After reading an essay by Robert Falck, which presumably is a response to a widely circulated rumour (see: CNet or Cult of Mac), I also had to wonder about the plausibility of a 3D display in an iPad. I won't revisit the arguments from Robert's piece (it is worth your time to read) but I do wish to argue from a similar vantage point. I believe there are severe problems with any projections of the next iPad using similar display technology as Nintendo's 3DS.
Nintendo's handheld seems like a fairly convincing analogue for the rumoured "iPad 3" because it is the only (effective?) consumer device which has a glasses-free 3D screen. To quickly recap: the 3DS uses a autostereoscopic parallax barrier to trick the brain into seeing a three-dimensional image from two flat images displayed simultaneously on screen. Each image is viewed by only a single eye and is kept out of sight of the other via the parallax barrier. There are a number of other glasses-free 3D technologies but this technology appears to be simple enough for mass market production and requires little to no software overhead.
This technology works fine and dandy on the handheld's smaller screen, but I cannot imagine the same can be said for the rumoured iPad. There are numerous reports of the 3DS' screen suffering from narrow viewing angles. Not a huge issue with a small handheld gaming machine whose light weight allows for it to be held in the "sweet" spot, but I suspect it will be a significant grievance for a larger screened and heavier iPad. Simply put, the opportunities to hold either a) your body or b) the device at the perfect angle merely to allow for the 3D effect are minimal, especially in a mobile environment.
Another factor which could pose serious problems for these rumours would be the screen's own resolution. For the parallax barrier to allow the 3D effect there needs to be two images shown on screen at the same time. If the iPad were to maintain a resolution of 1024x768, the physical number of horizontal pixels would need to double, hence the resolution of the iPad's screen would actually be 2048x768. I don't believe there are any products on the market with this resolution (on a single screen), the closest being an interesting range of televisions by Philips.
It is certainly possible for Apple to manufacture displays with this resolution, I'd wager this is unlikely but it is still possible. Notice that the iPad that I have described thus far is not completely analogous to the Nintendo 3DS because this version of the iPad has a fixed 3D depth whereas the 3DS has the capability to modify the depth all the way to being strictly 2D. If the iPad also had similar capabilities would that solve the issues I have argued thus far? Yes and No.
The viewing angles would be the exact same as the current iPad if the depth was set to zero, therefore prohibitively narrow viewing angles would only be a partial issue (i.e., only in 3D mode). Before the discussion gets away from us remember the resolution issue I mentioned earlier. If the display depth is set to zero, then there is no need to display two images on screen, so what happens to the onscreen image when the other half of the horizontal resolution is no longer occupied? Either the single image takes up the entire resolution, the image is expanded to fill the space while keeping the same resolution (i.e., stretching), or the image displays at its native resolution with areas of unused screen on either side (similar to the letter box effect on your television set), or the resolution of the single image is switched to occupy all of the vacant space. Obviously none of these solutions makes sense for a well polished and thoughtful product designed by Apple.
While I cannot conclude definitely whether the "iPad 3" will feature a 3D display or not, I must say that the screen technology from the 3DS is not a good fit. Apple has enough money lying about to make anything happen but taking this cue from Nintendo doesn't seem to be up their alley.