Extra data layers embedded in a rendered image — depth, normals, object IDs, motion vectors. Stores scene information for flexible post-work.
When working with modern rendering, not only RGB images land on your hard drive — you also get a collection of separate data layers that break down the scene into its components. These additional layers — depth values, surface normals, object masks, motion vectors — are your tools for staying maximally flexible in compositing. This is especially standard in VFX and for complex CGI shots: you render once, then manipulate a hundred times.
Practically, this works as follows: The renderer saves a depth map parallel to the standard beauty pass, which contains exact distance information — each pixel knows how far it is from the camera. You'll need this later for depth of field corrections, atmospheric layers, or fog effects, without re-rendering. Normal maps show the surface orientation of each pixel, allowing you to adjust lighting afterward or layer special effects like subsurface scattering. Object IDs or segmentation passes isolate individual elements of the scene — character, environment, water, light sources — so that each element can be color-corrected or modified individually without affecting the rest.
Motion vectors store the motion information between frames — how fast each pixel is moving. In compositing, you use this for motion blur, optical flow effects, or for tracking support in visual effects. In addition, there are specialized passes like Cryptomatte (a layering technique that automatically generates clean masks per object), ambient occlusion separation, or separate diffuse and specular components.
The decisive advantage: You save render time. Instead of rendering ten times for color corrections or effect adjustments, you do everything in compositing — significantly faster, significantly more cost-effective. For complex scenes, this is not optional, but the standard workflow. While file size grows exponentially, modern pipelines manage this via EXR sequences with zip compression. On set or during VFX supervision, you need to know which passes you need before the renderer starts — subsequent requests cost time and money.