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Do e-ink / e-paper screens work in the RGB, CMYK, or some other colour space? Will we need to support native CMYK displays in the near future? I'm designing a data structure with colour information and want to know whether the colour part ought to support expansion beyond four colour components (for, say, CMYKA).

Simon
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The current technology of electronic paper is constantly moving. Most current implementations, like Amazon's Kindle, only support 2 bit (4 levels) or 4 bit (16 levels, Kindle 2) gray scales. It depends on the software how color information is translated.

RBG or CMYK

More modern implementations support color. There are different methods used for creating color`. I.e., a combination of reflective and emitive technologies through filtering (e-ink), or a purely reflective method through electro wetting, like LiquaVista and Philips is creating. Also, compare LCD (mixed subtractive and additive), TFT (additive) printing (subtractive). Typically, RGB or RGBW is used for additive methodologies (e-ink, CRT, TFT, LCD), and CMYK for subtractive technologies (some implementations of electro-wetting like LiquaVista, all printing systems).

In a paper titled "Development of CMYK color display", Hiroki Yamada states that:

We would like to stress that RGB display and CMYK display are not conflicting visition. The aim of this study is to establish a mutually complementary relationship beween RGB and CMYK display.

Whether or not you have to write against a driver interface that supports RGB(W) or one that supports CMYK is doesn't really matter in practice, as converting from one system to another is a matter of a simple calculation.

Michael Murstam explains clearly in a Youtube discussion (!) how the different technologies relate. In "E-paper, the color challenge" Linda M. Casatelli explains how RGB and CMYK relate to liquid ink technologies.

Technology is heavily under development

Currently every new system may introduce a new color scheme. Once a new system is available, they'll create a development kit that you can use for writing to the screen. Most of the time, the device driver will take away the complexities of the color schemes and will typically support either RGB(W) or CMYK. Often, they'll allow you to send a device independent bitmap structure to the driver, and get a device dependent structure back.

Your datastructures should be created in such a way that you can easily convert between the two major color schemes.

Abel
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  • I'd like to see a reference for your claim about subtractive colour mixing w.r.t. "modern E-Ink-like displays". – sellibitze Aug 02 '11 at 18:59
  • @sellibitze: it follows from the technique (compare with inkjet printers, also subtractive) but try Wikipedia, it's explained there too: http://en.wikipedia.org/wiki/Electronic_Paper – Abel Aug 03 '11 at 17:21
  • @sellibitze, I just gave you a link. From that link, I quote _"The colours used are cyan, magenta and yellow, which is a so-called subtractive system, comparable to the principle used in inkjet printing for example"_. Can't get it clearer. – Abel Aug 04 '11 at 14:28
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    The thing is, the first explanation I found for a colored electro wetting display was just a monochrome layer with RGB subpixel filters on top. That's not subsractive mixing. But it's also not the only way to do it. For anyone, who's interested in the details, I suggest reading this paper: http://www.liquavista.com/files/LQV0905291LL5-15.pdf – sellibitze Aug 04 '11 at 16:27
  • I have to side with sellibitze on this one. It is a monochrome display with RGB overlay. Here's another link http://wiki.mobileread.com/wiki/E_Ink_Triton – Timofey Drozhzhin Dec 16 '12 at 10:58
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    @timofey and sellibitze, thanks for your inputs, I've updated the answer to include your comments. Yet, it isn't as black and white as you pose it ;). – Abel Dec 16 '12 at 14:10