Dual-Mode Display Details


Now you, like I, might be wondering still about the dual-mode display that One Laptop Per Child claims has:

"higher resolution than 95% of the laptop displays on the market today; approximately 1/7th the power consumption; 1/3rd the price; sunlight readability; and room-light readability with the backlight off"
and just how Mary Lou Jepsen achieved this feat.

Well Eric Lundquist asked Mary Lou this very question in his "Knocking Down the Barriers to the $100 Laptop" article for eWeek.com. To quote Mary Lou Jepsen's response:

What I came up with: a dual-mode display. Mode 1 is 800x600 (or higher—even 1024x768 looks surprisingly good!) color backlit with 1W MAX power consumption. Mode 2 is high resolution 1200x900 black and white reflective sunlight readable with 0.2W MAX power consumption. Mode 2 is also room light readable with the backlight off at again 0.2W power consumption. There are several keys to making this display work - they all add up to a large impact.
  1. I changed the pixel layout to diagonal stripes of color—this allowed me to increase and decrease the resolution of the panel horizontally and vertically (not just horizontally, which is what a standard layout would do).

  2. I eliminated part (or all) of the costly color filters with innovative backlight solutions. Truthfully I have a variety of solutions under development right now—the first version of this family of solutions just started working last week. This allows a lot more light throughput and thus much lower power consumption.

  3. I decided to not constrain the pixels to be always a certain color. Any pixel can either be a pre-assigned color or "black and white." This turns out to be more powerful than it seems. The sharpness (or resolution) of the display can be much higher this way.

  4. I eliminated much of the costly interface electronics. This allowed us to use a lower cost novel-TTL interface instead of the now typical LVDS (Low Voltage Differential Signaling). LVDS [is] expensive and power hungry and required for most LCDs for laptop resolution, but because for my display, each pixel can be color or monochrome we can achieve higher resolution than 95% of the laptops on the market today.

  5. Cutting the cost of the optical films in the LCD through innovative liquid crystal "mode" design while increasing again the efficacy of light through them.

  6. Moving to use LEDs in the backlight rather than traditional CCFLs (very small fluorescent lights). This is also better for the environment.
Wow, you go Mary Lou! Of course, folks might just be wondering who you are to be advancing LCD screens beyond anyone's imagination. Might you have display skills?
"I've spent 20 years in the display industry and despite making fantastic laboratory demos of holographic video, projection systems, head-mounted displays, microdisplays, city-block size holograms, and even moon-tv.."
"Moon-TV"? You got me there, I don't even have a clue what that is. I do know that if you want to simulate the One Laptop Per Child dual mode display at home you need to be following the work of Manu Cornet.

He already simulated the laptop's display with Xephyr, showing its color swizzling, antialiasing, and a postprocessing to restore good luminosity. Next up he's introduced "shrinking," reducing the size of images while keeping the color swizzling.

These half-sized images are a preview of the laptop's display as they approximate the OLPC's 200 dpi (vs. the 96 dpi of normal screens). If you want to check out the details, Manu has a review of several theme and graphical elements (fonts, thin lines, buttons, etc.) online.

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What's up with the constant sniping at this project? It may not be perfect or even possible, but it is the only game in town as far as I can tell.
Also the hardware design shows more imagination and innovative problem solving than ANY commercially available laptop, and for 1/4 the price.
It is easy to criticize, but I note a curious lack of suggestions in your posts, other than that the money could be spent on some other unnamed mystery project.


How about spending the $140 million dollars on "One Teacher Per School" (OTPS)