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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 [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 com-
       putation 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  edgeness
       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 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 usu-
       ally 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: reduc-
       ing one allows you to increase the other.

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).

netpbm documentation			   14 June 2006 	    Pammasksharpen User Manual(0)
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