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pnmscale
!!!pnmscale
NAME
SYNOPSIS
DESCRIPTION
SEE ALSO
AUTHOR
----
!!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__


Minimum unique abbreviation of option is
acceptable.
!!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


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.


__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), pnminterp(1),
pbmreduce(1), pnmenlarge(1),
pnmsmooth(1), pnmcut(1),
__pnm(5)__
!!AUTHOR


Copyright (C) 1989, 1991 by Jef Poskanzer.
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15 pages link to pnmscale(1):
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Last edited on Tuesday, June 4, 2002 12:22:43 am by "perry"
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