User Guide

369
ADOBE GOLIVE CS2
User Guide
Web graphics formats and options
Comparing web graphics formats
Web graphics formats fall into two categories: bitmap and vector. The bitmap formats—GIF, JPEG, PNG, and
WBMP—describe artwork as a series of colored dots called pixels. Each pixel in a bitmap image has a fixed size and
is therefore resolution-dependent, meaning that dimensions of the image depend on the resolution of the monitor on
which it is viewed. The vector formats—SVG and SWF—describe artwork mathematically, as a set of geometric
objects. Because of this, vector graphics are resolution-independent and can be scaled up or down without losing any
image quality.
GIF and PNG-8
GIF is the standard format for compressing images with flat color and crisp detail, such as line art, logos, or illustra-
tions with type. Like the GIF format, the PNG-8 format efficiently compresses solid areas of color while preserving
sharp detail; however, not all web browsers can display PNG-8 files. (See “Optimization options for GIF and PNG-8
formats” on page 370.)
Note: When optimizing images for i-mode cellphones, use GIF format. For more information, see “To add images to i-
mode pages” on page 472.
PNG-8 and GIF files support 8-bit color, so they can display up to 256 colors. The process of determining which
colors to use is called indexing, so images in GIF and PNG-8 formats are sometimes called indexed color images. To
convert an image to indexed color, GoLive builds a color lookup table, which stores and indexes the colors in the
image. If a color in the original image does not appear in the color lookup table, the application either chooses the
closest color in the table or simulates the color using a combination of available colors. (
See “To customize the color
table for GIF and PNG-8 images” on page 372.)
JPEG
JPEG is the standard format for compressing continuous-tone images such as photographs. Optimizing an image as
a JPEG format relies on lossy
compression, which selectively discards data. (See “Optimization options for JPEG
format” on page 373.)
JPEG2000
The JPEG2000 format builds on the JPEG standard with improved compression schemes and performance.
GoLive can import JPEG2000 files, but not create them. Though you use the Image object to import standard JPEG
files, JPEG2000 files require the generic Plug-in object. (See
“Adding multimedia” on page 349.)
Note: To display JPEG2000 files, most browsers require an additional plug-in.
PNG-24
PNG-24 is suitable for compressing continuous-tone images; however, it produces much larger files than JPEG
format. The advantage of PNG-24 is that it can preserve up to 256 levels of transparency in an image. (See “Optimi-
zation options for PNG-24 format” on page 374.)
Note: Internet Explorer for Windows doesn’t support transparency in PNG-24 files.