pnmscale - scale a portable anymap


   pnmscale scale_factor [pnmfile]
   pnmscale -reduce reduction_factor [pnmfile]
   pnmscale [{-xsize=cols | -width=cols | -xscale=factor}] [{-ysize=rows |
   -height=rows | -yscale=factor}] [pnmfile]
   pnmscale -xysize cols rows [pnmfile]
   pnmscale -pixels n [pnmfile]

   Miscellaneous options:
   -verbose -nomix

   Minimum unique abbreviation of  option  is  acceptable.   You  may  use
   double  hypens instead of single hyphen to denote options.  You may use
   white space in place of the equals sign to separate an option name from
   its value.


   Reads  a  PBM,  PGM,  or PPM image as input, scales it by the specified
   factor or factors and produces a PGM or PPM image as  output.   If  the
   input file is in color (PPM), the output will be too, otherwise it will
   be grayscale (PGM).  This is true even if the  input  is  a  black  and
   white  bitmap  (PBM),  because  the  process  of  scaling  can  turn  a
   combination of black and white pixels into a gray pixel.

   If you want PBM output, use pgmtopbm to convert  pnmscale's  output  to
   PBM.  Also consider pbmreduce.

   You can both enlarge (scale factor > 1) and reduce (scale factor < 1).

   When  you specify an absolute size or scale factor for both dimensions,
   pnmscale scales each dimension independently without  consideration  of
   the aspect ratio.

   If  you  specify  one  dimension  as a pixel size and don't specify the
   other dimension, pnmscale scales the unspecified dimension to  preserve
   the aspect ratio.

   If  you  specify  one dimension as a scale factor and don't specify the
   other dimension, pnmscale leaves the  unspecified  dimension  unchanged
   from the input.

   If you specify the scale_factor parameter instead of dimension options,
   that is the scale factor for both  dimensions.   It  is  equivalent  to
   -xscale=scale_factor -yscale=scale_factor .

   Specifying   the  -reduce  reduction_factor  option  is  equivalent  to
   specifying  the  scale_factor  parameter,  where  scale_factor  is  the
   reciprocal of reduction_factor.

   -xysize  specifies  a bounding box.  pnmscale scales the input image to
   the largest size that fits within the box, while preserving its  aspect

   -pixels  specifies  a  maximum total number of output pixels.  pnmscale
   scales the image down to that number of pixels.  If the input image  is
   already  no  more  than  that  many  pixels, pnmscale just copies it as
   output; pnmscale does not scale up with -pixels.

   If you enlarge by a factor of 3 or more,  you  should  probably  add  a
   pnmsmooth  step;  otherwise,  you  can  see  the original pixels in the
   resulting image.

   When the scale factor is not an integer (including all cases of scaling
   down),  there  are two ways to do the scaling.  Which one pnmscale does
   is controlled by its -nomix option.

   By default, pnmscale mixes the colors of  adjacent  pixels  to  produce
   output  pixels  that  contain  information  from multiple input pixels.
   This makes the image look  more  like  it  would  if  it  had  infinite
   resolution.   Note  that  it  means  the output may contain colors that
   aren't in the input at all.

   But if you specify -nomix, pnmscale never mixes  pixels.   Each  output
   pixel  is  derived  from one input pixel.  If you're scaling up, pixels
   get duplicated.  If you're scaling down, pixels get omitted.  Note that
   this  means  the  image  is  rather  distorted.  If you scale up by 1.5
   horizontally, for example, the even numbered input pixels  are  doubled
   in the output and the odd numbered ones are copied singly.

   When  the  scale  factor is an integer (which means you're scaling up),
   the -nomix option has no effect -- output  pixels  are  always  just  N
   copies  of  the  input  pixels.   In  this case, though, consider using
   pamstretch instead of pnmscale to get  the  added  pixels  interpolated
   instead of just copied and thereby get a smoother enlargement.

   pnmscale  with  -nomix is faster than without, but pnmenlarge is faster
   still.  pnmenlarge works only on integer enlargements.

   A useful application of pnmscale is to blur an image.   Scale  it  down
   (without  -nomix  )  to discard some information, then scale it back up
   using pamstretch.

   Or scale it back up with pnmscale and create a "pixelized" image, which
   is sort of a computer-age version of blurring.

   pnmscale  uses  floating point arithmetic internally.  There is a speed
   cost associated with this.  For some images, you can get the acceptable
   results   (in   fact,   sometimes   identical   results)   faster  with
   pnmscalefixed, which uses fixed point arithmetic.   pnmscalefixed  may,
   however, distort your image a little.  See pnmscalefixed's man page for
   a complete discussion of the difference.


   pnmscalefixed(1),    pamstretch(1),    pbmreduce(1),     pnmenlarge(1),
   pnmsmooth(1), pnmcut(1), pnm(5)


   Copyright (C) 1989, 1991 by Jef Poskanzer.

                           04 November 2000                    pnmscale(1)


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