NAME
    pnmscale - scale a PNM image

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
    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, 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, 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 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.