Render Terminal Text as a PBM Image with pbmtext

You will turn a short line, or text read from standard input, into a monochrome PBM image. You will also check the dimensions before opening the binary output, wrap a long line deliberately, and avoid the two input modes that most often produce surprising results. Allow about fifteen minutes. You need the netpbm package and a writable working directory. The examples use Netpbm 11.5.2, the version installed on this machine.

1. Check the installed command

Confirm which executable your shell will run, then record the Netpbm version:

$ command -v pbmtext
/usr/bin/pbmtext
$ pbmtext --version
pbmtext: Using libnetpbm from Netpbm Version: Netpbm 11.5.2
...

The full version output includes build details, so the trailing lines are omitted here. The manual page installed with this command is dated 29 May 2020. Where the manual describes release-specific options, this guide treats the installed 11.5.2 behaviour as authoritative.

2. Render one line to a new PBM file

Pass the text as the non-option argument and redirect standard output to a new destination:

$ pbmtext --builtin fixed 'Hello, Netpbm' > hello.pbm
$ file hello.pbm
hello.pbm: Netpbm image data, size = 105 x 24, rawbits, bitmap
$ head -n 2 hello.pbm
P4
105 24

pbmtext writes a PBM image, not a progress message, to standard output. The P4 header identifies a binary PBM. The exact dimensions depend on the font and text, so use file or the first two header lines as a quick check rather than expecting the sample size on every host.

3. Use standard input for multiple lines

With no non-option text argument, the program reads standard input. Each input line becomes an output line:

$ printf '%s\n' 'First line' 'Second line' | pbmtext --builtin fixed > two-lines.pbm
$ file two-lines.pbm
two-lines.pbm: Netpbm image data, size = 105 x 48, rawbits, bitmap

The output is one image containing both lines. A line ending is a separator, not a glyph. If you accidentally leave a command waiting for input, press Ctrl-D on an empty line to signal end of file, or cancel with Ctrl-C and rerun the command with an explicit file or pipe.

Tabs are expanded to spaces at tab stops every eight characters. This is useful for simple fixed-width text, but it is not a reliable layout technique with a proportional font.

4. Inspect dimensions without creating an image

Use --dry-run when you need the planned dimensions before writing a PBM:

$ pbmtext --dry-run 'Hello, Netpbm'
101 29

The two numbers are the planned width and height in pixels. This sample uses the default built-in bdf font, so its dimensions differ from the fixed font used earlier. The default font is a Times-Roman-style built-in font about 15 pixels high. You can select the ASCII-only built-in fixed font with --builtin fixed.

--text-dump is the other diagnostic mode. It prints the text after formatting, including tab expansion and replacement of characters that the selected font cannot render:

$ printf 'A\tB\n' | LC_ALL=C pbmtext --text-dump
A       B

--dry-run and --text-dump are alternatives. Supplying both is an error, and no PBM is produced:

$ pbmtext --dry-run --text-dump 'x'
pbmtext: You cannot specify both -dry-run and -text-dump

5. Fit a long line to a width

Use --width when a single input line must fit a particular number of pixels:

$ pbmtext --builtin fixed --width 40 'ABCDEFGHIJK' > wrapped.pbm
$ pbmtext --builtin fixed --width 40 --dry-run 'ABCDEFGHIJK'
40 48

For one line, pbmtext breaks the text between characters as needed. It does not understand words, so it may split a word and may leave white space at the start or end of a line. For input with several existing lines, it keeps those line boundaries and truncates each line to the requested width instead of reflowing the whole paragraph.

Do not combine --width with --nomargins expecting both settings to apply. The installed command reports that --nomargins has no effect when --width is specified. Choose the behaviour you actually need, then verify it with --dry-run.

6. Control margins and spacing carefully

By default, the image includes margins. The left and right margins are based on twice the widest character in the font, while the top and bottom margins are based on the tallest character. A one-line input receives smaller margins. Add --nomargins when the image should not receive those program-added margins:

$ pbmtext --builtin fixed --nomargins 'Label' > label.pbm
$ pbmtext --builtin fixed --nomargins --dry-run 'Label'
35 12

The glyphs can still contain blank pixels around their own edges. If the type must touch all four edges, crop the result with a separate tool such as pnmcrop; do not assume --nomargins removes font-internal space.

--space adds horizontal space between characters and accepts fractional pixels. --lspace adds whole-pixel space between lines. Negative values crowd text, but the manual warns that their results are not well tested. Start with non-negative values and inspect the image before using unusual spacing in a batch.

7. Treat Unicode and fonts as an encoding problem

The default mode reads a single-byte character stream. The default built-in bdf font uses ISO-8859-1, while fixed is ASCII-only. A character missing from the font is rendered as a space, which can look like lost text rather than a command failure.

For UTF-8 or another multibyte input stream, use --wchar and provide a matching ISO-10646-1 BDF font with --font. In this mode the text must come from standard input, not the command line:

$ printf '%s\n' 'Café £' \
    | LC_ALL=en_GB.UTF-8 pbmtext --wchar --font /path/to/unicode-font.bdf > cafe.pbm
$ pbmtext --wchar --font /path/to/unicode-font.bdf --text-dump \
    < /path/to/input.txt

Replace /path/to/unicode-font.bdf with a real readable font. The font encoding and the locale must agree with the input encoding. If the result is garbled, inspect both before changing spacing or margins. Standard-input lines are limited to 4,999 characters, and null bytes can produce abnormal results, so this is a text-rendering tool rather than a general binary-file converter.