rawtopgm - Online in the Cloud

PROGRAM:

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.

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