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Iray shader: Best way to change opacity?

2busy4render2busy4render Posts: 81
edited July 2018 in Technical Help (nuts n bolts)

I'm trying to take a liquid shader that is relatively clear and make it a bit less transparent. Changing the cutout opacity seems to work but I thought I read that there are better ways---using SSS and translucency or something like that---and that cutout opacity isn't really intended to be used for changing the surface in this way.

Editing to add: I just finished a render where I increased the cutout opacity and now my transparent surface looks gray or brown. So I think cutout opacity isn't the way to go.

Can someone share what they do to change opacity and why? Thanks in advance!

Post edited by 2busy4render on

Comments

  • glaseyeglaseye Posts: 1,312

    Create a primitive and apply the Iray water shader to it; study it settings (no opacity used). Vary the settings for REFRACTION (index/weight, abbe) in combination with glossy roughness... that may do the trick

  • 2busy4render2busy4render Posts: 81

    Thanks, glaseye. I tried that and read a ton of tutorials and posts, and now I'm thinking that cutout opacity is a short-cut way of doing this in some situations but it's not the best way. That is, it might achieve the desired effect but it's not what it is intended to be used for. I notice a lot of shaders I got with products use cutout opacity where it probably shouldn't be used. 

    In my case, I realized that the shader being set to .5 metalicity and setting translucency weights to between .3 and .5 got the desired effect. I was just trying to get beer spilled on a felt billiards table, and it took me about a week to get something passable. Iray is a lot of fun. 

  • Oso3DOso3D Posts: 15,045

    There are two broad elements:

    Realistic volume effects

    Not realistic volume effects (heh)

     

    Thin Shell is a parameter that tells the rendering engine whether to treat the surface as, well, a thin shell (Thin Shell: On), or to treat the surface as the surface of a simulated volume of material (Thin Shell: Off)

    If Cutout Opacity is anything but 1, the surface will be treated as a thin shell, even if you have it set off. (There's some weirdness with this, but good enough for now)

    Translucency uses a simple, well, translucency; the object will look like it's made of thin plastic, or be ... more solid plastic.

    Refraction looks like glass/water. With thin shell, it looks like a thin shell of whatever. There's a parameter 'Share Glossy Settings'; if it's on, Glossy roughness becomes refraction roughness (I suggest setting it off)

    Refraction color colors the material. Darker color absorbs more light.

    If Refraction Roughness is above 0, it creates an interesting blurring distortion. This works even if you have a thin sheet, like a plane, and can create interesting effects without needing a solid volume.

    Finally, if volume effects are working, you have Transmitted Color and Subsurface scattering.

    Transmitted color is like refraction color, but it sets it at a distance into the volume. So if you increase transmitted distance, the outer part of the volume has none of the transmitted color, and then it grades to the transmitted color at a certain depth. This can create some amazing effects. (You can create zones of colored space with Refraction index set to 1; there's no distortion, just... volumes of color)

    Note that transmitted color has an image map space... but it doesn't work. Never put a map here.

    Subsurface scattering gets 'cloudy' at a certain range. Great for creating clouded liquids, actual clouds/fog/haze, and so on. SSS direction shapes how strong the effect is along a light source; a positive value means it scatters more along the direction of light, a negative value means it's stronger when the light is behind you.

    Chromatic scattering is... weird, and I'm not sure I really get it. From what I understand the SSS is stronger based on the color of light, so it will let more of certain colors through.

     

    I think that covers it...

    Cutout opacity for simple effects, translucency for more complex, refraction/transmitted/sss for really realistic (but slower) stuff.

     

  • 2busy4render2busy4render Posts: 81

    Thanks Oso, that's also very helpful. The learning curve in Iray is steep, and my system isn't quite up to using the Nvidia shader in real time (so it's a lot of "move that slider", come back in a few minutes, and see what it does). Really appreciate the help though, cheers

  • MattymanxMattymanx Posts: 6,955

    For liquids and glass, Refraction weight and refraction index will be your primary controls for opacity instead of the opacity slider.

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