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CentOS 7.0 - man page for pamtilt (centos section 0)

Pamtilt User Manual(0)							   Pamtilt User Manual(0)

       pamtilt - print the tilt angle of a PGM file

       pamtilt [-angle=maxangle] [-fast] [-quality=q] [-hstep=n] [-vstep=n] [-dstep=n] [-astep=n]
       [-verbose] [pgmfile]

	   scanimage --mode Gray --resolution 300 >crooked.pgm
	   pnmrotate -b white `pamtilt crooked.pgm` crooked.pgm >straight.pgm
	   (then crop, threshold, etc.)

       This program is part of Netpbm(1)

       pamtilt tries to find the correct angle for untilting (de-skewing) a  scanned  text  docu-
       ment.   The output is a single floating-point number (the angle in degrees) for use as the
       argument to pnmrotate.

       'Document skew' is the name given to what happens when you feed a page into an image scan-
       ner at an angle: the resulting image is tilted.	pamtilt aims to correct that.

       pamtilt makes three iterations at successively finer increments, testing prospective rota-
       tion angles to find the best one.  pamtilt works best for straightening images with strong
       horizontal  lines  and does poorly with arbitrary photos.  If pamtilt has no confidence in
       its results, it prints the special value 00.00; you can check for this or just pass it  as
       a legal argument to pnmrotate.

       pamtilt	operates  on  the first plane of the input image, which is either PNM or PAM, and
       ignores any other planes.  Ordinarily, the input is PGM or GRAYSCALE PAM, so there is only
       one plane.

       pamtilt	works  on  bilevel  (PBM, BLACKANDWHITE PAM) images as well as grayscale, but you
       will minimize artifacts if you scan and rotate in grayscale before you apply  a	threshold
       to make a bilevel image.

       A few options have general utility:

	      Assume  a  maximum tilt angle of maxangle (measured in degrees).	The default value
	      is sufficient for most images, even those scanned somewhat carelessly.

	      The default is 10.0.

       -fast  Skip the third iteration for speed at the expense of accuracy.

	      Show on Standard Error the measurements computed at each tested angle.

       Here are some other options you can use to tune the operation of pamtilt but they're  sel-
       dom needed.  The default values accommodate a wide variety of input documents.

	      Require  a  signal-to-noise  ratio  of a least q on the first iteration to report a
	      valid result.  Larger values reduce the chances of obtaining a bogus result at  the
	      risk of obtaining no result at all.

	      The default is 1.0.

	      Set  the	horizontal  increment to check every nth column.  This value affects both
	      run time and memory requirements.

	      The default is 11.

	      Set the vertical increment to check every nth row.   Larger  values  usually  work,
	      reducing run time, but they increase the risk of incorrect results.

	      The default is 5.

	      Set  the	vertical  distance used when checking pixels in a column.  The default is
	      intended to minimize the effect of noise along a horizontal boundary.

	      The default is 2.

	      Set the angle increment of the first iteration, in degrees.

	      The default is 1.0.

       pamtilt implements a somewhat simplified algorithm inspired by: "Measuring Document  Image
       Skew  and  Orientation",  by  Bloomberg, Kopec, and Dasari.  In SPIE Volume 2422, Document
       Recognition II, pages 302-316, February 1995.





       pamtilt was new in Netpbm 10.30 (October 2005).

       Gregg Townsend wrote it and sent it to Bryan Henderson in August 2005.  Bryan  recoded  it
       to fit Netpbm conventions.

netpbm documentation			  28 August 2005		   Pamtilt User Manual(0)

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