Multiple layers with different composting??????

I wonder if you can help me grasp how to do this. I have a scene with some animation and some compositing, but what happens if i want to layer another object into the scene that has its own unique composting like blur, without blurring the first scene.
im guessing its something to do with render layers or channels or something. i just cant get my head around it.

Thanks.

Here’s the way I think about it:

(a) A “RenderLayer” … being yet another confusing use of the word, “layer” … is basically a filter. Only the data that matches the specifications “gets through” and becomes the output of the corresponding compositing node.

(b) Compositing, like the other node-based elements of the Blender system, is basically a “production assembly-line” for image data. Data “flows” from the input nodes (e.g. RenderLayer), through an arbitrary number of processing stages, to eventually arrive at the output node.

You can, indeed, create an entirely separate channel of data, selecting “that object” and everything related to it, and feed it through a set of processing steps, such as blurring or what-have-you, before finally combining this channel’s results into the rest of it. Really, you can do just about anything that you can dream up (and “plug up”). :slight_smile:

Now, you do have to be careful that what you come up with “makes visual sense.” For example, mixing together two separately-blurred things might not look convincing. Ordinarily, I find that my “noodles,” regarded left-to-right, have: selection --> color/contrast adjustment --> masking --> combining --> visual effects (such as blur) applied last. (Now, things like “vector blur” might have vector inputs that came from several sources and that, therefore, blur different areas of the frame differently, but the “blur” transformation itself is being applied only once.) That just seems to work out best for me.

“Bigger” projects are built out of multiple rendering steps, which create MultiLayer OpenEXR intermediate files. This is a file-format specifically designed (by ILM, with a little help from Blender!) as a “digital intermediate-file format.” The files are large, but numerically accurate and loss-less, and contain many different “layers” of information in the same file. (This is also an area where “RenderLayers” come into play …) Basically, it’s a big file of floating-point numbers.