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kolby
11-28-2014, 03:23 AM
Hi guys, I am doing some tests with new importance sampling feature. It looks like it generates bit more natural lighting but at the cost of higher render time. Or I am doing something wrong ? Can anyone explain me, how to use it properly ? How much samples ? It is usable only for hdr lighting ? When to use it, and when not ?

fazi69
11-28-2014, 07:07 AM
I will join You on that question. Can someone explain what it do exactly ? Is there positives and negatives ?

RebelHill
11-28-2014, 07:42 AM
Its pretty simple... when using a backdrop to illuminate a scene... so backdrop colour, hdri image world, etc... it just delivers a better render in the mjority of cases (actually, mostly when using images/hdri rather than simple colour bg, which benefits little).

And that's all there is to it... It has no effect for luminous geo, etc, only illumination from a backgrop.

erikals
11-28-2014, 09:09 AM
hm, so it doesn't remove the splotch problem when using interpolated ?

RebelHill
11-28-2014, 09:15 AM
Well... yes and no.

No in the sense that it does nothing to secondary/subsequent bounces, does nothing to light coming from geo (be that illuminated or bounced)... but yes in the sense that splotchies will propogate. So if your backdrop illumination has hot/sharply contrasting areas, that produces a splotch/hot hit from the first ray, which will then, in the case of bounces, "carry over" in subsequent ones. So by cleaning up that initial illumination, you provide a better start point for the further bounces.

Andy Webb
11-28-2014, 09:33 AM
Does it work if using an HDR image mapped to a sphere or does it only work with the Image World plugin?

RebelHill
11-28-2014, 09:43 AM
No... because that would be luminous geo... its backdrop only.

erikals
11-28-2014, 10:21 AM
Well... yes and no.

No in the sense that it does nothing to secondary/subsequent bounces, does nothing to light coming from geo (be that illuminated or bounced)... but yes in the sense that splotchies will propogate. So if your backdrop illumination has hot/sharply contrasting areas, that produces a splotch/hot hit from the first ray, which will then, in the case of bounces, "carry over" in subsequent ones. So by cleaning up that initial illumination, you provide a better start point for the further bounces.

thanks again :]
yes, maybe this image gives some clues

Interior importance sampling
https://www.lightwave3d.com/static/lw/gfx/features/2015/importance_sampling_06.jpg

the examples seem to only use e.g. only a single HDRI though,
so what if we add an extra say, Area Light, will it produce the same splotches as before ?

i know i should try this myself with the 2015 trial version, but it's a bit easier to ask http://erikalstad.com/backup/misc.php_files/smile.gif

RebelHill
11-28-2014, 10:38 AM
so what if we add an extra say, Area Light, will it produce the same splotches as before ?

Yes... importance sampling is ONLY for BACKDROP ILLUMINATION

erikals
11-28-2014, 10:50 AM
hm, thanks, bit of a minus there...

zapper1998
11-28-2014, 11:29 AM
Yes... importance sampling is ONLY for BACKDROP ILLUMINATION

OK

Thank You


hehehe

:)

Andy Webb
11-28-2014, 11:34 AM
This has brought up another couple of questions:

Should the gamma of an HDR image be set to 2.2, I ask because I've just read on a site you should do this as most HDR images use this gamma.

If I'm rendering using a colour space of sRGB should the light probe be set to sRGB or linear?

Cheers

kolby
11-28-2014, 12:44 PM
Ok, thanks for explanation.