imagewriter

Print black-and-white PNG images to an Apple Imagewriter or ImageWriter II dot-matrix serial printer.

Written in Ruby.

Requirements

• Ruby
• Serial adapter connecting to the printer. What works for me: Tripp Lite Keyspan USB to DB-9 serial adapter + DB-9 null modem + DB-9 to Mini DIN-8 cable

Installing

To install systemwide, use gem install imagewriter.

To use from the project directory, run bundle install once, then run bin/imagewriter directly.

Usage

Output is written to STDOUT, and should be redirected to the serial adapter of your choice.

Usage: imagewriter [options] filename.png
Vertical resolution is 144 dpi; horizontal resolution is adjustable.
Max printable width is 8 inches, or 8 * horizontal DPI pixels.
Options:
    -H, --horizontal DPI             Horizontal DPI. One of: 72, 80, 96, 107, 120, 136, 144, 160; default 144
    -q, --quality QUALITY            Print quality. 1 (fastest) to 7 (best); default 1
    -s, --sleep SECONDS              Sleep this many seconds between passes. Default 0.75
    -h, --help                       Print this help message to STDERR

Example:

imagewriter -q 5 foo.png > /dev/ttyUSB0

Why

I wanted better output quality and more predictable results than the CUPS ImageWriter driver provides. The technical manual for the ImageWriter II is not hard to come by, so I used it to write this.

How

It uses the standard interleaved-rows trick to achieve 144 vertical DPI. Writing 16 rows on each back-and-forth pass is the default and fastest setting, and matches the operation of extant ImageWriter drivers. Unsightly horizontal lines are commonly present in the output.

Higher output quality is achieved by writing fewer rows at a time, and dovetailing the vertical edges of each pass in order to soften the horizontal artifacts in the finished printout.

Flow control is not always easy to come by, so the output loop has a delay time in order to prevent buffer overruns (and garbage printouts). The default time of 0.75 seconds works well on an ImageWriter II.

What

Here, some examples should help. As is traditional, I have used Lenna as an example image (photo by Anna Huix for Wired Magazine). First the original image cast in black and white and cropped to 8"x10.5", then a quality 1 (fastest) rendering taking 6 minutes, then a quality 7 (best) rendering taking 23 minutes.

Who, When

Written by Pete Gamache over Thanksgiving weekend, 2020.

License, or not

This software is released into the public domain.