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pnmscale(1)									      pnmscale(1)

       pnmscale - scale a PNM image

       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

       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,  pnm-
       scale 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_fac-
       tor 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;  other-
       wise, you can see the original pixels in the resulting image.

       When  the scale factor is not an integer, 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, 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.

       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 discus-
       sion of the difference.

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

       Copyright (C) 1989, 1991 by Jef Poskanzer.

					 04 November 2000			      pnmscale(1)
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