Where is material's alpha channel?

[schultzeworks]

In the prior version [3.4], I could change the material 'affect alpha' from 1 to 0, and then the material would not be saved (as long as you used a PNG or similar.) It was GREAT for adding new backgrounds in Photoshop.

Now, that lovely option seems to be missing completely from V-Ray Next [current hotfix].

How do I achieve this effect?

[schultzeworks]

OK, I found one workaround .. or maybe this is the new method that is not listed in the documentation.

1] Make sure you are in advanced mode when looking at the material. There is an icon at the top right of the material's layers.

2] Turn on the Raytrace Section. It is off by default.,

3] Under the specific material, go to the Raytrace Properties > UNCHECK 'Visible to camera'

If you save the file as a PNG, it will work just like the old 'alpha = 0' process.

I sure wish the documentation kept up with the newly added features. That only took about an hour of my life.

[georgi.georgiev]

Hi,

Specifically for an Emissive material, you could use the Raytrace Properties rollout as you have done already. Another workflow would be use the V-Ray Wrapper material and slot the material there. With the V-Ray Wrapper material you have the option to control the Alpha Contribution and generally this is the recommended approach for most materials.

For more detailed information, please visit https://docs.chaosgroup.com/display/VNFR/Wrapper

[schultzeworks]

Hi,

Specifically for an Emissive material, you could use the Raytrace Properties rollout as you have done already. Another workflow would be use the V-Ray Wrapper material and slot the material there. With the V-Ray Wrapper material you have the option to control the Alpha Contribution and generally this is the recommended approach for most materials.

For more detailed information, please visit https://docs.chaosgroup.com/display/VNFR/Wrapper

I should have mentioned that am teaching a class and the last time I used the wrapper material, it was a complicated multi-step and non-intuitive mess. I need SIMPLE & repeatable processes to teach students who do not use V-Ray every day. Sorry, the wrapper material is WAY too complicated.

Plus, you guys changed a functionality that was in multiple prior versions and provided no guidance.

Finally, the solution above ALSO works for other non-emmissive materials as well. That's why I like it. Its simple and you actually have a shot at remembering it.

[Micha]

Hi,

Specifically for an Emissive material, you could use the Raytrace Properties rollout as you have done already. Another workflow would be use the V-Ray Wrapper material and slot the material there. With the V-Ray Wrapper material you have the option to control the Alpha Contribution and generally this is the recommended approach for most materials.

For more detailed information, please visit https://docs.chaosgroup.com/display/VNFR/Wrapper

georgi.georgiev I'm looking for a way to get no alpha for a window glass material which I use at my train interiors. I need no alpha at the windows so that the background is kept. I tested it at VfR2 and there I can set numerical values for the alpha contribution. At the VfR Next wrapper material I can choose between 0/1/-1 only. At VfR2 I was able to set 100 and the transparent window was without alpha transparency. Could it be possible to get a numerical input again?

Also I miss at the wrapper to set an alpha value which ignores the base material alpha, best a numerical input, but for now "allways 1" is needed.

General I would prefer to use more options direct at the Raytrace options, for example the alpha contribution.

[georgi.georgiev]

Micha,

For glass materials, you could adjust the Affect Channels parameter to All Channels, and this way the correct alpha will be produced in transparent areas. The option is available in the Reflection and Refraction rollouts of the material (Advanced settings).

[Micha]

georgi.georgiev Right, but I'm looking for a way to get a non correct alpha, the glass should be opaque at the alpha channel. I found now, that "color only" doe's the job for refractive glass. But since I try to keep the raytracing through the windows so simple as possible and use a reflection layer at the material only, this doesn't work, I don't get a "solid" alpha. So, back to the wrapper - could it be possible to get a full numerical control of the alpha contribution again? Could it be possible that the wrapper overwrite the basic material alpha contribution? Or is it a bug that the wrapper alpha contribution doesn't overwrite the base material alpha contribution? I would like to set it "1" and it is "1" like from a solid object.

[georgi.georgiev]

Micha

I might have misunderstood the case. I thought what was sought after was for a background to be visible behind transparent objects?

Could you please specify the exact workflow and results expected?

[Micha]

I miss a way to set the material alpha to opaque independent from the material opacity. For example for a simple window glass without refraction or a thin transparent material. The wrapper alpha allow to set three states (a) normal means like base material, (b) 0 and (c) -1. One state is missing - render alpha like solide/white/1.

Also I have seen now at the Override material an alpha control is missing too. Here the should be able to set 0 or 1 or better 0...1.

[georgi.georgiev]

Thanks for the feedback!

In this case, since you are using Opacity to produce transparency, there is no way to control the alpha contribution in the manner you seek. However, you could set up the material with Refraction (change the IOR to 1 if necessary) and adjust the Affect Channels to color only.

Regarding the V-Ray Wrapper material, the Alpha Contribution can be adjusted with a script to a value greater than 1, however, this is strongly not recommended and in the case with a reflective layer, you would not get realistic results!

[Micha]

Thank you for the workflow suggestion. I will try this.

For the long run it could be nice if you could set on the wish list that the wrapper alpha can overwrite the base material with 1 like it can overwrite with 0.

[kostenurka]

OK, I found one workaround .. or maybe this is the new method that is not listed in the documentation.

1] Make sure you are in advanced mode when looking at the material. There is an icon at the top right of the material's layers.

2] Turn on the Raytrace Section. It is off by default.,

3] Under the specific material, go to the Raytrace Properties > UNCHECK 'Visible to camera'

If you save the file as a PNG, it will work just like the old 'alpha = 0' process.

I sure wish the documentation kept up with the newly added features. That only took about an hour of my life.

nice found for quick switch, but at the end it requires 2 renders in total for 1 scene.. I'll focus on wrapper's solution.

[kostenurka]

thanks georgi.georgiev it works awesome!

[kostenurka]

georgi.georgiev I've just saw the Vray Next for Rhino Video on youtube. There you demonstrate the Cryptomatte render element in combination with Exr-IO plugin for Photoshop. Both are new to me, but so useful.
Can you please share, how do you get the alpha channel as a mask in photoshop beside each render element (see the print screen)?
My tries end up as bunch of layers where I have to apply photoshop's "Select color" to create a selection. Do you get automatically the mask or you post process it?

thank you

[schultzeworks]

OK, a final update for those who want a simple alpha channel solution (like in the prior version.)

The good news is that the matte-shadow is much easier to use in V-Ray Next. I've listed the steps on how to create a backdrop (floor and or wall) that will not save with the file.

- Create a 'backdrop' material that you like.
- Next, create a brand new matte-shadow material.
- In the matte-shadow material settings, there is an area where you can select a 'sub-material.' Pick the 'backdrop' original.
- I suggest re-naming the new wrapper material so it is obvious; I use 'backdrop-matte-shadow.'
- Assign the new 'backdrop-matte-shadow'' to the wall or floor geometry
- When you render, the areas will not render and be transparent. Easy!
- Just make sure to save the rendered image file in a format that has transparency, like .PNG