Working with Graphics and Tables - New Perspectives on Adobe Dreamweaver CS5, Comprehensive - page 236

Understanding Graphics and Compression
The NextBest Fest site plan calls for a graphic logo to be included in each page. The
logo will increase the brand recognition for NextBest Fest, which is a major goal of the
site. Because the logo was designed with the site metaphor in mind, it will enhance
the intended look and feel of the site. Other graphics will be added as needed to carry
the look and feel of the site throughout the pages.
Because graphics fi les are usually large, the graphics you add to a Web site are stored
in compressed fi le formats. Compression shrinks fi le size by using different types of
encoding to remove redundant or less important information.

The smaller the graphic's
file size, the faster the
graphic will load in a
browser.

Decision Making: Using Graphics Effectively
Graphics make a Web site more interesting and provide valuable information. For example,
maps and graphs can summarize information more succinctly and intuitively than words. As
a society, we are accustomed to distilling information from images. The graphics you add
to a Web site should enhance the feel you are trying to create and provide users with visual
clues about the page content and/or the site's intended message. Most important, the
graphics you add to a Web site should reinforce the site goals. When choosing graphics for
a Web site, consider what each graphic will add to the page.
• Will the graphic supply information or reinforce the page content?
• Will the graphic aid the user in navigating through the site?
• Will the graphic help the page to maintain the look of the site?
If the graphic does not add anything to the page, it should not be used.
Graphics you add to a site should be an appropriate file size. Consider the total file size
of all the graphics in the Web page and the connection speed the target audience will have.
If you are going to include only one graphic in a page, its file size can be larger. If you are
going to include several graphics in a page, the size of each graphic will contribute to the
amount of time it takes a user's browser to download the page. In this case, you might
want to make the file size of each graphic smaller. If the target audience uses a dial-up
connection, graphic-intensive pages will take longer to download, so keep the graphics to
a minimum or choose graphics with small file sizes. Evaluate each graphic's importance to
the page. A user is more willing to wait for a page to download if that page is interesting
and provides content the user is looking for.

Figure 5-1 lists the approximate times it takes to download fi les of various sizes over a
standard 56 kb/s (kilobits per second) dial-up connection, a DSL connection, and a cable
modem connection.

Figure 5-1 Approximate download times for different fi le sizes

Connection Type* Size of Page (in kilobytes)

10 kB 50 kB 100 kB 200 kB 400 kB

Dial-up 56 kb/s (approx.
5 kB/s)

2 seconds 10 seconds 20 seconds 40 seconds 80 seconds

DSL 1.5 mb/s or higher
(approx. 160 kB/s)

< 1 second < 1 second < 1 second 1.25 seconds 2.5 seconds

Cable modem 3 mb/s or
higher (approx. 380 kB/s)

< 1 second < 1 second < 1 second 1 second 1.1 seconds

*Speeds shown in their common forms of kilobit (kb) for dial-up and megabit (mb) for DSL and cable,
and then converted to kilobyte (kB) for comparison with Web pages of different sizes.