The following section describes basic concepts necessary to work with render layers:
The Master layer contains all the objects and materials in the scene. There is always a Master layer in your scene; it’s exposed in the Render Layer editor. It is only visible in the Render Layer editor if there is more than one layer (in which case it is non-renderable by default).
When you create new layers, you can make any objects or nodes (including lights) members of only that layer, multiple layers, or all layers. Only objects in a specific layer affect or contribute to that layer; this includes lights, reflections, shadows, and so on.
In addition to segmenting your scene into render layers, you can change the characteristics of each layer or object on a layer by creating layer overrides. (By definition, you can't override the characteristics of the Master layer.) Maya stores each of the layer and attribute overrides as changes between that layer and the Master layer. See the next section.
There are two types of overrides for attributes: per layer and per object.
There are two ways to create overrides: auto and manual.
Render layers affect the scene view, Hypergraph, Hypershade, and so on. Switching layers means that lights, geometry, or nodes are visible or not depending on whether those objects are in a particular render layer. (Previously, objects always appeared in the scene view and were either present or not present in a render.)
Visibility of Display layers and Render layers interact subtractively. That is, if you have a Display layer that contains objects and turn off visibility on that layer, you will also not see these objects in any of your Render layers.
Once you understand the basic concepts of Master layer, layer and object overrides (auto or manual), render settings, and presets, you can do the following on a layer-by-layer basis:
For examples of how to use layers, see:
You can render individual objects, groups of objects on layers, or attributes (passes) of your scene, then combine them using a compositing system. Compositing is the process of combining multiple images into one.
(You can also render global illumination passes separately.
To set up layers and passes, see Render layer overview and Work with render passes.
Rendering separate objects in layers and passes takes more time and effort to plan, but it offers the following advantages:
For example, you can render different layers with different render options. You can then color correct or add special effects to each rendered layer in a compositing application.
For example, you can change a ceramic vase to a glass vase without re-rendering the entire scene.
For example, you can quickly render the foreground layer where most changes occur, instead of the whole scene or background, where objects tend to be static. You can also render smaller portions of large scenes, reducing the load on computer memory.
When an image is stored not only with the three basic color channels but also with the alpha channel, the presence of the alpha channel can modify the color channels to some degree. For example, typically the color channels have been multiplied by the value of the alpha channel to take transparency into consideration.
Some compositors (as well as games engines) can use premultiplied images; others require separate image and alpha information, especially when they want to separate object color data from background color data. By default, Maya premultiplies images, but you can turn premultiplication off.
To turn premultiplication on or off, see Premultiply.
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