The Hardware of Reading Devices
“Electrophoretic ink” was originally prototyped in the 1970s at Xerox PARC, but wasnt’ brought to market until the mid-2000s as a high-quality reading display. E-ink use reflective light (like ink on paper), as opposed to the projected light of mosst computer screens (either old-style CRT or backlit LCD).
An e-ink display is a matrix of particles, each of which can turn black or white (or some point in between when charged. The display requires no electricity to maintain an image, only to draw a new image (e.g., when a ‘page’ is ‘turned’).
Modern e-ink displays are fairly high-resolution (upwards of 200 pixels per inch or PPI), have contrast ratios comparable to printed paper, and use very little battery power. The refresh rate, however, is very slow compared to conventional displays, making e-ink unsuitable to video, motion graphics, or even the kind of interactive interfaces we now take for granted.
E-ink was widely reported as the future of e-book devices when the Sony Reader and Kindle arrived (circa 2007), but general-purpose devices like the iPad seem to have put an end to e-ink idealism.
LCD and OLED Displays
LCD (liquid crystal display) is a very mature technology, having been the mainstay of computer screens for well over a decade. LCD screens are in all modern tablet devices as well. They are fairly high-resolution (upwards of 300 PPI in the iPhone4, but more commonly in the range of 125-150 PPI), have very high contrast ratios, and are extemely fast, making them very good for motion graphics. Most of these advantages are the result of years of engineering development. LCD displays use a lot of power, however, largely because a backlight is used continually to shine through the LCD pixels.
AMOLED (active-matrix organic light-emitting diode) is a newer variation that is easier to produce and uses less power because each individual pixel is a light source—therefore, black images are truly black and use no electricity. AMOLED screens are relatively new and haven’t penetrated the market fully yet. Many Android cell phones use these displays, especially Samsung, who have invested heavily in this technology.
Screen resolution, quality
The earliest modern computer displays (1980s-era Macintosh) were 72PPI, corresponding to the old printers’ measure of 72 “points” to the inch. While this was a handy reference, 72PPI is pretty crude for reading, and displays have been getting denser (higher resolution) ever since. Most modern laptop diplays are well over 00 PPI.
The first generation of laser printers (1980s) were 300DPI (dots per inch), which was judged “acceptable” but not great by printers and typographers. Most modern laser printers run at 600DPI (4x the original resolution), which is high enough to fool the eye into thinking there are no discrete dots at all. High-end professional output devices like printers “imagesetters” run at 1200 DPI or more, but the additiona resolution is in the aid of halftoning images rather than typographic quality.
Note that the practical difference between pixels and dots per inch is that a dot is a dot—that is, it is either black or white—whereas pixels can display shades of grey or colour. So a 300 PPI display has a far higher effective resolution than a 300 DPI printer.
Anti-aliasing is a method of shading the edges of a line to trick the eye into thinking that a jagged edge is actually smooth:
At last month’s Books in Browsers conference, Mary Lou Jepson claimed that doubling screen resolution increases reading speed by 50%!
http://www.youtube.com/watch?v=ikvwj54koLk (9:15 – 19:19)
Dedicated v. General-purpose Devices: A Generational Split?
Some better demographics data: