Compression types:

• GIF – best for graphics with areas of flat color, permits transparency, limits colors
  

• PNG – good replacement for .gif, patent-free
  

• JPG – best for photographs or complex illustrations, “lossy” compression means some information is discarded to make the image smaller
  

Yale's Web Style Guide (http://info.med.yale.edu/caim/manual/) has a good description of GIF and JPG and W3C covers PNG at http://www.w3.org/Graphics/PNG/.

GIF is a commonly used file format that compresses images with areas of single colors, as well as line drawings, very well. Licenses to use the format are built into many commercial applications, but some applications do not have licenses with Unisys ... PNG (portable network graphics) was developed to take the place of GIF. It is patent-free, and seems to work well on the web, but further discussion should take place to see if anyone has had problems using png files on EPA sites.

JPG handles colors well and is great for compressing photographs so they'll load fast, but still look good. Photoshop has a "Save for Web" feature that allows you to see multiple compression ratios side by side - you can decide how much data to discard (that's what lossy means) while maintaining image quality.