Convert a WBMP File to PBM Safely with wbmptopbm

You will convert a Wireless Bitmap file into a PBM image, either from a named file or from standard input, then verify that the result is a real image. The examples use the wbmptopbm shipped in Netpbm 11.05.02 on this machine.

Allow about ten minutes for a single conversion. You need a readable WBMP file, a shell and enough free space for the PBM output. These are ordinary user commands. You do not normally need sudo, and the converter does not alter the input file.

1. Check the installed command

Confirm that the command comes from the expected package before putting it into a script:

$ command -v wbmptopbm
/usr/bin/wbmptopbm
$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1
$ wbmptopbm --help
wbmptopbm: Use 'man wbmptopbm' for help.

The last result is normal for this build. The manual defines one optional positional argument, wbmpfile. There are no options specific to wbmptopbm; it also recognises options common to Netpbm programs, but this guide does not depend on unspecified common-option details.

2. Convert a named WBMP file

Pass the input path as the one positional argument and redirect standard output to a new PBM file:

$ wbmptopbm /path/to/input.wbmp > converted.pbm

wbmptopbm writes the PBM image to standard output. It normally prints no progress message, so silence is not a failure. Check the exit status and inspect the output without opening binary data in a text editor:

$ printf 'exit status: %s\n' "$?"
exit status: 0
$ file converted.pbm
converted.pbm: Netpbm image data, size = 8 x 4, rawbits, bitmap
$ wc -c converted.pbm
24 converted.pbm

The exact byte count depends on the dimensions and PBM encoding. The useful checks are a successful exit status, a non-empty output file and dimensions that match the source. The PBM magic number may be P4 for binary PBM output, so do not expect a human-readable pixel grid.

3. Use standard input when the WBMP is in a pipe

Omit the positional argument and pipe or redirect the WBMP into the command. This is useful when another tool has produced the file or when you do not want to create an intermediate copy:

$ some-wbmp-producing-command | wbmptopbm > converted.pbm

For a file that already exists, the equivalent is:

$ wbmptopbm < /path/to/input.wbmp > converted.pbm
$ file converted.pbm
converted.pbm: Netpbm image data, size = 8 x 4, rawbits, bitmap

Using standard input does not change the output format. It only changes where the input bytes come from. Keep the input and output redirections in the right order: < supplies WBMP data to the command, while > sends the resulting PBM data to a file.

4. Make a small round-trip test

If you need a known-good fixture, Netpbm's companion pbmtowbmp converts PBM to WBMP. The following creates a four-row, eight-column PBM in a pipeline, converts it to WBMP, then converts it back:

$ printf 'P1\n8 4\n0 1 0 1 0 1 0 1\n1 0 1 0 1 0 1 0\n0 0 1 1 0 0 1 1\n1 1 0 0 1 1 0 0\n' \
    | pbmtowbmp > sample.wbmp
$ wbmptopbm sample.wbmp > sample.pbm
$ file sample.pbm
sample.pbm: Netpbm image data, size = 8 x 4, rawbits, bitmap

This checks the installed converter's input and output path, not the visual quality of an unknown WBMP. Compare the round-tripped image with the original using an image viewer or another PBM-aware tool if the pixels matter.

Do not treat this test as evidence that every WBMP is supported. The local manual says that this program recognises only WBMP type 0, the type specified in the WAP 1.1 specification.

5. Protect an existing output file

Write to a temporary name in the same directory, verify it, then replace the old file only when the conversion succeeded:

$ wbmptopbm /path/to/input.wbmp > converted.pbm.new
$ test -s converted.pbm.new
$ file converted.pbm.new
converted.pbm.new: Netpbm image data, size = 8 x 4, rawbits, bitmap
$ mv converted.pbm.new converted.pbm

mv changes the directory entry; it does not rerun the conversion. If the command fails, leave converted.pbm in place and remove only the incomplete temporary file with rm converted.pbm.new after checking its name. If you have already overwritten a useful file, recovery depends on your backups or filesystem snapshots. There is no undo operation in wbmptopbm.

6. Diagnose a failed conversion

A missing or unreadable input is a path or permission problem, not a reason to run every command as root:

$ ls -l /path/to/input.wbmp
$ test -r /path/to/input.wbmp && echo readable
readable
$ wbmptopbm /path/to/input.wbmp > converted.pbm

With a missing file, the installed command exits non-zero and reports that it cannot open the file. Check the spelling, mount point and read permission first. Use elevated privileges only when your system administrator has deliberately granted access to the input location, and write the output into a directory your normal account can manage.

If the command rejects the file or produces no usable PBM, check whether the source is actually WBMP type 0. A file extension is only a name, not a format check. Preserve the original while investigating, and do not feed an arbitrary file into a batch replacement command.