You've seen the kinds of monster photos the Nokia 808 PureView can snap, and read how it's got a digital zoom that doesn't turn everything into a pixelated mess. But how does it actually perform these miracles, and what the hell is Nokia doing shoving a colossal 41-megapixel sensor in a phone anyway?
Nokia's been working in conjunction with the lens masters at Carl Zeiss for ages, but it set about the PureView technology project five years ago. The duo set out to revolutionise the camera phone market with "the next benchmark in imaging". Nokia believes that rudimentary megapixel bumps aren't worth the silicon, and that you have to at least double the resolution of the photo to actually see any convincing difference. Not to mention that 5MP images are enough for any consumer; it's just the way you create them that needs revolutionising.
It took an incredible number of man-hours and research to overcome the various challenges related to upping the ante in the imaging stakes. Nokia discovered that customers wanted a 3x zoom, but the problem was that optical zooms on a camera phone are near impossible due to size, and they reduce the amount of light you can get onto the relatively small sensor anyway. So the answer was a zoom that you could do purely digitally, and that wasn't a piece of garbage.
5MP is the ideal image size according to Nokia, so to zoom three-fold on a 5MP image you have to have a much higher resolution sensor. Doing the maths, it works out that you need a 41MP image sensor to get a 3x zoom without having to stretch and expand pixels, destroying the quality of the image in the process. What Nokia decided was the best approach was to use "oversampling".
The PureView technology takes 41-megapixels' worth of information and condenses it down to 5MP. In essence, 7 individual pixels are collated together and combined into one "superpixel". This process means you benefit from the same amount of light that would hit the much larger pixels of a 5MP sensor, if it fitted into the same physical footprint. You benefit from solid low-light performance and at the same time you can remove noise and digital artefacts from individual pixels through the oversampling process. It's all done at the raw sensor information level too, but its lightning quick utilising a dedicated processor to get the job done. The result is a super crisp 5MP image that's much sharper, with greater detail than an ordinary 5MP sensor can achieve.
Producing razor sharp images is all well and good, but having that massive sensor (as you can see above compared to regular camera phone sensors) allows lossless digital zoom too. It works by essentially zooming in on a 5MP patch on the image sensor. As you zoom the oversampling is decreased until you're seeing actual pixels -- you never go beyond real pixel information. You gradually lose oversampling, but it's not the kind of interpolation that digital zoom is marred with. The result is quite impressive, and certainly adds to the utility of a phone camera without the extra bulk of a moving optical zoom lens assembly.
Nokia and Carl Zeiss are quick to stress that massive megapixels aren't the be all and end all. Quality optics and intelligent image processing are just as important when you're trying to squeeze that kind of raw power into a phone. Carl Zeiss managed to make a relatively compact lens for the size of the sensor complete with a low f/2.4 aperture. While this is on par with the likes of the iPhone 4S, compact cameras normally fall in the 3 to 5 range so it has them soundly beaten. In general, the lower the f number the more light can hit the sensor resulting in better low-light performance. It also produces a faster potential shutter speed, so your pictures are sharper, even when you've got a bit of the shakes.
There's one big draw back to the current implementation of Nokia's PureView and that's size. The 808 PureView is a bit of a chubster, and Nokia's very aware that anorexic phones are the name of the game. To that end we're going to see the PureView technology in other guises. Nokia specifically said that it wouldn't just be restricted to 41MP sensors, and the bulk that comes with it.
That doesn't mean Nokia will skimp on imaging prowess though -- any PureView-packing phone will supposedly be the "best possible camera phone" in its class. That should give hope to anyone with skinny jeans looking for the next step in the camera phone revolution. Nokia's not done optimising the current 41MP form from the 808 either -- the next implementation should be smaller, although Carl Zeiss admits that there are physical limits to how small you can make a lens to fit the size of sensor due to the pure physics of optics.
At any rate you should be excited to see what Nokia's PureView technology is going to bring to the Lumia range. If it's able to replicate the kind of impressive picture quality and detail the 808 PureView is capable of, in a smaller, slimmer package, the next Lumia might be something truly lust worthy. I can't wait to see what it's got up its sleeve.