alpha read off greyscale issue

[Dune]

Has anyone enountered this? I made a greyscale version of a RGB branch.tif, with the alpha channel intact (I later checked; they are identical). In TG the opacity tab takes that greyscale image, alpha checked. But the rendered outcome is different from the alpha channel read in the RGB file, and also differs from a pure greyscale (no alpha) opacity map. Strange, huh?
Perhaps TG can't properly read a greyscale alpha channel, which thus would be a bug?
Left is flat grey mask, middle is RGB+alpha, right is greyscale+alpha.

[Kadri]

Any unpremultiply, premultiply thing ?

[Dune]

No, that's off by default.

[Kadri]

Curious. If it is not too much work could you post a basic example Ulco ?

[KlausK]

This may sound rather stupid but, what if you check the "use alpha channel" in that shader in the picture. It looks to me as if tg is adding the rgb grayscale values + the alpha channel values. Or am I completely off? Not that I know anything at all about alpha channels...
cheers, Klaus

[Dune]

I'll fix a non-ST sample.
@Klaus; the screendump is related to the plain greyscale mask, without alpha channel. With the other 2 I had the alpha checked.

[KlausK]

Sure, you wouldn`t miss something like that.
cheers, Klaus

[Dune]

No, I guess not, but sometimes you (I) tend to forget the most basic things 

I sent you a mail, Kadri. See what you think.

[bobbystahr]

Still waiting for TG to recognize greyscale values as transpaerncy/filter values so I can get back to what I was doing in Imagine 10 years ago myself.