Licensed under the GNU General Public License (GPL). This software comes with no warranty.
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unpaper is a post-processing tool for scanned sheets of paper, especially for book pages that have been scanned from previously created photocopies. The main purpose is to make scanned book pages better readable on screen after conversion to PDF. Additionally, unpaper might be useful to enhance the quality of scanned pages before performing optical character recognition (OCR). unpaper tries to clean scanned images by removing dark edges that appeared through scanning or copying on areas outside the actual page content (e.g. dark areas between the left-hand-side and the right-hand-side of a double- sided book-page scan). The program also tries to detect disaligned centering and rotation of pages and will automatically straighten each page by rotating it to the correct angle. This is called "deskewing". Note that the automatic processing will sometimes fail. It is always a good idea to manually control the results of unpaper and adjust the parameter settings according to the requirements of the input. Each processing step can also be disabled individually for each sheet. Input and output files can be in either .pbm or .pgm format, as also used by the Linux scanning tools scanimage and scanadf. Conversion to PDF can e.g. be achieved with the Linux tools pgm2tiff, tiffcp and tiff2pdf.
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Usage: unpaper [options] <input-file> <output-file> Filenames may contain a formatting placeholder starting with '%' to insert a page counter for multi-page processing. E.g.: 'scan%03d.pbm' to process files scan001.pbm, scan002.pbm, scan003.pbm etc.
-l --layout single|double Set default layout options for a sheet:
'single' - one page per sheet, oriented
vertically without rotation
'double' - two pages per sheet, rotated
anti-clockwise (i.e. the top-
sides of the pages are heading
leftwards, and the pages are
placed right-page above left-
page on the unrotated sheet)
Using this option automatically adjusts the
--mask-point and --pre/post-rotation
options.
-s --start-sheet <sheet> Number of first sheet to process in multi-
sheet mode. (default: 1)
-e --end-sheet <sheet> Number of last sheet to process in multi-
sheet mode. -1 indicates processing until
no more input file file the corresponding
page number is available (default: -1)
-# --sheet Optionally specifies which sheets to
<sheet>{,<sheet>[-<sheet>]} process in the range between start-sheet
and end sheet.
-x --exclude Excludes sheets from processing in the
<sheet>{,<sheet>[-<sheet>]} range between start-sheet and end-sheet.
--pre-rotate -90|90 Rotates the whole image clockwise (90) or
or anti-clockwise (-90) before any other
processing.
--post-rotate -90|90 Rotates the whole image clockwise (90) or
or anti-clockwise (-90) after any other
processing.
-M --pre-mirror Mirror the image, after possible pre-
[v[ertical]][,][h[orizontal]] rotation. Either 'v' (for vertical
mirroring), 'h' (for horizontal mirroring)
or 'v,h' (for both) can be specified.
--post-mirror Mirror the image, after any other
[v[ertical]][,][h[orizontal]] processing except possible post-
rotation.
--pre-wipe Manually wipe out an area before further
<left>,<top>,<right>,<bottom> processing. Any pixel in a wiped area
will be set to white. Multiple areas to
be wiped may be specified.
--post-wipe Manually wipe out an area after
<left>,<top>,<right>,<bottom> processing. Any pixel in a wiped area
will be set to white. Multiple areas to
be wiped may be specified.
--pre-border Clear the border-area of the sheet before
<left>,<top>,<roght>,<bottom> further processing. Any pixel inside the
border will be set to white.
--post-border Clear the border-area after processing.
<left>,<top>,<roght>,<bottom> Any pixel inside the border will be set
to white.
--pre-mask <x1>,<y1>,<x2>,<y2> Specify masks to apply before any other
processing. Any pixel outside a mask
will be considered blank (white) pixels,
unless another mask includes this pixel.
Only pixels inside a mask will remain.
Multiple masks may be specified. No
deskewing will be applied to the masks
specified by --pre-mask.
-bn --blackfilter-scan-direction Directions in which to search for solidly
[v[ertical]][,][h[orizontal]] black areas. Either 'v' (for vertical
mirroring), 'h' (for horizontal mirroring)
of 'v,h' (for both) can be specified.
(default: 'v,h')
-bs --blackfilter-scan-size Width of virtual bar used for mask
<size>|<h-size>,<v-size> detection. Two values may be specified
to individually set horizontal and vertical
size. (default: 20,20)
-bd --blackfilter-scan-depth Size of virtual bar used for black area
<depth>|<h-depth,v-depth> detection. (default: 500,500)
-bp --blackfilter-scan-step Steps to move virtual bar for black area
<step>|<h-step,v-step> detection. (default: 5,5)
-bt --blackfilter-scan-threshold <t> Ratio of dark pixels above which a black
area gets detected. (default: 0.95).
-bi --blackfilter-intensity <i> Intensity with which to delete black areas.
