Here's the starting point, an "out-take" photo of Liz (left, knitting) and Karen (right, with mask on) - on the days that we were doing the photo-shoots, all the photographers were taking snaps pretty much flat out, as anything could end up as a panel.
Liz' character's already been introduced at this point (the knitting wasn't intended as a prop - her grandson was due a few weeks after the shoot, and she had something to finish off - but it's been incorporated into the story as a "pocket universe" that her character is creating). This is the first sighting of Karen's character, who won't reappear for some time.
I want to create a rough mono-coloured background colour, and add linework over the top. First, to get the flat colour, I apply a threshold on a copy of the base layer:
I'll then use the "oilify" filter with a large mask size (32, IIRC?) to soften the edges. (No idea if PS has an "oilify" equiv, or what it's called...
A lot of fine detail's been lost here, but that's ok, as the next layer will retrieve it. I apply the cartoon filter now, on another copy of the original image:
and then threshold that to a very low value (2 or 3 of 255), to wipe out all the colour, and just leave the black linework:
I replace the white with transparent pixels (colour to alpha), so the previous layer is visible underneath. I also apply a layer mask to the linework layer, initially all black, and then paint in the areas where I want the lines to be seen (generally faces, hands, the ball of wool, some of the head dress of flowers, but leaving the silhouette blank for a pleasing graphic effect). This adds dramatic emphasis, and also allows me to fix up where the cartoon effect went wrong. As I recall, Karen's chin ended up looking strangely stippled, so I just expose the linework on the mask.
At this point, the working image file is done.I export to a jpeg and import that as a new layer on the page, then play around with the colours a bit more to get it to fit. Here's the finished art for the page, sans lettering.
The cross-hatching effect on the lower two panels and the cut-out at the top is rather more complicated - maybe I'll cover that another time.