While testing some Wings3D scenes, oort has told me that the HDRI/IBL scenes were too bright compared with, for example, TheBounty.
I've done some checks and I've found what I believe is a serious bug in YafaRay: when rendering scenes with IBL, energy is not conserved and sometimes (often) the shiny diffuse surfaces reflect more light than the light coming from IBL, what I think is very wrong.
For this test, I've created a very simple test scene with the following:
* To avoid any color management issues, I've disabled sRGB, set all to linear, gamma=1 and gamma input=1
* World background set to "constant color" 0.5,0.5,0.5, IBL enabled with gain 1.0
* Sphere with shiny diffuse set to color 1.0,1.0,1.0 and diffuse amount 1.0
Under the above conditions, I would expect the sphere to reflect the IBL light, that is 0.5,0.5,0.5
However, unfortunately, in YafaRay v3.0.0-beta it does not happen. The sphere is reflecting more than 0.5,0.5,0.5!!
I think this is not a problem in the Shiny Diffuse material but in the Integration/Sampling process, which worries me a lot, as it's a fundamental part of YafaRay.
I've tried to trace back this bug and it seems to go back a long way. I've built the code from the very old v0.1.2 and the same issue happens there.
My results are:
* Blender internal: correct, sphere reflects 0.5 (you cannot distinguish the sphere from the background in this example)
* Blender cycles: correct, sphere reflects 0.5 (you cannot distinguish the sphere from the background in this example)
* YafaRay v3.0.0-beta INCORRECT, sphere reflects MORE than 0.5 (you can clearly distinguish the sphere from the background in this example)
* YafaRay v0.1.2 INCORRECT, sphere reflects MORE than 0.5 (you can clearly distinguish the sphere from the background in this example)
I've attached the test scene for your reference.
Of course, this is a simple scene, but I would expect this issue to be quite bad when using other IBL with more contrast such as HDRI or Sky. Even when this seems to have been happening for a long time, for me this is now a maximum priority as it affects the realism of the scenes and the correct illumination of the objects. However, it will take me quite some time to figure out how to fix this, because I have the feeling that the TheBounty results are somewhat darker than they should, but I have to do more tests to confirm if this is true or not.