286 Chapter 15 – JPEG FormatJPEGs in AOL Browsers
Web Design in a Nutshell, eMatter Editionfor the entire image to download. Progressive JPEGs are also generally slightly
smaller than standard JPEG files.Disadvantages
One disadvantage to Progressive JPEGs is that they require more processing power
to display. The higher the specified number of passes, the more power it takes the
user’s machine to render them.
The other disadvantage is that they are not supported on older browser versions.
Netscape Navigator 2.0 and Internet Explorer 2.0 display Pro-JPEGs inline, but may
not support the progressive display. Pro-JPEGs are fully supported by versions 3.0
and higher of both Netscape and MSIE. If a browser cannot identify a Pro-JPEG, it
will display a broken graphic image.JPEGs in AOL Browsers*
The America Online 3.0 software uses a version of the Internet Explorer browser
that is integrated with Johnson & Grace compression technology for faster image
downloads. Unfortunately, the J&G compression has trouble rendering JPEGs
created with Photoshop 4.0 because of problems locating the header information
in the file. As a result, JPEG image quality gets mangled, displaying a blurry image,
sometimes with green, streaky artifacts.
Although users can turn off the “Use Compressed Graphics” option in their Prefer-
ences, you can’t count on them to do so. AOL’s recommendation is to use
Photoshop 3.0 instead. Some web developers have found that Photoshop 3.0-
created Progressive JPEGs survive their journey through the AOL grinder more
successfully, maintaining image quality closer to the original. (Note that Netscape
1.0 users and users with AOL 2.7 on the Mac platform will not be able to see Pro-
JPEGs in their AOL browser; however, they make up only 1% of AOL’s audience
as of this writing.) This problem is rumored to be fixed in the upcoming 4.0
version of the AOL software.
If you want to be absolutely certain your images look perfect for AOL users, stick
to GIF format.Creating JPEGs
Because JPEG is a standard file format, it is supported by all the popular graphics
tools. Adobe Photoshop, JASC Paint Shop Pro, Adobe ImageReady, and Macro-
media Fireworks all provide similar options for saving JPEGs.
Each tool provides sliders for controlling quality/compression ratios, although they
use different numbering systems. Adobe products use a 0–10 compression scale,
with the lowest setting corresponding to around 30 on the standard scale of 1–100.
Paint Shop Pro uses a scale from 1 to 100; however, it works as the inverse of the
standard scale with lower numbers corresponding to higher image quality and less
compression. Fireworks uses a percentage value from 1 to 100%.* Thanks for to Max Leach for his assistance with this topic.