Chapter 20. JPEG Format
JPEG
(which stands for Joint Photographic Experts Group, the standards
body that created it) is a compression algorithm used by files in the
JFIF format, commonly referred to as "JPEG files." JPEGs
use either the .jpg or
.jpeg suffix.
Like any graphics file format in widespread use on the Web, JPEGs are
platform-independent. In addition, JPEGs are fully supported for use
as inline images in Versions 2.0 and higher of Netscape Navigator and
Microsoft Internet Explorer, as well as in nearly all other current
browsers.
20.1. 24-Bit Color
JPEG images contain
24-bit
RGB color information, which means they are comprised of colors from
the true color space of millions of colors (see Chapter 3, "Web Design Principles for Print Designers" for a description of 24-bit color). JPEG files
can also carry grayscale images. This results in higher image quality
and more rich and subtle color variations. Unlike GIF files, JPEGs do
not use palettes for referencing color information.
Bear in mind, however, that when JPEGs are displayed on a system that
only supports 8-bit color, a browser reduces the colors in the image
to its built-in web palette, and some dithering occurs. In general,
however, dithering is often acceptable in photographic image areas.
For an explanation of the web palette, see Chapter 3, "Web Design Principles for Print Designers" and Chapter 22, "Designing Graphics with the Web Palette".
 |  |  | | 19.8. Minimizing GIF File Sizes |  | 20.2. JPEG Compression |
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