rawtopgm



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, repre-
       senting 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 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  pam-
              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  -topbottom  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
              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, oliver@fysik4.kth.se



netpbm documentation           14 September 2000       Rawtopgm User Manual(0)

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