# Rendering one pass only to avoid unnecessary computations in Cycles

Using Cycles, I only need to render one pass (depth map and surface Normals) of a 3D shape in the scene. I do not need the RGB rendering at all although most of the computation is spent on rendering RGBs. Un-checking Combined in Render Layers --> Passes seems to do nothing. Using nodes, connecting either depth map or Normal to the composite node will also do nothing as mentioned here too. I tried setting bpy.context.scene.cycles.samples to a pretty low number as the depth map quality seem not to change. But I need to set it to a higher number in order to get accurate surface Normals and this causes the computation become more heavy.

Although I do not fully understand the solution posted here, but I think it does not apply to my problem (or I don't know how to do it properly. So I wonder how I can do this?

• Possible duplicate of: blender.stackexchange.com/questions/102297/… – user1853 Mar 8 '18 at 0:24
• @cegaton Thank you! Would I get what I want by removing all the materials as well? I think this should be an easy solution. However, I wonder if there is non-invasive solution to do this? :) – Amir Mar 8 '18 at 0:39
• The combined pass cannot be disabled. So do whatever you can to make the render as efficient as you can to get the information on the passes you are interested in. An easy way to do this in cycles is to assign a simple shader to the whole layer, that will override whatever other materials are assigned to the objects in the scene. blender.stackexchange.com/questions/102297/… – user1853 Mar 8 '18 at 0:46
• The way cycles works doesn't permit this; the depth/normal/RGB information is gathered in the course of tracing many light paths throughout the scene. Simply disregarding the RGB information from those paths won't make the process faster. – gandalf3 Mar 8 '18 at 3:15
• The only thing you can really do is lower the samples (16 is probably plenty) and limit the bounces to 1. Or use BI (or possibly openGL). – gandalf3 Mar 8 '18 at 3:19