Thunderscan Author: Andy Hertzfeld Date: June 1984 Characters: Tom Petrie, Victor Bull, Bill Atkinson, Andy Hertzfeld Topics: 3rd party developers, Hardware Design, Software Design, Technical Summary: A clever device transforms a printer into a scanner --- Overview Thunderscan was an innovative product that turned an Apple ImageWriter printer into a high-resolution scanner by replacing the ribbon cartridge with an optical sensor, controlled by software running on an Apple II or Macintosh. It was developed by Thunderware, a small company founded by Tom Petrie and Victor Bull, and featured software crafted by Andy Hertzfeld. --- Development Background Andy Hertzfeld’s first project at Apple (1979) was low-level software for the Silentype thermal printer. Victor Bull, hardware designer on the Silentype, left Apple and teamed up with Tom Petrie at Thunderware. Thunderware had made popular products like Thunderclock, a calendar/clock card for Apple II. In 1984, Bull invited Hertzfeld to help develop an exciting new product for Macintosh—Thunderscan. --- The Concept The ImageWriter was the standard $500 dot-matrix printer for Apple II and Macintosh. Thunderscan used the precise stepper motors of the ImageWriter to scan images by swapping the ribbon cartridge with an optical sensor. Priced under $200, it offered superior resolution to flatbed scanners ten times its cost. The software managed scanning and rendering grayscale images on Macintosh. --- Challenges Speed: Scanning was slow because it captured one scan line per pass versus printing nine dots at a time, making full page scans take over an hour at highest resolution. Image Quality: Prototype Apple II software displayed blotchy images due to limited 1-bit-per-pixel display and simple thresholding. Printer Mechanics: ImageWriter wasn’t designed to move one scan line at a time; engineers tricked it into moving 3 steps up then 2 steps back to keep the paper tight. Bidirectional Scanning: Scanning in both directions could double speed but caused alignment issues; made optional in software. --- Software Development Hertzfeld leveraged Macintosh’s superior speed and Bill Atkinson’s expertise in grayscale rendering. Used modified Floyd-Steinberg dithering to display high-quality grayscale images approximated on 1-bit displays. Kept 5-bit grayscale data internally to allow image processing like brightness and contrast adjustment. Introduced innovative UX features like "inertial scrolling," allowing users to push and have the image continue scrolling smoothly. --- Product Lifecycle and Impact Software was finished in November 1984; Thunderscan launched December 1984. Sales grew from 1,000 units/month at launch to over 7,500/month by 1987. Became the least expensive, highest quality scanning option for Macintosh users during its peak. Over time, flatbed scanners became cheaper and better, overtaking Thunderscan. Total sales approximately 100,000 units. Software saw three major revisions adding features like grayscale printing and Macintosh II support. --- Legacy Thunderscan was praised for its clever engineering, solid software, and innovative features, inspiring many in the Macintosh community. It remains a landmark example of creative third-party hardware and software development in the early Macintosh era. --- User and Developer Comments Highlights Inspired users to create image viewing/editing software like GrayView. Noted for stable, solid software that integrated well with multitasking tools like Apple’s Switcher. Personal stories reflect gratitude toward key developers like Tom Petrie. Legacy of innovation and impact on professional careers acknowledged. --- Licensing The text of this story is licensed under a Creative Commons License.