Adobe Illustrator CS4 - Manual (Page 294)

287 USING ADOBE ILLUSTRATOR CS4
Importing, exporting, and saving
• 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.
• 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.
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 satisfactory
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
“ About Adobe PDF ” on page 281
Mark and bleed options for PDF
Bleed is the amount of artwork that falls outside of the printing bounding box, or outside the crop marks and trim
marks. You can include bleed in your artwork as a margin of error—to ensure that the ink extends all the way to the
edge of the page after the page is trimmed or to ensure that an image can be stripped into a keyline in a document.