Colored Alpha channel in postproduction problem

[rafa_sopata]

I have the following question:

Is it possible to save a RAW file in .EXR format with Alpha map pass/information for a Product that has SSS/Volumetric material with a colored alpha map (see attachments)? The background needs to be transparent in my case and when I open a RAW file in Photoshop the elements from SSS/Volumetric material look different than in VFB
It is important that everything is in one RAW file, it's part of the current pipeline

Thanks for the advice

[vladimir_krastev]

Hi, thanks for posting. Are you using VRayFastSSS2 material? Could you tell us a bit more about your workflow? How do you open the exr image?

[^Lele^]

If you load the EXR with the alpha channel as alpha channel, it'll load as mono.

[rafa_sopata]

Thanks for the answers

^Lele^ - yes Alpha channel as "mono" in .EXR is the problem here


vladimir_krastev - The workflow consists of 2 stages

Stage 1:
2k prev from VFB is saved as .jpg and sent to client for approval (product + LUT + whitebackground - all in VFB)

Stage 2:
After approval we render 4k .exr RAW file and in Photoshop there is automatic post production which gives TIFF file with 4x separate layers
- Product
-Shadow on ground
-Reflection on the ground
-White background

The problem occurs in VrayMtl for transparent materials with Fog color
Translucency None/valumetric/SSS (colored alpha channel it appears)

[rafa_sopata]

Also I found the information how to prepare the correct post production in Photoshop with colored alpha - and I need to do the following steps:

- invert the colored alpha channel - this way I will get the invered color
- multiply the inverted alpha by the background
- add your final image with plus operation to the background with already inverted alpha

The question is is it possible to save "colored" alpha chanell in .exr RAW file, because currently "mono" alpha chanell is saved

[^Lele^]

The question is is it possible to save "colored" alpha chanell in .exr RAW file, because currently "mono" alpha chanell is saved

Oh, sorry, i had it backwards.

The EXR format specification expects RGBA, with Alpha crucially represented as a single channel.
You can write an RGB layer with the alpha in it if you render Deep, and use the VrayOptionsRE to write it as RGB.
Unfortunately, i don't think PS would be very happy with the format.



We will extend the option to write an RGB layer for the alpha channel in non-deep rendering in the near future.
If you didn't use PS, it'd be trivial enough to recompose your thick EXR in nuke from individual layers, in which case you'd have the alpha saved as RGB as a matter of course.

[rafa_sopata]

Thanks for answer ^Lele^

Yes, Photoshop wasn't happy with deep EXR.

Do you plan to be exanded in non-deep in the next Fix? When can we expect this update?

Is there a way around this by saving the file to .vrim and then from ChaosPlayer to a RAW file with colored Alpha?

[^Lele^]

Do you plan to be exanded in non-deep in the next Fix? When can we expect this update?

The change is planned, timings are something we'd rather not share as they are always changing.