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Pammasksharpen User Manual(0)			 Pammasksharpen	User Manual(0)

NAME
       pammasksharpen -	Sharpen	an image via an	unsharp	mask

SYNOPSIS
       pammasksharpen  [-sharpness=realnum] [-threshold=realnum] maskfile [in-
       putfile]

       All options can be abbreviated to their shortest	 unique	 prefix.   You
       may  use	 two  hyphens instead 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 un-
       sharp mask, which you supply as another Netpbm image.

       An unsharp mask is generally a blurred version of the  original	image.
       The  sharpening computation is this: Calculate the "edgeness" of	a sam-
       ple in the input	image as the  signed  difference  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 edge-
       ness  to	 the  original	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 val-
       ues 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  pa-
       rameter	of unsharp mask	sharpening usually known as "radius."  In par-
       ticular,	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 ra-
       dius too	large.	You can	safely use the highest radius with  an	inani-
       mate  object, while a human face	demands	the least.  Landscapes fall in
       between.	 But it	really depends on the size of the details.   Fine  de-
       tail  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  de-
       tail  (more  pixels  involved), so can use a larger radius.  Radius and
       sharpness (see -sharpness option) interact: reducing one	allows you  to
       increase	the other.

OPTIONS
       -sharpness=realnum
	      This  specifies the magnitude of the sharpening.	It is the mul-
	      tiple 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(5), pam(5)

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(0)

NAME | SYNOPSIS | EXAMPLES | DESCRIPTION | OPTIONS | SEE ALSO | HISTORY | DOCUMENT SOURCE

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