Adobe INDESIGN 2.0 - USING HELP Help Manual page 368

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lossless; that is, data is not removed to reduce file size, and therefore image quality is
not affected. Using 4-bit ZIP compression with 8-bit data can affect the quality,
however, because data is lost.
JPEG compression is suitable for grayscale or color images. JPEG is lossy, which means
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that it removes image data and may reduce image quality; however, it works to reduce
file size with a minimum loss of information. Because JPEG eliminates data, it can
achieve much smaller files sizes than can ZIP compression.
CCITT and Run Length compression are only available for monochrome bitmap images.
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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 monochromatic images. Group 3, used by most fax machines,
compresses monochromatic bitmaps one row at a time. Run Length compression
produces the best results for images that contain large areas of solid black or white.
About resampling
InDesign can downsample or subsample a bitmap image to reduce the amount of data in
the image to no more than what an output device requires. You should resample bitmap
images when they contain more data than the output device can use, or when the
exported Adobe PDF file will be used on the Web. For a table showing different output
resolutions, see "Compressing and resampling images" on page
sampled at a higher resolution than the device can use, processing time is increased.
Resampling refers to changing the pixel dimensions (and therefore the display size) of an
image. When you downsample (decrease the number of pixels), information is deleted
from the image. When you resample up (increase the number of pixels), new pixels are
added based on color values of existing pixels.You specify an interpolation method—
average downsampling, subsampling, or bicubic downsampling—to determine how
pixels are added or deleted.
Downsampling averages the pixels in a sample area, and then replaces the entire area
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with the average pixel color at the specified resolution.
Subsampling chooses a pixel in the center of the sample area, and then replaces the
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entire area with that pixel at the specified resolution. Subsampling significantly reduces
processing time compared with downsampling, but results in images that are less
smooth. Subsampling is not recommended for high-resolution printing.
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369. If your images are
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