268 Chapter 14 – GIF FormatInterlacing
Web Design in a Nutshell, eMatter EditionBoth Macromedia Fireworks 1.0 and Adobe ImageReady 1.0 provide GIF
creation capabilities along with many fine-tuning controls over bit-depth, dith-
ering, and palette selection, which standard image editing programs lack, and
both programs condense GIF files very efficiently. Specific features are
discussed in the “Minimizing GIF File Sizes” section of this chapter.
Vector Drawing Programs
With the growing demand for web graphics, many vector-based drawing
applications now offer the ability to save bitmapped GIF files without
exporting the files and opening them in a program such as Photoshop (a big
time saver). In addition, simple graphics with solid fills, which are typical of
images created in vector-based drawing tools, are ideal for GIF compression.
Vector drawing tools such as Macromedia Freehand (versions 7 and higher),
Adobe Illustrator (version 7), Corel Draw, and Corel Xara offer GIF creation
capabilities.
Plug-ins
There are also a host of third-party plug-ins that can enhance the function-
ality of Photoshop and other software that supports Photoshop plug-ins. The
most notable of these are PhotoGIF from BoxTop Software (http://www.
boxtopsoft.com/) and HVS ColorGIF from Digital Frontiers (http://www.
digfrontiers.com/). Each provides tools that exceed Photoshop’s built-in
features for fine-tuning GIFs. Specific features are highlighted in the “Mini-
mizing GIF File Sizes” section of this chapter.
Shareware Utilities
In addition, there are dozens of utilities for both Mac and PC that perform
simple and specialized tasks. These utilities can be downloaded for free and
can be registered for a very modest fee. One example is GifConverter, which
will convert most existing graphic formats into GIF, and also allows you to
add interlacing. Another is Ulead GifSmartsaver, a very nice standalone GIF
optimization utility. Shareware.com is a valuable resource for finding such
utilities (search for “gif” athttp://www.shareware.com/).Interlacing
Normal GIFs are either displayed one row of pixels at a time, from top to bottom,
or they wait until the entire file has downloaded before the image appears. On
slow connections, this can mean potentially long waits with empty space and
generic graphic icons on the screen.
As an alternative, you can save a GIF87a or 89a with interlacing. An interlaced GIF
is displayed in a series of four passes, with the first hint of the upcoming image
appearing after only 1/8th (12.5%) of the file has downloaded. The first pass has
the appearance of a blurry mosaic; as more data flows in, the blurred areas are
filled in with real image information and the image becomes more defined. The
three subsequent passes fill in 25%, 50%, and 100% of the image information,
respectively.
Graphics programs that support the GIF format will provide an interlacing option
(usually a checkbox) in the Save as or Export dialog box. Simply turn the inter-
lacing on or off when you save the GIF.