I have a Photoshop file made up of several layers. In Photoshop, in the "Channels" tab you can see the RGB and alpha channels. I have details painted into the alpha channel. When I open this file in Krita, the alpha channel appears to be full white.

Where is my alpha channel data?

I cannot say off-hand. Could you share the psd file with me? If it's confidential, please send it to vurian@gmail.com, and I can take a look.

Sure. How can I attach a file here???

On the forum, that's hard, unless you use something like a dropbox link. But you can also just mail me at the address I mentioned.

OK, thanks. I emailed it to you.

Thanks! I'll check it later on -- having dinner now.

Okay, I think I got it. Photoshop and alpha channel is a bit complicated... There are two kinds of layers: the background layer that doesn't have an alpha channel by default, and the normal layers that always have an alpha channel. If you remove the default background layer, all layers have the normal alpha channel. That's the one Krita loads. Then there's the extra channels photoshop has: Alpha 1 etc. We haven't got that kind of channels in Krita at all, though we have transparency and selection masks that have a similar function. But as far as I can tell, the correspondence isn't 1:1, unless I am much mistaken. Krita cannot currently load the extra channels and make them into something that can be used in Krita. It's something we need to do and want to do, but nobody has had time to actually do it.

I sent this email to you with attachments:
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Thanks, I read your reply about the difference in alpha channels between Photoshop and Krita. It seems that there is currently a “break” between Photoshop and Krita. I have prepared a very simple test. I have a TGA file with an alpha channel. And I have the “same” image in a PSD format. When opened in Photoshop they appear as one would think they should. There is a collapsed background layer, and there is an alpha channel. But when I open these in Krita, the TGA appears correct but PSD lost the alpha information.

Attachments:
Alpha1.tga (TGA image with alpha channel)
Alpha1.psd (Same as Alpha1.tga but saved as PSD)
Photoshop_PSD.jpg (Photoshop screenshot of Alpha1.psd showing correct background layer and alpha channel)
Photoshop_TGA.jpg (Photoshop screenshot of Alpha1.tga showing correct background layer and alpha channel)

That's probably because photoshop loads the tga file as a background layer, which doesn't have an alpha channel, so it loads the alpha channel as a channel mask.

Hm, actually, Krita does save and load transparency masks as channels in psd format; but there's still a difference compared to your example. If I create an image with a transparency mask in Krita and save as psd, photoshop loads it with the mask/channel chained to the layer, and in your examples it's apparently not linked to any layer, but a separate thing that works on the whole image. I'm no longer sure how this works in Photoshop...

Ok, thanks. Looks like I just need to familiarize myself more with Krita.