Adobe Illustrator CS3 User Manual
Page 289
ILLUSTRATOR CS3
User Guide
283
The interpolation method you choose determines how pixels are deleted:
•
Average Downsampling
Averages the pixels in a sample area and replaces the entire area with the average pixel
color at the specified resolution.
•
Bicubic Downsampling
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 gradations.
•
Subsampling
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.
Compression
Determines the type of compression that is used. The Automatic option automatically sets the best
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.
•
ZIP compression
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 Quality
setting.
•
JPEG compression
Is suitable for grayscale or color images. JPEG 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 JPEG compression eliminates data, it can achieve much smaller file sizes than ZIP
compression.
•
JPEG2000
Is the new international standard for the compression and packaging of image data. Like JPEG
compression, JPEG2000 compression is suitable for grayscale or color images. It also provides additional advantages,
such as progressive display.
•
CCITT and Run Length compression
Are only available for monochrome bitmap images. CCITT
(Consultative
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.
Image Quality
Determines the amount of compression that is applied. The available options depend on the
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
compression with 4-bit images, or 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. Using 4-bit ZIP compression with 8-bit
data can affect the quality, however, because data is lost.
Tile Size
This option is only enabled when its corresponding Compression setting is JPEG2000. It determines the
size of the tiles for progressive display.
Compress Text And Line Art
Applies compression to all text and line art in the file. This method results in no loss of
detail or quality.
See also