Iray transperancy?
Scavenger
Posts: 2,674
in The Commons
I've heard you shouldn't use Cutout to make something transparant (like glass or a ghost) for Iray....that there are other settings to do this with....
I've been experimenting, and I'm not finding the other settings...can anyone help?
Let's say I have a basic plane with a picture map on it, and I want to make it translucent, like a transperancy print out.....what settings do I mess with to get this?
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Try fiddling with the refraction.
Interesting...I've had good luck with using Cutouts for transparency. But for designs on glass, I use the Cutout on top of the glass as a geoshell. That way, the glass shader is unaffected. The design is a decal on top of the glass. So, you can create a plane, use a glass shader on the plane. Then add the geoshell. Put your texture on the geoshell and create a cutout for that texture. That makes it possible to use whatever shader you like for the design. I did this for metallic lettering on frosted glass.
I first changed the wall to glass. In this case, because I needed to be able to resize the lettering design, I used a separate plane set flush on the glass for my lettering. It wasn't as easy as using a shell. But, it allowed me to move the signage around and scale it until it fit properly.
Will have to post the sample, later. Can't upload client work. :)
I think it depends on whether you are trying to achieve real transparency, eg: glass, water, or fake transparency, eg a ghost.
For real transparency you should use refraction etc settings to achieve this, but the use of cut out opacity for fake transparency is reasonable. As an example of fake transparency I wanted an anatomy shot showing a body's internal organs, but at the same time show the figures skin, but transparent enough to see the organs inside. I originally fiddled with the skins refraction settings, but eventually I found that setting cut out opacity to around 25% gave me the effect I wanted.
I have found a lot of situations where glass in Iray is easier to pull off appealingly with opacity and not refraction.
Refraction is best if you really need volume effects, like water, gels, and fog.
I agree. The reason I use decals and cutouts on top of a glass shader is to preserve the refraction and reflective effects of the glass. The cutout method for the lettering allows me to use a completely different shader for the lettering without affecting the glass underneath. So, the lettering looks like it is painted on the glass surface.
The one downside I find when using shells to add decals is that it is difficult to use a partial shell..meaning only a single body part is active. No matter what I do, the shell always seems to have some darkening effect on the layer beneath. It is very slight, but still noticeable. This only seems to occur with figures. I don't have the same problem with objects. I wonder if it has something to do with skin textures.
Cutout opacity works fine on things that shouldn't have refraction. Frankly, refraction shouldn't work on a basic plane since it's effectively two dimensional. If you want a refractive affect, start with a cube and alter the thickness to something like 3 cm (sheet of glass) on so.
AH...so the "don't use cut out" was for the physics of light, NOT the performance of the render engine. I see now! That helps a lot!
This cabinet comes with Iray shaders but by default the glass is quite opaque. Setting Cutout Opacity to 0.25 (or maybe a bit lower) fixes it. So it works quite well. I wonder though why a few of the vases seem to break the opaqueness when you view it in the Viewport.
My understanding is that the interactive Iray engine that the viewport uses does not cope well wihen dealing with transparencies behind transparencies. The render engine works fine, thought.
OK, I'm not using Interactive here though.
I agree we should be using meshes with volumue but Iray handles thin plane refraction quite well...not prefect but better than other engines in this regard.
Yes, I seem to get refraction out of even 0 thickness planes when applying a refractive glass shader. So, perhaps the shader is calculating a standard angle for refraction, regardless of real world physics. I don't know enough about how glass shaders work to say for sure. I can only say that I'm seeing the effect.
The reflection might be the more important effect for convincing the viewer that there is glass in front of a scene...depending of course on whether or not you actually want to see the glass or just the scene behind it.
The only issue I can see using thin plane refraction is that is magnifies what lays beneath the surface for water as an example. I should open that scene file and do some quick renders to show what I mean.