Adobe ILLUSTRATOR CS2 User Manual page 360

The Compression area of the Save Adobe PDF dialog box is divided into three sections. Each section provides the
following options for compressing and resampling color, grayscale, or monochrome images in your artwork.
Important: The Preserve Illustrator Editing Capabilities option (in the General preferences area) counteracts aggressive
compression and downsampling. If file size is a concern, deselect this option.
If you plan to use the PDF file on the web, use downsampling to allow for higher compression. If you
Downsampling
plan to print the PDF file at high resolution, do not use downsampling. Deselect the option to disable all downsam­
pling options.
Downsampling refers to decreasing the number of pixels in an image. To downsample color, grayscale, or
monochrome images, choose an interpolation method—average downsampling, bicubic downsampling, or subsam­
pling—and enter the desired resolution (in pixels per inch). Then enter a resolution in the For Images Above text
box. All images with resolution above this threshold will be downsampled.
The interpolation method you choose determines how pixels are deleted:
•
Averages the pixels in a sample area and replaces the entire area with the average pixel
Average Downsampling
color at the specified resolution.
•
Uses a weighted average to determine pixel color, which usually yields better results than
Bicubic Downsampling
the simple averaging method of downsampling. Bicubic is the slowest but most precise method, resulting in the
smoothest gradations.
•
Chooses a pixel in the center of the sample area and replaces the entire area with that pixel color.
Subsampling
Subsampling significantly reduces the conversion time compared with downsampling but results in images that are
less smooth and continuous.
Determines the type of compression that is used. The Automatic option automatically sets the best
Compression
possible compression and quality for the artwork contained in the file. For most files, this option produces satis­
factory results. Use Automatic (JPEG) if you need the greatest compatibility. Use Automatic (JPEG2000) for superior
compression.
•
Works well on images with large areas of single colors or repeating patterns, and for black-and­
ZIP compression
white images that contain repeating patterns. ZIP compression can be lossless or lossy, depending on the Quality
setting.
•
Is suitable for grayscale or color images. JPEG compression is lossy, which means that it
JPEG compression
removes image data and may reduce image quality; however, it attempts to reduce file size with a minimal loss of
information. Because JPEG compression eliminates data, it can achieve much smaller file sizes than ZIP
compression.
•
Is the new international standard for the compression and packaging of image data. Like JPEG
JPEG2000
compression, JPEG2000 compression is suitable for grayscale or color images. It also provides additional advantages,
such as progressive display.
•
CCITT and Run Length compression
Committee on International Telegraphy and Telephony) 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.
Determines the amount of compression that is applied. The available options depend on the
Image Quality
compression method. For JPEG Compression, Illustrator provides Minimum, Low, Medium, High, and Maximum
Quality options. For ZIP compression, Illustrator provides 4-bit and 8-bit Quality options. If you use 4-bit ZIP
Are only available for monochrome bitmap images. CCITT (Consultative
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