HDRI quality setup

[RickToxik]

It might be a dumb question, but I am having a real hard time to light my scenes with hdri. It seems whatever the sample limit I set, it's always grainy. Do I have to add some area lights too or is it me or..? A few tips would help. Thx

[natalievfx]

I have found the same issue. It really depends on the image. As all the pixels are basically just a bunch of little lights, you need to be careful what images you use. Images with a few strong light pixels can throw a bright grainy rays all over your scene. Try this image: http://www.zenofilm.at/DLM_Pro/download.php?80

[RickToxik]

Thank you natalievfx. I also noticed that I was getting different results with different hdri's.

I was trying with this excellent serie of hdri's
http://zbyg.deviantart.com/art/HDRi-Pack-3-112847728

It's just that I like them a lot, and I was getting better results in mental ray than octane with those. I don't know why, it's funny.

[Proupin]

The problem usually is that you need a hi-res hdri for reflections (actually, a hi-res LDR is good enough), but what works best for illumination is a blurred, low-res version of that same hdri. HDRI Shop has a specific function for that, 'diffuse convolution'.

Since we can't, for the moment, choose different maps for illumination and for reflections (or HDRI+sun for that matter), you're stuck with either one, or trickery.