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I was able to completely eliminate the firefly "effect" by reducing the gamma of the hdr map to .45.
Here is the result. (24 minutes::2527 samples::8800gts::octane1.022)

Blurying your HDR map should do the trick too. Razor sharp high resolution HDR maps are only suitable for reflections but not needed at all for illumination.
It would be nice to be able to dissociate the two kind of maps in the textured environment settings by the way. Any insight on that Radiance?

Amplitude wrote:Blurying your HDR map should do the trick too. Razor sharp high resolution HDR maps are only suitable for reflections but not needed at all for illumination.
It would be nice to be able to dissociate the two kind of maps in the textured environment settings by the way. Any insight on that Radiance?

Do you loose any quality in illumination by doing this ?

No, you don't. It is a technique called Diffuse Convolution and it comes from Paul Debevec researchs in HDR lighting.
Here are two links:
Diffuse and Specular Convolution How to:
http://gl.ict.usc.edu/HDRShop/tutorial/tutorial6.html

Diffuse convolution applied to illumination in Autodesk Softimage. You can see that there is virtually no loss in quality and it's way faster too. (here for Final Gathering).
http://www.softimageblog.com/archives/248

Amplitude wrote:No, you don't. It is a technique called Diffuse Convolution and it comes from Paul Debevec researchs in HDR lighting.
Here are two links:
Diffuse and Specular Convolution How to:
http://gl.ict.usc.edu/HDRShop/tutorial/tutorial6.html

Diffuse convolution applied to illumination in Autodesk Softimage. You can see that there is virtually no loss in quality and it's way faster too. (here for Final Gathering).
http://www.softimageblog.com/archives/248

Very interesting reading, thank you

Now, they mention both diffuse and specular convolution, to lit either diffuse or rough specular materials..but don't mention which one is better when both material types are common in scene.
Would I achieve similiar result simply by using gaussian blur on my HDRi ?
And what is the point of all these super high-rez HDRi (Dosch,Guthrie's) ? When they're still not high rez enough to use as background image ? Pure reflection as you mention (eg.glass windows, car paint..) ?

Thank you a lot for your insight, hope you can answer few more of these question

I'm not sure you can get away with gaussian blur , it should reduce fireflies by reducing the sampling of the environment but the real 'blur' your looking for is the Convolution blur available in HDRshop.

Afaik the point of high res HDRI is specular reflections yes...
This leads to the point why the sIBL (smart Image Based Lighting) system has been invented to sort these issues.
If you don't know what it is : it's a customizable collection of HDR images , with each version properly linked and set up in your host app. So basically it's a script that automates the setup of HDR environment using SuperHighRes for backgrounds, Highres for Specular reflections and lowRes Convolution Map for illumination.
Plugins exists for main 3D apps (Maya, XSI, MAX etc).
But right now none of that exports to Octane.

And I think Octane should really have the option to use different maps for illumination and specular reflections.

Here is the link to the sIBL page http://www.smartibl.com/sibl/how_it_works.html

That's awesome link too Now I understand completely, who knows how hard is it to implement this, maybe we'll get this later.

All those free collections, is this in resources yet... ? Should be

edit:
Now I remember: Radiance said we would be able to set custom background while using sun/sky system in next beta, but not sure if this applies to IBL too.

Doing the opposite, that is boosting the gamma, gives you nice soft shadows, as suggested here: http://bertrand-benoit.com/blog/2010/02 ... -lighting/
That's why I usually do, it produces fireflies, but guess what, we have a firefly-free future ahead of us with MLT and all that coming soon. I can also get rid of fireflies by downsampling and by blending two render passes together in Photoshop. If we had IBL (or plain old Reflection, Refraction and Illumination slots) would be awesome!

Great post, and great information, now I'm anxious to test both approaches.... and lot's of stuff to read!
Thanks