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    Command:

    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.
    
           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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