Hi,
again, something that was discussed many times. I have a problem with glass in my interiors. Of course, I’d like to have it as realistic, as I can get. I think I tried every known to my combination, but every time I have some problems. First of all, the most realistic effect was with just Glass BSDF and Refractive Coustics on, but, as we all know, I would have to use like billion samples to have a clear render. So, I have used Light Path node and mixed just Glass BSDF with Transparent and for windows that was fine. Well, not perfect, less light passes through, but works. Architects have designed wall with glass inside as well, and here more problems began. When I use same node setup, glass is almost 100% mirror and mirrored objects are distorted. (Attachments - solid with no glass, just to see what’s hidden, and render). Any pieces of advice? I have added a link to Dropbox to my .blend file. With different glasses materials objests are still distorted. I have triend just glass and thick box to match the glass inside.
Thanks! That solved a problem with glass beeing a mirror, but object are still distorted. Any ideas on that?
Edit: ok, nvm, solved. I did not delete math node. With no math node it works.
Hi, one more problem. I don’t even know how to approach it. The problem is that glass filters out a lot of light, and walls outside the windows are simply too bright. Is there any easy way to fix it with different glass node setup? Here is just and example of how it looks outside, and inside.
Distortion was there because of using two of Light Paths outputs. With one everything is alright. But anyway, I’ll remember to try lower IOR as well. Now I have a problem only with things outside being too bright.
The outside is too bright. It’s supposed to. Sun and sky at its brightest are waaaaaaay brighter than any indoor lights (incl reflected light, keep in mind dielectric albedo for such surfaces are way lower than white).
Just take a photo yourself and you’ll see you have to expose for either the inside or the outside. To cope with this, real photographers cope with this:
Accept blown out outside.
Shoot at different times.
Shoot at overcast.
Add ND filters to the windows (often used in film).
Supplement practicals with flashes, reflectors, or other photographic light equipment. Or brighten it up with no regards to practicals.
In the case of faking it in Cycles, expose for the indoors and reduce the transmission of the windows.
@CarlG, yeah, it should be brighter, it’s normal, but when I have sun light directly on the outside wall and inside one just next to the window, more or less in real life there are equal. Here, it is around 60/70% less bright with same material, just like glass is taking more than half of light. And it is not normal. Glass in windows should block around 5% of visible light. Here difference is huuuge and it’s filmic on low contrast. And I know how it works in real life, because i shot architecture and in moest cases I use 3 exposures per image. You can see some of my shots on trzykropy.pl.
And here is an example of image with caustics on, where difference is not that big between inside and outside, and with caustics off. Of course, using caustics with cycles inside are no to go, sooo, is there a way to make it any better?
ajarosz, if you wish to render realistic glass with Cycles, then caustics should be enabled. As you see that is not going to work because of the added ridiculous cost to render time so glass will have to be unrealistic. Luckily that is no big deal at all in architectural visualization. The only thing we see about window glass in interior photographs is reflections. The amount of light absorption if it is clear glass is really not something you need to worry about and refractions are really not that visible with glass thin like that, just render the reflections only and that will be fine:
@MartinZ- thank you, I’ll try that for sure!
So that’s a node for rendering only reflection, yes? Because using it makes objectletting light trought but in same time being 100% reflective, 0% transparent, and reflection is distorted in some way.
You would also loose energy if you live by the “everything has fresnel” rule (principled or other pbr approaches), combined with turning off caustics. Looks to me your floor is reflective, and something as strong as the sun would bounce specularly (with a direction, depending on the specular roughness) off that surface. If you shine a flashlight down on a mirror polished floor, you would see the circular hotspot in the ceiling. For rougher surfaces this size increase. For very rough/diffuse surfaces, there is an even illumination caused by complete randomness of the bounced rays.
I sometimes use a serial shader trick where I can control the diffuse reflections; using Lightpath/IsDiffuseRay to shader mix between previous shader (i.e. principled) and a Diffuse shader being fed the same color as the previous shader. It will bascially bounce light as if the previous shader was diffuse only, so although it prevents energy loss, all directionality will be lost. Only ways to accomplish this “correctly” is either to utilize caustics with a high filter value (we’re not trying to do caustics patterns, so high is good enough) or to help the lighting using manually setup fake bounce lights (like in the old days before GI was invented :)).
If using MartinZ’s trick above, make sure the flat glass panes are pointing toward the camera, or invert the IOR for backfacing if you can’t. Just preview fresnel output for back and front faces to see what I mean (it’s designed to work with total internal reflections caused in solid glass/real refraction).
@CarlG, thank you for a lecture. Yes, the floor is a bit reflective (average Roughness from material around 0.3 and specular 0.1). That was the phrase I was looking for -energy loss!
I’l try to use high filter value because it bugs me a lot. When I was working with 3dsmax/Vray, but here every single light causes more noise appears on the screen that it was with Vray. .
Thank you guys! Cycles and Blender are still a new things to me!
Yep. Thanks for pointing this out. I should have mentioned that I would only use planes without any volume for this and the normal direction is important. I would sometimes have 2 or more of the planes depending on the kind of windows - if the glass packet has double or triple glass in it, you can sometimes see double or triple reflections as well. Sometimes glass is uneven and would have some distortion in reflections, but I usually ignore this plus I have seen windows with surprisingly even and flat glass surface as well.
I wouldn’t bother with multiple reflections unless something prominent like a projector lens (where I just shift an image around to produce “depth”, based on viewing angle). Distortions I “would do” (but since I only do interiors…) on exterior buildings (reflecting the bright sky), not indoor stuff where reflections are quite dim (unless you nd the windows). I’ll use both dual reflections and distortions on display walls that are turned off though, but I’ll fake them on a single pane.
Guys, thank you very much! I have learned a lot in here! Reading what you write here leads to to one sentence: I know one thing, that I know nothing. But with your help I’m more happy with my renders. If you have any more tips about glass ,I’d love to hear them!
Hi, I use this material for glass in windows: http://pasteall.org/blend/index.php?id=49295
It is simple and it renders fast, giving fairly realistic results. The trick is to disable the object for all rays except the camera. This speeds things up a bit. The glass shader is simple mix between glossy and transparent driven by simple fresnel node.
I don’t simulate distortion in refraction. This effect is rarely visible. To simulate distorion in reflection you can simply put a normalmap into the material.
samples to have a clear render. So, I have used Light Path node and mixed just Glass BSDF with Transparent and for windows that was fine. Well, not perfect, less light passes through, but works. Architects have designed wall with glass inside as well, and here more problems began. When I use same node setup, glass is almost 100% mirror and mirrored objects are distorted. (Attachments - solid with no glass, just to see what’s hidden, and render). Any pieces of advice? I have added a link to Dropbox to my .blend file. With different glasses materials objests are still distorted. I have triend just glass and thick box to match the glass inside.
With no math node it works. 
Now I have a problem only with things outside being too bright.
You can see some of my shots on trzykropy.pl.
