Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] Bug Reporting => Topic started by: PastaJackal on 2018-03-06, 13:05:42
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This has been posted before, but I wanted to see if anyone had a workaround of any sort to deal with it
The issue occurs when a scene backplate using CoronaLightMtl is setup with a CoronaSun (most evident when sun is facing the camera at a low angle), there is a large shadow artefact which appears on surfaces with less than 0.8 glossy reflection. This becomes a huge issue when creating images using drone photography which only wraps around a cylinder correctly rather than a dome or sphere which could be plugged into the environment map channel. So essentially, any shaders with low glossy values are vulnerable to some very ugly jaggy shadows creating a highly unrealistic result.
I'm wondering if any others have found a way to work around this as I understand this bug may be too difficult to completely resolve. Even implementing some kind of cheat in the next version (I'm using 1.7 hotfix 2) solely for these situations would be great.
Thanks for reading!
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Try turning on caustics in your window glass.
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Issue occurs even without glass or other elements present.
In this example, the backplate material was created with a CoronaLightMtl plugged into a CoronaRaySwitchMtl with GI channel left empty (this is to avoid using max's object properties to eliminate shadows and GI contribution).
Have been testing numerous methods like CoronaMtl self-illumination but all fail.
The only real way I can see of getting it to work is by creating a spherical map (not sure how to do that when some backplates are incomplete) and using that in the scene environment overrides.
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This is a known light transport bug - https://coronarenderer.freshdesk.com/support/solutions/articles/5000516180-known-bugs-and-limitations
I'll look into this and try to think of some workaround.
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The only workaround seems to be disabling "visible in reflections" for the Light Material.
This will obviously change the way your scene looks (there will be no reflections of the background anywhere).
Sorry for this. It's a known issue, reported many times, and a very serious one. We are aware of that, and I am sure our team will find a solution, but right now we don't have any time frame when it could be expected...
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No worries. Thank you for taking the time to look into this maru. Much appreciated :)
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hello, I come back to this subject because it seems that there is still no solution found...I admit that I do not quite understand that you are not developing a credible alternative to be able to use any photograph in background with the management of reflection and refraction (as with vray and the "light material" which works perfectly..). For a rendering engine dedicated specifically to architectural representation, I find these limitations very annoying.
I know that these limitations have been known for a long time but I am surprised that you still cannot find a satisfactory solution.
Do you have any views on this?
Thanks a lot
Mienda
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hello, I come back to this subject because it seems that there is still no solution found...I admit that I do not quite understand that you are not developing a credible alternative to be able to use any photograph in background with the management of reflection and refraction (as with vray and the "light material" which works perfectly..). For a rendering engine dedicated specifically to architectural representation, I find these limitations very annoying.
I know that these limitations have been known for a long time but I am surprised that you still cannot find a satisfactory solution.
Do you have any views on this?
Thanks a lot
Mienda
Corona is a highly phsycally-based renderer and does not tolerate un-physical effects as well as some other renderers do (including V-Ray, which is more flexible in this regard). In real life, you cannot have an object which is visible directly, but does not affect lighting in any way. That's why it's problematic for Corona. We have this issue logged and it is acknowledged by our developers, but it is possible that finding the right solution requires careful planning and time to make sure that other parts of the renderer do not get broken. It is possible, that fixing this single issue would mean re-writing half of Corona core and would introduce many unexpected side-effects.
On the other hand, I agree that the ability to use background plates, which would be visible only directly, is an expected feature (similar to rayswitchers, shadowcatchers, etc).
One workaround for now would be to try making scenes as physically-correct as possible, meaning using real geometry instead of background plates, or replacing the background in post-production.
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+1 this is needed badly. Having reflections match the backplate is essential to realism.
Maru - your solution in your last post just isn't feasible on a large scale. It works to a degree on something like a small garden when you'd never really know if the trees/plants in the reflections matched those of the backplate.
But for more commercial interiors, apartment block terraces where the environments are a sea of lights, complex buildings and recognised landmarks, rather than random vegetation, then it's not quite so simple or quick to achieve - we could always ask clients if they're happy to pay for another week of production time whilst we model the environment :)
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Thank you very much Maru for this detailed answer.
I am well aware of the limitations due to the physically correct rendering engine but it is also true that I think it is also quite necessary to put in place tools to "cheat" reality in order to make it more "true" ! . For example the corona light material if we uncheck "emit light" becomes physically unrealistic (all luminous objects (however weak the light emitted by them) emit light...)).
However thank you very much and I can't wait to see this limitation bypassed and to add a request I can't wait to see the "geo patterns" implemented in corona.
regard's
Mienda
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6 Years later (to the day, tomorrow)
AND we still don't have a proper solution to this... smh
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I guess the solution is make you backgrounds spherical and use them in the environment override slot rather than on a cyclinder.