pnmscale


SYNOPSIS
       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  dou-
       ble  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.



DESCRIPTION
       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 combina-
       tion 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 speci-
       fying the scale_factor parameter, where scale_factor is the  reciprocal
       of reduction_factor.

       -xysize  specifies  a bounding box.  pnmscale scales the input image to
       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 resolu-
       tion.   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 hori-
       zontally, 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 pam-
       stretch 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.



   PRECISION
       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 pnmscale-
       fixed, which uses fixed point arithmetic.  pnmscalefixed may,  however,
       distort  your  image a little.  See pnmscalefixed's man page for a com-
       plete discussion of the difference.


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


AUTHOR
       Copyright (C) 1989, 1991 by Jef Poskanzer.
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