Author Topic: Aberrations in reflections of phisical metal gold material  (Read 567 times)

2023-11-29, 18:50:00

Arzillo

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I have encountered this problem with Corona render, if there are several objects close together or an object that almost intersects and you use the physics trying to reproduce gold as a metal a sort of chromatic aberration occurs on the multi-reflection, basically it creates a strong iridescent red that I don't know how it is possible to eliminate. I created this test object, but it does the same if you put three spheres together for example, or anything that creates multiple levels of reflection on surfaces. Do you have any ideas?

2023-11-29, 19:19:12
Reply #1

James Vella

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Metals are highly reflective, so why dont you just render the object without other objects near it? Use render passes or similar?

2023-11-29, 19:53:44
Reply #2

Arzillo

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I only put in an example, in my case it is a gold jewel that has these 'anomalies' by having many intersections... a rendering engine like Corona should reproduce a correspondence with the physical reality of the materials, but maybe I am doing something wrong.

2023-11-29, 20:28:33
Reply #3

Beanzvision

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What exactly are you going for? Do you have any references images you can share? There are many types of gold finishes. If it's polished, then yes, it will reflect back on itself. It works like this in the real world too.

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2023-11-30, 09:56:54
Reply #4

TomG

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If you're talking about the color of the reflections, may want to check into tone mapping - the reflections are likely quite bright, and so things like the ACES OT being on or off could make a difference here, as could other things that affect highlight clamping.
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2023-11-30, 12:47:05
Reply #5

davetwo

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The OP it talking about the phenomena where gold reflecting gold seems to multiply the saturation/colour of the reflections so that they appear orange.

This is replicated in the real world (see attcheed) but certainly seems rather pronounced in Corona (It's looked odd to me before too).

I'm not sure if this is a shortcoming in Coronas material - or if the real-world metals always have more imperfections/coatings/grease etc which diminish the effect.


2023-11-30, 14:05:16
Reply #6

pokoy

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 I guess OP has a point, colored reflections *are* heavily saturated and they are less pronounced with increasing roughness of the material but when glossy, are pretty much impossible to get rid of. With the gold mtl preset, the coating with greenish absorption helps a bit but not really.

Tried to replicate the example posted above, and while it's not a 100% match, you can clearly see the strong red tint in reflections which is not as pronounced in the example. Image attached.
« Last Edit: 2023-12-01, 13:36:06 by pokoy »

2023-11-30, 21:25:58
Reply #7

cgrobo

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I ran into this issue a while ago when working with sinks. The reflection colors reflect upon themselves. The solution is to use a rayswitch material with desaturated reflections. Attaching a simple setup with ComplexFresnel.

2023-12-01, 13:39:41
Reply #8

pokoy

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I ran into this issue a while ago when working with sinks. The reflection colors reflect upon themselves. The solution is to use a rayswitch material with desaturated reflections. Attaching a simple setup with ComplexFresnel.
Workable workaround definitely, thanks for the suggestion - updated example render attached.

Though I still have my doubts as the default behavior leads to too saturated reflections if no workaround is used and has probably implications in general, maybe even for refractions? Plus, depending on the scene and material count it might be cumbersome to set all the material overrides needed. Maybe a general solution or a parameter to desaturate the Mtl's reflected color would be good to have... Still, a usable workaround for now.

2023-12-08, 16:55:48
Reply #9

maru

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This is expected not only in rendering, but also in real life and is purely dependent on the color of the surface (the "filter" color so to say).
If you don't want any red hues in your reflections, just decrease the amount of red component in the color. :)
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