NAME

       pnmscale - scale a portable anymap

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 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.

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 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 ratio.

       -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.

   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 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.

SEE ALSO

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

AUTHOR

       Copyright (C) 1989, 1991 by Jef Poskanzer.

                                         04 November 2000                             pnmscale(1)