man > pammasksharpen(1)

Pammasksharpen User Manual(1)          General Commands Manual         Pammasksharpen User Manual(1)

NAME
       pammasksharpen - Sharpen an image via an unsharp mask


SYNOPSIS
       pammasksharpen [-sharpness=realnum] [-threshold=realnum] maskfile [inputfile]

       All  options can be abbreviated to their shortest unique prefix.  You may use two hyphens in‐
       stead of one.  You may separate an option name and its value with white space instead  of  an
       equals sign.


EXAMPLES
          pamgauss 5 5 -sigma=.7 -tupletype=GRAYSCALE | pamtopnm > gauss.pgm
          pnmconvol -nooffset gauss.pgm myimage.ppm > blurred.ppm
          pammasksharpen blurred.ppm myimage.ppm > sharpened.ppm




DESCRIPTION
       This program is part of Netpbm(1).

       pammasksharpen  reads  a Netpbm image as input and produces a sharpened version of it, in the
       same format, as output.  It does this via an unsharp mask, which you supply as another Netpbm
       image.

       An unsharp mask is generally a blurred version of the original image.  The sharpening  compu‐
       tation is this: Calculate the "edgeness" of a sample in the input image as the signed differ‐
       ence  between  the sample value and the corresponding sample in the unsharp mask.  This tells
       how different the pixel is from its neighbors.  Add a multiple of the edgeness to the  origi‐
       nal  sample  to  get the corresponding output sample.  Clip as necessary.  This causes pixels
       that are brighter than their neighbors to get even brighter, while  pixels  that  are  dimmer
       than  their  neighbors get even dimmer.  This makes edges -- places where pixel values change
       quickly in space -- stand out more.

       The unsharp mask must be the same dimensions and have the same maxval as the input image.


   The Unsharp Mask
       You usually create the unsharp mask as a Gaussian blur of the original image, which  you  can
       do using pamgauss and pnmconvol as in the example above.  The convolution kernel you use with
       pnmconvol is normally a square with side length an odd number of pixels.

       When  you  create  an  unsharp mask like this, you will have to choose the side length of the
       convolution kernel.  That length implements the parameter of unsharp mask sharpening  usually
       known  as  "radius."  In particular, a radius of R pixels corresponds to a convolution kernel
       2R+1 pixels on a side.

       Radius is a very important parameter; you can ruin an image with a radius too large.  You can
       safely use the highest radius with an inanimate object, while a human face demands the least.
       Landscapes fall in between.  But it really depends on the size of the details.   Fine  detail
       needs a smaller radius, or else you may obliterate tiny detail of the same size as the Radius
       width.  A large image often has larger detail (more pixels involved), so can use a larger ra‐
       dius.   Radius and sharpness (see -sharpness option) interact: reducing one allows you to in‐
       crease the other.


OPTIONS
       In addition to the options common to all programs based on libnetpbm  (most  notably  -quiet,
       see ]8;;index.html#commonoptions\ Common Options]8;;\ ), pammasksharpen recognizes the following command line options:




       -sharpness=realnum
              This  specifies  the magnitude of the sharpening.  It is the multiple of edgeness that
              gets added to each sample as described above.

              realnum is a nonnegative real decimal number.  Zero means no sharpening at all.

              This parameter is known as "amount" in ImageMagick.

              The default is 1.0.

              This option was new in Netpbm 10.30 (October 2005).  Before that,  the  sharpness  was
              always 1.0.


       -threshold=realnum
              This  minimum amount of edgeness that will be considered edgeness at all.  i.e. if the
              magnitude of the edgeness is less than this, pammasksharpen will treat the edgeness as
              zero.

              A nonzero value may be necessary here to avoid speckling in smooth areas.

              This is a fraction of the maxval (so it is in the range [0, 1.0]).

              The default is 0.

              This option was new in Netpbm 10.34 (June 2006).




SEE ALSO
       pnmconvol(1), pamedge(1), pamsharpness(1), pamsharpmap(1), pamarith(1), pnm(1), pam(1)



HISTORY
       pammasksharpen was new in Netpbm 10.23 (July 2004).

DOCUMENT SOURCE
       This manual page was generated by the Netpbm tool 'makeman' from  HTML  source.   The  master
       documentation is at

              http://netpbm.sourceforge.net/doc/pammasksharpen.html

netpbm documentation                        14 June 2006               Pammasksharpen User Manual(1)