There are many things that can give an extra natural look to an image. But to my point of view and what i use to see in my daily works/test/practice/research is Light bounce quality. And this is more obvious when it come to interior rendering. Speaking of that particular case it is obvoius to said that if we consider X complex interior project done by a very talented professional artist and add some limitation about light bounce and engine algorithm settings you will end up with this :
From more natural look to more CGI look : Max bounces 64 Min bounce 2
Bidirectional guided path engine : 32 + 32
simple Bidirectional engine : 32 + 32
Guided path engine + (IDLCS) : 32
Simple path engine : 8
Simple path engine : 4
Simple path engine : 2
For example heavy optimisation for speed matter like low clamping / low bouncing ray tend most of the time to cut a lot in term of hyper realism (not talking about pretty or plausible renders). I believe that sometime smart algorithm and high bouncing settings can bring an extra obvious boost to final raw output that can't be seen otherway.
There is a correlation between corona default ray deph and image quality i thing : (25 by default )
There is also a correlation between brighter indigo output and light bounce. just saw it in the past with personal test ( Walls was so bright even at low light intensity
) : This is a quote from indigo features description page : https://www.indigorenderer.com/unbiased-rendering
Optimised for maximum quality
Indigo's CPU engine runs with a ray depth of many thousands by default.
While other, biased renderers commonly use a default of around 4-8 bounces and would struggle with a setting that high, Indigo is purpose-built for it and delivers great performance.
There is also another things i think could impact final output independly of artsits level. YES "energy conservation"
. here again it is about light bouncing quality/intensity . With something like this feature don't tell me that an interior scen will look the same even if you turn ON/OFF energy conservation. if light become darker and darker or less dark as it bounce arround object sure the output will be impacted. Add to that it mostly affect Diffuse or matt surfaces and ....
http://www.cgchannel.com/2018/09/isotro ... e-ifx-4-0/
Multiple scattering improves rendering of matte surfaces
New shading features in Clarisse iFX 4.0 include multiple scattering for reflected and transmitted light.
The software’s previous single scattering model minimised computation times, but caused surfaces to darken unrealistically as their roughness values increased.
The new implementation (shown above) approximates true multiple scattering – “while [it isn’t] strictly Lambertian diffuse reflection, it’s very close” – and is fully energy-conserving.
According to Isotropix, it has no impact on render time, and will be enabled by default
look at the final ball this is not tone mapping issue.
Again on Energy conservation and albedo strengh i always look at theses images with huge "
" in my head. Please look how bright is object even with diffuse white set to only 80%. we are not at 100% and it look like supernova ("yes i exagerated to make you see what i mean). from here :
https://coronarenderer.freshdesk.com/su ... is-albedo-
Some renderer are very senssible to setting like light bounce setting / albedo value. BTW i will retry to perform some test about that light behaviour question with today renderers state but i'm pretty sure of the results.