Operation Manual

Working with Graphics, Animation, and Multimedia 73
To prevent display of this kind, Web designers often use a Web-safe
palette of 216 colors that don’t dither in Web browsers operating in
256-color environments. The safe palette is actually a 6x6x6 RGB
“color cube” using evenly-spaced red, green, and blue values from 0 to
255 along its axes. 51 happens to be the interval in the series of values
(0, 51, 102, 153, 204, 255). So, for example, the RGB definition
“0,102,51” would be a safe color, while “0,102,52” would not. To
create Web-safe colors in a paint program, define new colors using
RGB values that are either 0 or divisible by 51.
For your convenience, WebPlus includes two swatch panels
incorporating the Web-safe colors. (Look for
WEBSAFE1.GIF and
WEBSAFE2.GIF in the /WEBPLUS/9.0/SAMPLES folder.) You can paste
either one into your paint program’s “canvas” area and pick colors from
it using the program’s eye dropper tool. Or you can load the supplied
WEBSAFE.PAL palette so it’s used in the color selection table. It’s
especially important when anti-aliasing graphics to ensure that the edge
colors the program applies come from the safe palette. (You can also
select the palette for use in a site via Tools/Palettes>WebSafe.plt.)
As a rule, if you’re concerned with 256-color display, save low-color
bitmap images created in your paint program in the .GIF format using
the safe palette. Avoid using a unique palette per image; if you have
multiple GIFs per Web page, different palettes may clash and all
images will suffer.
Performance
“Performance” may seem like an odd aspect of graphic design, but it’s
actually one of the key factors in how users will judge your Web site.
As with colors, not all your users will have systems that match yours
for speed. Technically, performance means load time: how long it takes
for your whole page, including text and graphics, to display completely
in a Web browser. In practice, it’s hard to measure, and subjective
factors intrude. Connection bandwidth, server speed, and modem rating
all play a part. As discussed earlier, it’s always wise to design the safe
area of each page to give visitors something to look at, read, and/or
think about, and thus offset the perception of delay while the rest of the
page loads.
Load time is a function of the total size of all the page objects that need
to load; and graphics usually take up the lion’s share. That’s why we
can talk about the “performance” of your page as a function of the total
file size of its graphics.