Convert PBM Images to Zinc Bitmaps with pbmtozinc

You will finish with a Zinc Interface Library Version 1.0 bitmap declaration generated from a PBM image. The installed command is Netpbm 11.5.2, from Debian package netpbm 2:11.05.02-1.1build1. Allow about ten minutes for a small conversion and a basic check.

You need a readable PBM file and a writable destination directory. The normal conversion is unprivileged. Do not use sudo just because the command is part of an image package. Elevation is only relevant if the input or destination permissions genuinely require it.

1. Check the installed command

Confirm which executable will run and record the local Netpbm version. This is read-only and does not need elevated privileges:

$ command -v pbmtozinc
/usr/bin/pbmtozinc
$ pbmtozinc --version
pbmtozinc: Using libnetpbm from Netpbm Version: Netpbm 11.5.2
pbmtozinc: Built from source dated 2024-03-31 09:09:47

The version output contains build details as well as the version. The package version can also be checked when the machine uses Debian's package database:

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

Checkpoint: if command -v finds a different executable, stop and check that you are testing the intended installation.

2. Confirm the input is a PBM

pbmtozinc accepts one optional input file. With no file, it reads standard input. It does not resize, threshold or redraw the image; it converts the PBM data it receives. A simple header check helps catch a wrong file before conversion:

$ head -n 3 /path/to/input.pbm
P1
8 4
0 1 0 1 0 1 0 1

P1 is the plain PBM form. A binary PBM may begin with P4; the installed Netpbm reader handles PBM input in the usual Netpbm formats. If the file is generated by another program, keep a copy of the original while testing.

3. Convert to a Zinc source file

Pass the PBM path and redirect standard output to a new file:

$ pbmtozinc /path/to/input.pbm > /path/to/output.zinc
$ printf 'exit status: %s\n' "$?"
exit status: 0

The output is source text, not a PNG or another Netpbm raster. A small 8 by 4 input produces output with this shape:

USHORT /path/to/input[] = {
  8
  4
 0x5500,0xaa00,0x3300,0xcc00};

The declaration name is derived from the input name. The first two values describe the image dimensions, followed by the Zinc bitmap data. Exact data values depend on every pixel in the PBM, so do not edit the generated words by hand to repair a source image. Fix the PBM and convert it again.

Checkpoint: verify that the destination exists, is non-empty and begins with the expected declaration:

$ test -s /path/to/output.zinc && echo 'output is non-empty'
output is non-empty
$ sed -n '1,5p' /path/to/output.zinc
USHORT /path/to/input[] = {
  8
  4
 0x5500,0xaa00,0x3300,0xcc00};

4. Use standard input when a pipeline is clearer

Omit the file operand to read PBM data from standard input. This is useful when another trusted Netpbm command produces PBM, or when you want the input name to be the converter's fallback name:

$ pbmtozinc < /path/to/input.pbm > /path/to/piped.zinc
$ sed -n '1p' /path/to/piped.zinc
USHORT noname[] = {

The output declaration is named noname when standard input has no file name. If the consuming source expects a particular identifier, use a named input file or rename the declaration deliberately after checking the generated content. Keep the input and output redirections separate so the shell cannot feed an empty, newly truncated output file back into the command.

5. Protect an existing output

Shell > truncates an existing destination before pbmtozinc starts. That is a destructive overwrite of the output file, although it does not alter the PBM input. For a safer replacement, convert to a temporary file in the same directory, inspect it, then move it into place:

$ tmp=$(mktemp /path/to/pbmtozinc.XXXXXX)
$ pbmtozinc /path/to/input.pbm > "$tmp" && test -s "$tmp"
$ sed -n '1,4p' "$tmp"
$ mv -- "$tmp" /path/to/output.zinc

The final mv replaces the old output only after a successful conversion and non-empty check. If conversion fails, remove the temporary file and the old output remains:

$ rm -- "$tmp"

Only run that cleanup when tmp still names the temporary file you created. If the replacement was a mistake, restore the old file from your normal backup before doing more conversions. The command itself has no undo facility.

6. Diagnose a failed conversion

A missing or unreadable path normally causes a non-zero exit status. Check it without changing permissions:

$ test -r /path/to/input.pbm && echo readable
$ ls -l /path/to/input.pbm

If the input is not a Netpbm image, the program exits with status 1 and reports a bad magic number, for example:

pbmtozinc: bad magic number 0x6e6f - not a PPM, PGM, PBM, or PAM file

Do not treat a zero exit status as proof that the picture looks right. Check the dimensions and inspect the Zinc source in the consumer that will compile or load it. Keep the original PBM until that later step succeeds.