I searched this but gave up wading through the 500 hits on the forum…
I’m working out some kinks in a job material - making beer bottle glass actually - and I can’t figure out whether to use make a brown glass with fog color and fog multiplier only, or with some refraction color, or with both? I am not clear why we have both (an attenuation distance and a colour is all we need for reality IMO). Could someone let me know which way and maybe why?
I can hit something that looks not bad about 6 different ways, but I want the most realistic/accurate approach so it works more intuitively with lighting etc.
Bumping the thread. I am still hoping for some guidance on this one but also have another problem/question to ask about: I am finding that with tinted/dark glass of any kind that the light falloff/absorption is really hard to control. See the attached thumbnails to see what I mean.
In one I have the backlight set at intensity of 5, in the 2nd at 500, and the 3rd at 5000. The 4th image shows the material settings. GI is BF and
No matter what I do, or how bright the light goes, I just cannot get much light through those bottles once they start to stack up. Even single layers of that glass material does not brighten up in a way that makes sense to me. At 100 or 1000X the light the single layers of brown glass should be blown out totally IMO.
I have the material’s cutoff at 0 and the reflect/refract at 50 each (not limited in the render dialog either). I have tested it with many variations of refract and fog colours/values and this is as good as I can get it. It just does not behave in a realistic way, at least to me. (I am using single bounce of BF GI in this example, and both types of GI caustics are turned on. Adding secondary bounces did not make a noticeable difference in the image)
Is there something I am doing wrong with the material, or is this just how Vray works with transparency?
I have to say that the Maxwell/Fry approach with attentuation distance and a refract colour is far easier to work with, and seems to behave much more realistically.
I did try working with just the refract colour, but I’m trying to get something that looks more realistic and the refract colour just wasn’t doing the trick. Even working with the fog parameter I had trouble getting a good result and ended up cheating a bit and adding a falloff map to the refract colour. That allowed me to darken the edges a bit more and gave me a more realistic looking bottle glass.
Falloffs are a great artistic addition ot materials in general I think, allows one to pop edges off without having to kill oneself placing bounce cards and lights.
Seems to be normal beer bottle behavior. The brown seems to multiply to a really dark color. The green ones are a little brighter. Maybe illuminating the surface beneath could give a nice effect and brighten up the bottles.
I don’t know… I can see what you mean in the examples, but none are really backlit which does change things. The renders do seem close in some ways, but the light just seems to fall off extremely sharply and it doesn’t feel natural. None of the people looking at the job I was working on thought it looked right either. These are pro art directors and photographers as well - people who “should” know I guess. Doesn’t mean we were right, but it suggest that something was not quite there.
I’m running a test with Maxwell to see if my feeling that it works better there is correct. It is never apples to apples, but I can at least see if the light falloff seems more in line with my expectations.
Some other photo examples that ‘feel’ better to me
So after rendering another few hundred versions (and one very slow version on Maxwell) I have come back to the conclusion that the problem is just me - surprise, surprise.
The Maxwell images are very, very similar in effect. I can’t get quite the same lighting (at least not without spending a lot more time than it’s worth) but the falloff of light is extremely close - clearly it’s just me and my client’s expectations being off.
I do think there are some more subtle caustic things that happen in Maxwell that maybe aren’t happening in the BF GI caustics, or not yet anyway, and that gives some bits of life in the glass that are missing in my Vray renders. Perhaps that is all it is.
are you sure its not that it couldnt be improved with more irregular environment stuff or a white reflector board above / behind / right of camera?
(dont want to suggest soemthing you’ve considered but..)
Robert: I gave up on using photon mapped caustics as I found them too hard to setup and too hard to control. Following a number of threads I opted to use BF GI so I could get caustics that way. Slower, but supposedly accurate. It does not have quite the same look as Maxwell/Fry type caustics right out of the gate, at least not to me.
Glyph: This test was not meant to be a great lighting setup, more to just experiment with a particular problem I was having on a recent job. In any case, the issue was that no matter how I lit the scene the stacks of bottles were going totally black very quickly, seemingly too quickly. The bottles could be better lit for sure, but that might have hidden the problem I was looking into. Thanks for the thoughts though.
For me accuracy is only really important in that the more they act like ‘reality’ the easier it is for me to intuitively setup materials and lighting. In the final result though, as long as they look good I am happy.
Good caustics is one of the things that brought me to Maxwell/Fry type rendering in the first place though as glass/liquids just ‘sparkle’ in those, at least with so much less hassle.
So I spent yet more time and made some lighting and material tweaks and I’m getting much happier with the material. I still think there are too many controls/knobs for fog though
In an attempt to get a bit closer to what I saw in Maxwell I opted to render with DOF (VrayPhysicalCamera) and I ended up with a ton of noise, but also some big splotchy areas. I think these are caustics that have not quite cleared, being exaggerrated by DOF, but I’m not really sure. Any guesses?
IMages below: clip of the hi-res first, and then a scaled down version of the whole thing. Once it’s resized down it looks okay, but that’s a cheat. Bit of post colour/contrast work on these, but no sharpening/noise etc.
Renders settings were pretty high. BF, no secondary, at 15 subd, Adaptive DMC 1/40 .009 threshold, min samples 6. I raised the DOF samples to 12. It’s sort of a quasi-Universal settings approach.
If those grainy blotches are caustics, and I wanted this cleaner, especially in there, which settings should I be cranking up?