Larger values will leave less noise-pixels
around former black areas, but may delete
page content. (default: 20)
-ni --noisefilter-intensity <n> Intensity with which to delete individual
pixels or tiny clusters of pixels. Any
cluster which only contains n dark pixels
together will be deleted. (default: 4)
-ls --blurfilter-size Size of blurfilter area to search for
<size>|<h-size>,<v-size> 'lonely' clusters of pixels.
(default: 100,100)
-lt --blurfilter-step Size of 'blurring' steps in each
<step>|<h-step>,<v-step> direction. (default: 50,50)
-li --blurfilter-intensity <ratio> Relative intensity with which to delete
tiny clusters of pixels. Any blurred area
which contains at most the ratio of dark
pixels will be cleared. (default: 0.01)
-gs --grayfilter-size Size of grayfilter mask to search for
<size>|<h-size>,<v-size> 'gray-only' areas of pixels.
(default: 50,50)
-gp --grayfilter-step Size of steps moving the grayfilter mask
<step>|<h-step>,<v-step> in each direction. (default: 20,20)
-gt --grayfilter-threshold <ratio> Relative intensity of grayness which is
accepted before clearing the grayfilter
mask in cases where no black pixel is
found in the mask. (default: 0.5)
-p --mask-point <x>,<y> Manually set starting point for masking.
Multiple --mask-point parameters may be
specified to process multiple pages on one
sheet. Cannot be used in conjunction with
--pages. (default: middle of image)
-m --mask <x1>,<y1>,<x2>,<y2> Manually add a mask, in addition to masks
automatically searched around the --point
coordinates (unless --nomask is specified).
Any pixel outside a mask will be considered
a blank (white) pixel, unless another mask
covers this pixel.
-mn --mask-scan-direction Directions in which to search for inner mask
[v[ertical]][,][h[orizontal]] border. Either 'v' (for vertical
scanning), 'h' (for horizontal scanning)
of 'v,h' (for both) can be specified.
(default: 'h' ('v' may cut paragraphs on
single-page sheets))
-ms --mask-scan-size <size>|<h,v> Width of virtual bar used for mask
detection. Two values may be specified
to individually set horizontal and vertical
size. (default: 50,50)
-md --mask-scan-depth <dep>|<h,v> Height of virtual bar used for mask
detection. (default: -1,-1, using the whole
width or height of the sheet)
-mp --mask-scan-step <step>|<h,v> Steps to move virtual bar for mask
detection. (default: 10,10)
-mt --mask-scan-threshold <t>|<h,v> Ratio of dark pixels below which an edge
gets detected, relative to max. blackness
when counting from the starting coordinate
heading towards one edge. (default: 0.1)
-mm --mask-scan-minimum <w>,<h> Set minimum allowed size of an auto-
detected mask. Masks detected below this
size will be ignored and set to the size
specified by mask-scan-maximum. (default:
100,100)
-mM --mask-scan-maximum <w>,<h> Set maximum allowed size of an auto-
detected mask. Masks detected above this
size will be shrunk to the maximum value,
each direction individually. (default:
sheet size, or page size derived from
--layout option.
-mc --mask-color <color> Set color / gray-scale value to overwrite
pixels which are not covered by any
detected mask. This may be useful for
testing in order to visualize the effect
of masking. (value: 0..255, default: 255)
-dn --deskew-scan-direction Directions in which to scan for rotation.
[v[ertical]][,][h[orizontal]] Either 'h' (for horizontal scanning,
starting at the left and right edges of a
mask) or 'v' (for vertical scanning,
starting at the top and bottom), or 'v,h'
(for both) can be specified.
(default: 'h' ('v' may be confused by
headlines or footnotes))
-ds --deskew-scan-size <pixels> Size of virtual line for rotation
detection. (default: 1500)
-dd --deskew-scan-depth <ratio> Amount of dark pixels to accumlate until
scan is finished, relative to scan-bar
size. (default: 0.66)
-dr --deskew-scan-range <degrees> Range in which to search for rotation,
from -degrees to +degrees rotation.
(default: 2.0)
-dp --deskew-scan-step <degrees> Steps between single rotation-range
detections.
Lower numbers lead to better results but
slow down processing. (default: 0.1)
-dv --deskew-scan-deviation <dev> Maximum deviation allowed between results
from all detected edges to perform auto-
rotating, else ignore. (default: 1.0)
-W --wipe Manually wipe out an area. Any pixel in
<left>,<top>,<right>,<bottom> a wiped area will be set to white.
Multiple --wipe areas may be specified.
This is applied after deskewing and
before automatic border-scan.
-mw --middle-wipe If --layout is set to 'double', this
<size>|<left>,<right> may specify the size of a middle area to
wipe out between the two pages on the
sheet. This may be useful if the
blackfilter fails to remove some black
areas (which e.g. occur by photo-copying
in the middle between two pages).
-B --border Manually add a border. Any pixel in the
<left>,<top>,<right>,<bottom> border area will be set to white. This is
applied after deskewing and before
automatic border-scan.
