Manual: pammasksharpen

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 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 unsharp 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 sample 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	dim‐
       mer.  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 pn‐
       mconvol 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
       radius.	Radius and sharpness (see -sharpness option) interact: reducing one allows you to increase the other.

OPTIONS
       In addition to the options common to all programs based on libnetpbm (most notably  -quiet,  see	  Common Options  ),
       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 edge‐
	      ness 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)