Adobe Photoshop CS is possibly the best program for manipulating digital photographs. But it's also a capable program for coloring scanned artwork. This is especially valuable because it's easier to draw on paper, with a pencil or a pen, than it is to sketch on screen, if only because you can see an entire piece of paper without zooming or panning. And it can be easier to add colors in Photoshop than it is to hassle with conventional paints or assemble fussy mechanicals.
I'll show you how to apply color to scanned line art in Photoshop ($649; www.adobe.com). Throughout this process, you won't harm a single stroke in the original drawing. It really is the best of all worlds.
Create the Art
I drew a butterfly with a common Sharpie pen on a piece of inexpensive copier paper. While these are admittedly low-tech art tools, I prefer them to anything Photoshop has to offer. I then scanned the drawing.
Prepare the Scan
The first step of coloring the artwork -- coloring inside the lines -- requires that you select the lines and send them to a separate layer. Your natural tendency might be to reach for the Magic Wand tool. But there's a simpler way that produces better results.
Go to the Channels Palette If the palette isn't already on screen, choose Window: Channels. Because I scanned the artwork as a gray-scale image, the palette lists one channel, Gray.
Load the Channel as a Selection One of the fantastic things about channels is that you can convert them to selection outlines. Anything that's white becomes selected; anything that's black becomes deselected. To load the selection, press the 1 key and click anywhere on the Gray item in the Channels palette.
This is one of those weird times in Photoshop when a shortcut -- in this case, 1-clicking -- is your primary means of performing an operation. It's not the only way; if you prefer, you can click on the icon at the bottom far left of the Channels palette. But there is no equivalent menu command. None. I swear, sometimes the whole program seems like one big secret passageway.
After you 1-click, you should see marching ants all over the place. Every white pixel inside the image is now selected. There's just one small problem: you want to select the black lines, not the white background.
Reverse the Selection Choose Select: Inverse or press 1-shift-I. Photoshop deselects the white pixels and selects the black ones.
Make a New Layer Choose Layer: New: Layer or press 1-shift-N to add a new layer to your image. Inside the New Layer dialog box, name the layer Line Art, and click on OK.
Fill the Selection with Black The selection transfers to the new layer automatically. Press the D key to reset the default colors (black and white). Then press option-delete to fill the selection with black. The black lines are now relegated to their own layer.
Select the Background Layer Click on the Layers tab or press F7 to bring up the Layers palette. Then click on the Background item to make it active.
Deselect and Fill with White Now that we have the butterfly transferred in all its glory to the Line Art layer, you can get rid of the background butterfly. Press 1-D to deselect the artwork. Then press control-delete to fill the Background layer with white. (Or, if you prefer the long way, choose Edit: Fill, change Use to Background Color or White, and click on OK.)
Lock the Transparency of the Line Art Layer Click on the Line Art layer to select it. Then click on the first Lock icon -- the one that looks like a checkerboard -- near the top of the Layers palette. This prevents you from changing the opacity of individual pixels in the layer. The opaque pixels stay opaque, and the transparent pixels stay transparent; all you can change is the colors. The upshot is that any brushstroke you apply will appear strictly inside the lines.
Convert the Image to RGB Currently, your butterfly is a single-channel gray-scale image. That's perfect for scanning black-and-white line art because it keeps the file size to a minimum. However, it also means we can't paint in color -- unless you count shades of gray as color. To open up the spectrum, choose Image: Mode: RGB Color.
At this point, Photoshop brings up a message that's very easy to ignore. But don't. The program is telling you that it wants to flatten your artwork and toss out all the work you've done. Ostensibly, this clumsy solution is intended to avoid the color shifts that sometimes result when you recalculate blend modes. The problem is, those shifts are most likely to occur when you convert between RGB and CMYK, and they simply can't happen when you convert from gray scale to RGB. So be very sure to click on Don't Flatten (or press the D key).
Color the Line Art
Photoshop offers two painting tools, the paintbrush -- also known as the Brush tool -- and the pencil. The pencil paints jagged lines, so it's most useful for changing individual pixels. The paintbrush is more versatile, allowing you to modify the sharpness of a line and tap into a wealth of controls that the pencil can't touch. Click on the paintbrush tool in the toolbox or press the B key.
Select a Color and Brush Choose Window: Color or press the F6 key to display the Color palette, and dial in your favorite butterfly-painting color. I decided on red, which is R: 255, G: 0, and B: 0. Next, go to the Options bar and click on the arrow to the right of the word Brush to bring up a pop-up palette of brush options.
Adjust the Master Diameter Value Adjusting this value changes the size of the brush. For our purposes, a large brush, something in the neighborhood of 150 to 200 pixels, works well.
Use the Hardness Value This will adjust the softness of the brush. A Hardness value of 100 percent results in an antialiased brush (mostly sharp with a tiny bit of softness). Set the Hardness to 0 (zero) percent to create a fuzzy brush.
Alternatively, you can ignore both the Master Diameter value and the Hardness value and select a predefined brush from the scrolling list.
To hide the pop-up palette and accept your changes, press enter or return. Or just start painting in the image window. (Press the escape key to hide the palette and abandon your changes.)
You can change the brush attributes incrementally from the keyboard. You use, of all things, the bracket keys. Press the left-bracket key ([) to reduce the brush diameter; press the right-bracket key (]) to increase it. Press shift-[ to make the brush softer; press shift-] to make it harder. These shortcuts may seem weird at first, but when used properly, they can be enormous time-savers.
Paint Inside the Butterfly Paint as much of the butterfly as you like, wherever you like. As you do, Photoshop confines your brushstrokes to the interior of the lines.
Make Your Insect Iridescent To add more colors, select a different foreground color from the Color palette and keep painting. Or read the continuation of this process at find.macworld.com/0014. There, you can learn how to add a random collection of colors with a single brushstroke.
Converting colors between RGB spaces, such as Apple RGB, sRGB, and NTSC, can be complex. The $65 BabelColor 1.2 ( www.babelcolor.com ), from The BabelColor Company, is designed to ease the way. With it, you can compare and convert coordinates between 13 RGB spaces, and display two separate RGB spaces at the same time.
The company says that BabelColor is aimed at print and Web designers, as well as professional colorimetrists. Color novices should welcome the included help manual explaining basic theory and detailed equations. -- terri stone