Render Passes (AOVs)
Separate layers of a render for compositing
Also known as: AOV · Render AOVs · Render layers · Blender passes · Arnold AOV · Multilayer EXR
Definition
Render passes, also called AOVs, are separate images saved from a single render, each containing one part of the result: diffuse, specular, reflection, ambient occlusion, depth, normals, object ID and more. Saved together, usually in a multilayer EXR file, they let you adjust and combine the parts in compositing without rendering again, for example to strengthen reflections, relight an object or add depth of field afterward.
In production
Render the passes you will actually use, such as ambient occlusion, depth, cryptomatte or object ID, and emission, since each pass adds render time and memory. Save in EXR at 16 or 32 bits so values are not clipped. Blender, Maya with Arnold, Houdini with Karma and Unreal's Movie Render Queue can all output them. Portfolio artists use passes to polish final images.
Tools that use Render Passes (AOVs)
See also
Compositing
Combining render layers into the final image
Texture File Formats (TGA, PNG, EXR)
Which image format to use for game textures
Bit Depth
8-bit, 16-bit and 32-bit textures
Arnold Renderer
Maya's default path-traced renderer
Karma Renderer
Houdini's built-in renderer
Ambient Occlusion
Soft contact shadows