LCD is the answer? To what question?
I'm reading this ETech Preview article and having a hard time reconciling the observations and predictions there like "LCD is the cool new technology" with real life data and technology curves.
The article described the OLPC display as "OLPC's breakthrough low-power transflective display". I too had believed that once. These days, I just have questions and concerns. This OLPC teardown article in EETimes by Porteligent teardown expert David Carrey shares one. That article states:
"The dual-mode LCD--supplied by AUO--is a curious bit of technology. Despite much talk of fancy diffraction gratings and other trickery to implement a combination color-backlit and monochrome-reflective display, we couldn't detect anything other than a fairly standard pixel stackup and construction vs. a standard transflective-LCD construction. The RGB pixel filter arrangement is based on diagonal striping instead of the normal adjacent RGB triad, and thus requires some special addressing and dithering. Otherwise, we saw little evidence of a radical approach to the LCD."
So.. when I see "bring the revolutionary engineering used in the XO to the broader consumer market", I find myself struggling to understand what the facts are. Don't get me wrong, I'm not interested in putting down anyone's efforts, I would just like to understand the details. A bit of accurate technical information and perhaps a response to David's article would be nice to see.
The article also states:
"I have a Kindle and I have to hit the page turn button when I'm three-quarters of the way down the page, and wait for it to refresh while I read the rest of the page. And then if I get stuck on something, then I have to go back. And we really need something with video, or a way to do fast page change and color. And I believe it's actually a lot easier to do that with standard LCD."
A full grayscale page update time on a Vizplex display with a broadsheet controller (in Kindle-2 and Sony PRS700) is 800ms. A black-and-white update is 260ms. I've not encountered a scenario where there's a serious usability issue like "wait for it to refresh while I read the rest of the page" with any E-Ink display panel from the last year. I'm able to show that a low spec electrophoretic system with minimal software optimization is able to do fairly reasonable interactive content (fennec on e-ink, live drawing with rgbpaint) even with standard uncustomized apps. The latency issues (beyond the stated update numbers) in my demonstrations thus far are software limitations rather than hardware imposed constraints.
I agree with the article that current electrophoretic technology is not yet satisfactory for displaying video. I also agree that the technology path to get color with electrophoretic displays may lead to incomplete color gamuts and non-optimal reflectivity. I don't dispute the "a lot easier to do that with standard LCD" part but I think that's an odd comparison to make. The LCD will always consume static power. That is, you have to power the display to hold the image. That's an apple. The electrophoretic scenario consumes no static power. It is non-volatile. That's an orange.
"And one of the advantages of electrophoretic is supposed to be the power consumption, in that you don't need to refresh the screen every 30th or 60th of a second, with all of the pixels, and doing that takes power, because it holds its charge. But as a result, you have to unwrite the charge before you can write something in. And the voltage which you have rewrite it at is hard. And so if you actually look in at the details, the advantage, kind of when looked at from a systems perspective, according to everything that we know, it kind of disappears."
Ok, I think this is unfair. What voltage problem? Yes, there's power needed to update the display and of course there's voltage on the gate drivers but its not a problem. How is that significantly different from the source/gate drives on an LCD panel? If there is a problem, I'd like to know exactly what that is . Taken from a systems perspective, there is an order of magnitude difference in power consumption between an LCD display and an electrophoretic display. That's why the e-book readers of the past 2 years have been using electrophoretic displays rather than LCDs. Statements like "it kind of disappears" without explaining the details of how such a conclusion can be drawn seem problematic to me.
"I run Linux, pretty nice. I run Ubuntu. And still the question, is what's the motherboard doing on? What's the CPU doing on? What is all of that doing on right now when nothing is changing..."
Yay, now that is a reasonable issue!
The article described the OLPC display as "OLPC's breakthrough low-power transflective display". I too had believed that once. These days, I just have questions and concerns. This OLPC teardown article in EETimes by Porteligent teardown expert David Carrey shares one. That article states:
"The dual-mode LCD--supplied by AUO--is a curious bit of technology. Despite much talk of fancy diffraction gratings and other trickery to implement a combination color-backlit and monochrome-reflective display, we couldn't detect anything other than a fairly standard pixel stackup and construction vs. a standard transflective-LCD construction. The RGB pixel filter arrangement is based on diagonal striping instead of the normal adjacent RGB triad, and thus requires some special addressing and dithering. Otherwise, we saw little evidence of a radical approach to the LCD."
So.. when I see "bring the revolutionary engineering used in the XO to the broader consumer market", I find myself struggling to understand what the facts are. Don't get me wrong, I'm not interested in putting down anyone's efforts, I would just like to understand the details. A bit of accurate technical information and perhaps a response to David's article would be nice to see.
The article also states:
"I have a Kindle and I have to hit the page turn button when I'm three-quarters of the way down the page, and wait for it to refresh while I read the rest of the page. And then if I get stuck on something, then I have to go back. And we really need something with video, or a way to do fast page change and color. And I believe it's actually a lot easier to do that with standard LCD."
A full grayscale page update time on a Vizplex display with a broadsheet controller (in Kindle-2 and Sony PRS700) is 800ms. A black-and-white update is 260ms. I've not encountered a scenario where there's a serious usability issue like "wait for it to refresh while I read the rest of the page" with any E-Ink display panel from the last year. I'm able to show that a low spec electrophoretic system with minimal software optimization is able to do fairly reasonable interactive content (fennec on e-ink, live drawing with rgbpaint) even with standard uncustomized apps. The latency issues (beyond the stated update numbers) in my demonstrations thus far are software limitations rather than hardware imposed constraints.
I agree with the article that current electrophoretic technology is not yet satisfactory for displaying video. I also agree that the technology path to get color with electrophoretic displays may lead to incomplete color gamuts and non-optimal reflectivity. I don't dispute the "a lot easier to do that with standard LCD" part but I think that's an odd comparison to make. The LCD will always consume static power. That is, you have to power the display to hold the image. That's an apple. The electrophoretic scenario consumes no static power. It is non-volatile. That's an orange.
"And one of the advantages of electrophoretic is supposed to be the power consumption, in that you don't need to refresh the screen every 30th or 60th of a second, with all of the pixels, and doing that takes power, because it holds its charge. But as a result, you have to unwrite the charge before you can write something in. And the voltage which you have rewrite it at is hard. And so if you actually look in at the details, the advantage, kind of when looked at from a systems perspective, according to everything that we know, it kind of disappears."
Ok, I think this is unfair. What voltage problem? Yes, there's power needed to update the display and of course there's voltage on the gate drivers but its not a problem. How is that significantly different from the source/gate drives on an LCD panel? If there is a problem, I'd like to know exactly what that is . Taken from a systems perspective, there is an order of magnitude difference in power consumption between an LCD display and an electrophoretic display. That's why the e-book readers of the past 2 years have been using electrophoretic displays rather than LCDs. Statements like "it kind of disappears" without explaining the details of how such a conclusion can be drawn seem problematic to me.
"I run Linux, pretty nice. I run Ubuntu. And still the question, is what's the motherboard doing on? What's the CPU doing on? What is all of that doing on right now when nothing is changing..."
Yay, now that is a reasonable issue!
Labels: olpc-en
posted by jayakumar at 3:38 PM
7 Comments:
Please excuse the awful quality of the pictures; I took them with my phone camera.
Wax on
Wax off
I don't understand what you mean by wax on, wax off. What would you like to communicate here?
To make sure, I'm being clear and not being dense. A transflective LCD is a standard thing. The point is nothing unique or new about that, if that is what you're trying to convey by saying wax on, wax off. Further, if your intent with the pictures was to show the quality of the LCD, thank you, I have an XO-1. By coincidence, I'm the author of the cs5535audio driver that is used for the XO-1.
Fair enough. What I was trying to show was the difference between full illumination and no illumination; I guess their "big deal" is that they're so used to laptop LCD displays being solid black (and therefore invisible with no illumination) that seeing something that does it differently is new to them. I guess they don't look at pocket calculators very often.
Indeed, the diffraction grating did not make it into production, the XO uses regular color filters. The ingenuity in the panel design is in fact to not having expensive new features in there, but recombining existing ones to get a cheap high-quality display. Yes anybody could have done that in hind sight so it's easy to dismiss now.
One of the genius ideas is to put the color filters behind the reflective layer, so that in much more light is reflected (albeit without color). The unique pixel layout produces a very sharp 200 dpi image using a much cheaper panel that could otherwise only display around 100 dpi. And you can consider the DCON chip as part of the display, which reduces the power consumption when used as an e-book, the cpu can be powered off while the screen stays on.
Bert, I think it is worse than just people dismissing it as a simple idea. The assessment is that the display is no different than a normal transflective display.The EETimes article which I linked to says: "we couldn't detect anything other than a fairly standard pixel stackup and construction vs. a standard transflective-LCD construction.". I'm not an expert. I'm just a curious engineer, so I read the article and then also asked several people who had examined the OLPC display. The conclusion was identical. Perhaps all 3 of those individuals and the article is wrong. If so, then OLPC ought to publicize a document to explain how their design is different. That would correct the perception if it was wrong. Open discussion and debate would be the best way to prove what is true.
Also, are you saying that prior to OLPC, no one ever built a transflective LCD with the color filter behind the half mirror? I don't know the answer, I just want to know if that is what you are saying.
Your remark about DCON is understood. But that's not unique to OLPC either. Many embedded devices have buffered LCDs that can keep the LCD active while the CPU can be fully hibernated. I believe there's even a standard that encompasses this concept: MIPI-DSI controllers are controllers that support buffered LCDs so the host can suspend without losing display output.
As far as I know, putting the filters behind the reflection layer is indeed new. Doing away with sub-pixels for a color display seems new, but only makes sense with the filters behind. The DCON does the required color swizzling and anti-aliasing, and use of a buffered LCD is new at least for laptops (at much higher res). EETimes remarks on the LEDs but fails to mention how OLPC got the cost down while getting high quality (which is why LED backlights are usually more expensive): by color-matching high-tolerance cheap white LEDs in batches instead of using low-tolerance expensive LEDs as other manufacturers do.
If there was anything "fancy" in the display that could not be manufactured in a standard LCD plant the screen would have become expensive. That's why you won't see anything unusual by popping the hood open. Reminds me of the blind men and the elephant ...
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