A Complete Guide to Web Design

34 Chapter 3 – Web Design Principles for Print Designers

Graphics on the Web

Web Design in a Nutshell, eMatter Edition

System Colors in Web Pages

If an 8-bit display allows 256 colors, and there are 216 colors in the browser’s Web

Palette, you may be wondering what happens to the other 40 colors. Normally, the

browser allows colors from the user’s system palette to fill in the extra 40 color

slots. These extra colors can go a long way in smoothing out colors that can’t be

recreated accurately using Web Palette colors alone. This is particularly true for

grayscale images, which are difficult to reproduce using only the four web-safe

gray tones in the Web Palette.

There is a bug in Netscape 4.0 on the Macintosh that prevents system colors from

seeping in to help render images on web pages. This version of the Netscape

browser maps everything strictly to the Web Palette, resulting in inferior image

quality. This is most noticeable in grayscale images, which shift to the Web

Palette’s yellow-green and lavender shades in an attempt to display the image

accurately. This bug only affects Macintosh users with 8-bit displays using

Netscape 4.0 (probably a very small percentage of your audience). For more infor-

mation on this issue, seehttp://www.artware.de/nc4petition/.

Graphics on the Web

Print designers will need to adapt their graphics production skills for the Web to

take into account the peculiarities of graphics that are distributed over a network

and displayed on computer monitors.

Graphic File Formats

As of this writing, nearly all of the graphics that you see on the Web are in one of

two formats: GIF and JPEG. A third worthy contender, the PNG file, is struggling

for browser support and attention. What follows is a very brief introduction to the

“big three” of online graphic formats. More detailed descriptions are provided in

the chapters dedicated to each format.

The ubiquitous GIF

The GIF (Graphic Interchange Format) file format is the traditional darling of the

Web. It was the first file format to be supported by web browsers and it continues

to be the format for the vast majority of graphics on the Web today.

GIFs are indexed color files with a maximum 8-bit palette capacity, which means

that a GIF can contain a maximum of 256 pixel colors. Because they compress

color information by rows of pixels, GIF files are most appropriate for graphics

that contain areas of flat color.

See Chapter 14,GIF Format,for complete information on the GIF file format.

The handy JPEG

The second most popular graphics format on the Web today is the JPEG (Joint

Photographic Experts Group) format. JPEGs contain 24-bit color information—

that’s millions of colors, as opposed to GIF’s 256. They use what is called a “lossy”

compression scheme, which means that some image information is thrown out in