Dark Glass Shadows

Support Lighting and Rendering
1

Hello,

I’m working on a project involving a glass of wine. I made a test of the glass with Cycles, and I’m pretty glad of the result (See the image below. I’m open to suggestions of improvements however).

TestGlass.png700×500 256 KB

But the shadow on the plane is desperately dark. I tried many tricks to get a transparent shadow and believable caustics, but I couldn’t figure out how to do. Moreover, the top of the glass shouldn’t be so black. Is there someone to help me ?

Technical informations :

2

Thank you for your answer. Your test is impressive. I wish I could get such a beautiful result.
By the way, I don’t need real caustics. Just believable transparent shadows like on your image.
You can find my scene file here.

3

Do a search for my ubershader and check the node group inside for “Fake shadow/caustics”. That will get you a really nice looking result, especially for fairly simple shapes.

4

The problem is the use of the Light Path node in the FDA_BackgroundShader node group:

upload.png1424×605 167 KB

What you’re telling Blender here is to use the unchanged background for glossy and camera rays. And while using that low contrast background for camera rays causes no harm, using it for glossy rays somehow also influences the generation of caustics - quite frankly, I’m not sure why that is… But if you “mute” the Add node by selecting it and hitting “M” you will immediately see the caustics appearing in your render.

Anyway, that HDRI produces a significant amount of fireflies, perhaps due to the small, very intense light source (sun). You will need very many samples to get a clean result out of that. The HDRI in my render uses three large light sources, which will resolve much faster.

BTW, I usually use another technique to “enhance” the HDRI lighting:

upload.png1064×845 175 KB

Mind you, though, that in my default setup the HDR background is not visible to the camera - the camera just sees a plain color. If you want to see the unaltered HDR environment in the camera instead, you will need to connect the node group’s Color input to the bottom Background node’s color input (green dotted line).

5

I’d suggest that you get some professionally-shot reference pictures, not just of “a wineglass,” but of “a wineglass in the context that you intend to use in the total shot.” Sometimes a glass of wine is shot on a perfectly reflective (e.g. glass) table, with no other light other than what is passing through the glass . . . but, I don’t see it being done very often. (Certainly not, as in post #2, where you can “see the set,” and maybe the photographer and his camera as well.) In your post #1, my eye hardly sees the glasses: it’s drawn away by the “WTF?-shadows.”

Quite often, wineglasses are shot on a nice, attractive, tablecloth, because, well, restaurants always use tablecloths. (Unless they’re one of those places that have sawdust and peanut-shells on the floor. :wink: ) Maybe a wooden table, a deck, or some other nice environmental setting that is not mirror-like. It’s a matter of aesthetics, of course, but as for me, I just want to see enough reflective-action to show me where the glass surface is. (I want the wine in the glass to have a nice, reflective appeal, and I don’t want the wine to be upstaged by the glass.) As for shadows, likewise, only enough to provide a 3D effect … not to “ape” the shape of the glass itself, nor to in any way be doubled. If a sharp(er) light-point is needed, you might position it on the rounded lip-edge of the glass, almost-subliminally reminding the viewer where their own lips will be when they imbibe the tasty Almighty Product.™

Lighting in such photographs is usually soft, and coming in from several angles, except for a single point-light source whose sole purpose is to shine off the glass and/or its content. (If you want to see some exotica concerning “the bottle, itself,” surf through some archives from Absolut® vodka, or various other Vodka [in particular, for some reason …] photography. Look through high-end men’s magazines.)

Consider some web-sites that address the physical photographing of glass, for instance:

… to Google only a few. :wink:

Your CG-generated image, IMHO, should be favorably comparable to a real one, as taken by a pro in a product shot. (Say, where “the product” is not “the glass” … or, maybe even if it is.) The same considerations apply. You should come up with “a great photograph,” even though no physical objects are involved. And these (my … IMHO™…) notions, by the way, dramatically reduce the interplay of light and shadow.

(As one teacher told me … “Having bought your photography services, they don’t want you to sell the presence of the photographer … they want you to sell the product, and nothing else. Do a great job of that, and they’ll hire you again.”)

6

Whaou !! Thx IkariShinji. Here’s the result of the new version without the “Is Glossy Ray” connection in the world settings (and one entire night of rendering because of the 50000 samples used to produce proper caustics :eyebrowlift2:) :

TestGlass2b.png700×800 383 KB

To be honest, I didn’t really understand why they used the “Is Glossy Ray” connection in the settings explained here, but I know now that it’s useless :eyebrowlift:.
By the way, even if the result here is quite what I expected, an entire night of rendering is not reasonnable. I’m working on the way to produce fake believable caustics using the technique explained by m9105826, but for now the result is not satisfying.

@IkariShinji : I don’t get the point of using a “cosine” node in your HDRI settings ?

7

Don’t ask me, ask him…:eyebrowlift:

Part of the problem with your scene is that particular HDRI, which produces quite some noise. And I’m not sure if the volumetric shaders also contribute to the noise issue. Just for comparison: My bottle and glass render was rendered with just 2500 samples and is almost noise free…

Anyway, back to my initial post: Cycles is not optimized for situations like that - yet. If you’re into lighting simulations, you might have more fun with other render engines…