VFB vs MaxFB alpha WRONG

[Morne]

Hi all

I suddenly have an issue with my alpha channels!

I'm using LWF and saving out to exr.

In my VFB my alpha channel through the windows are correct. Pretty much black and white.
But in the exr and also if I clone the FB to a max frame buffer, my blacks turn to grey!

All other channels are fine and working as it should, just the alpha is suddenly buggered

[vlado]

If you right-click on the alpha in the V-Ray VFB, is the value black or just very dark?

Best regards,
Vlado

[Morne]

I have no idea what is going on here now


Thats a screen grab. The VFB is on the left and the cloned Max FB on the right.

In the VFB if I right click on the black, it reads 41,41,41

if I open the exr in photoshop it looks like the image on the rigth and the eye dropper also measures 41,41,41
?!?


And like I say, this weirdness is only in the alpha. All other channels are correct. I've restarted my pc already to check if maybe that will help, but it doesnt

[Morne]

Its almost like I'm having double gamma or something...

[Morne]

Heres my settings:



And I've just noticed my ZDepth also behaving incorrect as in the same as alpha. When cloned or opened in PS, black isnt as black as in VFB (although it measures the same with eye dropper)
???

[Morne]

I think I'm going nuts
Just tested this on a new fresh scene on a different pc and its doing the same!

HUH?!?

[vlado]

Nevertheless, it would be good if you can get me a scene to vlado@chaosgroup.com

Best regards,
Vlado

[Morne]

Hi Vlado I've sent you the email, but also here for others to see.

Here's a fresh scene that does the same. It appears as if it is a gamma issue only with alpha and zdepth.
If I manually save out the channel as a jpg and override gamma out as 1,0 then it looks like the VFB. But if I just save the jpg with defaults (2.2) then it looks like the Max cloned.

So then theoretically I should be able to just change the opened EXR alpha to a gamma of 0.4545 in PS and it should be fine?

(I mailed the scene but couldnt attached the zip here in the forum for some reason)

[Morne]

I use LWF and I save to vrimg and then extract each element to EXR

I mentioned the jpg results because that was part of my troubleshooting, not my actual workflow. So where do we go from here?

[svetlozar.draganov]

Alpha Channel in VFB is not affected by the gamma-settings - not sure if this is expected or not.
3DSMax Buffer is affected by gamma-settings - and that's why the alpha in Max Frame Buffer is different than the same alpha in VFB.

[Morne]

Alpha Channel in VFB is not affected by the gamma-settings - not sure if this is expected or not.
3DSMax Buffer is affected by gamma-settings - and that's why the alpha in Max Frame Buffer is different than the same alpha in VFB.

Then how do you explain my linear EXR image on photoshop (ONLY the ALPHA) getting a gamma of 2.2 and not looking the same as the VFB?

[svetlozar.draganov]

It's the same reason - Photoshop automatically applies sRGB profile to RGB and Alpha channels, Vray apply it on RGB-channel but not in Alpha-one that's why they differs.

Can you share with us what is the exact worflow you are using ? A simple scene would will be also very helpful.

[Morne]

Errr no, something changed in 2014. It always was working like it should in 2013 and before...

I doubt it is the gamma thing in 2014 because I tested it, even if I change the gamma via maxscript, it still does same behaviour. Before 2014 it didnt do this...

[svetlozar.draganov]

Can you send us example scenes and screen-shots about this.
This is what I got with Max 2014.



When EXR is displayed in a Linear Space it looks exactly like in the VFB - if the profile is changed to sRGB it is different.
It works this way for Max 2013 as well.

[mcnamex]

image bit depth probably in ps set to 16 bit or 8 bit...?