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Electronic ink: The whole story in black and white

But why not in colour?

Electronic books are popping up everywhere, but in the quest for colour it's worth remembering that ink isn't just used to print books.

Every time El Reg covers electronic books we get questions about why such devices aren't colour yet, and what's so great about electronic ink compared to other screen technologies, not to mention when compared to old-fashioned liquids? Understanding the technology behind e-ink, and its more-interesting applications, might not make anyone rush out to buy a Kindle but it's not going to do any harm either: so here we go.

Those who've not seen an e-ink display can't get electronic books at all, but many who have seen e-ink at its best still struggle to understand why anyone would be content with a greyscale display and refresh rate measured in seconds. The 20 or so devices that will be on the shelves by early next year will be greyscale at best, because colour is a technical bitch, but the more-interesting applications of e-ink don't need colour anyway and it's those that are going to change the perception of what a computer display is.

The current generation of electronic books are almost exclusively based on technology from E Ink, a company spun off from the Massachusetts Institute of Technology 12 years ago. In June E Ink announced that it was to be acquired by its biggest customer; Taiwanese component manufacturer Prime View International, but come September the deal had to be renegotiated thanks to a growth in demand of more than 250 per cent, combined with reduced production costs, which made E Ink a whole lot more attractive.

The oh-so-valuable E Ink property is based on a series of fluid-packed microcapsules, one for each screen pixel, which contain tiny balls coloured black and white and charged negative and positive respectively. By changing the charge underneath the capsules the balls can be made to sink, or float, with shades of grey achieved by mixing black and white areas within a single capsule.

E Ink Technology

Reflected light in black and white, image lifted from Wikipedia

The amazing thing about this process is that once the balls have been moved they remain in place without charge being applied, so you can literally smash an E Ink screen and the shards will still display the last thing rendered. E Ink screens can't be back-lit any more than a newspaper can, despite Sony's attempts to fit a side light to one of their readers, the use of reflected light makes the screen more visible the better the light. So it's ideal for reading the latest bonkbuster on the beach but not so good for torch-lit reading under the covers.

E Ink's technology can also be applied to any surface onto which it can be glued, so while most e-book readers are using glass or inflexible-plastic screens there's nothing to stop a manufacturer applying the microcapsules to the back of something more interesting.

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