Convert a PBM Image to DjVu Bitonal RLE with pbmtodjvurle

You will convert a Portable Bitmap (PBM) image into DjVu Bitonal Run-Length Encoding (RLE), leaving the original image untouched and capturing the binary result in a new file. The normal workflow is a pipeline or a shell redirect because the installed command writes its result to standard output. Allow about ten minutes if the PBM file is ready.

You need a Linux shell, the netpbm package, and a readable PBM file. These examples use Netpbm 11.5.2 from Debian package netpbm 2:11.05.02-1.1build1. The installed manual describes pbmtodjvurle as a PBM-to-DjVu Bitonal RLE converter and says it has no command-specific options.

1. Check the installed command

Confirm which executable will run and ask it for help. Both commands are ordinary, read-only checks and do not need elevated privileges:

$ command -v pbmtodjvurle
/usr/bin/pbmtodjvurle
$ pbmtodjvurle --help
pbmtodjvurle: Use 'man pbmtodjvurle' for help.

The brief help message is normal for this Netpbm tool. The manual page is the useful command reference here: the program accepts a PBM input file, or reads standard input when no file is supplied, and produces DjVu Bitonal RLE on standard output.

Checkpoint: verify the package version if you are documenting a script or investigating a difference between machines:

$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1

2. Convert a PBM file to a new RLE file

Redirect standard output to a destination that does not already contain something valuable:

$ pbmtodjvurle /path/to/input.pbm > /path/to/output.rle

A successful run normally prints no progress message. Check the exit status immediately, then confirm that the destination is non-empty:

$ printf 'conversion status: %s\n' "$?"
conversion status: 0
$ test -s /path/to/output.rle && printf '%s\n' 'RLE output is non-empty'
RLE output is non-empty

The output is binary, so do not inspect it in a text editor or expect file to identify it with a friendly image description. A small valid result begins with an RLE header, but the safest first checks are the exit status and file size. Keep the PBM input until a later DjVu reader or conversion step has accepted the result.

3. Use standard input and output in a pipeline

With no input filename, pbmtodjvurle reads standard input. This lets another Netpbm program feed it directly, or lets you make the input source explicit with a shell redirect:

$ pbmtodjvurle < /path/to/input.pbm > /path/to/output.rle
$ printf 'pipeline status: %s\n' "$?"
pipeline status: 0

A single hyphen is also accepted as the input filename on the installed command:

$ pbmtodjvurle - < /path/to/input.pbm > /path/to/output.rle

Do not confuse the two sides of the command. The input is selected by the optional argument or standard input; the result goes to standard output, which the shell redirect saves. There is no output filename argument in this installed build.

4. Avoid overwriting an existing result

Shell redirection with > truncates the destination before the converter starts. If the output name already matters, write a temporary result and move it into place only after conversion succeeds:

$ pbmtodjvurle /path/to/input.pbm > /path/to/output.rle.new
$ status=$?
$ if [ "$status" -eq 0 ] && [ -s /path/to/output.rle.new ]; then
>     mv -- /path/to/output.rle.new /path/to/output.rle
> else
>     printf 'conversion failed with status %s\n' "$status" >&2
>     rm -- /path/to/output.rle.new
>     exit "$status"
> fi

The mv replaces the old output only after a successful, non-empty conversion. The final rm removes a failed temporary file and is destructive only to that newly created file. If you are adapting this pattern, check the paths carefully before running it. No command in the normal conversion needs sudo; use elevated privileges only when the input directory or destination is genuinely protected, and prefer fixing ownership or permissions instead.

5. Diagnose the common argument mistake

The installed binary accepts at most one command-line argument, the input filename. Passing an output filename as a second argument fails before conversion:

$ pbmtodjvurle /path/to/input.pbm /path/to/output.rle
pbmtodjvurle: Program takes at most 1 argument -- the input file name. You specified 2

This is worth calling out because the installed manual's synopsis displays an optional rlefile position, while the Netpbm binary on this machine rejects two arguments. Follow the behaviour of the installed executable: redirect standard output instead of supplying a second filename. If another host behaves differently, record its Netpbm version and rerun the help and conversion checks before changing a script.

If the command reports an input error, first check the path and readability without changing anything:

$ ls -l /path/to/input.pbm
$ test -r /path/to/input.pbm && printf '%s\n' 'input is readable'
$ pbmtodjvurle /path/to/input.pbm > /tmp/pbmtodjvurle-check.rle
$ printf 'status: %s\n' "$?"
status: 0

Replace the temporary path with a location you control. If the status is non-zero, do not treat a partially written file as a valid conversion. Remove or quarantine it after checking the status, then correct the input format or path. A PBM file must be a Netpbm bitmap, not a similarly named colour image.