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 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 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, rawtopgm 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 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 ALSO¶
pgm(5),
rawtoppm(1),
pnmflip(1)
AUTHORS¶
Copyright (C) 1989 by Jef Poskanzer.
Modified June 1993 by Oliver Trepte, oliver@fysik4.kth.se