When it comes to text, how small is too small? The experts say a six point font is the minimum for readability, but as [James Bowman] shows us, you can get away with half of that.

The goal is to produce a 40-character display on a 24 mm x 24 mm LCD that has a resolution of 240 x 240 to show a serial terminal (or other data) on the “TermDriver2” USB-to-Serial adapter. With 24 lines, that’s a line per millimeter: very small text. Three points, to be precise, half what the experts say you need. Diving this up into 40 columns gives a character cell of six by nine pixels. Is it enough?

The raw font on the left, the subpixel rendering on the right. For once, it’s better if you don’t click to enlarge.

Not by itself, no. That’s where the hack comes in: sub-pixel rendering. After all, a “white” pixel on an LCD is actually three elements: a red, a green, and a blue subpixel, stacked side-by-each. Drive each of those subpixels independently and 240 pixels now becomes 720. That’s plenty for a 40 column terminal.

The article discusses how, in general terms, they pulled off the subpixel rendering and kept the font as legible as possible. We think it’s a good try, though the colored fringe around the characters can be uncomfortable to look at for some people — and then we can’t forget the physical size of the characters being 1 mm tall.

If this trick were being used on a larger display with a 240-wide resolution, we’d say “yes, very legible, good job!”– but at this size? We hope we can find our reading glasses. Still, it’s a neat trick to have in your back pocket for driving low-resolution LCDs.

It may not surprise you that aside from improving legibility, subpixel rendering is also used for pixel (er, sub-pixel) art.

The full set of glyphs in their subpixel-rendered glory.

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