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
11       [inputfile]
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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

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

71       -sharpness=realnum
72              This  specifies the magnitude of the sharpening.  It is the mul‐
73              tiple of edgeness that gets added to each  sample  as  described
74              above.
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76              realnum  is  a  nonnegative  real decimal number.  Zero means no
77              sharpening at all.
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79              This parameter is known as "amount" in ImageMagick.
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81              The default is 1.0.
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83              This option was new in  Netpbm  10.30  (October  2005).   Before
84              that, the sharpness was always 1.0.
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87       -threshold=realnum
88              This minimum amount of edgeness that will be considered edgeness
89              at all.  i.e. if the magnitude of  the  edgeness  is  less  than
90              this, pammasksharpen will treat the edgeness as zero.
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92              A  nonzero  value  may  be  necessary here to avoid speckling in
93              smooth areas.
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95              This is a fraction of the maxval (so it  is  in  the  range  [0,
96              1.0]).
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98              The default is 0.
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100              This option was new in Netpbm 10.34 (June 2006).
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SEE ALSO

106       pnmconvol(1), pamedge(1), pamsharpness(1), pamsharpmap(1), pamarith(1),
107       pnm(1), pam(1)
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HISTORY

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

115       This manual page was generated by the Netpbm tool 'makeman'  from  HTML
116       source.  The master documentation is at
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118              http://netpbm.sourceforge.net/doc/pammasksharpen.html
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120netpbm documentation             14 June 2006    Pammasksharpen User Manual(0)