normally i do also learn sthg. new while having such a discussion, and did quite a bit, but have to give up on it now.Proupin wrote:"Vray RT is unbiased so it will not use any of the render engines available such as irradiance map or light cache, if these are set, Vray RT will simply ignore them." source. They're probably lying though... and it's not only GPU accelerated, you can actually choose CPU as well, haven't you heard?
Maxwell is based on MLT, not some generic "gi algorithm" (source), and it's the same method used by Kerkythea, Indigo and LuxRender. Maxwell has passes, then the others could have them too... I'm guessing GPU/Cuda/Vram limitations make this hard or something. Maybe RS can somehow specify what they think will be supported in the future regarding passes...
I agree progressive rendering is just 'the way' unbiased rendering methods get to their respective solutions, it is not the reason, but they all share a progressive render nonetheless in orther to be interpolation (bias) free. That's why imo directlighting rendered this way is unbiased. there are just no bias errors to be found.
There is this question in the fryrender faq: fryrender is an unbiased render engine. What does that mean? too long to paste here, it states that with unbiased methods there are no artifacts caused by interpolation of light samples, like the ones irradiance maps (biased) produce. There is also a similar explanation in wikipedia, and there is a link to a small article which is pretty clarifying... no trace of 'randomly shot rays' or other properties you seem to give to the unbiased concept... do you have any sources for what you're stating? glad to learn from you guys.
i misquoted vray rt as comlpetely biased, because this are no longer separate products, what means biased and unbiased are just options. i have the same sources like you, all over the net. they explain raytracing, pathtracing, metropolis light transport, monte carlo methods and how they work together, and what they mean. if you don't think that any of this has to do with the calculation of rays, i can't help
i still haven't gathered much informations about unbiased renderers, that can render passes, especially ambient occlusion, refraction, reflection, shadows (what was all on the wishlist of the posters here). other passes like depth, material characteristics, etc. are pretty straight forward and imo method independent.
only exeption to all that is maxwell, providing shadow and even reflection channels. i don't know how it works, but at least i have found a post quoting a method to fake a shadow pass: http://www.lux-render.net/forum/viewtop ... 738#p23323 (by the way, the luxrender wiki has also nice explanations about unbiased rendering; i even think i have read the word "ray" somewhere). good advantage for maxwell, but even there the reflection pass (right from the maxwell documentation) doesn't look quite like i imagine a reflection pass should look like.
imo the whole discussion was also a bit off, because of a diffuse use of terms (also from my side).
so the point is, octane is unbiased, it uses pathtracing and "population monte carlo" alogrithms, and it is a gpu only renderer. and thus not compareable to renderers that are cpu based, because the use of the gpu for calculations implies specific limitations. and this means not every method available with cpu based calculations can be ported to a gpu. octane was even the first one to implement something mlt "alike" (=pmc) in addition to common pathtracing that most other gpu accelerated renderes still use.
so, if you find gpu based unbiased renderes, which provide several passes, just post'em here - would be of course interesting how they do it...
