradeoffs.

I haven't noticed it being much slower, on my end. And if it is, the convenience of reducing the amount of image sequences I'm working with to about 1/12 outweighs it -- you're also reducing yourself to a fraction of the nodes in comp... and making sense of a complex node network can be daunting till you've done a few gigs in one. It's as un-like the After Effects workflow as it can possibly be. You're dealing with a telephone switchboard, or a fusebox.

If you're doing the Mental thing (as opposed to AOVs) check out the ctrl_buffers and puppet MegaTK shaders -- they both do the multichannel exr thing and can dance around Maya's built-in passes to boot. I love ctrl_buffers, but alas, no Mac support, no source code, so it's not for me.

--T

[mixermanic]

I've replied on this (http://forums.cgsociety.org/showthread.php?p=6086916#post6086916) thread to try and consolidate the dual discussions! :)

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