Web Design in a Nutshell, 3rd Edition

Use aliased edges

One way to avoid halos is to keep your image and text edges aliased (as shown in Figure 29-7). That way there are no stray pixels between your image and the background color.

Figure 29-7. Transparent graphic with aliased edges (no halo effect)

In Photoshop, the Marquee, Lasso, and Magic Wand selection tools all have the option of turning off anti-aliasing in their respective Option palettes. You can also choose to turn off anti-aliasing when creating text.

The advantages to aliased edges are that they are halo-proof and require fewer pixel colors (which potentially means smaller file sizes). The disadvantage is that the blocky edges often look just as bad.