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?