Render Passes

Render Passes

Render passes, also called AOVs or arbitrary output variables, are separate images rendered from the same 3D scene that isolate different aspects of the final image. Instead of rendering one final image, you render the beauty pass, the diffuse pass, the specular pass, the shadow pass, the reflection pass, and many others. Each pass contains specific information that the compositor can use to adjust the final look.

The beauty pass is the main render, the final image with all lighting and shading applied. But having the individual components separated gives you enormous flexibility in compositing. If the specular highlights are too bright, you can reduce the specular pass without affecting the diffuse. If the shadows are too dark, you can adjust just the shadow pass. This non destructive workflow is essential for professional compositing.

Z-depth passes store the distance from the camera to every visible surface. This is a grayscale image where white is close to the camera and black is far away. The depth pass is used for depth of field effects, fog, and atmospheric perspective. It can also be used to place 2D elements at the correct depth in the scene. Depth passes are usually rendered as 32-bit float EXR files for maximum precision.

Normal passes store the surface normal direction at every visible point, encoded as RGB colors. This is useful for relighting in compositing. If you decide the lighting on a CG character is wrong, you can use the normal pass to add new lights in compositing without re rendering. Material ID passes assign a unique color to each material, making it easy to select specific objects for color correction.

Motion vector passes store the velocity of every pixel, which is used for motion blur in compositing. Cryptomatte passes store object IDs with anti aliased edges for perfect selections. World position passes store the 3D position of every visible point. The more passes you render, the more control you have in compositing. Modern EXR files can store dozens of passes in a single file, keeping your pipeline organized.