Is HDRI Lighting Generally Noisier?

[BigAl3D]

Was wondering if, in general, lighting a scene with and HDRI introduces more noise than traditional Corona lights or Sky/Sun lighting?

[Nejc Kilar]

Yes indeed, you're right :) I'm not that privy on the math but from my understanding it has to do with how much more difficult sampling an HDRI sphere is compared to a known quantity type setup such as the Corona Sun & Sky system.

That said, depending on the HDRI, you might get more colorful lighting in the scene as the HDRIs sometimes have different amounts of clouds in them as well as a ground etc. I still use them to this day for interiors although the big problem with them is obviously the fact you can't just be like "yo, make the sunlight more diffuse" :)

[burnin]

FYI, image size plays quite a role in computing. The bigger it is (resolution & bit-depth), the more resources it takes. Ages ago, when  this tech was introduced, we used different sizes for different purposes (large 8bpc for background, medium size for reflections/refractions and small HDR for lighting... to fit it all in RAM and get some decent rendering times. Few engines still support this workflow.

[BigAl3D]

Thanks for the info. In my case, I had a car with a studio look, but black and white, so what I should have done is use the image for reflections and place more Corona lights around. I will compare and post back for others to learn.

[romullus]

Unless you're rendering long animation where every saved second counts, i would say it doesn't matter if HDRI is slightly noisier than native lights. You just render few minutes longer, or use denoiser. Choose the method that is more convenient to use, or brings you closer to the result that you want and don't care about the noise.

[BigAl3D]

In this case, it's only a 4-second shot, but the client wanted it super smooth. With my two Macs rendering, it was taking 7 hours and I didn't have much time for mistakes. I also had several similar shots. I've had good results using 5% noise and denoiser, but these were noisier still, even after the denoiser was cranked up.

When I have a moment, I'll post some images. At some point, a render farm will come into play I know. Thanks again for the info.

[burnin]

Hmm, could also be that specific HDRI map. IME, some can be quite 'wicked' and need a bit of TLC. Also IIRC, some years back there were few such issues... w/ extensive noise using HDRIs in Corona Sky... need to check forums... 

[maru]

IIRC in Corona the resolution of the HDRI doesn't matter (or not much). Environment light is also nicely optimized now, not like in the old times when we had to use portals.
What could help with render times is increasing the Light Samples Multiplier to something like 4. Then the lighting generated by the enviro (and other light sources) should render less noisy faster, at the cost of other effects like GI or glossy surfaces.