Adobe Training - Learn Photoshop and Adobe Creative Cloud
Melissa Piccone is an Adobe Certified Instructor with over 20
years of experience in Photoshop and Design   I originally wrote
this article way back when (1995-96?), before the software that
is around today was created. The basic concepts still apply, but
the techniques have become obsolete. I highly recommend using
Adobe's products for web development, including Photoshop, Image
Ready and GoLive. They are my personal prefrences.  Quick Update
and Overview:  JPG = good for photos, continuous tone images
(gradients), millions of colors, lossy compression (each time
you save, more quality loss) - small files - always save for web
- don't use a jpg for print - too big  GIF = good for graphics,
solid colors, logos, - one color can be transparent (not very
useful), can be animated, between 2 - 256 colors, small files
for graphics, larger files if using a photo  PNG = 8 bit and 24
bit - 2-256 colors for 8 bit, millions for 24 bit. 8 bit not
helpful - lossles