Adobe GOLIVE CS2, User Manual, Page: 415 / 724

406 ADOBE GOLIVE CS2
User Guide
Compression options for Adobe PDF files
When you export to PDF or edit a PDF preset, you can set the following compression options for images. You may
want to experiment with these options to find an appropriate balance between file size and image quality.
Downsampling
To downsample color, grayscale, or monochrome images, GoLive combines pixels in a sample area
to make one larger pixel. You provide the resolution of your output device in dots per inch (dpi) and enter a
resolution in pixels per inch (ppi) in the For Images Above box. For all images with resolution above this threshold,
GoLive combines pixels as needed to reduce the image’s resolution (ppi) to the specified dpi setting. The interpo­
lation method you choose determines how pixels are deleted:
• Average Downsampling To
Averages the pixels in a sample area and replaces the entire area with the average pixel
color at the specified resolution.
•
Subsampling To
Chooses a pixel in the center of the sample area and replaces the entire area with that pixel color.
Subsampling significantly reduces the conversion time compared with downsampling but results in images that are
less smooth and continuous.
•
Bicubic Downsampling To
Uses a weighted average to determine pixel color, which usually yields better results
than the simple averaging method of downsampling. Bicubic is the slowest but most precise method, resulting in the
smoothest tonal gradations.
Compression Determines the type of compression that is used:
• Automatic (JPG/ZIP)
Determines automatically the best quality for color and grayscale images. For most files, this
option produces satisfactory results.
•
JPG
Is suitable for grayscale or color images. JPG compression is lossy , which means that it removes image data
and may reduce image quality; however, it attempts to reduce file size with a minimal loss of information. Because
JPG compression eliminates data, it can achieve much smaller files sizes than ZIP compression.
• ZIP
Works well on images with large areas of single colors or repeating patterns, and for black-and-white images
that contain repeating patterns. ZIP compression can be lossless or lossy, depending on the Image Quality setting.
•
JPG 2000
Is the international standard for the compression and packaging of image data. Like JPG compression,
JPG 2000 compression is suitable for grayscale or color images. It also provides additional advantages, such as
progressive display. The JPG 2000 option is only available when Compatibility is set to Acrobat 6 or later.
•
Automatic (JPG 2000/ZIP)
Determines automatically the best quality for color and grayscale images. This option
is available only when Compatibility is set to Acrobat 6 or later.
• CCITT (Consultative Committee on International Telegraphy and Telephony) and Run Length
Are only available
for monochrome bitmap images. CCITT compression is appropriate for black-and-white images and any images
scanned with an image depth of 1 bit. Group 4 is a general-purpose method that produces good compression for
most monochrome images. Group 3, used by most fax machines, compresses monochrome bitmaps one row at a
time. Run Length compression produces the best results for images that contain large areas of solid black or white.
Image Quality Determines the amount of compression that is applied. For JPG or JPG 2000 compression, you can
choose High, Medium High, Medium, Medium Low, or Low quality. For ZIP compression, only 8-bit is available. If
you use 8-bit ZIP compression with 4-bit or 8-bit images, the ZIP method is
lossless ; that is, data is not removed to
reduce file size, so image quality is not affected.