-Bn --border-scan-direction Directions in which to search for outer
[v[ertical]][,][h[orizontal]] border. Either 'v' (for vertical
scanning), 'h' (for horizontal scanning)
of 'v,h' (for both) can be specified.
(default: 'v')
-Bs --border-scan-size <size>|<h,v> Width of virtual bar used for border
detection. Two values may be specified
to individually set horizontal and vertical
size. (default: 5,5)
-Bp --border-scan-step <step>|<h,v> Steps to move virtual bar for border
detection. (default: 5,5)
-Bt --border-scan-threshold <t> Absolute number of dark pixels covered by
the border-scan mask above which a border
is detected. (default: 5)
-w --white-threshold <threshold> Brightness ratio above which a pixel is
considered white. This is used when
converting to black-and-white mode
(default: 0.9)
-b --black-threshold <threshold> Brightness ratio below which a pixel is
considered black (non-gray). This is used
by the gray-filter. (default: 0.5)
--no-blackfilter Disables black area scan. Individual sheet
<sheet>{,<sheet>[-<sheet>]} indices can be specified.
--no-noisefilter Disables noisefilter. Individual sheet
<sheet>{,<sheet>[-<sheet>]} indices can be specified.
--no-blurfilter Disables blurfilter. Individual sheet
<sheet>{,<sheet>[-<sheet>]} indices can be specified.
--no-mask-scan Disables auto-masking around the areas
<sheet>{,<sheet>[-<sheet>]} searched beginning from points specified
by --point or auto-specified by --layout.
Masks explicitly set by --mask will still
have effect.
--no-mask-center Disables auto-centering of each mask.
<sheet>{,<sheet>[-<sheet>]} Auto-centering is performed by default
if the --layout option has been set.
--no-deskew Disables auto-rotation to a straight
<sheet>{,<sheet>[-<sheet>]} alignment for individual sheets.
--no-wipe Disables explicitly wipe-areas.
<sheet>{,<sheet>[-<sheet>]} This means the effect of parameter
--wipe is disabled individually per
sheet.
--no-border Disables explicitly set borders.
<sheet>{,<sheet>[-<sheet>]} This means the effect of parameter
--border is disabled individually per
sheet.
--no-border-scan Disables automatic border-scanning at the
<sheet>{,<sheet>[-<sheet>]} edges of the sheet after most other
processing has been done.
-n --no-processing Do not perform any processing on a sheet
<sheet>{,<sheet>[-<sheet>]} except pre/post rotating and mirroring,
and file-type conversions on saving.
This option has the same effect as setting
--no-blackfilter, --no-noisefilter,
--no-blurfilter, --no-grayfilter,
--no-mask-scan, --no-deskew, --no-wipe,
--no-mask-center, --no-border-scan and
--no-border simultaneously.
--no-qpixels Disable qpixel-mode for deskewing
(internally rotate a 4x bigger image and
reshrink afterwards).
--no-multi-pages Disable multi-page processing even if the
input filename contains a '%' (usually
indicating the start of a placeholder for
the page counter).
-t --type pbm|pgm Output file type. (default: as input file)
-T --test-only Do not write any output. May be useful in
combination with --verbose to get informa-
tion about the input.
-q --quiet Quiet mode, no output at all.
-v --verbose Verbose output, more informational messages.
-vv Even more verbose output, show parameter
settings before processing.
-V --version Output version and build information.
unpaper is available for download at http://download.berlios.de/unpaper/unpaper-1_0.tgz.
You may also want to browse the source-code online in the CVS archive of the project development site.
A typical sequence of application would be:
; Scan multiple sheets of paper to .ppm-files (for scanners without automatic ; document feeder, use any scan software to manually scan sheets): scanadf -o sheet%03d.ppm ; Convert .ppm-files to gray-scale .pgm-files: for i in `ls *.ppm`; do ppmtopgm $i > $i.pgm; done ; Run unpaper, performing all auto-corrections an all sheets except on the ; title sheet 1, and without auto-detection of masks (incuding deskewing and ; centering) on sheets 100-110 and 200: unpaper -v --layout double --exclude 1 --no-mask-scan 100-110,200 sheet%03d.pgm unpaper%03d.pgm ; Convert generated .pgm-files to individual .tiff-files: for i in `ls unpaper*`; do ppm2tiff $i $i.tiff; done ; Combine individual .tiff-files to one multi-page-tiff: tiffcp *.tiff all.tiff ; Create PDF-document from multi-page-tiff: tiff2pdf -z -o Document.pdf all.tiff
The source sheets need not to be scanned from paper directly but could also originate from a previously created PDF-document or other files. This way, unpaper can be used to 'clean' existing documents. There are several tools to convert other file formats to .pgm/.pbm-files for processing with unpaper.
The SANE project http://www.sane-project.org/.
Written by Jens Gulden 2005.
Modifications under the GPL are welcome.
Hosted on