Michael: Created page with "HowTo improve the quality of scanned documents. == Step 0: Generate PNM files == If you already have a set of PNM files from [http://www.sane-project.org/man/scanadf.1.html scan…"

2013-03-12T11:48:23Z

Created page with "HowTo improve the quality of scanned documents. == Step 0: Generate PNM files == If you already have a set of PNM files from [http://www.sane-project.org/man/scanadf.1.html scan…"

New page

HowTo improve the quality of scanned documents.

== Step 0: Generate PNM files ==
If you already have a set of PNM files from [http://www.sane-project.org/man/scanadf.1.html scanadf(1)] you can skip this step.

If you have a PDF document, split it into 1 PNM file per page with:
pdftoppm -r 300 scanned.pdf pages

== Step 1: Deskew the pages ==
Run [http://www.flameeyes.eu/projects/unpaper unpaper] to fix page rotations and remove noise at the edge of the page. It's amazing how much each page is rotated when fed through an ADF.

unpaper -v -ni 2 -ms 100,100 -dn bottom,right --no-border-align --no-grayfilter page-%02d.ppm fixed-%03d.ppm

Options:
* -ni 2: Dot your I's. The default "noise" parameters of 4 lonely pixels may remove all dots from the 'i' characters.
* -ms 100,100: Try not to truncate headers and footers where text extends beyond the rest of the body text.
* -dn bottom,right: Detect skew-angles from the right-hand-side and bottom. The values given here should depend on the scanned content. Choose side(s) where there is a definitive column where the content starts.
* --no-border-align: Don't reposition content to the centre of the image. This option can cause pages with content only at the top of the page (eg. a single paragraph) to be moved to the centre.
* --no-grayfilter: Don't remove large blocks of gray, as is used for table headings etc.

== Step 2: Recombine images into PDF ==
The [http://www.imagemagick.org/script/convert.php ImageMagick convert] utility can be used to re-create a PDF document from a set of images.

convert fixed-0*.ppm -colorspace Gray -unsharp 0.5x0.5+0.5+0.008 -page A4 -quality 100 "Output.pdf"

ScanningToPDF - Revision history

Michael: Created page with "HowTo improve the quality of scanned documents. == Step 0: Generate PNM files == If you already have a set of PNM files from [http://www.sane-project.org/man/scanadf.1.html scan…"