One place we should definitely not skip when trying to improve our render time is the Performance panel in Render tab.
Rendering to tiles makes better use of the processor power. In the newest Blender version, the numbers in the tiles section means their size in pixels, but understanding which size works best is a bit baffling. Tests showed that GPUs work best with 256 x 256 tiles while CPU makes best use of the 64 x 64 tile size (regardless of whether we are talking about BI or Cycles on CPU).
Large projects rendered in Blender Internal can make use of the Baking panel options. This means a bit more work than simply getting some settings right but a lot of render time can be saved by transforming shading information into UV mapped textures. This works only with meshes that have been UV unwrapped. The bake drop down menu offers more ideas of what can be pre-rendered this way, like AO, shadows, displacements, mirror and specular colors or texture layers into one.
Cycles can also benefit from pre-rendering tricks: complex geometry can be baked in BI as normal maps, then used on simplified variants of the meshes in Cycles. Static backgrounds can be pre-rendered and composited in the final render. This extra effort might not be justified for most types of still images but is to be considered when rendering animations of complex scenes.
One other place you might want to visit when optimising a scene is the Simplify panel in the Scene tab. This panel allows you to have a set of alternate settings for the main render time killers like subdivision and sss, and use it for faster render tests or comparing different values.
This concludes our 7 part mini course on how to optimize your render time. It’s far from complete, and I am sure there are more things to add to it. We’ll do that in time, as we learn about more ways to save on rendering time. If you have any tips, please share them in the comments.
