How to Render transparent Glass on a Transparent background?

[Anonymous]

Hello! 

I have some glass I want to render. I have figured out how to render them on a transparent background but now I'm wondering how to make the glass transparent as well so its not completely solid and has transparency when I put it in photoshop? I can't seem to figure it out.

Thanks so much in advance. 

[mspeer]

Hi!

This is renderer dependent.

What makes "white/neutral" tranparent glass visible for a viewer are

1. Reflections of Environment

2. Refractions of Environment

Solutions for Arnold:

A) (Recommended) Render in 3D against the same background you want to use later in 2D, or

B) Set Opacity for the object and disable Opaque in Shape node.

C) Try different Opacity settings and different Layer Composite Modes (like Multiply) in Photoshop to get a suitable result (maybe render out different layers for better control).

[Anonymous]

this is hard for me too.i want to render a man from green screen behind the glass(made in arnold maya) so help

[CrepMaya]

Hi there Ashley, 

I have just found out how to render onto a transparent BG, when you are using the Arnold Skydome go into the attribute editor material settings, visibility and turn the 'Camera and Transmission' settings down to zero, this should work. 

I am also rendering with an EXR, AOV's are merged and I have the following applied;

RGBA, Background and transmission.

I hope you have already found a way, 

Cheer, 

Thomas. 

@Anonymous @Anonymous @mspeer 

[mspeer]

Hi!

@CrepMaya 

This was not the problem.

As @Anonymous posted "I have figured out how to render them on a transparent background".

The problem is the alpha channel, which also can't be seen in your screenshot, but usually it's solid white for the object.

[CrepMaya]

Thank you for the notice, I should have added my screenshot of Photoshop too, as you can see in the screenshot it is transparent and I have drawn a line on the layer behind to illustrate. 

I might be misunderstanding the question but this how I read it, 

Sorry in advance if it is not of the same topic. 

[mspeer]

Hi!

These questions are still open

- How did you achieve the transparency in Photoshop?

- How does your alpha look like?

- What is your workflow, material settings?

Simply removing a background does not make the alpha transparent, only using Geometry -> Opacity does, but that does not preserve refractions or solid parts of an object.

Please provide more details about your setup, workflow and maybe add a scene-file.

[Stephen.Blair]

It depends on the scene and the background, if any, but what about Transmit AOVs to get alpha for transmission?

[mspeer · Accepted solution]

Hi!

In the newer Maya/Arnold versions (this thread was from 2017) there is a new Attribute "Transmit AOVs", this leads to a non-solid alpha channel ,which can help to achieve an acceptable result, but you can't simulate the behavior of glass with a simple alpha channel, so there is no one-button solution for this.

Here is a very easy example and you see the difference between the rendered scene against black and the the composite against black by using the alpha channel from "Transmit AOVs".

You can render more elements / AOVs and use a complex setup for compositing, which will get you much closer to what you want to achieve, but as you don't get real refractions you will never get a plausible result.

However it may work good enough in certain cases, based on your Maya scene and where you want to add this as composite, so as you said, it's also scene-dependent.

Here a second example with a very simple background.

There is no way to get a proper result just with a simple alpha channel.

[akinbiyibab]

If anyone's going through this thread confused, just make sure to Turn off Transmission as well as the Camera in the Skydome attributes, I think someone mentioned it on thread, but it wasn't clear that this was the correct solution.

Other issue might arise, when rendering glass but setting the Transmission as well as the camera to zero gives you a transparent background and creates and alpha channel for the Transparent material

...bye bye white solid thingymabobby

[d.raszkova]

Hey there, to i tried everything and its still not workin, the glass turns out black. Can u help me please?

[akinbiyibab]

Is it black because it’s completely transparent? Do you have an object behind it?