Render layers

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[edit] What are Render Passes?

When creating computer-generated imagery or 3D computer graphics, final scenes appearing in movies and television productions are usually produced by Rendering (computer graphics) more than one "layer" or "pass," which are multiple images designed to be put together through digital compositing to form a completed frame.

Rendering in passes is based on a traditions in Motion control photography which pre-date CGI. As an example, in motion control photography for a visual effects shot, a camera could be programmed to move past a physical model of a spaceship in one pass to film the fully lit beauty pass of the ship, and then to repeat the exact same camera move passing the ship again to photograph additional elements such as the illuminated windows in the ship or its thrusters. Once all of the passes were filmed, they could then be optically printed together to form a completed shot.

The terms "Render Layers" and "Render Passes" are sometimes used interchangeably. However, rendering in layers refers specifically to separating different objects into separate images, such as a foreground characters layer, a sets layer, a distant landscape layer, and a sky layer. Rendering in passes, on the other hand, refers to separating out different aspects of the scene, such as shadows, highlights, or reflections, each into a separate image.

[edit] Render Layer Overview (still needs editing)

Render Layers allows objects to be rendered into separate plates to save on render time, re-rendering, render crashing. But render layers can render more than just individual objects. Render layes can also render different visual aspects and qualities of objects. For instance a render layer can consist solely of an object's specularity, transparency (alpha), or even it occlusion and reflectivity.

Simple render passes include: Beauty, alpha, shadow, reflectivity and specularity. Though many artists and studios may use more this set of five will cover many aspects involved with successfully utilizing render layers. Other render passes include: depth, color, diffuse and occlusion.

Beauty: This is the most common render pass as it encompasses the colors of objects, the specularity and shadowing of the objects as well.

Alpha / Geometry Mattes: This render layer, most often seen as a side effect of rendering a scene with

Shadow: This render layer encompasses the shadows cast from one objects onto other objects. A large reason to render the shadows as a separate pass it to later control the density and range of shadows in post production.

Reflectivity: Any colors or objects reflected onto the object is now rendered inside this layer. This is often used when adding a slight dreamy feel to a sequence by slightly blurring the reflections off objects.

Specularity: Though this is already rendered in the Color and Beauty render layers, it is often also required to separate out the specularity from the colors of the objects.

___Other Render Layer Types___

Depth: In order for a compositing package to understand how to layers objects in post production, oftentimes depth masks (or channels) are rendered, making it easier to sort objects in post without requiring alpha channel trickery.

Color: This render layer describes the color of the rendered objects. In Maya 7 it covers both the diffuse and specular colors of the given objects without the object's shadowing.

Diffuse: This layer is responsible for rendering strictly the color, having nothing to do with specularity or self-shadowing.

Occlusion: An occlusion pass is a visual stunner. It is often used to add a higher level of depth in the imagery. In essence, its purpose is to darken all the nooks and crannies of the objects. The closer objects are to each other the darker those parts will appear in the occlusion pass. This simulates the effect of light being blocked out by narrow spaces and close objects.

Uses: Rendering in layers saves a lot of time when rendering. Although more rendering is done, and more images are created, the renderer deals with a smaller number of objects and render qualities when rendering each image. Render Layers make it easier to add visual effects in post production, where it is much cheaper (by cost of time and cpu intensity) to create such effects. Render Layers also make it easier to create a desired visual effect in post production. Post production is where color, tonal, density, luminance, chroma, saturation and other such visual qualities are edited and perfected creating an overall, cohesive look to the image.

Lighting: Creating render layers also allows post production artists to have more control of scene lighting by rendering objects into separate layers as defined by the lights. For instance, if all objects are put into 3 render layers each render layer can have its own light. Thereby allowing the post production artists to have control of the lighting in post production.

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Note: This essay written with a practice and understanding Maya 7. Other 3D rendering packages may have differences in their terminology or execution.