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Thread: Suspecting bug in clearcoat

  1. #16
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    Okay... so, while I know a bug report has been submitted and that Newtek confirmed that it was a bug, I just wanted to add my experiences / interpretation of clearcoat for reference. Perhaps it will help people who want to work with it, but so far have not found themselves able to because of fireflies.

    In my experiences with clearcoat, I have come to believe that the percentage for it is not the amount per se... it's the coverage of the object by the clearcoat.

    So, when I use clearcoat, I set it for 100% (full coverage). The specular setting (again, in my experience) is really what controls how strong the effect is.

    Using that logic, if you set clearcoat for 1%, you are covering only a small area of each polygon at angle of the object... and using a high specular with that very small area causes blow out. That's where the fireflies come from.

    Try this experiment.

    Using the dragon, preferably with an HDRI textured environment and environment light set at 1.0 lx (no other light source) set the clearcoat for 100% and the specular for 1%.

    You should get a beautiful render in just a few minutes using relatively low render settings.

    These are the render settings I used (sorry, wish I could post an image but I can't);

    RENDER TAB

    All boxes checked at the top (Raytrace Shadows, Reflection, Refraction, etc.)

    Diffuse Bounces 5
    Ray Recursion 6
    Transparency Recursion 6
    Reflection Recursion 4
    Refraction Recursion 4
    Ray Precision 10
    Reflection Samples 10
    Refraction Samples 10
    Subsurface 1

    (Global MipMap, Flare, Light, Edge are at the default of 1)

    Enable Noise Filtering checked
    Render Tile Size 8

    GLOBAL ILLUMINATION

    Monte Carlo - Brute Force

    Intensity 100%
    Rays 1

    Caustics, Sample Backdrop, ISBG Sampling checked

    ISBG Samples 1024

    CAMERA SETTINGS

    Here, I think the only setting that might be important is Samples.

    I turned off Adaptive Sampling and set the Minimum Samples to 15 (although I think you could still get great results with minimum samples of 10).

    No Motion Blur or Particle Blur for this one, and no DOF.


    The render takes about six minutes on a dual Xeon system at 1920x1080. For faster renders, I'm sure the settings can be played around with to get a good mix of speed and quality.

    Give it a try using these settings and let me know what you think.

  2. #17
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    Quote Originally Posted by David_CGC View Post
    Admittedly, I'm not a programmer, but I don't understand why the renderer can't have a sanity-check of some sort. If it gets a result on a single pass (or even every pass!) of a single pixel that's a hundred or a thousand times brighter than the other passes, and the surrounding pixels, it's far more likely that the value is an error than that there's one impossibly-bright object in the scene that's smaller than a single pixel in the render (well, hundreds of such objects scattered around the frame). I basically do it manually to clean up fireflies in my stills, cranking down the exposure of an exr render until the fireflies are all that's left, and then using that as a mask and using content-aware fill on my main layer.
    Ridiculously bright spots are a valid part of the rendering equation. You see them when the sun glistens off a tiny drop of water, or some glitter, or a bit of sand, or just about anything. Ideally, given a near infinite number of aa passes/samples, it should resolve into some kind of picture. Unless, of course, the bright spots are errors, like these.

  3. #18
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    I suspect clearcoat is using a non-physically plausible specular type.

  4. #19
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    I've mentioned this in a couple of other threads about fireflies, but the idea doesn't seem to "catch on". IMO, this is a day-one bug in LW2018 in that the Intensity of the Light's reflections are not attenuated with distance as is their illumination. So, even a low-intensity Light at quite a distance from a specular (or in this thread, metallic and clear-coated) Surface will produce "hot spots" on flat facets of the surface.

    Attached is a sample scene to demonstrate the "problem" which contains:

    1. A 50% Specular unsmoothed blue sphere with flat facets
    2. A Distant Light, 0.1 lux, about 283 meters from the object
    3. A Point Light, 3.141 lux, almost 40 meters from the object
    4. An Area Light, 3.141 lux, shrunk down to (.1,.1,.1), over 40 meters away from the object


    Each of the Lights was carefully positioned to reflect in one of the facets of the unsmoothed sphere.

    Click image for larger version. 

Name:	Fireflies_LightVisibilityInReflections_Setup.jpg 
Views:	19 
Size:	869.5 KB 
ID:	143504

    With GI off and a plain gray background, as can be seen in the render none of the Lights have sufficent illumination to show any color at all on the object, but all three of them show "hot spots" as reflected in the Specular surface:

    Click image for larger version. 

