Why Thumbscrew Won't Output GIFs

A lot of people ask me for GIF support for one of two reasons:

• Smaller file size than the default PNG

• More widely compatible with browsers on that other OS.

While I can understand and sympathize, Thumbscrew won’t support GIF output until Apple’s CoreGraphics does. That said, there are (to me) compelling reasons not to use GIFs for a photo thumbnailing application, especially one that generates drop shadows:

• GIFs don’t actually support an alpha channel, so even if you did get GIF output, you only get to replace one indexed color with a transparency. This would lead to ugly output unless you matched the background, in which case, why bother with transparency at all?

• GIFs are not the best image format for photo-realistic content.

My advice to users who want smaller file size (or more widely compatible file format) is to use JPEGs with an opaque background color to match your site.

I will be evaluating pngcrush to see if it would at all be applicable. You all aren’t the only ones who’d like to see the size of the PNGs come down.