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Thread: Phantom Reflection

  1. #1
    Curmudgeon in Training Ma3rk's Avatar
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    Phantom Reflection

    'Tis my day for weirdness I guess.

    I've a mirror (that I'm about to replace with just about anything other than a mirror)) that's picking up a "reflection" but I can't figure out what from.

    At first I thought it was the wall surface, but no. I put an object (red arrow) between the mirror and the apparent source, but that didn't block it. I then but another object (a black slab) between the camera & mirror & that was able to block it. I gave that a partial dissolve & edge colors to show where.

    But there's nothing there in the scene other than the 64 lights, but the angle is wrong.

    I've tried different surfaces on the mirror but have the same result. Started with dielectric but this screen grab is just using standard to simplify things; Raytrace only & Glossy reflections off in each case though.

    Any suggestions as to how to diagnose this?

    TNX

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    "Never be a cat in a cartoon. Never." Chief Wiggum

  2. #2
    TrueArt Support
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    But there's nothing there in the scene other than the 64 lights, but the angle is wrong.
    Use binary search algorithm.
    https://en.wikipedia.org/wiki/Binary_search_algorithm
    Split objects to two equal groups. Check 1st halve. Check 2nd halve.
    Continue splitting again. Until there is 1 light.
    It'll find light (if light is causing it), in log2(64)=6 repetitions (because 2^6 = 64)

  3. #3
    Curmudgeon in Training Ma3rk's Avatar
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    I didn't have to get quite that anal, but I did track the offending light down.

    And it IS a bug. I just don't know if it's a known one but will send a note & point them to this topic I guess.

    Just the right set of camera & object placement & properties is what revealed this. The light in question is a Primitive used in a table lamp, with a shade on, three rooms & about 6 walls away. I just happened to only have the one lamp on in the Bedroom which is what threw me. If I'd had both on it would have made more sense, & I'd have figured it out much sooner as in the third image.

    Take a look:

    Where I started:

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    Mirror now excluded:

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    Both BdRm lamps ON and NOT excluded:

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    Overhead Wire view:

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    "Never be a cat in a cartoon. Never." Chief Wiggum

  4. #4
    Super Member kolby's Avatar
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    Miracle !
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  5. #5
    So you're saying the specular is not being occluded by geometry, because it just looks like a specular hotspot, reflecting in the mirror?. The only other thing i could suggest is a material elsewhere has a very low roughness value, and it's a bounce specular. Try and disabling reflection (So it's just pure light specular, not indirect specular) to see if it's some sort of weird indirect reflection?

    It's a solvable bug, since you can safely exclude those materials from those lights. It could be a ray precision issue, light leak because of a geometry error, try double precision? Otherwise report it.

  6. #6
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    Casa Fugazi ?

    Good work on this stuff Ma3rk

    Last edited by gar26lw; 05-24-2019 at 08:03 AM.

  7. #7
    Curmudgeon in Training Ma3rk's Avatar
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    Quote Originally Posted by Tobian View Post
    So you're saying the specular is not being occluded by geometry, because it just looks like a specular hotspot, reflecting in the mirror?. The only other thing i could suggest is a material elsewhere has a very low roughness value, and it's a bounce specular. Try and disabling reflection (So it's just pure light specular, not indirect specular) to see if it's some sort of weird indirect reflection?

    It's a solvable bug, since you can safely exclude those materials from those lights. It could be a ray precision issue, light leak because of a geometry error, try double precision? Otherwise report it.

    Ya, that's how I started assuming it was a material setting, toggling various settings, but not the case. So as you say I just excluded those lights for that particular object.
    "Never be a cat in a cartoon. Never." Chief Wiggum

  8. #8
    Curmudgeon in Training Ma3rk's Avatar
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    [QUOTE=gar26lw;1571730]Casa Fugazi ?

    Good work on this stuff Ma3rk /QUOTE]

    Yup. Thanks.

    https://www.daz3d.com/fg-moderno-casa


    I'd forgotten that from Wolf of Wall St.
    "Never be a cat in a cartoon. Never." Chief Wiggum

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