Someone asked a question in the comment section of the blog the other day about color E-ink screens. He wanted to know when we would see a color screen on a note-taking device, but I misunderstood and thought he meant better color screens.
After I realized my mistake, I thought this was a great question that merited getting answered in its own blog post. So here it is:
When Can We Expect Better Color E-ink Screens?
Well first of all, I think we have a decent color E-ink screen now. The Kaleido screen on the Pocketbook Color is a major improvement over the Triton color E-ink screens. I think either ereader with this screen (Poke2 Color, Pocketbook Color) is worth buying if you want a color screen.
There is a chance we could get a larger screen, but I do not expect a better quality screen any time soon.
I would not wait for the next-gen color screen because its launch date cannot be predicted (such as Amazon pulling a rabbit out of their hat). A better screen is going to require a breakthrough in screen resolution and another breakthrough in the number of shades supported by E-ink screens (currently 16).
I will need to address those separately.
Screen Resolution
Kaleido screens are limited to 100 PPI because because the highest resolution screens which E-ink can put on an ereader top out at 300 DPI (dots per inch).
We do not usually use the term DPI with respect to E-ink screens, but I am using it here so I can explain how Kaleido screens differ from Carta screens. The reason I use 300 DPI is to make the point that the highest resolution screen E-ink can put on an ereader squeezes 300 dots or addressable locations into an inch of screen.
Edit: And those 300 dots are measured on the diagonal, not vertically or horizontally. (Check the math, and you’ll find I am right.)
If it helps, you can think of the 300 DPI as 300 boxes which can each contain one value. Actually, I think that is a great analogy, so I will use it for the rest of this post.
If you wanted to use those 300 boxes for grayscale, you can have a 300 PPI Carta screen such as on the Kindle Paperwhite.
But if you want a color E-ink screen, you’re actually going to need to use three of those boxes for each color pixel, giving you a 100 PPI Kaleido screen. The thing is, a color pixel is actually made up of 3 different color pixels (red, green, and blue), which means you need to have three different “boxes” for a color screen.
This usually never comes up for LED and LCD screens because everyone just assumes there will be RGB pixels, but with E-ink screens we are used to grayscale, where there is only a single color (shades of gray). We’ve spent years only thinking in terms of grayscale pixels, so it comes as a shock when we gain color but have to sacrifice screen resolution.
(BTW, the older Triton color E-ink screens required four “boxes” for each color pixel. That’s why it had such low resolution.)
In conclusion, we will not get a higher resolution Kaleido screen until E-ink can produce a higher resolution grayscale screen. Since that is by definition a breakthrough, there’s no way to predict when it will happen.
Color
The other major limitation for Kaleido screens is the number of colors supported. It can show 4096 colors, and due to the limitations of E-ink tech that is literally the best it can do at this time.
A pixel on an E-ink screen can display up to 16 shades of any single color. With most ereaders, that is 16 shades of gray (from white to black), which is great for displaying text (and really okay for displaying images).
But with a Kaleido screen we’re talking about 16 shades of red, green, or blue.
The reason the Kaleido screen can do 4096 colors is that the 16 shades of red crossed with the 16 shades of blue crossed with the 16 shades of green gives you 4096 colors. (Seriously, check the math.)
We’re not going to get additional colors on a Kaleido screen until E-ink releases a screen which can do, say, 24 or 32 shades of gray. Since that is by definition a breakthrough, there’s no way to predict when it is going to happen.
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Does that help any?
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