Convert a PPM Image to HP PCL 5 Colour with ppmtolj

You will turn a PPM image into an HP LaserJet PCL 5 Colour file that can be sent to a compatible colour printer. The examples use Netpbm 11.5.2, provided here by package version 2:11.05.02-1.1build1. Allow about ten minutes if the PPM is already prepared. The conversion itself normally takes only a moment.

You need a readable PPM file and the netpbm package. The command writes PCL to standard output, so redirect it to a new file. It does not require sudo when you can read the input and write the destination directory.

1. Check the installed command and input

Confirm which executable your shell will run, then check the input without changing it:

$ command -v ppmtolj
/usr/bin/ppmtolj
$ file /path/to/input.ppm
/path/to/input.ppm: Netpbm image data, size 1200 x 800, ...

The exact file description varies with the image. It should identify a PPM image and show plausible dimensions. The installed manual page is dated 4 September 2000, while the installed package is newer, so this guide describes the command available on this machine and avoids assuming that newer releases have additional options.

Checkpoint: if command -v prints nothing, stop and install Netpbm through your normal package-management process. Do not create a replacement script called ppmtolj in the working directory, because that can hide which program is actually being tested.

2. Make a PCL file with the default settings

Choose a new destination and redirect the command's standard output:

$ ppmtolj /path/to/input.ppm > /path/to/output.pcl
$ printf '%s\n' "$?"
0

A status of 0 means that ppmtolj completed successfully. The command normally has no progress display because the converted data is being written to the redirected output stream. The result should be recognised as HP PCL printer data by common file-identification tools:

$ file /path/to/output.pcl
/path/to/output.pcl: HP PCL printer data
$ wc -c /path/to/output.pcl
84217 /path/to/output.pcl

Your byte count will differ. Check that it is non-zero and that the output is not a text log accidentally captured in place of the conversion.

3. Protect an existing output file

Shell redirection with > truncates its destination before ppmtolj starts. If the name already contains a useful print file, use a temporary name in the same directory and replace the old file only after checking the result:

$ ppmtolj /path/to/input.ppm > /path/to/output.pcl.new
$ test -s /path/to/output.pcl.new
$ file /path/to/output.pcl.new
/path/to/output.pcl.new: HP PCL printer data
$ mv /path/to/output.pcl.new /path/to/output.pcl

The mv is the state-changing step. If conversion or verification fails, leave the existing output alone and remove the incomplete .new file after inspecting it. Deleting that temporary file is irreversible, so identify the exact path before using rm. There is no undo for a successful replacement unless you made a backup first.

4. Select the printer resolution

Use -resolution when the target printer or workflow requires a particular output resolution. The manual accepts only 75, 100, 150, 300 or 600:

$ ppmtolj -resolution 300 /path/to/input.ppm > /path/to/output-300.pcl
$ test -s /path/to/output-300.pcl && file /path/to/output-300.pcl
/path/to/output-300.pcl: HP PCL printer data

Do not pass an arbitrary DPI value and expect it to be rounded. If your printer documentation specifies another value, resolve that compatibility question before sending a file. The option describes the required output resolution; it is not an image-resizing command.

The manual does not state a default resolution. Do not build a script around an assumed default. Pass -resolution explicitly when reproducibility matters, especially if files will be exchanged between hosts or queued for a different printer.

5. Reduce the output or alter printer setup information

-delta enables delta row compression, which can reduce the size of the PCL file without changing the source PPM:

$ ppmtolj -resolution 300 -delta /path/to/input.ppm > /path/to/output-compressed.pcl
$ wc -c /path/to/output-compressed.pcl

File size depends on the image, so do not promise a particular reduction. Verify the file and test it on the intended printer before using it for a production queue.

By default, the program writes positioning information, including the sequence ESC&l0E. Use -float to suppress that positioning information. Use it only when the receiving PCL workflow supplies or deliberately omits its own positioning context:

$ ppmtolj -float /path/to/input.ppm > /path/to/output-float.pcl

-noreset suppresses the reset sequence at the beginning and end of the output. That can matter when another carefully controlled PCL stream surrounds this image, but it removes the command's normal reset boundaries. Treat it as a printer-integration option, not a general optimisation. Test it with the exact queue or spooler before deployment.

6. Apply gamma correction only with a known requirement

-gamma accepts an integer parameter and defaults to 0. It changes the image correction applied during conversion:

$ ppmtolj -gamma 1 /path/to/input.ppm > /path/to/output-gamma.pcl
$ test -s /path/to/output-gamma.pcl && echo 'PCL file written'

The manpage does not define a useful table of gamma values or describe a visual result for each integer. Do not guess at a value because a print looks too light or too dark. Make a small test file, compare the physical output with the uncorrected version, and record the chosen value alongside the print workflow.

7. Combine options for a controlled conversion

Options can be combined. This example requests an explicit resolution, delta compression, gamma correction, no positioning information and no reset sequence:

$ ppmtolj -resolution 300 -delta -gamma 1 -float -noreset \
    /path/to/input.ppm > /path/to/controlled.pcl
$ test -s /path/to/controlled.pcl
$ file /path/to/controlled.pcl
/path/to/controlled.pcl: data

Some file-identification tools may report a customised stream simply as data, especially when reset information has been suppressed. That label alone is not a failure. Check the exit status, non-zero size and the target printer or PCL consumer. If you do not need a surrounding PCL stream, omit -float and -noreset so the output retains the normal setup and reset sequences.

8. Diagnose failures without sending a bad job

If the command cannot open the input, check the path and read permission:

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

If it cannot create the output, check the destination directory rather than adding sudo immediately:

$ test -d /path/to
$ test -w /path/to && echo writable

Use elevated privileges only when your system administrator has deliberately granted them for the input or destination. Running the converter as root does not repair an invalid PPM, select a compatible printer mode or make a damaged PCL stream safe. Keep the original PPM until a test print or downstream validation succeeds.

Do not send an unverified file to a live printer queue. A PCL file can cause a printer to consume paper, and -float or -noreset can be wrong for a shared queue even when conversion succeeds. Test with a small image first and follow the queue's normal cancellation procedure if the printer starts producing unexpected output.