Render a Single Line of Text as PBM with pbmtextps

You will create a raw PBM image containing one line of text, inspect its dimensions, and choose margins and resolution deliberately. The examples use Netpbm 11.5.2, installed from package netpbm on the reference system. Allow about ten minutes. You need a shell, pbmtextps, and a writable working directory. No command here needs elevated privileges.

1. Check the installed command

Confirm which executable will run and record the Netpbm version before building a script around it:

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

The program invokes a PostScript interpreter to render the image. The manual page is dated 17 February 2023, while the installed library reports Netpbm 11.5.2. Treat the installed behaviour as the useful baseline when moving this command to another distribution.

Checkpoint: if command -v finds nothing, stop and install Netpbm through your normal package-management process. Do not download an unrelated replacement into a system directory.

2. Render ordinary ASCII text

Pass the text as one shell argument and redirect standard output to a new PBM file:

$ pbmtextps 'Hello, PBM' > hello.pbm
$ pamfile hello.pbm
hello.pbm: PBM raw, 265 by 109

The exact width depends on the characters, but this command produced a raw PBM with 265 columns and 109 rows on the reference system. The output is always raw PBM; the common -plain option does not select an ASCII PBM format here.

Keep the input in quotes when it contains spaces or shell punctuation. If you supply several arguments, pbmtextps joins them with one space. Thus pbmtextps hello world renders the same text as pbmtextps 'hello world'. It renders one line only, and newline characters in the input do not create multiple image rows.

3. Choose a font and physical scale

The default font is the PostScript font named TimesRoman, the default size is 24 points, and the default resolution is 150 dots per inch. Font size is converted into pixels through the resolution. For example, 24 points at 150 dpi is 50 pixels before the character shape and margins are considered.

Use a known installed font and an explicit size when repeatability matters:

$ pbmtextps -font=Helvetica -fontsize=18 -resolution=100 \
    'Hello, PBM' > hello-100dpi.pbm
$ pamfile hello-100dpi.pbm
hello-100dpi.pbm: PBM raw, 123 by 22

Font names are PostScript names, not file names. The manual suggests listing available names with Ghostscript:

$ gs -c '(*) {==} 256 string /Font resourceforall'

Check that gs is installed before using that lookup. A misspelled font is a distraction trap: pbmtextps silently falls back to the default font instead of reporting the invalid name. If the shape matters, compare a known sample or inspect the generated image rather than trusting a successful exit status.

4. Control the whitespace around the type

By default, the top and right edges are cropped to the type. The default left margin is half the font size, and the default bottom margin is equivalent to 1.5 times the font size below the baseline. Use -crop when you need every side cropped:

$ pbmtextps -crop -font=Helvetica -fontsize=18 'Tight' > tight.pbm
$ pamfile tight.pbm
tight.pbm: PBM raw, 47 by 22

-crop is equivalent to setting all four margins to zero. Do not combine it with -leftmargin, -rightmargin, -topmargin, -bottommargin, -ascent, -descent, or -pad. The command rejects conflicting margin choices.

For a controlled white border, give margins in points:

$ pbmtextps -leftmargin=8 -rightmargin=8 \
    -topmargin=6 -bottommargin=6 'Label' > label.pbm
$ pamfile label.pbm

Use -ascent and -descent instead when separate images will share a baseline. They measure from the baseline, which makes horizontal concatenation more predictable. Use -pad when separately rendered lines must have equal vertical spacing even if their letters have different heights.

5. Supply encoded text when shell input is inconvenient

For ASCII text, -asciihex lets you pass PostScript ASCII-HEX rather than literal characters:

$ pbmtextps -asciihex 48656c6c6f > hello-hex.pbm
$ pamfile hello-hex.pbm
hello-hex.pbm: PBM raw, 135 by 109

Whitespace in the encoded input is ignored. You may include the PostScript delimiters, but quote them because < and > have shell meaning:

$ pbmtextps -asciihex '<48656c6c6f>' > hello-hex-delimited.pbm

Netpbm 11.5.2 also supports -ascii85. Choose one encoding option, never both. There is no way to pass an ASCII NUL byte as a command-line argument.

6. Inspect or improve the rendering

Use -dump-ps when you need to inspect the PostScript program or feed it to another PostScript consumer. It changes standard output from PBM to PostScript, so do not give that output a .pbm name:

$ pbmtextps -dump-ps 'Hello, PBM' > hello.ps
$ head -n 2 hello.ps
/FindFont {/Times-Roman findfont} def
/fontsize 24.000000 def

This is an inspection or hand-off mode, not a second image format. For smoother-looking text, render at a larger resolution and scale the PBM down with pamscale. Verify the scaled file with pamfile before passing it to another tool.

7. Protect existing output

Shell redirection with > truncates its destination before pbmtextps runs. That is destructive if the file already contains a useful image. Write to a new temporary name, verify it, then replace the destination only after checking the result:

$ pbmtextps -font=Helvetica 'Replacement' > label.pbm.new
$ pamfile label.pbm.new
$ mv label.pbm.new label.pbm

The mv command changes the directory entry and can replace the old file. If the render fails, leave the original alone and remove only the incomplete label.pbm.new after inspecting it. Do not use sudo to bypass a permissions problem in a working directory; fix the destination or directory ownership through your normal administration process.