appleseed Users Forum

SPPM problem

I Setup one scene with 4 light around a head model, then I use “final render” with different settings to render it :

  1. SPPM, the result is strange

Below is the setting

  1. Path Tracer, this seems normal

The head has both brdf and bssrdf.
As @Mongo3 said in

I can not find the reason

Setting up SPPM is a bit tricky. One reason is the optimal sampler settings are quite different from path tracing and additional photon mapping parameter need to be adjusted too.

Basically it boils down to:

  • Use as many Light Photons per render pass as memory allows.
  • Use the Uniform Sampler with a low number of samples (2-4 ) and increase the number of Render Passes accordingly. The Photon map gets regenerated at every pass.
  • Reduce the initial photon gathering search radius Initial Radius from 0.1 (it is measured in % of the scene diameter) to lower values 0.05 - 0.01 if fine details seems to be too blurry. The image will become more grainy but less blurry - the grainy structure will disappears later with more passes when the render converges.
  • Set the main object receiving lighting as a Photon Target in the appleseed object properties. This helps sampling efficiency.

We have several threads discussing SPPM in appleseed: