The real problem is cost of course. Part of that is e-ink is still governed under a patent you must license and pay royalties to if I recall correctly
I suspect that the current technology works by "setting" in place whole regions of the screen at once, and that this kind of process is inherently slow. Maybe in a (not so distant) future it'll be possible to have individual pixels changing, in a similar way as an mp4 doesn't update all the image when not necessary.
Or not. So many technologies just embank somewhere and find their niche.
It's all tradeoffs, improving one number only to a limited extent and only at the expense of other numbers. Ie, faster action at the expense of worse image. No free lunch or getting around it by handwaving 'advancement'.
Trade-offs are a problem, but in this case i don't see any physical reason for this to be a theoretical trade-off. More like a limit of the current technology.
Why? Nobody said that the cell is "reset". The cell is modified. The resulting state depends on the former state. This causes ghosting.
To achieve what you are suggesting, the procedure would be e.g. to first set the pixel black, then white (reset to a base state), then the greyscale value of the intended content. This would slow down rendering dramatically, and make regions flicker.
And, note, this may be something that some "EPD waveforms" do - but there are tradeoffs... E.g. Fast? Ok, lose the greyscales. Detailed? Ok, get lots of flashing at update. Mid-way? Ok get some degree of ghosting.
E-ink displays are hardly new and lots of people have been thinking about/working on the slow refresh rates for over 2 decades. Do you really think that anything you can come up with on HN in 5 minutes without any knowledge of the tech is something people hadn't thought of before?
EPD displays already have that capability.
When you modify the dots you use a modality that is sensitive to former states. What happens in full-screen refresh is a cleanup to redraw on the best former state for the cleanest output.
Which means that the resetting operation kinda works globally anyways, masking out everything between the xmin, xmax and ymin, ymax.
I'm really speculating here, but this was my impression every time I saw individual areas changing without a gobal refresh.
Recall correctly meaning you were involved and have direct knowledge or meaning you read it as an unsubstantiated comment somewhere here?
This is a common myth that's echoed without a source. It's not patent, it's scale - there are literally 6 billion (LCD) smartphone users out in the world (it might be up to 7B by now), with lots of those users owning multiple smartphones. And of course, there are loads of other devices with LCDs: laptops, desktop monitors, TVs, self-checkout kiosks at supermarkets, smartwatches, tablets, LCDs on a fridge for some reason, etc etc etc.
E-ink is orders of magnitude lower in production scale, without a clear way of expanding the market beyond just ereaders/enotes (which are a luxury; you can read ebooks on a smartphone/tablet and most people own one of those already), and possibly supermarket smart-pricetags.
So, does that mean E-ink faces zero competition? No! DES screens are competing against e-ink with their cofferdam tech (where instead of sprinkling on microcapsules, they capsule structure is built directly onto the substrate; it reduces thickness and theoretically increases pixel density, but loses the "grain" effect of E-Ink's MED in favor of a less-aesthetic regular grid shape).
If E-Ink could improve refresh rates then they absolutely would - it's the most visible feature they could possibly add, and is directly applicable to e-readers, which are currently their biggest market. And their biggest buyer is Amazon, who have poured a whole lot of money into the tech (and who sell Kindles at-cost or below) and if it really were patents blocking faster-refreshing screens then Amazon would just buy E-Ink, outright. It's not new - look up LiquaVista; they were bought up by Amazon, Amazon's not afraid to buy up companies. Plus, E-Ink still have to compete against second-hand e-readers they've already sold; there are E-readers from 2012 that will read a .epub just fine, and that's all you really need for an e-reader.
If you're wondering why Amazon killed LiquaVista, BTW, apparently it's because shrinking the pixels horizontally causes a chromatic aberration effect when the vertical color-layers are viewed from an angle, so shrinking the pixels horizontally also requires shrinking them vertically, which makes it extremely difficult to manufacture the pixels without them leaking and causing a terribly low yield rate. Also it didn't help that a bunch of the original company's VC raising was done just before 2008.