Operation Manual

300
USING ILLUSTRATOR
Importing, exporting, and saving
Last updated 11/8/2011
More Help topics
“About Adobe PDF” on page 293
“Printing and saving transparent artwork” on page 434
“Create Adobe PDF files” on page 293
Compression and downsampling options for PDF
When saving artwork in Adobe PDF, you can compress text and line art, and compress and downsample bitmap
images. Depending on the settings you choose, compression and downsampling can significantly reduce the size of a
PDF file with little or no loss of detail and precision.
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.
Downsampling If you plan to use the PDF file on the web, use downsampling to allow for higher compression. If you
plan to print the PDF file at high resolution, do not use downsampling. Deselect the option to disable all downsampling
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
subsampling—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:
• Average Downsampling Averages the pixels in a sample area and replaces the entire area with the average pixel
color at the specified resolution.
• 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.