rawtopgm(1)rawtopgm(1)NAMErawtopgm - convert raw grayscale bytes into a portable
graymap
SYNOPSISrawtopgm [-bpp [1|2]] [-littleendian] [-maxval N] [-head
erskip 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 information at the start of the file (to which raw
topgm 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 repre
sented 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 sam
ple in the input. If the value is 2, The most sig
nificant 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 fol
lowed 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 Molec
ular Dynamics and Leica confocal format, for exam
ple, 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 pnmflip .
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 ALSOpgm(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)
