User manual

Methods of compression
Distiller applies ZIP compression to text and line art, ZIP or JPEG compression to color
and grayscale images, and ZIP, CCITT Group 3 or 4, or Run Length compression to
monochrome images.
Suitable compression methods for different art types A. ZIP B. JPEG C. CCITT D. Run Length
You can choose from the following compression methods:
● ZIP works well on images with large areas of single colors or repeating patterns, such as
screen shots and simple images created with paint programs, and for black-and-white
images that contain repeating patterns. Acrobat provides 4-bit and 8-bit ZIP compression
options. If you use 4-bit ZIP compression with 4-bit images, or 8-bit ZIP with 4-bit or 8-
bit images, the ZIP method is lossless, which means it does not remove data to reduce file
size and so does not affect an image's quality. However, using 4-bit ZIP compression with
8-bit data can affect the quality, since data is lost.
Note: Adobe implementation of the ZIP filter is derived from the zlib package of Jean-
loup Gailly and Mark Adler, whose generous assistance we gratefully acknowledge.
● JPEG (Joint Photographic Experts Group) is suitable for grayscale or color images, such
as continuous-tone photographs that contain more detail than can be reproduced on-screen
or in print. JPEG is lossy, which means that it removes image data and may reduce image
quality, but it attempts to reduce file size with the minimum loss of information. Because
JPEG eliminates data, it can achieve much smaller file sizes than ZIP compression.
Acrobat provides six JPEG options, ranging from Maximum quality (the least
compression and the smallest loss of data) to Minimum quality (the most compression and
the greatest loss of data). The loss of detail that results from the Maximum and High
quality settings is so slight that most people cannot tell an image has been compressed. At
Minimum and Low, however, the image may become blocky and acquire a mosaic look.
The Medium quality setting usually strikes the best balance in creating a compact file
while still maintaining enough information to produce high-quality images.
● CCITT (International Coordinating Committee for Telephony and Telegraphy) is
appropriate for black-and-white images made by paint programs and any images scanned
with an image depth of 1 bit. CCITT is a lossless method. Acrobat provides the CCITT
Group 3 and Group 4 compression options. CCITT Group 4 is a general-purpose method
that produces good compression for most types of monochrome images. CCITT Group 3,
used by most fax machines, compresses monochrome images one row at a time.
● Run Length is a lossless compression option that produces the best results for images that
contain large areas of solid white or black.