Being a Thomas Boutell fan, I was a pretty excited to get this note in my mailbox recently:
I am writing with regard to Lynda Weinman's excellent article, "Pro-or-Anti-Aliasing." [Web Techniques, July 1997] Her coverage of the PNG format and anti-aliasing is correct with regard to true-color images. However, she draws the conclusion that since true-color images are often large, PNG's transparency is not practical for use on the Web.
Actually, PNG also supports 8-bit palette images, just like GIF -- and it supports transparency for these images better than GIF does: The artist can set the level of transparency for every color in the palette. If you want to have four identical versions of red, except with different levels of transparency, you can go right ahead and do that.
This approach is an effective way to improve on the very limited transparency of GIF without introducing the large file sizes of true-color PNG. It's up to you to decide how to "spend" your 256 palette entries; depending on your needs, you might use more unique colors, or more levels of transparency for colors that appear in border areas. It should not be difficult for future versions of graphics programs to make these decisions intelligently when saving an 8-bit PNG version of an image with an alpha mask.
Tom Boutell
President
Boutell.Com, Inc.
