Pro-or-Anti-Aliasing
By Lynda Weinman
My husband Bruce (www.stink.com) is a professional illustrator who recently took on a Web-design project. Things were moving along swimmingly until his client showed his work to some higher-ups, who decided they liked the icons he had designed for navigation buttons and background tiles, but wanted to change his color scheme to match a promotional booklet they'd recently published.
Bruce had created custom illustrations and "anti-aliased" them against the same green he had selected as a hexadecimal background color for the HTML of his Web-page prototype; that is, he blended the colored edges of the graphics to their backgrounds. The client's desire to replace the background color -- a small change conceptually -- could have resulted in an enormous undertaking had Bruce not used Photoshop layers for his artwork. This month's column will review anti-aliasing procedures, while touching on many related and fun subjects such as bit-depth, GIF transparency, file size, Photoshop layers, and alpha channels.
One-bit Masks versus 8-bit Masks
Why is it a big deal to change the color of an anti-aliased image? In
Figure 1, for example, the edges of the blue graphic blend into the white background, creating a series of increasingly lighter blue pixels around the edge that eventually fade to white. The problem with changing the color behind the image is that there's no easy way to isolate the blended pixels around the edges to make them fade to a different color.
