Author Topic: Interior Scene Light Bleed Corona 6  (Read 4533 times)

2020-09-17, 04:29:37

MAY3D

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Hi all

I have just moved to V6 from V5 and I'm getting, what looks like, light bleed in the corners of my interior scene, between the ceiling and walls (see image for reference, area affected circled in green). I didn't see anything like this in the previous version of Corona. This is a newly created scene, though I have a mix of new geometry and library assets and I merged in a CoronaSun & HDRI from a previous (V5) scene. Can anyone offer some suggestions of how to fix it?

Points to note:
- I have made sure all geometry has thickness
- I have tested with and without Adaptive Light setting
- I am using Overrides for Direct Visibility & Refraction, these are set to white. The light bleed does change when I turn these off, but it doesn't go away
- This area shown on the render is a reflection in a mirror (I used the Corona Library Glass Mirror material)
- Lights in scene include CoronaSun, HDRI, Corona Sphere (wall sconces) and Corona Disc (ceiling spotlights, these are turned off in LightMix)
- I have unticked "use old (pre-V6) colour mode" on the CoronaSun.

The light bleed does seem to be coming from the Environment/Sun. I used to work predominantly with Vray and I would know which settings to adjust to fix such issues, but with Corona I don't know how/if it's possible. Render times are also a little high already, so I'd like to avoid any settings that may push this higher, if possible.

Thanks in advance
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2020-09-17, 09:37:34
Reply #1

romullus

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This looks like lack of precision in UHD calculation. Check render setup, UHD rollout and see if precision is set to <1. If it is, then reset it back to 1 and see if it helps. You can even try to increase this value to 2-4 if 1 is not enough.
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2020-09-17, 14:37:22
Reply #2

patrick.testa

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One thing I usually do in my scenes to avoid similar problems is to create a simple and rough bounding box (of course with holes for the windows...) around the interior. I found it useful expecially for actual small holes or misallignments that I may have left in the geometry...
I assign it a neutral gray or black material without reflections to avoid useless calculations or unwanted light bounces.

2020-09-17, 14:43:23
Reply #3

MAY3D

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Thanks Romullus, precision is currently set to 1 (everything is pretty much default in the render settings). I thought this might be the culprit, as it's the closest comparable setting to what I was used to in Vray. I'll try upping it as you've suggested and see if it helps.

Are there any other settings I can look at tweaking that could have a knock on effect to the UHD Cache? E.g. I'm rendering at 1080x1080 (for Instagram), would the UHD behave better at a higher resolution? I'd like to avoid longer render times if I can, but render quality takes priority.
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2020-09-17, 14:48:02
Reply #4

MAY3D

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One thing I usually do in my scenes to avoid similar problems is to create a simple and rough bounding box (of course with holes for the windows...) around the interior. I found it useful expecially for actual small holes or misallignments that I may have left in the geometry...
I assign it a neutral gray or black material without reflections to avoid useless calculations or unwanted light bounces.
Thanks, the scene is fully contained already though. I have shelled walls (derived from a box), shelled planes for floor slabs and then a shelled spline for the ceiling; there's literally nowhere for the light to come in where the light leaks are showing, it's weird. I don't recall having any such issues in version 5, but maybe it's just specific to this scene, rather than an issue with version 6.
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2020-09-18, 15:40:45
Reply #5

patrick.testa

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I just noticed that the problem doesn't occur in a directly visible object but in a mirror! Maybe the solution is to be searched in other parameters, related to reflections and not to the light itself?
It remembers me of a similar problem I had with an object that had a displacement applied and which looked bad in a mirror that showed its back side. Unfortunately in that case I modified the object instead of looking for a solution for a more precise reflection, and so I don't know where to point you for a possible solution... Sorry

2020-09-18, 16:12:06
Reply #6

TomG

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Note that if you are using Screen Space for displacement, then anything not directly visible to the camera (e.g. something that shows up in a mirror) will not have as high a quality of displacement applied. That's how Screen Space saves memory usage :)

You can enable World Space to avoid this, either for the scene as a whole (though that could greatly increase memory usage), or you can use the Corona Displacement modifier so that one object that needs to look right in reflection can use World Space while the rest of the scene uses Screen Space.
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2020-09-18, 16:30:30
Reply #7

patrick.testa

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Thanks Tom! I was just experimenting with that as I had some free time but I must say that in a test scene it works pretty well also with screen space! But of course everything works well in test scenes with teapots... problems always occur in production! ;)

2020-09-18, 17:34:59
Reply #8

maru

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@MAY3D - this is interesting. Would it be possible for you to share the scene with us? If so, please use the uploader in my signature and after the upload let me know what was the file name. You can simplify the scene if you wish (e.g. remove most objects so that the issue is still visible). Thanks to this scene we may be able to improve our UHD / 4K solvers.

