Alpha for materials

[vladimir.nedev]

The difference in the first 2 images is caused by the color corrections (most likely the sRGB VFB correction) being applied to the masked alpha, but not to the normal alpha render element.
I will try to fix this and write back here when it is done.

Greetings,
Vladimir Nedev

[peterL]

mmh, stupid question here ... how can I access the nightly builds, I only see

'Apr 09, 2015 30006 windows 64 bit Access expires: 31 Aug 2015'

in the download section ...

thx

[vladimir.nedev]

mmh, stupid question here ... how can I access the nightly builds, I only see

'Apr 09, 2015 30006 windows 64 bit Access expires: 31 Aug 2015'

in the download section ...

thx

Please read this thread for information on how to get access to the nightly builds : http://forums.chaosgroup.com/showthr...ith-no-dongles

Greetings,
Vladimir Nedev

[vladimir.nedev]

Also if you turn on Matte Surface in Object properties you get this:
Click image for larger version. Name: alpha-matte.jpg Views: 3 Size: 27.9 KB ID: 24702:

Can you send me the scene for this ? I am not able to reproduce it. Maybe it depends on the chosen image sampler.

Greetings,
Vladimir Nedev

[janko22]

I have the scene at work so I'll send it tomorrow. But it's just a cube with 3 polys with 3 different materials and 3 alpha masks in them. The wierd aliasing is happening on the edges of adjacent materials. And matte surface is turned on.

[vladimir.nedev]

I have the scene at work so I'll send it tomorrow. But it's just a cube with 3 polys with 3 different materials and 3 alpha masks in them. The wierd aliasing is happening on the edges of adjacent materials. And matte surface is turned on.

Oh, I get it now. This happens because those edges have no discernible difference to V-Ray. So only 1 image sample is probably taken there.
The only way to fix it would be to increase the "min subdivs" in the image sampler.

Greetings,
Vladimir Nedev

[janko22]

Just tested this with today's build. It seems that if my materials are different enough alphas are OK as you can see here:

[janko22]

However if I put the same color on all 3 materials alphas become a mess:






Isn't there a way to tell Vray to evaluate alpha output separately from main color output, so that it looks black vs. white for sampling instead of red vs. red?

[vladimir.nedev]

However if I put the same color on all 3 materials alphas become a mess:
[ATTACH=CONFIG]24722[/ATTACH]
[ATTACH=CONFIG]24723[/ATTACH]
[ATTACH=CONFIG]24724[/ATTACH]
[ATTACH=CONFIG]24725[/ATTACH]
[ATTACH=CONFIG]24726[/ATTACH]

Isn't there a way to tell Vray to evaluate alpha output separately from main color output, so that it looks black vs. white for sampling instead of red vs. red?

There probably is, but it will be somewhat of a hack. And it might slow down the rendering for some specific settings for the image sampler.
For example if the "max subdivs" is too high(something like a 100) and the "noise threshold" too low, it might turn out that the additional sampling
on the edges between the alpha outputs will increase the render time significantly.

I will add it as an option to the image sampler, something like "Anti-alias masked alpha outputs". It will be disabled by default.
I imagine that it won't be needed in a lot of cases, since the edges between the alpha outputs will already be anti-aliased,
because of the different materials that they mask.

I will write back here when I add it, so you can try it out.

Greetings,
Vladimir Nedev

[janko22]

Great, thank you!

[janko22]

Maybe you can do something with Alpha Contribution in Vray object properties tab? So that it only effects what is in material group and specific alpha, because than you get normal aliasing but now it effects alpha output globally.

[vladimir.nedev]

Maybe you can do something with Alpha Contribution in Vray object properties tab? So that it only effects what is in material group and specific alpha, because than you get normal aliasing but now it effects alpha output globally.

If you set the "alpha contribution" of one of the masked materials to something different than 1.0, the V-Ray image sampler sees the edge in the main Alpha render element,
and that's why the anti-aliasing works correctly in this case. But I don't think it will be convenient to have to go and change the alpha contributions just for this.

What I plan to do is something similar, I will lie to the image sampler that each masked alpha element has a different color, thus forcing it to anti-alias the edges between them.
The rendered result will still be a white alpha, that you can use normally in post-production.

Greetings,
Vladimir Nedev

[janko22]

Thanks again.

[vladimir.nedev]

Here is alpha in material group:
[ATTACH=CONFIG]24699[/ATTACH]

Here is the main alpha:
[ATTACH=CONFIG]24700[/ATTACH]

And here is difference blending in Photoshop:
[ATTACH=CONFIG]24701[/ATTACH]
You can see that there is a white line, the image should be completely black if the two alpha outputs were the same.

For tomorrow's nightly build (the one from 2015-06-18 ) the VFB color corrections are no longer applied to the masked alpha outputs, so that white line should be gone.

Note that the color corrections are still applied if you load an image from the History window and then save it, as the History window images are saved as .vrimg files
and the specific information needed to disable the VFB color corrections is not part of the .vrimg format yet. We will fix this eventually,
the only workaround for now would be to disable all VFB color corrections (including the default sRGB correction) in this case. Basically uncheck all buttons in the bottom tool-bar of the VFB.

Greetings,
Vladimir Nedev

[vladimir.nedev]

However if I put the same color on all 3 materials alphas become a mess:
[ATTACH=CONFIG]24722[/ATTACH]
[ATTACH=CONFIG]24723[/ATTACH]
[ATTACH=CONFIG]24724[/ATTACH]
[ATTACH=CONFIG]24725[/ATTACH]
[ATTACH=CONFIG]24726[/ATTACH]

Isn't there a way to tell Vray to evaluate alpha output separately from main color output, so that it looks black vs. white for sampling instead of red vs. red?

Tomorrow's nightly build (the one from 2015-06-19) will have the new option for anti-aliasing the masked alpha outputs.
It will be under the "Image sampler" roll-out at the very end. It is called "Anti-alias masked render outputs".
This special anti-aliasing is disabled by default, since it can increase render times a lot if used with very high max subdivs or low threshold for the image sampler.
So you should use it with caution. Please give it a try, I can tweak how it works in case you run into problems with specific settings/scenes.

Greetings,
Vladimir Nedev