rawtopgm(1) - man - phpman

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Convert a raw greyscale image to a PGM image.

Convert a raw greyscale image to a PGM image
rawtopgm {{width}} {{height}} {{path/to/image.raw}} > {{path/to/output.pgm}}
Convert a raw greyscale image to a PGM image, assume the image to be a square
rawtopgm {{path/to/image.raw}} > {{path/to/output.pgm}}
Convert a raw greyscale image in which the pixels come bottom-first instead of top-first to a PGM image
rawtopgm {{width}} {{height}} {{-bt|-bottomfirst}} {{path/to/image.raw}} > {{path/to/output.pgm}}
Ignore the first `n` bytes of the specified file
rawtopgm {{width}} {{height}} {{-h|-headerskip}} {{n}} {{path/to/image.raw}} > {{path/to/output.pgm}}
Ignore the last m bytes of each row in the specified file
rawtopgm {{width}} {{height}} {{-r|-rowskip}} {{m}} {{path/to/image.raw}} > {{path/to/output.pgm}}
Specify the maxval for the grey values in the input to be equal to `n`
rawtopgm {{width}} {{height}} {{-m|-maxval}} {{n}} {{path/to/image.raw}} > {{path/to/output.pgm}}
Specify the number of bytes that represent each sample in the input and that the byte-sequence is to be interpreted as little-endian
rawtopgm {{width}} {{height}} -bpp {{1|2}} {{-l|-littleendian}} {{path/to/image.raw}} > {{path/to/output.pgm}}

rawtopgm(1) General Commands Manual 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|-topbot‐‐
tom] [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 lit‐
tleendian, 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 parame‐
ters, 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 immedi‐
ately 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 lat‐
ter 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 bot‐
tom 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 AT fysik4.se

14 September 2000 rawtopgm(1)