how to isolate scanned linework in photoshop!
below is a way to isolate your lineart for coloring, etc. (i’m not saying it’s the best way, but it’s definitely a way, and it saves me a bunch of time and heartache.)
scan your lineart at high resolution grayscale. (i use 600ppi; def don’t go lower than 300ppi.)
use the levels toggles to get it from grayscale to crisp(ish) black and white. (you won’t be paint-bucketing anything and don’t need to worry about halo/aura, so feel free to season-to-taste, just be aware that anything not-black is going to end up partially transparent at the end of this. the super important thing is to make sure you’re getting rid of any paper texture that you don’t want from the original scan.)
strike a balance that feels good to you—if you go too far in one direction, the lines will get porous as the lighter bits etc inside them go white. too far in the other direction, and the lines can start to feel thick and goopy. if you’re using pencil lines, you can always err on the side of retaining the nuance of the texture, then double the resulting linework layer a couple times to beef them up.
anyway, it’s a matter of preference. just fuss with it until it feels right; that’s what toggles are there for!
make corrections/touchups to the linework by drawing over it with black and white. it will be more annoying to make changes later, so you might as well get as much of it over with now as you can.
go to the channels pane. (if it’s not currently open, you can find it under the window dropdown menu.)
hold down the command key (or ctrl on windows, i think?) while clicking inside the little thumbnail of the gray channel. this will select the %white in every pixel.
make a new layer!
inverse the selection (cmd+shift+i). this will select the %other-than-white in every pixel, so gray pixels are now partially selected, black pixels fully selected.
it’ll look almost exactly the same as it did before, but the selection edges will appear to be slightly inside the linework instead of slightly outside it.
with the empty layer selected, fill the selection. (i always fill in with black to begin with, but do as you like; it doesn’t matter even slightly.)
note that the little thumbnail for your linework layer now has stuff in it! (yes i know i spelled ‘cintiq’ wrong in my workspace preset, sorry.)
delete the background layer with the scanned image in it — oh my gosh!
this is an important and exciting step: lock the transparency of the linework layer by either hitting the “/” key while it’s selected or by clicking the tiny checkerboard icon in the lock row at the top of the layers panel. a little hollow padlock (vs the solid padlock of a locked-layer) will appear next to the name of the layer. (note: i also put a white layer behind the lines at this point bc it’s easier to see what i’m doing.)
now that the lines are transparency-locked, you can do whatever the hell you want to them: fill with different colors…
…apply gradients, paint over certain areas to make them different colors, whatever! as long as you do all the coloring on other, non-linework layers, the lines will stay safe, and you’ll be fine.
you can make a photoshop action of the channel-selecting through new-layer-filling steps. after that, turning a cleaned-up black and white scan into isolated lineart becomes a magical, instant, nearly one-click process.
hope this was helpful! good luck!
all the best,