render a specific region in animation

lordofarda

So I'm playing around with this player piano I made in Maya 2009 and I want to render out an animation of it playing a song. The question I have is: since the camera is stationary during the whole thing, and only the keys will be moving, is there a way to do a kind of ipr type thing where I render out the piano, then select the keyboard region, and then only have that part of the frame render for the animation?

It would turn a 20 hour render into a 5 hour render if it's possible

Oh, and I'm rendering in Mental Ray

somacruz145

I think you can do that by rendering one image of the whole scene and using it as the scene's background. Then just leave the keys and parts that occlude it. Alternatively you could render out the keys only and then make an opacity map to go along with it by coloring the keys white and the rest of the scene black (100% saturation).
Hope that helps

lordofarda

I've read around a bit and everywhere says I need to do this with render layers. Well, looking at tutorials and whatnot for them I'm just as confused as ever. All the tutorials I've seen just set up layers for specularity/diffuse/shadows and the likes. They also mostly just use plug and play settings for the scene that they are working on and not explaining WHY I should be doing things, so it's really hard to figure out what to do in my situation.

Anybody know of a tutorial that gives reasons WHY you do things in render layers instead of just telling you to put this number in here?

I don't know, maybe I'm just missing something. This is why I just stick to modeling, rendering is to confusing.

Melak

Hmm I don't know maya, but have you already tried the lighting & geometry cache? I think it will load everything from cache, speeding up the renderings unless something changes. Then again, geometry caching might stop the animation part from being rendered at all, I don't know :S

Dmitri

Hopefully it's not too late to help you out. Rendering in layers is the right direction to go here.

Why you render things in layers? Lets say you render out an animation that's X frames long. But wait- the specular was set far too high for the entire animation. If it wasn't rendered in layers you would have to go back and render the entire animation again with the specular fixed. But by rendering in layers you could just use some compositing software to tone down the specular. This means you don't have to go back and re-render the entire animation- it can be fixed without opening up Maya. So short answer: 1) it can save you time, and 2) sometimes to make a certain effect you need to do some post production compositing.

In the context of your problem. I would add the piano to one render layer and add the keys to a different layer. Instead of changing the layers to specular/reflection/ect... just leave them with everything being rendered. From there render each layer to a separate images (alternatively, a layered PSD). Because of how simply your scene is set up, you can just overlay the keys on top of the piano. I'd suggest trying it on a very simple test scene- then applying it to the piano scene first.

Hopefully that makes some sense- I did try to find a good tutorial, but you're right about most of them not explaining their reasoning very well. Cheers!