Author Topic: Reflective vinyl decals?  (Read 2609 times)

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Offline eobet

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Reflective vinyl decals?
« on: September 21, 2017, 12:36:34 am »
Anyone have any idea how to do reflective tape materials like these:





Now, the materials are really difficult to photograph the way your eyes see them, so I guess it's difficult to render too...

Feels as if, depending on the angle the light hits the material, it should become emissive to the camera? Because it's very important that the light emission is not uniform across the entire surface, like it would be with a normal emissive material.

Offline mattjgerard

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Re: Reflective vinyl decals?
« Reply #1 on: September 21, 2017, 07:06:22 am »
YEs, this would be a very big challenge to get right inside keyshot 100%. I've shot video and stills of 3M retroreflective sign sheeting for years, and even when its technically correct, it looks wrong, because of the reason you stated, the material looks like it is emitting light. Which means it is doing its job, but that's not what your eyeball and brain expect :)

So, for my video and stills work, there was always post work in photoshop. One thing I'm learning is that an image should never be considered "finished" right out of the renderer. And for an image like this, you might be compositing 2 different renders, and doing some post bloom and glow work. Lots of reference images will be very helpful to you in this case. Use KS to create the assets you need to finish your work in photoshop. I've had to do that for a lot of my LED behind cloudy plastic work, and the ending images are very pleasing.

Please post your progress, as this is a new application that I've yet to see!

Offline Søren

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Re: Reflective vinyl decals?
« Reply #2 on: September 21, 2017, 11:00:58 am »
There is no simple way to do this in KeyShot at the moment.

Take a brief look at https://en.wikipedia.org/wiki/Retroreflector - the reason these materials look like they do is, that they reflect light straight back at the observer. In contrast a flat metal surface (or any other specular like reflection) reflects light at the angle of incidence - not back the way it came from.

Using an emissive will never give the correct behaviour since it does not reflect light in one direction, but emits it in all directions.

Here is a suggestion on how to reproduce this (note: I have not tested this myself).
Try to model (in your modelling software of choice) a plane with a hexagonal pattern of recessed half-cubes (see second and third figure on the Wikipedia article). Then import into KeyShot and assign a metal material (e.g. with a pure white color) and add a small bright light source behind the observer (e.g. using a small bright HDRI editor pin og point light). This should give you the desired effect. Render out an animation or an XR to evaluate the result, since the viewer position is extremely important here. You will need at least 5 ray bounces (default is 6 so you should be fine).

You can find additional inspiration on surface geometries in the wikipedia article.

Note: you may be tempted to use a normal map for the recessed cube pattern, but that will not work.

Hope this helps.
Søren

Offline MWo

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Re: Reflective vinyl decals?
« Reply #3 on: September 21, 2017, 03:01:14 pm »
hello Søren.

I tried exactly that way on cylinder with layers with tiny gaps above but with not satisfying results. An advanced material as base and white metal with hexagon normal map. And on top a dielectric in yellow and a bump map. The result goes in a right direction but not the correct solution. Maybe I have to play with for a while.

And I noticed some things. KS7.1 did not a normal map when applied from the lib. I have to activate the option. And the interior mode solves very different to product mode.

Do far. This is a challenging nut!

Cheers
Marco

Offline DriesV

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Re: Reflective vinyl decals?
« Reply #4 on: September 22, 2017, 04:09:28 am »
As Søren mentioned, the only way to achieve this accurately now is to model the actual surface details.
I went ahead and made a cubic pattern as geometry.

Attached is a sample scene with animation to highlight the light behavior and the rendered animation.
Good luck recreating this on any non-planar geometry. ;D

Dries

Offline DriesV

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Re: Reflective vinyl decals?
« Reply #5 on: September 22, 2017, 05:33:01 am »
A little carousel animation...

Dries

Offline mattjgerard

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Re: Reflective vinyl decals?
« Reply #6 on: September 22, 2017, 06:30:10 am »
Just for fun, here is part of the project I did with 3M's sign sheeting group way back in the day (can't believe they are still using these videos!) Their DG3 tech uses "truncated cube corners" which are just that, tiny little corners of glass cube cut off, and truncated a bit along one axis to pack even more of them on the sheeting. You can have a look at some of the tech specs of the sheeting, and get deep into retroreflective physics to try to understand how they work and that might help you rebuild it.

https://www.3m.com/3M/en_US/road-safety-us/resources/road-transportation-safety-center-blog/full-story/?storyid=328c8880-941b-4adc-a9f9-46a1cd79e637

Its interesting stuff if you like techy physics stuff. I might try my hand at something like this. They use a different tech in their road tape marking products, standard cube corners for the tape and glass beads for the painted lines.

Offline MWo

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Re: Reflective vinyl decals?
« Reply #7 on: September 22, 2017, 11:00:15 am »
Great solutions Dries. I have to check the files.

Have a great weekend @all