View Full Version : Help with compositing..

01 January 2010, 06:46 PM
Hi all - I posted this under animation but on reflection I might get a better response from this part of the forum...

Need some advice about handling compositing for an animation we are working on- something we have never needed to do before so it is a completely new discipline- and have no idea where or how to start.

The scene is quite a high poly city scape, the camera remains static. Elements within the scene are animated, the sky, people, animals, boats etc... However the majority (buildings) remain static over the 2min cycle.

Is it possible (and how) to render out the scene and composite it together so the static element could be rendered out as one (still) image and the animated elements composite on top. I'm sure this is possible but how would the shadows be handled as they need to fall on the static elements. We can render the whole scene out but time is not on our side and it seems unnesciary to render out the elements that are not animated 3600 times :)

Max 2010 with VUE plugin generating sky & landscape.

Any advice greatly apreciated.


01 January 2010, 08:46 PM
you can render out a beauty frame of your static objects, and then use there geo for shadow and reflection passes of the moving objects.

01 January 2010, 04:10 AM
As a rule of thumb, I separate out these channels of information (to start)

Color Specularity Diffuse Shadows that are cast by the object upon itself Shadows that are cast by the object onto other surfaces The illumination that is projected by each light (note that "light" and "shadow" are kept separate and don't really consider the characteristics of what is being illuminated or shaded) Z-depth Alpha (transparency) And everything goes into separate files. "Once done once, it's done."

If you have each of these channels of information, pure and distinct, you can now "blend" them together, much like a multi-track "mixdown" of audio. A modern CG package uses "node networks" (aka "noodles") to blend these various channels of information any way you might want to. Once you've got the raw information, your "rendering" per se is basically finished; the rest is a much faster process. (So you've got 40 or 50 channels in play at once... so what?)

And "cheating" is more fun than it ever was in a country song. :) There are lots of ways to come up with an effect if you put your mind to it...

So yes, you can do it this way, and this is precisely how you want to do it. You might feel like "it's a lot of extra work" until you start to "do the mix" and you find that you can fiddle with absolutely anything in nearly real time. If you find something is not quite right, you can likewise zero in on exactly what's wrong and fix "only that," quite possibly without re-rendering anything new. It's truly a "digital darkroom."

01 January 2010, 09:59 AM
Thanks for athe replies guys- especially sundial.

As I am very new to compositing I wonder if I could induldge you further...

I think I grasp the basic concepts and can see how actually this process will save a lot of time in future as well as for this project.

My only questions that remain is about the actual how to and workflow..

My understanding from your replies is that I need to render out all the elements that make up the "still" portion of the image (without the shadow "layer") and combine these all together which will form the still background of the animation. Then render out the frames of the elements that are animated and composite those onto the background. Then run a shadow pass (sorry if my terminology is incorrect here) of everything and composite that into the movie?

So for creating the shadow pass which will contain the information of 3600 frames of still and moving shadows how would I do this without rendering out the full image. I used render elements (Max 2010) and whilst that gave me a shadow layer it rendered out the full image and then gave me the shadow. I'm thinking if I turned of the visibility of all the objects in the scene and rendered out the shadows this might work- or am I barking up the wrong tree.

Many thanks again for your help and sorry if my questions are obvious/stupid but this is my first look around the digital darkroom door :)

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01 January 2010, 09:59 AM
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