Graphics Programs Reference
In-Depth Information
Compression
The Compression area of the Save Adobe PDF
dialog box offers several options for reducing
file size. You do not need to downsample, but
you might want to if you want to better match
the output resolution of a particular printer or to
reduce file transfer times.
The interpolation method you choose determines
how pixels are deleted:
Average Downsampling. This method
averages the pixels in a sample area and
replaces the entire area with the average
pixel color.
Subsampling. This method chooses a pixel in the center of
a sample area and replaces the entire area with that color.
Bicubic Downsampling. This method uses a weighted aver-
age to determine pixel color. It generally yields better results
than Average Downsampling. This is the slowest but most
accurate method.
The Compression setting offers three compression methods:
Zip. This works well for images with large areas of single
colors or repeating patterns.
JpeG. This is suitable for grayscale or color images. JPEG
compression eliminates data, so it usually results in much
smaller file sizes than ZIP compression.
JpeG2000. This is the new international standard for image
data compression. Like JPEG compression, JPEG2000 com-
pression is suitable for grayscale or color images. It also pro-
vides additional advantages, such as progressive display.
The Image Quality setting determines how much compression is
applied. The settings will vary based on the compression method
you choose, but they are clearly labeled.
You c a n s ele c t t he c onve r t 16 B it / C h a n nel I m a g e t o 8 B it s /
Channel check box if you're working with a 16-bit image. This can
significantly reduce file size but is not a good option if you're creat-
ing a PDF for professional printing. This option is grayed out if the
image you are working with is already in 8-bit mode.
 
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