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Thread: Importance sampling

  1. #1
    Super Member kolby's Avatar
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    Importance sampling

    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 ?
    Last edited by kolby; 11-28-2014 at 04:43 AM.
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  2. #2
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    I will join You on that question. Can someone explain what it do exactly ? Is there positives and negatives ?

  3. #3
    Goes bump in the night RebelHill's Avatar
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    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.
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  4. #4

    hm, so it doesn't remove the splotch problem when using interpolated ?
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  5. #5
    Goes bump in the night RebelHill's Avatar
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    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.
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  6. #6
    Time Traveller Andy Webb's Avatar
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    Does it work if using an HDR image mapped to a sphere or does it only work with the Image World plugin?
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  7. #7
    Goes bump in the night RebelHill's Avatar
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    No... because that would be luminous geo... its backdrop only.
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  8. #8
    Quote Originally Posted by RebelHill View Post
    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/l...ampling_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
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  9. #9
    Goes bump in the night RebelHill's Avatar
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    Quote Originally Posted by erikals View Post
    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
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  10. #10

    hm, thanks, bit of a minus there...
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  11. #11
    Michael Nicholson zapper1998's Avatar
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    Quote Originally Posted by RebelHill View Post
    Yes... importance sampling is ONLY for BACKDROP ILLUMINATION
    OK

    Thank You


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  12. #12
    Time Traveller Andy Webb's Avatar
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    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?

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  13. #13
    Super Member kolby's Avatar
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    Ok, thanks for explanation.
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