The Studio Workshop: ID passes - Part One

The Studio Workshop: ID passes - Part One

Because nobody demanded it....ID passes!

Yes, despite a tonne of positive response to last week’s Studio Workshop blogs, not one of you took the bait to ask me about ID passes. Well, the jokes on you, because I'm going to talk about them anyway!

ID passes are a simple and yet incredibly effective way to have more control in NUKE. Basically they are a way to isolate one part of your render, allowing you to composite elements without affecting the rest of your image. For example; you could render out a house, then create an ID pass for the windows, allowing you to add a colour correct node to them separately. Creating ID passes is a process that happens at the end of your Maya project, around the time you create all your other Render passes/layers, just before you batch render.

An easy way to look at an ID pass is that you are creating three separate alpha channels, for three separate objects, in one layer. Rather than have these alphas stored in the alpha channel, you store the alpha information in either the red, green or blue colour channel. The image above is a quick example I've made, it's a fairly accurate representation of a house, I think you'll agree!

Doing this is incredibly easy; firstly, open your hypershade and create 4 surface shaders. Leave one as it is, and call it 'Black', and use the colour swab to make the other three 'Red', 'Blue' and 'Green' respectively, and name them accordingly. Create a new layer with your desired geometry, no need to worry about lights, IBL, etc. Inside this layer (which later, of course, you will accurately name because you all read last week’s “Naming Conventions” post), give all the geometry the ‘Black’ surface shader.

Now you can isolate certain parts of your model by adding the Red, Blue and Green shaders to different parts of your model. In the above picture, you'll see my walls are blue, my windows are red and my door is green. When I hit render, I get mainly black image with bright colours showing my surface shaders. This means when I get into NUKE, I can colour correct the walls, windows and door with separate nodes, allowing a much greater element of control, by extracting the information in the red, blue and green channels.

To be continued in Part Two…

0 Comments Ash Miles

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Ash Miles
Fri 27 Apr 2012: 12:17pm

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