Hi, I'm new to Krita and I'm trying to reproduce some things that I'm used to do in Photoshop. I want to select the Alpha channel of a tif image to create a mask. My goal is to display a background throught a window. The window zone in the image is black in the alpha channel.

In Photoshop I would cntrl click the Alpha channel to load the selection. Then with that selection I would create a quick mask. There's also an option in the selection menu that lets you load a selection from the channels. I don't know how to achieve this with Krita.

If I understood you, you should do:

1. select -> select opaque.
2. select -> invert selection.
3. layer -> convert -> the mask you want.

Expect it help!

It doesn't work . Maybe I wasn't clear enough so I'm going to put a link to the image in PS so that it's easier to see what I'm trying to achieve.

http://oi68.tinypic.com/140xaaq.jpg

I'm still not much sure, you're trying to select the black area and convert int a transparency mask? You can use the similar color selection tool to select black and so use the step 3 to convert it to a transparency mask. Please let me know if it help and sorry the confusion.

Oh you want to maintain the original layer, sorry the confusion. You should select the layer and add a transparency mask, now with the areas you want to make transparent selected, go to the mask and erase, now I believe it will work.

This maybe ?

Right click on layer -> Split Alpha -> Alpha into mask. Then you can choose white-black mask , and draw on it. Alt-Click on mask layer thumbnail to hide everything except mask (I don't know how to make it semitransparent).
After all, you can bake mask into alpha back ( Right click on mask -> Split Aplha -> Write as Alplha ).


Also "alpha inheritance" can be used for some tasks, instead masks (seems to me, layers grouping and blending have less surprises than masks in Krita):
Create 2 layers, bottom layer's alpha will be used as mask, top layer will be used is for painting.
Click on "alpha inheritance" button of top layer in "Layers" docker. If you want background under these two layers - bottom "mask" and top painting layers should be put in one layer group folder.

Sorry... Again... About my confusion. I was in need os a sleep.
Dobrokotov pointed a good Idea, when you can, use alpha inheritance always (create a new layer and use it as alpha for the next up layer), basically because it is one click and can be easily cascaded on other layers.
Unfortunately it did not stick to what you want.

Apart from the first solution there is a simpler and better quality one, use color to alpha filter, it is extremely simple, and you can apply it non destructively too.

1. go to filter -> color -> color to alpha
2. select the black color and adjust threshold to a value where it fits your need (values where only pure black areas are affected).
3 . select the option create filter mask.



If some area goes alpha and you did not want it, just edit the filter mask, painting white on the filter where you want black to not be alpha.

Still no luck. The thing is the windows should already have the alpha channel in the correct way (it was generated by the 3D program), but I can't see it in krita. I can paint the selection myself like you suggest, but it won't be accurate.

If Krita cannot see the alpha channel you didn't save it out right, or there's a bug in which case that should go to bugs.kde.org.

I tried exporting to other formats to see if it was a problem only with tif files. Targa and OpenEXR work perfectly and the alpha channel now looks the way it should