Colour in alpha channels multi channel exr

[ali_cgi]

Hey when I have colour in my alpha channel, using fog, I cant get this information to save in the multichannel exr, just greyscale. If I save out single channel I get all this info
is this possile ideally without a separate image file.
I want to use the inerted alpha to multiply over backplate to apply the correct colour to the fog to the comp build.
Thanks

[nikolay.kusht]

At this point, it is not possible to get the Color Alpha in a multichannel exr.

[ali_cgi]

Ahhh great to get this implemented as it would be really handy for producing accurate beauty builds in comp.
Is there a way in maya to create an alpha via extra tex or something similar? Thus allowing us to write it into a 3 channel exr layer?

[nikolay.kusht]

You could try adding a Custom Color render element with the Alias set to "2". This would give you the extra alpha channel.

[ali_cgi]

excellent! works perfectly! Is there any info on what the other alias channel numbers relate to?

[nikolay.kusht]

The Alias can also be used to reference other render elements through their Vray Alias [vrayRE] attribute (found in Extra Attributes rollout; not the cleaner Extra VRay Attributes rollout). Unfortunately, we don't have an official list with all the alias corresponding values.

Here are some examples:
GI render element = 108
MaterialID = 115

[ali_cgi]

Has this all changed in vray 5? i cant get the alpha with the custom color anymore

[nikolay.kusht]

We managed to reproduce this and it seems that this is a bug(VMAYA-10090). I will write here when we have any news or progress on this one.