September 7th, 2012 at 11:38 pm by Dr. Drang
The trick of Apple’s Retina graphics isn’t simply producing hardware with high-resolution displays, it’s also producing software that understands how and when to use pixel-doubling tricks to produce the best output without making everything tiny. This is especially true when it comes to rendering text. Oddly enough, Apple did something very similar almost 30 years ago with the original ImageWriter.
The original Mac came with a 72 dpi black and white screen. The Mac’s first printer (and mine) was the ImageWriter, which had a resolution of 144 dpi. You can see where this story is going, can’t you? When printing out images from, say, MacPaint, each pixel on the screen became a 2×2 block on paper—just as non-Retina images are pixel-doubled when rendered on a Retina screen. But, just as in our modern Retina world, fonts were handled differently.
There were no outline-based fonts on the original Mac; those didn’t arrive until the LaserWriter. But most of the fonts came in several bitmapped sizes, and that was the basis for the trick Apple used to get the smoothest text possible out of the ImageWriter. When you wrote a document in MacWrite using, say, Geneva 12 for the body text, the ImageWriter would use the bitmapped letterforms of Geneva 24 to put the dots on the paper. The same was true for other fonts and sizes; the printed letter bitmaps came from the double-sized version of that font.2
This made for pretty smooth text (for the time), but there were some small, non-WYSIWYG consequences. Because Susan Kare designed each font size by hand to take advantage of the pixels available, the letterforms had subtle differences as you moved from one size to another. One that I have a distinct memory of—but, maddeningly, cannot find visual proof of—is the descender of the y. At 12 points (or maybe it was 10 points) and smaller, the descender was a straight diagonal line. There simply weren’t enough pixels around to be able to put a hook on the end. But at 18, 20, and 24 points, there was more breathing room, so Kare included the hook. Thus, the printed y had a distinctly different look from the one on the screen.3
I’m not seriously suggesting that the ImageWriter was an influence on the Retina display software. A lot of water has gone under the bridge since the mid-80s, and I doubt that anyone involved in handling the double resolution of the ImageWriter was still at Apple when Retina displays came out. Well, I can think of one person. I wonder…
Although he’s come close. When I started reading this post about dithering, Thomas’s first mention of the ImageWriter made my heart sink. “He’s beaten me to it,” I thought, cursing my procrastination. His return to dithering in today’s post was the kick in the pants I needed to just write this thing and get it out of my head. ↩
And if there were no double-sized version of the font used in the document? I don’t remember. If you do, please leave a comment. ↩
As I was Googling for images to confirm my memory about the y, I ran across this old post from John Gruber, in which a reader reminds him about font rendering on both the original ImageWriter and the 216 dpi ImageWriter LQ. As you might guess from the unusual resolution, the ImageWriter LQ used triple-sized fonts to render smooth text on paper. ↩