0
$\begingroup$

What are the differences between the Glossy > Direct and Glossy > Indirect passes in Cycles?

enter image description here

enter image description here

$\endgroup$
4
$\begingroup$

As you might know, Cycles is a Path Tracer, which calculates light "rays" shooting out of the camera, bouncing around, and then finding a light source. This, however, is the opposite of reality, where a light shoots out photons, which bounce around and make their way to our eyes.

Glossy Direct

A Glossy Direct pass produces a black and white result (a fac, or factor) that shows exactly what part of a scene is made up of visible Glossy BSDF materials.

In the following scene, there is a plane with a Glossy BSDF shader that is reflecting a blue-hued Diffuse BSDF shaded cube. It renders like this:

enter image description here

The Glossy Direct pass shows this:

enter image description here

Note how it excludes the background, the part of the plane hidden by the cube, and even the reflection of the cube. What it shows is only the rays that hit the Glossy BSDF and go directly to a light source.

These rays:

enter image description here

Not these rays:

enter image description here

Or these rays:

enter image description here

Or even these rays:

enter image description here

Glossy Indirect

A Glossy Indirect pass produces an in color result; at least partially. It is black everywhere except for any reflections.

In the same scene as above, the Glossy Indirect pass renders like this:

enter image description here

Note how it shows only the reflection of the blue cube. This can be especially helpful, because it can first be turned into an alpha mask pretty easily (see the Matte > Color Key node), which allows for compositing on reflections. See how it is used in gandalf3's answer on Post-processing Lightsabers in Blender. It can also be used just by itself. You can edit out the floor of a scene and leave yourself with just an object and it's reflection, which can produce a very cool result:

enter image description here

Above result composited like this:

enter image description here

These are just a few of the possibilities.

For the technical side of things, a Glossy Indirect pass shows these rays, which bounce off the glossy, hit any obstructions, bounce back to the glossy, and then find a light source. They indirectly touch glossy and find light:

enter image description here

Hope this helped and happy Blending!

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.