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Thread: Unified Sampling and filter type

  1. #1
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    Default Unified Sampling and filter type

    I've been trying out unified sampling, and it is very promising. Something I've noticed are artifacts show up depending on which filter is being used. I have been using Mitchell to get the cleanest result, but that seems to generate light dots at edges, like a sharpen filter. Triangle doesn't do this. This is just by making a plane primitive and a light. A higher quality setting seems to resolve it, but it doesn't do this with regular anti aliasing. I'm using Maya 2012 SP2, so probably an old version of MR 3.9.1.48

    Another question, does unified sampling have any influence on final gather when it's not in brute force mode?

  2. #2
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    Mitchell creates data where it doesn't exist. That is the nature of a sync type filter. If you want sharper detail, try gauss with a smaller window like 2 2 or even 1.6 1.6, eg.

    As for non-brute force FG, it will be calculated like regular interpolating FG wherever each sample occurs. So that will not affect FG point density, or rays, but could still make something look smoother. If you are going to reduce your filter window, for example, the greater number of samples from unified could help you.
    Barton Gawboy
    Training and Special Projects, NVIDIA ARC
    LAmrUG Forum Originator

  3. #3
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    There is also a bug when using unified sampling with triangle filter and filter size with float value (here it's triangle 2.2 2.2)

    It's not happening with regular sampling and with other filter type.

    unified_multipixel_tirangle_float.jpg

    edit : mental ray for maya 3.9.1.36

  4. #4
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    Can you send me that scene as an mi file? I can't reproduce using 3.10, and I want to double check it.

    By the way, did you know that with unified sampling, you can now set filter type separately for each user framebuffer? Not sure when that will get integrated into DCC apps, however.
    Barton Gawboy
    Training and Special Projects, NVIDIA ARC
    LAmrUG Forum Originator

  5. #5
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    Here it is !
    unified_multipixel_tirangle_float.mi

    It's only a sphere and a plane both with mia_material_x

    And I only knew the default option that allow disabling filtering for render pass.

  6. #6
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    OK, I duplicated it; when the filter window size is scalar/float with fractional part, for example 2.2 2.2 in your file not just integer like 2 2. In general, fractional filter window sizes should work, but there may be an issue here in unified. And it is there for triangle, mitchell and lanczos.

    For what its worth, we'd prefer smaller gauss windows for those desiring sharper looks. Now triangle doesn't introduce data where there isn't data, but mitchell and lanczos do.
    Barton Gawboy
    Training and Special Projects, NVIDIA ARC
    LAmrUG Forum Originator

  7. #7
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    Yes, it was not a problem, changing the filter type is not a big deal. But I wanted to report it.

    I try to avoid using lanczos or mitchell, and especially when dealing with high range image.

    I will try using gauss with a small window ! I was always avoiding this filter because it was to soft with default filter size.

  8. #8
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    For what its worth, we'd prefer smaller gauss windows for those desiring sharper looks. Now triangle doesn't introduce data where there isn't data, but mitchell and lanczos do.
    Bart would this be the case for regular AA as well, or just unified?

  9. #9
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    Yes, that is a preference based on the mathematics of filtering. Use your judgement based on your eyes. But consider the alternate smaller gauss window in your judgements. As sampling per pixel goes up, it makes more and more sense to use it that way, because there will be enough samples in that small window.
    Barton Gawboy
    Training and Special Projects, NVIDIA ARC
    LAmrUG Forum Originator

  10. #10
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    Quote Originally Posted by bart View Post
    Yes, that is a preference based on the mathematics of filtering. Use your judgement based on your eyes. But consider the alternate smaller gauss window in your judgements. As sampling per pixel goes up, it makes more and more sense to use it that way, because there will be enough samples in that small window.
    Hi all
    Bart when you talk about smaller gaus window, you refer to width and height values that appears in render setup panel, tab renderer?? (in 3dsmax)
    thanks a lot
    cheers
    richard

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