rawtopgm

rawtopgm(1)                                                        rawtopgm(1)



NAME
       rawtopgm - convert raw grayscale bytes into a portable graymap

SYNOPSIS
       rawtopgm  [-bpp  [1|2]]  [-littleendian]  [-maxval  N]  [-headerskip N]
       [-rowskip N] [-tb|-topbottom] [width height] [imagefile]


DESCRIPTION
       Reads raw grayscale values as input.  Produces a PGM  file  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  informa‐
       tion  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  Stan‐
       dard 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 significant 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, raw‐
              topgm assumes the pixels go bottom to top, left to  right.   The
              Molecular  Dynamics  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 pnm‐
              flip .

              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 -top‐
              bottom  to  mean  exactly the same thing.  The reasons these are
              named backwards is that the original 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  bot‐
              tom.   Today,  we think of it as simply specifying the format of
              the input data so that there are no wrong results.


SEE ALSO
       pgm(5), rawtoppm(1), pnmflip(1)


AUTHORS
       Copyright (C) 1989 by Jef Poskanzer.
       Modified June 1993 by Oliver Trepte, oliver@fysik4.kth.se



                               14 September 2000                   rawtopgm(1)