https://forum.kde.org/viewtopic.php?f=83&t=141175 I was private messaged to add this to the bug tracker, as well as a summary. Summary: Channels docker should allow the following and does not. A.) Selection tools need to use the black and white channel image for their logic and computation if you are in a single channel or combination of channels rather than sample the original full color image. Useful when removing greenscreen or photoblue backrounds from art. Useful in lineart to grab ink, but not blue pencil from scans too. As it stands now, you're forced to junk through hoops to get these selections. Such as merging all your layers, then taking the merged master and dividing that into three channels. Then sometimes having to apply an alpha. B.) Painting on in channels mode should only paint in the active channels. A mark made in the red channel with blue and green hidden should not contribute to marking blue and green as well. This functionality is needed for normal-map touchups.
C.) If I use levels or some other adjustment function, while filtered by channel, I expect the adjustment to only apply to active channels. Right now, using the levels command in the channels docker, while filtered to any individual color, still changes the level of all channels.
Krita really doesn't have channels like photoshop does, where channels are a kind of selections. Reworking Krita to work like Photoshop is a big project. WISHGROUP: Big Projects