Color E-Paper not without problems

[Alexander Turcic]

Yesterday we heard that color e-paper based on E Ink wouldn't be ready for prime time this year (perhaps next year, but who knows?). It was stated by the chairman of PVI that there were still "barriers to achieving satisfying results." What kind of barriers? Coincidentally, the Technology Review runs an article on their website today with the following relevant information:

• Color displays normally require four subpixels--red, green, blue, and white--to create each full-color pixel. "That costs you in terms of resolution," says Pieter van Lieshout, head of product research and development for Polymer Vision [creator of the Readius].
• The other consequence of using a color filter is that it reduces the brightness of a display, says Sri Peruvemba, vice president of marketing at E-Ink.

So, with existing technologies, take away resolution and brightness - two of the main selling points of e-paper technology - and you get color. Not a very satisfying equation.

The article mentions Philips Research, who is working on a better solution, referred to as in-plane electrophoretics (IP-EPD), where the display is changed by electrically controlling the in-plane distribution of the pigment particles on the foundation.

By carefully controlling the voltages at electrodes positioned on the edges of the pixels, it is possible to spread the colored particles across the pixel or remove them from view altogether by hiding them behind the electrodes, says Lenssen. This means that different shades of color can be achieved by controlling how many of each group of colored particles are visible. To create white, all of the particles are simply shifted to the side to reveal the white substrate beneath the two microcapsules.

Unfortunately, both Mr. van Lieshout from Polymer Vision and Peruvemba from E Ink believe that this technology is still too early to be used for first generation E Ink color displays. They also argue that color filters (with all their disadvantages, see above) are easier and cheaper to produce.

This all means that it will be very interesting to see how well the first commercial color e-paper will perform compared to their grey ancestors.

[mtravellerh]

Bad news indeed!

[kacir]

I do not understand.

With monitors you ADD green, blue, red LIGHT to achieve colors. Funny thing is, that 100% red + 100% blue + 100% green do not give you white light. It is just our eye that perceives it as white light.
see http://en.wikipedia.org/wiki/RGB

When printing on papers, instead of adding light, you SUBTRACT. That is why a color printer uses Cyan, Magenta and Yellow ink to mix ink dots on paper and achieve colors. Most often CMYK is used, adding blacK, so you so not use 100%C + 100%M + 100%Y, but instead you only use 100%K.
see http://en.wikipedia.org/wiki/CMYK

Elektrophoretic displays http://en.wikipedia.org/wiki/Electrophoretic_display do not mix light. They work more like paper. So I would expect, that instead of RGB pixels they would mix CMY(K) colors.

[pdurrant]

It all depends on how the dots are arranged.

It the dots are all separate, then you need to use RGB, as the light reflecting from them adds.

If the dots overlap (as in printing), then you need to use CMY, as they combine to remove light reflected from each (overlapped) dot.

Cyan absorbs Red light, reflecting Green and Blue light
Magenta absorbs Green light, reflecting Red and Blue light
Yellow absorbs Blue light, reflects Red and Green light

So you can show a Red dot either by using a Red dot (which absorbs Blue and Green light, reflecting Red light), or by using a Magenta dot overprinted on a Yellow dot (The Magenta Dot absorbs the Green light, and the Yellow dot absorbs the Blue light, leaving only the Red light reflected.)



So, if a colour display is made with separate side-by-side dots, it must use Red, Green and Blue pigments.

If a colour display has (say) a structure perpendicular to the page that consists of three pixels one on top of each other, it must use Cyan, Magenta, Yellow pigments.

I think that an ebook display using the latter (CMY & perhaps black), would lead to a brighter, higher-resolution display.

And I suspect that it might be easier to make in the long run - each pigment would cover a whole layer of the display, while for the other display the pigments need to be right next to each other in the same layer.

Originally Posted by kacir

I do not understand.

With monitors you ADD green, blue, red LIGHT to achieve colors. Funny thing is, that 100% red + 100% blue + 100% green do not give you white light. It is just our eye that perceives it as white light.
see http://en.wikipedia.org/wiki/RGB

When printing on papers, instead of adding light, you SUBTRACT. That is why a color printer uses Cyan, Magenta and Yellow ink to mix ink dots on paper and achieve colors. Most often CMYK is used, adding blacK, so you so not use 100%C + 100%M + 100%Y, but instead you only use 100%K.
see http://en.wikipedia.org/wiki/CMYK

Elektrophoretic displays http://en.wikipedia.org/wiki/Electrophoretic_display do not mix light. They work more like paper. So I would expect, that instead of RGB pixels they would mix CMY(K) colors.

[kacir]

Thank you pdurrant for an excellent explanation.

[moriakaice]

Originally Posted by Alexander Turcic

This all means that it will be very interesting to see how well the first commercial color e-paper will perform compared to their grey ancestors.

