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I'm a game artist, many of my tasks revolve around punching up the detail of normal maps or working to translate photographs into game ready assets. I also often have to recolor assets that are purchased from asset stores or are creative commons. What does all this have in common? Using channels frequently.

Right into the meat of things, I'll be using a format that summerizes the workflow, explains how the workflow breaks down in krita, and then what I consider to be the fixed and expected behavior. If any of this isn't clear, I will be happy to make a video for youtube about it that demonstrates the workflow in photoshop and Krita.

TL;DR = Krita's channel docker should function like photoshop's channel docker. The current workaround of splitting layers into four channels is cumbersome for normal tasks and inadequate in others.

1.) Normal maps.

Workflow: I have additional normal map refinements, normal map A. I have the original baked normal map, normal map B. I wish to combine them. I disable normal map B. I go into channels, blue channel specifically, only normal map A is visible. Using levels, I drop blue from 255 to 128. I re-enable both layer A and B. I set A to overlay, and it is placed above B in the layer stack. This results in a combined normal map.

Krita issue: Playing with the channels through the levels filter, while just looking at blue channel of normal map A, ends up changing the levels of red and green as well.

Expected/fixed behavior: If I have red/green unchecked, the levels function should only be acting on the blue channel.

Workaround: Split layer. This adds many more steps and increase the time per normal map improvement.

2.) Building masks from channel sections of multiple or singular layers. Removing blue sky from hair or foliage, recoloring channel details or similar tasks.

Workflow: Have something I want to cut out. Very strong blue sky behind subject, subject has no blue or very little blue. Go into blue channel, use magic wand tool and an appropriate level of fuzziness to select out the blue as best as possible through the black and white blue channel's stark value difference. Use this selection to create a new alpha mask on the existing layer. If there are issues with the mask, I can push the midpoint of grey up/down, or also point with an overlay brush to sharpen blacks/whites.

Workflow B: needing to recolor hair, fur or skin. Same as above, expect it involves multiple layers. Thankfully the channels tool shows all the layers as one black and white image flattened together, if only one color channel is active. Over in photoshop, I can make masks/selections based off this display.

Krita Issue: Magic wand still seems to be sampling the full color image.

Expected/fixed behavior: Selection tools should have sampling logic for the black and white image in the channel tab that respects which channels are active.

Workaround: If it is a singular layer, you can still split the layer into 4 layers to work from. There is no direct work around if your scene his comprised of multiple layers, outside of having to split every single layer involved, and combining every single channel with it's alpha, and then combining all those channel+alpha layers into a final mask.