Market-Ready Color E-Ink Displays: Still Not Suitable for eReaders
For many years, eBook readers with color displays have been eagerly anticipated. In the meantime, there were even a few devices—such as the PocketBook Color Lux—that used a color E-Ink display (with Triton 2 technology). However, they all had the same issues: the RGB color filter degraded contrast, and the viewing angle stability wasn’t particularly good. While built-in lighting improved readability to an acceptable level, the criticism remained that the color representation looked somewhat pale due to the filter’s transparency.
Ultimately, this technology did not take hold. It then seemed as though a different company than E Ink Holdings might achieve the breakthrough. Liquavista presented impressive demo videos as early as 2013. The company’s acquisition by Amazon fueled rumors that a Kindle with new display technology was on the horizon. But it never materialized, and eventually, the Liquavista website went offline in 2018. It’s safe to assume this was the end of electrowetting display technology in the consumer market.
ACeP Displays as Beacons of Hope
Nevertheless, E Ink Holdings never stopped researching color e-paper displays and introduced ACeP technology in 2017. ACeP stands for “Advanced Color ePaper.” It’s termed “Advanced” because it managed to solve virtually all the disadvantages of Triton technology with a different approach. Instead of using an RGB color filter to achieve color representation, the ACeP technology utilizes the familiar microcapsule technique, presenting all colors directly in the E-Ink display. The result: The colors are noticeably more vibrant than with the old technology, the contrasts are better, and the color display features over 32,000 colors independent of the viewing angle.
Back then, it was claimed that the technology could be market-ready in about two years. And they kept their promise, because in February 2019, E Ink Holdings announced the production of such screens for everyday use. The bad news: For now, the displays are only being used in Japan. TOPPAN Printing Co. Ltd. and Isetan Mitsukoshi are using ACeP displays for so-called Point-of-Purchase displays. In short: These are probably static advertisements.
Slow Refresh
The main reason for this use lies in the biggest disadvantage of the ACeP display: the screen refresh takes a very long time. Currently, it’s still too long for use in consumer electronics.
The refresh time is specified by Beck Elektronik for an already available development kit as 25 seconds. It appears to be the exact same display that the Isetan Shinjuku Store in Tokyo will use.
The reason for the slow refresh lies in the construction of the screen. The CMYW color particles (Cyan, Magenta, Yellow, White) are aligned one after the other. This takes longer than what is typical with grayscale E-Ink displays. This makes this type of display—at least for now—unsuitable for use in eBook readers.
Nonetheless, the technical specifications are quite interesting: The resolution of 1600×1200 pixels on a 13.3-inch screen diagonal results in a pixel density of 150 ppi. The display weighs 110 grams and can display 32,000 colors. The back is made of glass, so the well-known Mobius technology with a flexible backside, which protects against breakage, is not used here.
The reflectivity is specified at 35 percent (E-Ink Carta: 44 percent; E-Ink Pearl 40.7 percent) and the maximum contrast ratio at 10:1 (E-Ink Carta: 15:1; E-Ink Pearl 10:1).
Apart from E Ink, another company is currently researching color e-paper displays. ClearInk recently presented corresponding prototypes at SID 2019, which can even play videos with power-saving display capabilities.
