Photoshop tip: Remove white from scanned drawing

Scanning your drawn or painted artwork is a great way to combine the best of both worlds... the beauty of a hand-rendered image plus the flexibility of digital image making. This electric tea kettle is a character in my next picture book, so he’ll be the victim today. He’s painted with black watercolor in a dry brush technique on regular Strathmore drawing paper. Once scanned into Photoshop (at 300 pixels per inch) you can see the problem, the white paper background.Before anything further can be done, the image must be made more contrasty with Levels. The main task is to get rid of the paper texture, since the line work is already black. This is done in the Levels dialog box by moving the right arrow towards the center until the paper is really white. (If a drawing is scanned in, you can also darken the gray lines if desired by moving the left arrow towards the center.) The image below shows before Levels on the left, after on the right. Not sure if it will show up very well, but it’s better not to have a bunch of stray pixels all over the place as we continue. (Unless you want the paper texture for some reason, in which case Levels can make it more visible. Just play with the arrow sliders.)The easy way to get rid of the white is to change the blending mode in the Layers palette to Multiply. Many artists do this and it works fine. The Multiply technique works best for black or dark lines, because of the way Multiply mode interacts with the layer(s) underneath. If you want to color the lines and/or move parts of them around without getting bungled up with pieces of invisible white you need to completely separate the line work from the white paper and here’s how (on the Mac):
1 Make sure in the Layers palette that your scanned art is highlighted and in Normal mode. (A layer is highlighted when you click on it.)
2 Be sure the Channels palette is open. While holding down the Command key, in the Channels palette click on the RGB layer. This selects the white.
3 Hold down these three keys Command>Shift>the letter i. This inverts the selection.
4 Press Command>Option>letter J. A dialog box will come up, name the new layer Lines.
5 Turn off (click eyeball) the original scanned layer. You should see the black lines in their own layer.
6 With black as the foreground color and the Lines layer highlighted, hit Option>Shift>Delete. This fills any remaining pixels with black.
Make a new layer underneath the lines, and fill it with white or whatever color. Your image should look similar to the picture above, but the difference is that only the lines are on the layer, which allows you to color them any way you like. To color the lines, be sure to lock the layer first, by pressing the ?/ key. Locking the layer means that transparency will be preserved, only already-existing pixels can be painted on. You unlock it with the same key.

So here are the kettle lines, colored all crazily. This just can’t be done in Multiply mode.
The kettle will probably end up more like this, actually:So, I hope this tip is useful, if a tad geeky. I’m still using CS 1 but this has worked for many versions of Photoshop, so should still be there. The author Deke McClelland wrote about this technique in Photoshop 4 Studio Secrets, which is where I heard about it.