1Pammasksharpen User Manual(0)                    Pammasksharpen User Manual(0)
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NAME

6       pammasksharpen - Sharpen an image via an unsharp mask
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SYNOPSIS

10       pammasksharpen  [-sharpness=realnum] [-threshold=realnum] maskfile [in‐
11       putfile]
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13       All options can be abbreviated to their shortest  unique  prefix.   You
14       may  use  two  hyphens instead of one.  You may separate an option name
15       and its value with white space instead of an equals sign.
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EXAMPLES

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

27       This program is part of Netpbm(1).
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29       pammasksharpen reads a Netpbm image as input and produces  a  sharpened
30       version  of it, in the same format, as output.  It does this via an un‐
31       sharp mask, which you supply as another Netpbm image.
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33       An unsharp mask is generally a blurred version of the  original  image.
34       The  sharpening computation is this: Calculate the "edgeness" of a sam‐
35       ple in the input image as the  signed  difference  between  the  sample
36       value and the corresponding sample in the unsharp mask.  This tells how
37       different the pixel is from its neighbors.  Add a multiple of the edge‐
38       ness  to  the  original  sample to get the corresponding output sample.
39       Clip as necessary.  This causes pixels that  are  brighter  than  their
40       neighbors to get even brighter, while pixels that are dimmer than their
41       neighbors get even dimmer.  This makes edges -- places where pixel val‐
42       ues change quickly in space -- stand out more.
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44       The  unsharp  mask must be the same dimensions and have the same maxval
45       as the input image.
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48   The Unsharp Mask
49       You usually create the unsharp mask as a Gaussian blur of the  original
50       image,  which you can do using pamgauss and pnmconvol as in the example
51       above.  The convolution kernel you use with  pnmconvol  is  normally  a
52       square with side length an odd number of pixels.
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54       When  you create an unsharp mask like this, you will have to choose the
55       side length of the convolution kernel.  That length implements the  pa‐
56       rameter  of unsharp mask sharpening usually known as "radius."  In par‐
57       ticular, a radius of R pixels corresponds to a convolution kernel  2R+1
58       pixels on a side.
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60       Radius  is a very important parameter; you can ruin an image with a ra‐
61       dius too large.  You can safely use the highest radius with  an  inani‐
62       mate  object, while a human face demands the least.  Landscapes fall in
63       between.  But it really depends on the size of the details.   Fine  de‐
64       tail  needs a smaller radius, or else you may obliterate tiny detail of
65       the same size as the Radius width.  A large image often has larger  de‐
66       tail  (more  pixels  involved), so can use a larger radius.  Radius and
67       sharpness (see -sharpness option) interact: reducing one allows you  to
68       increase the other.
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OPTIONS

72       In  addition  to  the options common to all programs based on libnetpbm
73       (most notably -quiet, see
74        Common Options ⟨index.html#commonoptions⟩ ), pammasksharpen recognizes
75       the following command line options:
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80       -sharpness=realnum
81              This  specifies the magnitude of the sharpening.  It is the mul‐
82              tiple of edgeness that gets added to each  sample  as  described
83              above.
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85              realnum  is  a  nonnegative  real decimal number.  Zero means no
86              sharpening at all.
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88              This parameter is known as "amount" in ImageMagick.
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90              The default is 1.0.
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92              This option was new in  Netpbm  10.30  (October  2005).   Before
93              that, the sharpness was always 1.0.
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96       -threshold=realnum
97              This minimum amount of edgeness that will be considered edgeness
98              at all.  i.e. if the magnitude of  the  edgeness  is  less  than
99              this, pammasksharpen will treat the edgeness as zero.
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101              A  nonzero  value  may  be  necessary here to avoid speckling in
102              smooth areas.
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104              This is a fraction of the maxval (so it  is  in  the  range  [0,
105              1.0]).
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107              The default is 0.
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109              This option was new in Netpbm 10.34 (June 2006).
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SEE ALSO

115       pnmconvol(1), pamedge(1), pamsharpness(1), pamsharpmap(1), pamarith(1),
116       pnm(1), pam(1)
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HISTORY

121       pammasksharpen was new in Netpbm 10.23 (July 2004).
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DOCUMENT SOURCE

124       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
125       source.  The master documentation is at
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127              http://netpbm.sourceforge.net/doc/pammasksharpen.html
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129netpbm documentation             14 June 2006    Pammasksharpen User Manual(0)
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