  The use of computer generated images to train Deep Neural Networks is a
viable alternative to real images when the latter are scarce or expensive. In
this paper, we study how the illumination model used by the rendering software
affects the quality of the generated images. We created eight training sets,
each one with a different illumination model, and tested them on three
different network architectures, ResNet, U-Net and a combined architecture
developed by us. The test set consisted of photos of 3D printed objects
produced from the same CAD models used to generate the training set. The effect
of the other parameters of the rendering process, such as textures and camera
position, was randomized.
  Our results show that the effect of the illumination model is important,
comparable in significance to the network architecture. We also show that both
light probes capturing natural environmental light, and modelled lighting
environments, can give good results. In the case of light probes, we identified
as two significant factors affecting performance the similarity between the
light probe and the test environment, as well as the light probe's resolution.
Regarding modelled lighting environment, similarity with the test environment
was again identified as a significant factor.
