User manual

Using Image Settings options
The Image Settings options control how scanned images are filtered and compressed in
the Adobe PDF document. Default settings are suitable for a wide range of document
pages, but you may want to change settings for higher quality images, smaller file sizes, or
scanning issues.
Two controls determine how each scanned page is represented in the PDF document:
● For Color/Grayscale, select either Adaptive or JPEG.
● For Monochrome, select JBIG2, Adaptive, or CCITT Group 4.
Only one of these two controls is applied to each scanned page. After you click the
Acrobat Scan control, you can choose the scanned page size, resolution, number of colors,
and bits per pixel in the scanner's TWAIN interface. When you press Scan in the TWAIN
interface, the scanner starts, and Acrobat receives and processes the scanned page,
applying the Monochrome control to 1-bit per pixel black-and-white input, or the Color/
Grayscale control.
Adaptive
Divides each page into black-and-white, grayscale, and color regions and chooses a
representation that preserves appearance while highly compressing each kind of content.
Adaptive compression works on grayscale and RGB input greater than 150 ppi or on
black-and-white input greater than 400 ppi. At lower resolution, only one kind of image is
used in the adaptively compressed output. The recommended scanning resolutions are 300
ppi for grayscale and RGB input, or 600 ppi for black-and-white input.
JPEG
Applies JPEG compression to the entire grayscale or RGB input page. (See Methods of
compression.)
JBIG2
Applies the JBIG2 compression method to black-and-white input pages. At high quality
settings (with the slide bar set far to the right, at 0.95 or higher), the page is compressed
using the lossless method. At lower quality settings, text is highly compressed. JBIG2
compressed text pages typically are 60% smaller than CCITT Group 4 compressed pages,
but processing is slow. JBIG2 compression is compatible with Acrobat 5.0 (PDF 1.4).
CCITT Group 4
Applies CCITT Group 4 compression to black-and-white input page images. This fast,
lossless compression method is compatible with Acrobat 3.0 (PDF 1.2). (See Methods of
compression.)
Slide Bar
Use the slide bar to set the balance between smallest file size and maximum image
quality. The slide bar does not affect black-and-white output for CCITT Group 4. If the
slide bar covers a numerical range between 0.0 and 1.0, with 0.0 being the lowest quality
and 1.0 being the highest, then at the position 0.95, the JBIG2 implementation switches to
lossless compression. For JPEG output, the default setting gives compact pages of good
quality; higher settings result in more accurately compressed, less compact pages; lower
settings increase compression and reduce quality. For Adaptive compressed output, the
slide bar determines both the JPEG quality of gray and color output images and the use of
low-resolution images to represent some page content.
Deskew
Rotates the skewed page so that it appears vertical and not at an angle.
Background Removal
Affects gray and color input but has no effect on black-and-white input. This filter makes
nearly-white page areas white. If the background is not white, Adaptive applies JPEG
compression, resulting in poor compression. Low, Medium, and High settings increase the
darkness of the not-quite-white clutter, which the filter makes white. For good results,
calibrate your scanner using its contrast and brightness or other controls so that a scan of a
normal black-and-white laser printer page has dark gray or black text and a white
background. With this calibration, the Background Removal filter should produce good
results for its Off or Low settings. However, if something printed on the backside of a
page shows through, or if off-white paper or newsprint is scanned, the Medium or High
setting may be preferred to clean up the page.
Edge Shadow Removal
Removes dark streaks that occur at the edges of scanned pages, where the scanner light is
shadowed by the paper edge.
Despeckle
Removes isolated black marks in black-and-white page content. Low uses a basic
peephole filter. Medium and High use both a peephole filter and a large area filter that
removes larger spots farther from nearby features.
Descreen
Removes halftone dot structure. Most printing technologies represent a continuous range
of color by controlling the size of tiny dots (yellow, cyan, magenta, and black) on a page.
Higher resolution scans typically preserve some of this unwanted dot structure. If it is not
removed, the dot structure reduces JPEG compression significantly, and it may cause
Moire patterns when viewing or reprinting a PDF.
The Descreen filter typically works best on 200 to 400 ppi grayscale or RGB input or, for
Adaptive compression, on 400 to 600 ppi black-and-white input. The Auto setting
(recommended) allows Acrobat to choose when to descreen; it applies the filter for 300
ppi or higher grayscale and RGB input, and disables it for 200 ppi or lower input. The Off
setting disables the filter. Consider choosing the Off setting when scanning a page with no
pictures or filled areas, or when scanning at a resolution higher than the range at which the
filter is effective.
Halo Removal
On (recommended) removes excess color at high-contrast edges, which may have been
introduced during either printing or scanning. This filter is used only on color input pages.