Name:	Fireflies_LightVisibilityInReflections.jpg 
Views:	29 
Size:	16.2 KB 
ID:	143503

    The Distant light is a LONG way away from the object, but still produces an extreme hotspot in one of the facets of the sphere.

    I postulate that when these inadequately attenuated hot spots are reflected (or re-reflected) in the micro-facets used to implement Roughness, it produces the fireflies. IMO, the reflection of a Light should attenuate with distance at approximately the same rate as the Light's illumination intensity. Personally, I would rather have the reflection of a Light be able to be completely disabled by clearing the Visible to Camera flag in the Light's Properties.

    Hopefully, the bug submitted by lertola2 in a previous post and "fixed internally" will have fixed this Light Reflection problem not just for Clearcoat, but for reflective surfaces in general (including Specular and Metallic).

    mTp
    Attached Files Attached Files
    Last edited by MonroePoteet; 12-07-2018 at 04:20 PM. Reason: sentence clarification / structure; add re-reflected

  5. #20
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    I suspect you would have to have a separate render buffer for every light.

  6. #21
    Electron wrangler jwiede's Avatar
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    Unfortunately, as they've apparently "moved on" from LW2018 development, that apparently means said fix (w.r.t. a serious problem present since LW2018's initial release) will conveniently (for Newtek, not LW2018 customers) arrive in a for-pay version upgrade.

    I really hope they do the right thing and release the fix for LW2018, given how long we've been complaining about firefly problems, and how significant a defect they represent (neither limiting LW to LDR rendering nor turning off "glossy reflections" represent broadly-acceptable solutions or even workarounds, they're both too limiting). Whether they've "moved on" or not, it's a significant, broadly-impacting defect in the current product, and as such, merits a fix for the current product.
    Last edited by jwiede; 12-07-2018 at 05:55 PM.
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  7. #22
    Electron wrangler jwiede's Avatar
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    Quote Originally Posted by Dan Ritchie View Post
    Ridiculously bright spots are a valid part of the rendering equation. You see them when the sun glistens off a tiny drop of water, or some glitter, or a bit of sand, or just about anything. Ideally, given a near infinite number of aa passes/samples, it should resolve into some kind of picture. Unless, of course, the bright spots are errors, like these.
    When the sun or similarly bright source glistens off invisibly-micro-scale reflectors, though, it doesn't yield a hyper-bright long-distance-visible reflection, and thus the problem. These fireflies are both much too bright and much too large (esp. relative to roughness micro-facets) to be reasonable representations of such micro-scale reflections. It's an energy-conservation problem: These are much, much brighter (and larger) reflections than their responsible sources should be able to produce given size and distance of camera, even with full sun as source.

    Just a SWAG, but what we're seeing is almost as if all the micro-facets representing a given pixel were all (or even most) reflecting in the precise same direction, that or somehow the energy return is being wildly magnified for each micro-facet. Also, that it seems to happen even when roughness is set to 0% implies either there's some roughness being added* (in certain cases, esp. self-reflection) even when set to 0% or something similar is occurring. Having higher roughness values obviously worsens the effect. Regardless, it's a problem, and certain specular settings appear to exacerbate it significantly.


    *: To clarify: By itself, that's not unreasonable. There's really no such thing as "material roughness = 0%" at the scales we're discussing. However, in combination with whatever else is occurring, it makes the issue difficult to avoid.
    Last edited by jwiede; 12-07-2018 at 06:26 PM.
    John W.
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  8. #23
    skeptic lertola2's Avatar
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    Quote Originally Posted by MonroePoteet View Post
    I've mentioned this in a couple of other threads about fireflies, but the idea doesn't seem to "catch on". IMO, this is a day-one bug in LW2018 in that the Intensity of the Light's reflections are not attenuated with distance as is their illumination. So, even a low-intensity Light at quite a distance from a specular (or in this thread, metallic and clear-coated) Surface will produce "hot spots" on flat facets of the surface.

    Attached is a sample scene to demonstrate the "problem" which contains:

    1. A 50% Specular unsmoothed blue sphere with flat facets
    2. A Distant Light, 0.1 lux, about 283 meters from the object
    3. A Point Light, 3.141 lux, almost 40 meters from the object
    4. An Area Light, 3.141 lux, shrunk down to (.1,.1,.1), over 40 meters away from the object


    Each of the Lights was carefully positioned to reflect in one of the facets of the unsmoothed sphere.

    Click image for larger version. 

Name:	Fireflies_LightVisibilityInReflections_Setup.jpg 
Views:	19 
Size:	869.5 KB 
ID:	143504

    With GI off and a plain gray background, as can be seen in the render none of the Lights have sufficent illumination to show any color at all on the object, but all three of them show "hot spots" as reflected in the Specular surface:

    Click image for larger version. 