But, uhm, isn't FLEPia already using e-Ink and colors? So didn't we already see how it performs compared to grey?

[TadW]

Originally Posted by moriakaice

But, uhm, isn't FLEPia already using e-Ink and colors? So didn't we already see how it performs compared to grey?

Please don't quote me, but I think the Fujitsu FLEPia is based on a different bistable display technology - called Reflex LCD - from the company Kent Displays. E Ink claims that the refresh rate for their color prototypes is a lot faster than that of Reflex LCD. Hopefully so ... the FLEPia takes about a second to fully refresh its screen.

[moriakaice]

Originally Posted by TadW

Please don't quote me, but I think the Fujitsu FLEPia is based on a different bistable display technology - called Reflex LCD - from the company Kent Displays. E Ink claims that the refresh rate for their color prototypes is a lot faster than that of Reflex LCD. Hopefully so ... the FLEPia takes about a second to fully refresh its screen.

https://www.mobileread.com/forums/sho...24&postcount=5 + https://www.mobileread.com/forums/sho...9&postcount=82 + whole topic: https://www.mobileread.com/forums/showthread.php?t=42537

As for Reflective LCD, maybe you thought about JetBook?

And they display it gradually, so you can start reading much, much faster instead of waiting for the full page to load.

[TadW]

Uhm, no. I think you are confusing E Ink with e-paper in general. The one post you quoted, this one, just made this clear.

E Ink is one possible technology to realize e-paper. But there are other technologies working on a solution, and one is "Reflex LCD", which is based on cholesteric LCD (unlike E Ink) and which is used by the FLEPia (I am sure now because I double checked).

You can read more about Reflex LCD here:

http://www.kentdisplays.com/advantages/advantages.html

[moriakaice]

Originally Posted by TadW

Uhm, no. I think you are confusing E Ink with e-paper in general. The one post you quoted, this one, just made this clear.

E Ink is one possible technology to realize e-paper. But there are other technologies working on a solution, and one is "Reflex LCD", which is based on cholesteric LCD (unlike E Ink) and which is used by the FLEPia (I am sure now because I double checked).

You can read more about Reflex LCD here:

http://www.kentdisplays.com/advantages/advantages.html

Oh, thanks for that! It always seemed the same for me, be it e-Ink or this Reflex LCD. Now it's a bit clearer. Sorry for the confusion caused.

[ProDigit]

has anyone ever tried drawing small dots of RGB on a white piece of paper, and can they verify if it is real black?

I understand the downside of color e-ink, as it was something we already expected (especially the resolution issue).
Probably the only way is to have a reflective white or metallic background, and a super transparent TFT layer in front; though that will also mess with the brightness of the device.
Another thing is they could use double layer screens; in the back your RGBW color e-ink; in the front a layer like from a solar powered calculator which will display transparent or black.
That would give deeper blacks, but also probably would take from the bright white, and take more battery.

The resolution should not be an issue since color generally only is used for photos; and text which is black generally only needs the high resolution.
What they need is small magnetic rotating cubes, that will rotate according to the magnetic field applied. a cube has 4 sides, so on one pixel you could have 4 colors; but they won't be able to display intensity.

At most for e-ink we would expect it to display 256 colors anyways; I don't know if 16bit colors (16Mil colors) is feasible.

[pdurrant]

Originally Posted by ProDigit

has anyone ever tried drawing small dots of RGB on a white piece of paper, and can they verify if it is real black?

Umm... no. (Apologies if I missed the joke). Lots of small RGB dots on white paper will look white (or grey).

There are other technologies around that might work well in ebook readers. Just a couple of examples:

1. Ntera's Nanochromic inks - they're transparent/coloured bistable inks that change in response to a low-voltage electric field. They're more into signs and things at the moment, but so was eInk when they started.

2. Opalux's Photonic colour technology, which uses an interestingly structured rubber material to generate any colour from a single pixel.

Lots of development work to be done on both, but either might provide us with cheap, robust, colour ebook reader displays..... in five to ten years time.

[brecklundin]

There is a piece on Engadget today that the color from PVI is going to be delayed a bt longer than expected. Apparently the color hue's are just not there yet. To be honest given how eink works I am surprised they can get any color to work.

http://www.engadget.com/2009/05/08/p...ny-reader-com/

[Phogg]

Originally Posted by ProDigit

At most for e-ink we would expect it to display 256 colors anyways; I don't know if 16bit colors (16Mil colors) is feasible.

Comic books did fine for decades with a narrow color pallet.

[DaleDe]

Originally Posted by Phogg

Comic books did fine for decades with a narrow color pallet.

PVI has said it would be 8 bits, 256 colors. The netronix site (also PVI) has some specs.

Dale