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Contents:

1. Digital Magic
2. Painting By Numbers
3. A Revealing Image
4. As Easy as Calling Up a Log
5. A Lunar Odyssey
6. Fun with Fuzzy Filters
7. Building Color
8. A Digital Toolbox

A Lunar Odyssey

The wind still howls and sleet rattles against the windows. But now you and your friends are exploring the surface of the Moon. This is the second time you've taken this lunar excursion; your first journey was two weeks ago at the telescope. In all your years of lunar observing you'd never seen anything like it. Individual craters filled the CCD frame. The detail was remarkable. Every few seconds a new image appeared; to save a good one, you pressed a function key. You went a little nuts and left your friends with 15 megabytes of lunar pictures.

Tonight you're back to look over the images, and to take home some copies of the best. You quickly click the mouse twice and a picture of the crater Archimedes pops onto the screen. The picture looks good to you just as it is.

"That's a nice image," she comments, "but we can make it a lot better. " She stares intently at Archi-medes for a moment. "It needs a soft mask . . . oh, about 7 pixels square I'd say. Look, here's how you can tell. See how the light from this bright crater rim diffuses about 3 or 4 pixels out? The fuzziness is everywhere, but you're going to fix that."

"Click on Filters and then Unsharp Mask," he suggests. "Then click '7 by 7.'" You do as you're told, noting that there must be a dozen filters and a dozen choices besides 7 by 7.

A moment later the image of Archimedes clears. It's as if someone pulled a sheet of waxed paper off the screen. The fuzz evaporates and Archimedes stands sharp-rimmed with craterlets on its floor.