Now, im not new to this myself(been scanlating since january and head editor of my team for this time) but I am not very good at all with raw scans other than leveling it, cleaning it and making the blacks black. One thing i did want sometimes in the more complicated manga there are greys that arent exactly uniform because the greys in one whole section are darker than another and i was wondering if there was a way to duplicate the effect in photoshop when redoing greys. I mean the only thing i could think of is a gradient but i dont know how to apply it to the scan.
do the grey normally
make a new layer, set it to multiply => select the grey area, take the gradient paint bucket and fill (by clicking at one point and then another point, making a line from where the first color (ie black) start, and to where the 2nd color (ie white) shall end)
note: everything behind the first point is going to be in the first color, and everything beneath the 2nd point is going to be in the second color.. you might click outside the image also, if you want it to be not totally white at the end)
note2: using shift if u want the gradient to be like perfectly horizontal or vertical
note3: you might also use normal mode type of layer BUT lower the opacity of the gradient layer
note4: sometimes if you want to have an oblique gradient at the end (like outside of the panels in OP flashbacks..) you can use the smudge tool on the gradient layer