pnmscale(1) - man - phpman

pnmscale(1)                            General Commands Manual                           pnmscale(1)



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 sep‐
       arate 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 pbm‐‐
       reduce.

       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, pnm‐‐
       scale 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 con‐
       tain 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, pix‐
       els 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 com‐
       puter-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 re‐
       sults) faster with pnmscalefixed, which uses fixed point arithmetic.  pnmscalefixed may, how‐
       ever, 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)