first, open the file you scanned, I use one of old work I did in summer.
Second, you need to take out the gray and make white more white, black more black using LEVEL!
you can go to
edit - adjustment - level
or you can just
ctrl(or command for mac) + l
And you can take out the gray by changing numbers on the left and right, or moving the arrows
(I usually don't move the arrow in the middle. Left arrow is for adjusting black, middle is for gray, and right is for white)
I usually change the number on the right to 40-60,
and one on the left to 220-235
Then you can see your drawing gets darker with no gray! aha!!!
third, you need to go to channel which is placed right next to layers window, and click "Load channel as selection"
I don't exactly know what this button does, but it selects all the whites on the image.
then you see the weird bling bling shiny lines on your image.
it means all the white pixels are selected
then, you go to
Select - Inverse
or just ctrl + shift + i
Forth, go back to layers window, make a new layer by clicking little button on the bottom of the layers window, and fill out the selection with paint bucket tool
short cut for filling out is
d - x - ctrl + delete
after that, you can deselect the selection by
ctrl + d
then you see only black lines are picked on new layer!
and you can color your work!
.... actually, you can have the same effect with changing the property of your scanned image to multiply , but good thing about this technique is......
you can change the color of your lines!
you can do whatever you can do with it, I use this every time I do my illustration.
this is when I was working with the same technique.
(the photoshop looks weird because I was using photoshop CS5)
I hope this helps you
If you have any question, feel free to leave a comment!