Things you may try:
- Switch from the UHD Cache to the new 4K Cache (in the secondary GI solver rollout)
- Setting the UHD Cache preset from "still" to "animation"
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2020-09-22, 05:58:08
Reply #9

MAY3D

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Thanks all, appreciate the input.

@patrick.testa & TomG - I'll double check my reflection & displacement settings, see if there's anything I can improve there.

@Maru - I will try and upload the scene for you today. It's a personal project, more than happy to share if it helps bring improvements 👍🏻
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2020-09-22, 07:39:27
Reply #10

MAY3D

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...
Things you may try:
- Switch from the UHD Cache to the new 4K Cache (in the secondary GI solver rollout)
- Setting the UHD Cache preset from "still" to "animation"
I've tested all of the above and found the following:
Precision set to 2 cleans the render up and the additional render time seems negligible (though I only tested on a small region)
Animation preset gives similar results as above, but requires longer to render
4K Cache with precision set to 1 improves things a bit, but the results are still a little "splotchy". Render times are a bit quicker though.

I checked my materials, I have no displacement applied and the mirror material is very simple (0 diffuse, 1 reflection - as per material library "Glass Mirror), so there isn't really much I can tweak there.

Hopefully Maru can figure it out :)

EDIT:
I realised I had refraction set to 1 on the mirror material, so I changed that to 0 thinking it might be the culprit... no joy! Re-rendering at 1920x1080 with refraction at 0 and UHD Cache precision set to 2, the problem seems to have actually gotten worse! 🤔
« Last Edit: 2020-09-22, 08:55:04 by MAY3D »
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2020-09-22, 10:38:35
Reply #11

sprayer

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Try to increase precision even more

2020-09-22, 18:05:11
Reply #12

maru

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I am still investigating this, but I have a clue:
I rendered the image so that the issue would appear, and then checked LightMix items one by one. I saw that the splotches are clearly visible in the "Ceiling Lights" element.
I then right-clicked on this "Ceiling Lights" name in the LightMix tab of the VFB to select those objects in the viewport.
Then I isolated them and took a closer look at those light objects. It appears that:
- The small disk-shaped Corona Lights used in the setup have "illuminate on both sides" option enabled, and one side is facing a reflective inside of the light fixture.
- Even after disabling the "both sides" option, they are facing the wrong direction, so they are still shining inside the fixtures.
- They have directionality enabled.
- There is a Corona Light Material "Standard_19" used in the setup, which has "Emit Light" option enabled. This seems unnecessary as it is only a directly visible part of the light setup.

I can still see some splotches, but they seem to be less intensive. I will continue my investigation, but I suggest checking the scene for similar errors (i.e. small, strong, directional light sources shining into reflective objects).

Update: ok, still getting splotches after some tries... will continue tomorrow.
« Last Edit: 2020-09-22, 18:36:45 by maru »
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2020-09-23, 00:51:09
Reply #13

MAY3D

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Thanks Maru, I'll rectify those light settings. Appreciate you taking the time to look into this.
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2020-09-23, 16:24:16
Reply #14

maru

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After stripping the scene a lot, and investigating a bit more, it appears that:
- The biggest "issue" is the door, which is opened just a little bit, letting a tiny ray of light in. It is just hard to sample efficiently. The situation is acceptable when a solid color is used for the enviro lighting, but it gets worse if an HDRI is used.
- When seen in reflections (e.g. mirror as in this case), the UHD Cache results may sometimes look worse (splotchy).
- It gets even worse if the materials are complex - for example all walls are reflective.

I don't see anything wrong with your scene (other than the issues I listed in my previous post), so I can only suggest:
- Simplifying the scene as much as possible (like removing wall reflectivity, making sure light sources are simple, etc)
- Changing the UHD Cache settings - switching to the animation preset and/or increasing the precision value to 2 or more

I will also pass the scene to our dev team, as I think it is really interesting for debugging purposes and could make Corona better. Thanks. :)

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« Last Edit: 2020-09-23, 17:08:43 by maru »
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