Send a Correctly Shaped PBM Image to an AT&T 4425 Terminal

You will send a PBM image to an AT&T 4425 terminal using Netpbm's pbmto4425, with a preprocessing pipeline that accounts for the terminal's unusual pixel shape. The examples use Netpbm 2:11.05.02-1.1build1, installed on this machine.

Allow about 15 minutes if the terminal connection and input image already exist. You need a shell, an AT&T 4425 or a compatible VT100-like terminal with mosaic graphics, and Netpbm. This command emits terminal control sequences. Do not run it against a shell session you need to keep readable unless you are prepared to reset that terminal afterwards.

1. Confirm the command and the input format

Check that the executable is installed:

$ command -v pbmto4425
/usr/bin/pbmto4425
$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1

The command accepts one optional argument, pbmfile. With a filename, it reads that file. With no filename, it reads standard input. The input must be a PBM image, not an arbitrary PNG, JPEG or colour PPM file. Convert or preprocess other formats with the appropriate Netpbm tools before this final step.

Checkpoint: identify the exact file you intend to display and make a copy if it is the only copy. pbmto4425 only reads the image in these examples, so the source file is not changed.

2. Display a small PBM file directly

Use a file argument for the simplest test. This example makes a tiny checkerboard in PBM plain text format:

$ cat > /tmp/4425-test.pbm <<'EOF'
P1
4 2
0 1 0 1
1 0 1 0
EOF
$ pbmto4425 /tmp/4425-test.pbm

A compatible terminal switches to 132-column mode and renders the image with mosaic graphics. The terminal may appear to clear or reposition the cursor because the program sends terminal control sequences before the image data. That is expected output, not text to capture in a log.

To verify the command without relying on a visible terminal, redirect its output to a temporary file and check the exit status:

$ pbmto4425 /tmp/4425-test.pbm >/tmp/4425-test.output
$ printf 'exit status: %s, bytes: %s\n' "$?" "$(wc -c </tmp/4425-test.output)"
exit status: 0, bytes: 44

The byte count is specific to this two-row test image and this installed build. Your image will produce a different count. A zero status means the program processed the input successfully; it does not prove that the receiving terminal supports the 4425 graphics character set.

3. Send an image through standard input

Pipelines are useful when another Netpbm command prepares the image. For a direct stdin test, use the same PBM file:

$ pbmto4425 < /tmp/4425-test.pbm >/tmp/4425-stdin.output
$ printf 'exit status: %s\n' "$?"
exit status: 0

When you send to a real terminal, the last redirection is normally omitted:

$ pbmto4425 < /path/to/image.pbm

Do not put a filename after a pipeline unless that is the input you mean to use. For example, in some-command | pbmto4425 image.pbm, the filename is the program's input source and the pipe is not used as the image input.

4. Shape the image for the terminal

The 4425 mode used by pbmto4425 has a resolution of 264 columns by 69 rows. The terminal's pixels have an aspect ratio of 1:2.6, so an image that looks square in a normal bitmap will look stretched unless you scale it first.

The manpage's recommended sequence scales horizontally by 2.6, constrains the result to 264 by 69, converts to greyscale, dithers to black and white, then sends the PBM result to the terminal:

$ pamscale -xscale 2.6 input.pam \
    | pamscale -xysize 264 69 \
    | ppmtopgm \
    | pamditherbw \
    | pbmto4425

Replace input.pam with the image you want to process. The first scale compensates for the terminal's vertical pixel shape. The second keeps the output within the terminal's available dimensions. ppmtopgm reduces colour information to greyscale, and pamditherbw produces the black-and-white image that pbmto4425 expects.

The displayed result depends on the source dimensions, image content and terminal. If the pipeline reports an input-format error, stop at each stage and inspect the format expected by that installed Netpbm tool rather than feeding the error text into the next stage.

5. Recover the terminal after a test

pbmto4425 puts the terminal into 132-column mode. After a test, return to a normal terminal display with the terminal's reset or mode command. On a shell that understands ANSI control sequences, this is a common recovery attempt:

$ printf '\033c'

This resets the terminal, so it can discard other terminal state as well. Use the reset procedure documented for your terminal or terminal emulator if that command is unsuitable. If you redirected output to a file, remove only the disposable temporary files when you have finished inspecting them:

$ rm -f /tmp/4425-test.pbm /tmp/4425-test.output /tmp/4425-stdin.output

This cleanup is optional and affects only the three files created by the examples. Never substitute a broad path or an unreviewed variable in a removal command.

6. Diagnose the likely failures

• "command not found": Netpbm is not installed or pbmto4425 is not on PATH. Check with command -v before changing the shell environment.
• Unreadable output: confirm that the receiving device is an AT&T 4425 or a compatible mosaic-graphics terminal. A normal terminal emulator may accept the control sequences but lack the required character set.
• Wrong proportions: use the 2.6 horizontal scale and the 264 by 69 limit from the manpage's pipeline. The converter does not automatically correct an image's aspect ratio.
• Input errors: check that the final stream is PBM. pbmto4425 has no image-conversion option and no command-line options specific to it.
• Nothing appears in a log: that can be normal. The output is terminal data, including control sequences and mosaic characters, rather than a textual report.

There are no elevated-privilege steps here. Do not use sudo to solve an image-format, terminal-mode or PATH problem. Privilege will not add mosaic graphics support or repair a malformed PBM stream.