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Rawtopgm User Manual(0)                                Rawtopgm User Manual(0)



NAME
       rawtopgm - convert raw grayscale bytes to a PGM image


SYNOPSIS
       rawtopgm

       [-bpp [1|2]]

       [-littleendian]

       [-maxval N]

       [-headerskip N]

       [-rowskip N]

       [-tb|-topbottom]

       [width height]

       [imagefile]


DESCRIPTION
       This program is part of Netpbm(1).

       rawtopgm  reads  raw  grayscale  values  as input and produces a PGM image as output.  The input file is just a
       sequence of pure binary numbers, either one or two bytes each, either bigendian or  littleendian,  representing
       gray  values.  They may be arranged either top to bottom, left to right or bottom to top, left to right.  There
       may be arbitrary header information at the start of the file (to which rawtopgm pays no attention at all  other
       than the header's size).

       Arguments  to  rawtopgm  tell  how  to interpret the pixels (a function that is served by a header in a regular
       graphics format).

       The width and height parameters tell the dimensions of the image.   If  you  omit  these  parameters,  rawtopgm
       assumes  it is a quadratic image and bases the dimensions on the size of the input stream.  If this size is not
       a perfect square, rawtopgm fails.

       When you don't specify width and height, rawtopgm reads the entire input stream into storage at once, which may
       take a lot of storage.  Otherwise, rawtopgm ordinarily stores only one row at a time.

       If you don't specify imagefile, or specify -, the input is from Standard Input.

       The PGM output is to Standard Output.


OPTIONS
       -maxval N
              N  is  the maxval for the gray values in the input, and is also the maxval of the PGM output image.  The
              default is the maximum value that can be represented in the number of bytes used for each  sample  (i.e.
              255 or 65535).


       -bpp [1|2]
              tells the number of bytes that represent each sample in the input.  If the value is 2, The most signifi-
              cant byte is first in the stream.

              The default is 1 byte per sample.


       -littleendian
              says that the bytes of each input sample are ordered with the least  significant  byte  first.   Without
              this  option,  rawtopgm assumes MSB first.  This obviously has no effect when there is only one byte per
              sample.


       -headerskip N
              rawtopgm skips over N bytes at the beginning of the stream and reads the image immediately  after.   The
              default is 0.

              This is useful when the input is actually some graphics format that has a descriptive header followed by
              an ordinary raster, and you don't have a program that understands the header or you want to  ignore  the
              header.


       -rowskip N
              If  there  is padding at the ends of the rows, you can skip it with this option.  Note that rowskip need
              not be an integer.  Amazingly, I once had an image with 0.376 bytes of padding per row.  This turned out
              to be due to a file-transfer problem, but I was still able to read the image.

              Skipping a fractional byte per row means skipping one byte per multiple rows.


       -bt -bottomfirst
              By  default,  rawtopgm  assumes the pixels in the input go top to bottom, left to right.  If you specify
              -bt or -bottomfirst, rawtopgm assumes the pixels go bottom to top, left to right.  The Molecular  Dynam-
              ics and Leica confocal format, for example, use the latter arrangement.

              If  you  don't  specify -bt when you should or vice versa, the resulting image is upside down, which you
              can correct with pamflip.

              This option causes rawtopgm to read the entire input stream into storage at once, which may take  a  lot
              of storage.  Ordinarly, rawtopgm stores only one row at a time.

              For backwards compatibility, rawtopgm also accepts -tb
               and -topbottom to mean exactly the same thing.  The reasons these are named backwards is that the orig-
              inal author thought of it as specifying that the wrong results of assuming the data  is  top  to  bottom
              should  be  corrected by flipping the result top for bottom.  Today, we think of it as simply specifying
              the format of the input data so that there are no wrong results.




SEE ALSO
       pgm(1), rawtoppm(1), pamflip(1)


AUTHORS
       Copyright (C) 1989 by Jef Poskanzer.  Modified June 1993 by Oliver Trepte, oliverATfysik4.se



netpbm documentation           14 September 2000       Rawtopgm User Manual(0)