64
ADOBE ACROBAT 8 STANDARD
User Guide
Edge Shadow Removal
Removes dark streaks that occur at the edges of scanned pages, where the scanner light is
shadowed by the paper edge. Choose Off, Cautious, or Aggressive.
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, which can reduce JPEG compression, cause moire patterns, and make
text difficult to recognize. Suitable for 200–400 ppi grayscale or RGB input or, for Adaptive compression, 400–600
ppi black-and-white input. The Automatic setting (recommended) applies the filter for 300 ppi or higher grayscale
and RGB input. Select Off when scanning a page with no pictures or filled areas, or when scanning at a resolution
higher than the effective range.
Halo Removal
When On (recommended), removes excess color at high-contrast edges, which may have been intro
duced during either printing or scanning. This filter is used only on color input pages.
Scanning tips
•
Acrobat scanning accepts images between 10 and 3000 ppi. If you select Searchable Image or Formatted Text &
Graphics for PDF Output Style, input resolution of 72 ppi or higher is required, and input resolution higher than
600 ppi is downsampled to 600 ppi or lower.
•
On the Color/Grayscale menu in the Optimization Options dialog box, apply lossless compression to a scanned
image by choosing CCITT for black-and-white images or Lossless for color or grayscale images. If this image is
appended to a PDF document, and the file is saved by Save, the scanned image remains uncompressed. If the PDF
document is saved using Save As, the scanned image may be compressed.
•
For most pages, black-and-white scanning at 300 ppi produces text best suited for conversion. At 150 ppi, OCR
accuracy is slightly lower, and more font-recognition errors occur; at 400 ppi and higher resolution, processing
slows and compressed pages are bigger. If a page has many unrecognized words or very small text (9 points or
smaller), try scanning at higher resolution. Scan in black and white whenever possible.
•
When Recognize Text Using OCR is disabled, full 10-to-3000 ppi resolution range may be used, but the recom
mended resolution is 72 and higher ppi. For Adaptive compression, 300 ppi is recommended for grayscale or RGB
input, or 600 ppi for black-and-white input.
•
Pages scanned in 24-bit color, 300 ppi, at 8-1/2–by-11 inches (21.59-by-27.94 cm) result in large images (25 MB)
prior to compression. Your system may require 50 MB of virtual memory or more to scan the image. At 600 ppi,
both scanning and processing typically are about four times slower than at 300 ppi.
•
Avoid dithering or halftone scanner settings. These can improve the appearance of photographs, but they make it
difficult to recognize text.
•
For text printed on colored paper, try increasing the brightness and contrast by about 10%. If your scanner has
color-filtering capability, consider using a filter or lamp that drops out the background color. Or if the text isn’t
crisp or drops out, try adjusting scanner contrast and brightness to clarify the scan.
•
If your scanner has a manual brightness control, adjust it so that characters are clean and well formed. If characters
are touching, use a higher (brighter) setting. If characters are separated, use a lower (darker) setting.
Recognize text in scanned documents
You can use Acrobat to recognize text in previously scanned documents that have already been converted to PDF.
OCR runs with header/footer/Bates number on image PDF files.
1
Open the scanned PDF.