Change Alpha channel to custom greyscaled image

[Asmark]

I have now tried to empty the whole internet, trying to figure out a “simple problem” for hours. I’m a game developer, finally getting to go self employed. Therefore I’m not willing to pay for PhotoShop anymore, and want to go with Krita, like most others.

The problem occurs when I want to change the alpha channel of a texture, to a custom alpha gryscaled (black and white) image. It seems that everytime a seperate the channels from an image (R,G,B,A), even the ALPHA CHANNEL has an alpha channel. And when trying to split/seperate THAT alpha channel, the same happens and so on. Really frustrating thing, since it was so easy to just copy paste an image into the greyscaled alpha channel in photoshop.
I have read the development book, and watched dosens of videos, and I still cannot figure out why this happens. Please, someone help me. Thank you!
Sincerely,
Mathias

[Takiro]

I’m kinda confused about what you are trying to do. The alpha channel is just the transparency value of an image you can’t like put a whole image in there. Maybe it’s just terminology because there are some (although only a few things) that seem similar but are actually different things in photoshop and Krita.

Maybe you can give a bit more detail about the steps you perfomed in Krita so far and what your goal is. For me it sounds like you just split a layer by channel.

[Lynx3d]

Well layers always have an alpha channel, and separating creates layers from channels, so that’s expected.

So you want to replace the alpha channel completely with a new grayscale image, do I understand that correctly?

This should be possible by using ‘Convert’ → ‘to Transparency Mask’ on the greyscale image (it’ll be added to the layer below), and then in the context menu of that new mask do ‘Split Alpha’ → ‘Write as Alpha’.

[Reptorian]

If you want to replace the alpha entirely, I do it this way.

1. Create a color curve adjustment layer on top and set Alpha to max
2. Create a group layer above the newly created adjustment layer.
3. Insert your custom image.
4. On the group layer, add a cross-color adjustment mask, and use luminosity to alpha. Set the left point to 0.
5. Set Group Layer to Destination In Blending Mode.

[Asmark]

Okay, so I just figured it out. There is an option to import/export an image into the Transparency Mask Layer.

Select the image that you want to import the alpha to

Go to Layer - Import/Export - Import as Transparency Mask

Then right click the Transparency Mask

Click Split Alpha - Write As Alpha

Thank you all for your valid inputs! I deeply appreciate it, really!