Light through Frosted Glass

[markdd]

I am working on a set that is almost entirely made of heavily frosted Plexiglass or Perspex. I am OK with making a texture for the glass itself but can see no way of stopping the light passing through the glass in the way it would if it was clear. Is there any good work around/technique/trick for creating the effect of the light hitting the perspex and seeing the "shadowless" light that passes through the glass?

 

Any help would be really appreciated.

 

Thanks

[Kevin McAllister]

Mark,

 

This is partly about your texture and partly about your render settings I think. The C4D rendering engine is capable of rendering very realistic glass. Whether the light passes through or not is about the transmission, index of refraction and blurriness in the transparency channel of your texture. In order to see these effects though you need to turn on blurriness and caustics in your Custom Renderworks settings.

 

Kevin

 

[grant_PD]

So the idea here would be that a light source (unseen) hits a diffuser (the frost) which then scatters the light into a very diffuse light source. If trying to recreate the physics stumps you (or VW) , just think about what you would see:

A luminous panel that emits a very scattered light.

 

This could be a texture with the "glow" shader on, actually emitting light.  Or it could be a texture with the "glow" shader without emitting light (< 100% strength) with an area light just in front of it, set to emit either soft or no shadows. 

[markdd]

Thanks Kevin and Grant. I'm pretty pleased with the results so far. I like the soft light through the glass. I'm going to add another layer with a glow texture and see where that takes me as well.

 

Here is the file and an image. If anybody would like to make some improvements or suggestions then please feel free! For instance, I would love to know how to get rid of those tile shaped artefacts in the shadows and also if there was a way to get rid of the graininess.

frosted_glass.vwx

Edited April 12, 2017 by markdd

[PVA - Admin]

The weird tiles are coming from the only light source bing caustic photons, generally when you use caustics you should also have another type of light source in the scene as well to represent the "real" light. You CAN just leave it so that the light shows caustics AND regular light, but I find that hard since you only get once brightness control for both and caustic lights often need to be turned way higher than regular light sources. It also can help to completely enclose the scene, as you need light to bounce properly to limit splotching with just a few sources of light.

As for the frostiness, you might just need to check the box in the Edit Texture dialog under Shadows for "Cast" and "Receive", without Cast it makes light artificially ignore the textured geometry entirely and splash onto the floor with no diffusion or loss of brightness. Let me know if the attached is closer to what you had in mind, I changed MANY things to try and get a more resource (render time) efficient method, as Caustics and Blur will work but are VERY resource hungry. This example uses a Noise reflectivity with a slight blur in that shader, and a Glass transparency with both a low refraction to get closer to ice or water and a reduction in transmission to get that opaque look you expect from frosted glass but the scene renders in less than a minute on a 1080p display on the design layer:


 

I also added a red ball in the background to get an idea of how transparent it actually was, in case you plan to have things show through it. If you can post a real life photo of the effect you're going for I can give it another go, I had planned on a segment on glass for the Summit, for instance this example attempts to explain absorption which might be useful to understand if you need frosted glass with varying thicknesses:

frosted_glass-JimEdit.vwx

[PVA - Admin]

Side note, the frosted test I posted I don't consider to be a presentation quality at all, just a proof of concept for an efficient way of doing it. If its close but faulty or not the direction you meant at all, let me know and I can provide specifics.

[markdd]

What I would like to achieve is the soft light that comes through frosted glass. This is an example of what I have managed to achieve so far, but the graininess is not good. But the lighting effect is just what I am aiming for!

 

Thanks

 

 

Soft_Light_effect.vwx

[PVA - Admin]

If this method fits all other needs (it does look pretty cool), then I suspect the only way to downplay the grain is to duplicate the light that is emitting caustic photons on High or Very High (if what you've got in the second shot is made similarly to how your first example was) in order to get more caustic photons, since you can't manually set the value to anything other than Low/Med/High/VeryHigh. However, they should have "Show Caustic Photons Only" enabled and not be emitting normal light at all or you'll get a supernova wash out of bright light.

[markdd]

Tripling the sources gives this result which is a big improvement. This is exciting for me as I am always needing to replicate this kind of effect. Could I put in a wish list request for a more robust Caustics light object that will create smooth images? A google search brought up a few forums for other 3d render software packages where this issue was discussed without any satisfactory solutions (that I could understand!)

 

Thanks

[barkest]

Could you give the frames a key color and select in PS and then clean up?

[markdd]

Sadly I don't know photoshop at all well and that might be a software package too far for me. Vectorworks already provides too much of a distraction on its own!! It would be great if the caustics could be improved a bit so that single light source renders like this one could be less grainy. I got some pretty neat effects while I was investigating this though.

[PVA - Admin]

(EDIT: Originally posted in another rendering thread erroneously, apologies.)

Another thing I completely forgot because sometimes I'm dumb: Backlit Reflectivity.

That reflectivity shader will let the objects textured with it spread light that strikes them as you originally requested. Now, I am not sure how it plays with Caustics, but this super simple example shows the very basics of what it does:

 

If you already have the solution you like though, please feel free to ignore. Rendering is about getting the look you want, and while I can make suggestions, your preference is what matters most.

 

 

Backlit Test.vwx

[grant_PD]

No lights, just your plexi as an emitter. 

backlit_plexi.vwx

[markdd]

Very nice effect. Not quite what I'm after because the light doesnt project through the glass but I will use it for something someday soon I have no doubt. Thanks for sharing.