Author Topic: Emulating Tale Lamps (different specular transmission colors on same surface)  (Read 572 times)

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Offline zooropa

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Hi. I would like to achieve (using Rhino) a thicken surface with different areas defined by not the same color transmission.

Similarly to a car's tale lamp where we can appreciate a translucent plastic changing colors:



Ideally I would like to avoid needing to close each of my areas (option 1 on the image). I am trying to cut different silhouettes on a thickened cylinder in rhino. The option 3 seems to be the right way: applying those changes on a map in a closed volume. The problem is I  can not uv map "easily" in Rhino for mac, plus I would really like to control those areas by surfaces and not by a map.
The option 2 its the same as one with the difference that each of my volumes are closed. In this case I need to separate my volumes in order to avoid the intersection, which I am also trying to avoid.

Is it possible to create a contiguous open volumes with different materials but achieve the feeling of a unique "mesh" on the overall  ?

I might suspecting than more that a keyshot advice It has to do with physics expectations. I have been observing the whole day to tale lamps (specially from old cars) and it seems to be a single surface injected with different colors. To be honest I do not know if this is exactly what is happening or if that surface is actually 3 different ones really well fixed next to each other and they are actually closed volumes.

As a second aspect I think I am trying to cheat optics: cause I want to avoid the overlapping of the two transmission colors that gives me this third color (quite disturbing). You can appreciate it in each of the transmission colors changes (regardless of the option posted in the screenshot).

Hope someone can through some insights about what I am looking for: Tale lamp (as the reference) effect.

Thanks

« Last Edit: April 04, 2019, 08:49:42 am by zooropa »

Offline mattjgerard

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This might be oversimplifying things, but could you do this with different colored labels on a single object? The alignment might be tricky, but if its just a simple diffuse material with no texture that can wrap around the object there might not be any seams visible.

As for the 3rd color at the junction, let me know if you figure that one out. We have LED tubes that are segmented red/green with no divider in between and of course we get the odd color shift in between, which logically is expected, but not observed in the actual product.

Offline mattjgerard

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Here's what I got with 5 min-

Basic glass main material
transparent plastic as the label with a tight gradient black and not quite white in the opacity channel. I set the red's gradient position, duplicate the label and inverted the gradient using the INVERT tickbox for the yellow, and it kept the joint of the 2 colors right on. The one thing I didn't do before keyshot crashed on this project, so I couldn't save it was to put a light source of some sort in there.

EDIT: In re-reading your post, I notice that you want to control this by surfaces in Rhino, not with mapping in KS. As far as I know KS doesn't do polygon selections for materials, in the way that Cinema 4d would for example. I think the only way you can have 2 different materials on one object is through labels, and labels won't respect any mapping that is set in Rhino unless you can UV map them. I am curious to see if Polygon Selections would come over from C4D in any way. I'll have to try that if I get a chance.
« Last Edit: April 04, 2019, 12:19:44 pm by mattjgerard »

Offline Eugen Fetsch

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Just a side note to the node setup: You can have a hard edge between materials, if you uncheck the "Blend" checkbox in the color gradient node. ;)

Offline zooropa

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@mattjgerard

Thanks so much for your time and insights. I am using Rhino that works with nurbs (not polygonal). You can actually in Rhino cut things with curves and there will be two different surfaces. Please find attached the sample. I can control the area I want in Rhino. Probably Keyshot convert it to polygons within KS. But I am thinking how to make this work without closing those two surfaces when they meet. A translucent plastic transition between open surfaces. Mmm still wondering if I am trying to do something it is not possible. In case it is not , how the tail lates are done wonder too.

Thanks so much time for your time. Labeling its part of masking and I am trying to design what I want by actually operating in a mesh. But might not be possible ?

Offline zooropa

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Just a side note to the node setup: You can have a hard edge between materials, if you uncheck the "Blend" checkbox in the color gradient node. ;)

Yes, thats how the third option is done on the first screenshot ;)

Offline RRIS

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Offline zooropa

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Offline DetroitVinylRob

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A few tips that may or may not serve your efforts in automotive tail lamp type rendering:

(the bad news) Any form of "faking" a transparent CAD material volume will show compromise.

In my experience as a long time automotive designer and lighting rendering guy is that best results come from physically accurate CAD models and accurate material specifications. Let the ray tracing do all the hard work and heavy lifting of refraction and reflection! I've never found a rendering "cheat" that portrays a realistic enough result(.)

Create for example, a tail lamp lens that are approx. 2.3mm thick, using a PMMA plastic spec for RI and abbe # with a dielectric material. For coincident (surface laying on another surface) transparent surfaces of different colours, remove the face (if a very complex geometry) that is the lighter/more transmissive hue or offset (a simple geometry) so that it doesn't touch. (the good news) IF you do build accurate CAD models (especially with transparent materials) and use accurate material specs, KeyShot really does handle the rest!

As a rule, I agree and also find that coincident model faces of different transparent material selections (or a transparent with coincident faces to an opaque object) will not render properly.

AND also, do realize that a material face will reflect/refract what it sees (snell's law) in the render scene around it. Reality is a bit messier then a simple choreographed render scene...

Again, just my 2ยข

« Last Edit: May 07, 2019, 07:33:23 am by DetroitVinylRob »

Offline RRIS

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Coincident faces are a pain, but I tend to fix that in Keyshot by moving the part 0,01mm for example, or doing a tiny scale. Easy fix that usually works just fine.