Do e-ink / e-paper screens work in the RGB, CMYK, or some other colour space?

Question

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).

Answer 1

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.