Everything in digital art is channel information and Nuke can manage many more than the standard red, green, blue and alpha channels. This is particularly important when 3D rendered output is composited typically consists of such channels as reflection, ambient occlusion, motion etc. It is also important in the management of alphas that typically need intense management within the composting workflow.
Channels and layers
one of the advantages of Nuke is that it can acomadate hundereds of channels in its node stream, which is of particular appeal to a CG artists whose output is often in the form of many separate passes.
In Nuke a CG compositor can darken an image by a shadow pass, lighten it by a lighting pass and add a reflection pass to the result, all without leaving a single node stream workflow (in other node-based compositing app such an operation would have necessitatated a far more sprawling approach where many seperate feeds are merged into one).
The management of these streams can be a bit confusing, but I will not go into it in great detail. However, one distinction that needs to be made is the difference between layers (also called channel sets) and channels. A layer is a collection of channels. RGB can, in this regard, be considered a layer.
The ShuffleCopy has the ability to move both these elements around. In the code snippet on the Noise page the RGB of one image is being moved into the motion layer of another.
The channels group of the Viewer window is another place where layer management is important.
Alphas, masks, mattes
Alphas, masks and mattes are three different flavors of channel imformation. Fundementally they are all the same thing (grey scale imformation), the only difference between them being the purpose to which they are put:
- Channel imformation used to restrict the effect of a node is a mask.
- Channel imformation, the form of which coincides with the 'hero' element of the rgb, is an alpha.
- Channel imformation used to isolate the element in a Merge operation is a matte.
Howvere, these terms are used very interchangebly so watch out.
A complex script can contain many channels being used for various purposes. With all this info the script can easly become messy to look at and difficult to read. Nuke has an elegant way of handling this. A channel can be injected into the stream eaither as an
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