When you render to passes, you might not want this pass to be added to the "Combined" pass, to allow using "Combined" for compositing too.

You can Enable/disable adding the pass by clicking holding CTRL on the pass buttons with a small grey dot. A black dot then means it's excluded from "Combined".

Note that you can also define this way how "Combined" is assembled without rendering to passes. In the screenshot to the right that's done for Specular and AO.

The Blender Render Pipeline allows to render unlimited amounts of RenderLayers, and for each of these RenderLayers a number of passes. This distinction is simple; a RenderLayer defines which (types of) geometry is handled, the Passes store shader results.

Three new options for RenderLayers now allow further control over pass render and composite:

• Light Override: give the RenderLayer a name of a Group, and this layer will only render Lamps inside of this group. This allows to render multiple layers (each with passes!) with different lamps, for later compositing.
• Material Override: give the RenderLayer a name of a Material, and this layer will only render that Material for all faces. Useful to make masks for example, with a Material with a global coordinate blend.
• Enable/Disable layer: the first icon button to the left of the RenderLayer name allows to disable it from render. With all pass/layer options useful for tests, or to setup preview renders.

You enable passes with the RenderLayer Panel in the Scene Buttons.

For each Render Layer you have to set first the layer options (Solid, Halo, Ztransp, Sky and Edge). Passes are only available for the Solid and Ztransp layers (since this shades actual faces).

The render option "Save buffers" will create a temporary .exr file with all passes. You can force re-reading this file in the Compositor window with hotkey "R".

Combined

This is the default pass, RGBA, and always available during rendering for display updates. If set, it will render with all render options and accumulate passes here. Here you'll also find halos and edge render.

Z

Delivers one float value, the distance from camera, in Blender units. Is not anti-aliased, but the Z value of the closest sample in a pixel.

Vec

Speed vectors, for vector motion blur. Two times two values.

Nor

The rendered normal, 3 float values ranging from -1 to 1.

UV

For those faces that have UV texture faces assigned, it writes UV values in this pass. For proper masking purposes, it writes an alpha value as well. See the UV Mask Node page.

IndexOb

Every object can have an index number (Object Context buttons, "Object and Links" panel, button named "Pass Index". These values get rendered in this pass, as a single float value. You can use this for generating masks as needed for compositing. Note this pass cannot store anti-aliased indices. See the Index Mask Node page.

Col

The raw color, RGB floats, as returned from a Material and Texture.

Diff

The raw diffuse, RGB floats. without any shadow or specular or ambient. It does include the Color from Material and ramps.

Spec

The specular component, RGB floats. It is masked out by shadow already.

Shad

This is the shadow pass, RGB floats, retrieved by dividing diffuse with shadow by diffuse without shadow. Multiply this pass with the diffuse pass to get it combined.

AO

The Ambient Occlusion pass. RGB floats. It is the 'raw' pass, not converted to 'diffuse' as used for the Combined pass (so it does not store options "Add", "Sub" or "Both"). When this is the only pass active, no shading or shadow calculation happens.

Refl

The ray-traced and/or environment mapped reflection pass, RGB floats. This is the difference of diffuse with and without reflection. Add this pass to combine it.

Refr

The ray-traced refraction pass, RGB floats. This is the difference of diffuse with and without refraction. Add this pass to combine it.