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I was doing some test renderings and this one ran overnight and got upto an SL of 22 but has some distinctive white speckles. Any ideas what is causing this?

Here I was testing the use of real glass via a pane of glass on either side of the mullions between the glass. The panes of glass are geometrically speaking, boxes, which are 1/8" thick. The mullions are thinner than the space in between the glass panes so there are no coplaner faces there.



-Brodie

Two funny answers that come to mind...(can't answer seriously because I can't explain it)
1. Don't blame us for not cleaning the window!!!
2. OK, next time be careful when you sneeze!

That is just how it goes with glass -- the initial caustics clear quickly but once you get to the high sampling levels it begins to become more accurate... which means a whole new level of noise to resolve. I'm testing it regularly but I've had glass things go all the way up to SL 35 and not be fully resolved when dealing with sunlight.

For what I'm seeing here AGS seems like it would be the better option... as it is most times.

Best,
Jason.

I'm not normally a purist when it comes to glass. Often times I'll end up using a completely opaque material...essentially metal really. It looks like AGS is where I'll end up but for a different reason than I would have thought. My understanding was that the real glass would look more accurate but AGS was faster. But based on my test, I'm not sure, and not just because of the speckles. My reference photos also show the mullions as being very obviously white. The real glass (i used the high grade glass from the wizard) makes it very obvious that the mullions are in between the glass panes (which i'm having difficulty with using AGS), however it really grays them out as well.

reference


AGS test


-Brodie

Another advantage of AGS for Sketchup users is it can be single sided.

Glass is more realistic but it requires a much long render to reach maximum realism -- it clears to something usable quickly but once you see the high SL version you realize the subtleties you were missing. I only use real glass when I have a need to show off the glass object as "The" point of the render.

Best,
Jason.

What you are seeing in that render are rays that pass through the glass, bounce off of the mullion material, back through the glass and then to the camera. Those rays are refracted twice which Maxwell requires extreme time/power to render to completion. It's the old "sunlight behind glass" problem. You can do a tiny resolution render of that small area to see what it looks like after mega S.L.

Very interesting bub. After seeing my reference photos and reading your post, I sort of wonder if the white speckles are the 'correct' areas and the reason the mullion seems so dark is because of these unresolved rays which are lolligagging on their way back to the camera.

-Brodie

Exactly -- there is still alot of calculations that have to take place for the full realism of the glass to kick in... doing a very small test render you can see how far it would have to go to get there.

Best,
Jason.

Brodes

Mate I've got two suggestions that may work.

1. Try a double layer of AGS,

2. Pull a face of the mullions and just off the mullions (say 0.5mm) and paint this with an AGS with say 20% roughness.

No promise these will work though just ideas.