Name:	Fireflies_LightVisibilityInReflections.jpg 
Views:	29 
Size:	16.2 KB 
ID:	143503

    The Distant light is a LONG way away from the object, but still produces an extreme hotspot in one of the facets of the sphere.

    I postulate that when these inadequately attenuated hot spots are reflected (or re-reflected) in the micro-facets used to implement Roughness, it produces the fireflies. IMO, the reflection of a Light should attenuate with distance at approximately the same rate as the Light's illumination intensity. Personally, I would rather have the reflection of a Light be able to be completely disabled by clearing the Visible to Camera flag in the Light's Properties.

    Hopefully, the bug submitted by lertola2 in a previous post and "fixed internally" will have fixed this Light Reflection problem not just for Clearcoat, but for reflective surfaces in general (including Specular and Metallic).

    mTp
    I am not sure if this scene points out a bug or not. Are you trying to demonstrate that lights so distant from the an object should be so dim that they should not be visible in reflections? All the rays from a distant light are parallel so it makes not difference where a distant light is placed. Only its rotation matters so its not surprising that a distant light is visible in the reflection. For the area light you have normalize turned on. I was watching RebelHill's tutorial on lighting last night and he pointed out that with normalize turned on for area lights then they will give out the same amount of light no matter what size they are. So a very small area light with normalize turned on should be the same as a point light. If you turn normalize off then the area light is not visible in the reflection which is how it should be I think. So for the point and area light I take it that you think the reflection is too bright given how far they are from the sphere? But how can we tell how bright they should actually be?

    I agree that it would be good if turning off visible to camera would also make lights invisible in reflections.

  9. #24
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    Quote Originally Posted by lertola2 View Post
    I am not sure if this scene points out a bug or not. Are you trying to demonstrate that lights so distant from the an object should be so dim that they should not be visible in reflections? All the rays from a distant light are parallel so it makes not difference where a distant light is placed. Only its rotation matters so its not surprising that a distant light is visible in the reflection. For the area light you have normalize turned on. I was watching RebelHill's tutorial on lighting last night and he pointed out that with normalize turned on for area lights then they will give out the same amount of light no matter what size they are. So a very small area light with normalize turned on should be the same as a point light. If you turn normalize off then the area light is not visible in the reflection which is how it should be I think. So for the point and area light I take it that you think the reflection is too bright given how far they are from the sphere? But how can we tell how bright they should actually be?

    I agree that it would be good if turning off visible to camera would also make lights invisible in reflections.
    Also, did you set up a falloff node for any of them? If not, aren't they all essentially unlimited light, i.e., their intensity doesn't fall off with distance at all?

  10. #25
    skeptic lertola2's Avatar
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    Quote Originally Posted by RPSchmidt View Post
    Also, did you set up a falloff node for any of them? If not, aren't they all essentially unlimited light, i.e., their intensity doesn't fall off with distance at all?
    The lights do have inverse squared falloff set (except for the distant light of course) so they don't have to have nodal falloff I think.

  11. #26
    Registered User gdkeast's Avatar
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    Yes, I totally agree. I would hope known and documented bugs are fixed in 2018 before "onto the next."

  12. #27
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    Well, as I said, it's only a hypothesis. To me it makes no sense that a 0.1 lux DistantLight (with 0.0 Angle) almost 300 meters away from an object which does not illuminate that object at all (or just barely) would show a huge, bright reflection in it. To me it makes no sense that a POINT Light would show any sizeable reflection at all.

    If I replace the Area Light with a luminescent sphere of the same size and same distance from the faceted, specular sphere, I have to increase the luminosity of it to over 2000% for it to be visible in the reflection at all, and then it appears as a tiny, indistinct dot. To me it makes no sense that a 3.141 lux Area Light which doesn't illuminate the faceted sphere at all would have a bright, distinct reflection on that object.

    In conclusion, I hope LWDG can provide some relief from the fireflys, whatever their source may be!

    mTp

  13. #28
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    To me it makes no sense that a 0.1 lux DistantLight
    Agreed with that. Unfortunately, for direct lighting it's still more practical to use some fakery to get things done. If somebody knows that there's an accepted solution to this, please speak up.

  14. #29
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    Quote Originally Posted by jwiede View Post
    Unfortunately, as they've apparently "moved on" from LW2018 development, that apparently means said fix (w.r.t. a serious problem present since LW2018's initial release) will conveniently (for Newtek, not LW2018 customers) arrive in a for-pay version upgrade
    I've been out of touch because of work upheavals... What have I missed with regards to development announcements?

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