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Archive for February, 2012

The secret behind Nokia’s 41-megapixel camera phone

Saying a smartphone has an excellent 5-megapixel camera doesn’t make for good headlines, but that’s what Nokia’s promising with its 41-megapixel 808 PureView. Well, that, and a usable digital zoom.

When Nokia announced the 41-megapixel 808 PureView smartphone at MWC 2012, CNET’s associate editor Lynn La said “it is a phone that has so many megapixels, its megapixels have megapixels.” That, it turns out, was a pretty accurate statement.

But, before I get into what that all means, judging by comments I’ve read there seems to be some confusion about the largeness of the sensor. The 808’s image sensor is not only larger in resolution, but physical size. It’s larger than the ones in most–if not all–current smartphones as well as the majority of point-and-shoots.

Nokia conquers the camera phone with the 808 PureView (photos)


The 8-megapixel iPhone 4S, for example, has a 1/3.2-inch type sensor while most compact cameras use a 1/2.3-inch type sensor. The 808’s in comparison is a 1/1.2-inch type, which is quite a large sensor for a mobile device. (Do the division and you get the approximate diagonal measurement of the sensor.) That’s 2.5 times larger than the one Nokia used in its 12-megapixel N8.

Of course, packing a larger sensor with more than three times the number of pixels doesn’t translate into better photos: smaller pixels collect less light, which worsens image quality. The thing is, Nokia doesn’t really want you to use the full resolution of its sensor. Not for giant photos, anyway.

Instead, the 808 defaults to a 5-megapixel resolution. Through a process called pixel oversampling (though some might call it pixel binning), Nokia combines seven pixels into one superpixel. Doing that helps eliminate image noise in low-light conditions and, according to Nokia, makes noise virtually nonexistent when shooting in good lighting. So while the 808 can be set to take 38- or 34-megapixel images depending on the aspect ratio used–4:3 or 16:9, respectively–it’s not why Nokia used such a high-resolution sensor.

The pixel oversampling also allowed Nokia to develop a lossless digital zoom, which is probably the most important part for a lot of people. Basically, as you zoom out the amount of oversampling reduces until you’ve reached the limit of the actual resolution. In other words, if you have it set for 5 megapixels you can continue to zoom until it’s no longer oversampling and simply using a 5-megapixel area of the sensor. There is no upscaling or interpolation, it’s just a 5-megapixel photo. At that resolution, it will give you about a 3x lossless zoom for photos and a 4x zoom for movies shot in full HD. Reduce the resolution, and you get more lossless zoom.

For controlling the zoom, Nokia’s added a new slide zoom feature that lets you slide your finger up and down anywhere on the display to smoothly move in and out. And with no moving optics, you won’t hear the zoom while recording.

Speaking of optics, Nokia’s lens choice makes things even more interesting. The Carl Zeiss 5-element lens has one high-index, low-dispersion glass lens instead of being all plastic like other smartphones. It has a large f2.4 aperture with a 26mm focal length for 16:9 and 28mm for 4:3. Nokia claims the combination along with the large sensor size will give you some nice background blur for close-ups; the 808 can focus as close as 6 inches from a subject. (Add in the lossless zoom and you can get very close to what you’re shooting and presumably still get great fine detail.)

Also, with no optical zoom, the camera uses the f2.4 aperture through the range of the zoom. Optical zooms on compact cameras use increasingly smaller apertures as you extend the lens, which means you have to use higher ISO sensitivities and slower shutter speeds to avoid blur. The 808’s f2.4 lens and digital zoom won’t have that issue, so it can keep ISO low for less noise and still use faster shutter speeds.

If you’re interested in more details on all that the sensor, lens, and processing combination of the Nokia 808 PureView has to offer, read Nokia’s white paper on the subject.

Lastly, I’ve seen some mentions that this is comparable to Lytro’s sensor technology, but it’s really not. Lytro’s sensor design is unique, while the 808’s sensor is pretty much a traditional design just with a super-high resolution, which Nokia takes full advantage of to produce better photos.

At least, that’s what Nokia’s saying. We’ll have to wait till we get our hands on one to know for sure.

Why You Can’t Dismiss Nokia’s 41-Megapixel Phone

My first reaction upon hearing about Nokia’s 41-megapixel 808 Pureview was that it was an absurdity, a perfect example of the very worst of consumer electronics, and a total miss. But the more I read, the better I understood that this phone isn’t just some freak of nature with a ridiculously high number attached to it. It’s just the slightly awkward first steps of a serious move by Nokia to differentiate itself.

If you’ve only skimmed the news, there are some things you should probably know about this strange beast of a camera.

First, the 41 megapixel figure is really misrepresentative, not to say untrue. It doesn’t take 41-megapixel photos in any way, shape, or form. Even in the special high-res creative mode, it “only” produces 38 megapixels. Mostly it will be taking normal-size shots, between 3 and 8 megapixels. So what the hell does this 41 megapixel figure even mean?

It means Nokia is being smart about the way cameras at this size actually work. I wrote a while back about how HD does not always mean high definition, and cameraphones were an excellent example of this. Their tiny sensors and bad lenses meant that while they may produce pictures of a certain size, the quality was sorely lacking. This was because they insisted on wringing every possible pixel out of an incredibly small sensor.

The 808′s sensor (supposedly manufactured by Toshiba) is not small. At 1/1.2″, it’s four or five times the size of most cameraphone sensors, including the one in the iPhone 4S. Bigger in fact than the sensors in most point-and-shoots. Now, when you make your sensor bigger, you can either keep the same resolution but have bigger wells or photosites (which detect light and make up pixels), which usually improves sensitivity. Or you can keep the same photosite size and just put more of them on the sensor, which improves resolution. In this case Nokia has done the second thing.

But they’ve done it almost to an absurd amount, and they know that their lens, good as it is (and fairly fast — F/2.4 is solid, though there’s lots of distortion right now), can’t really resolve detail well enough that 41 megapixels would be necessary. Even on full-frame cameras that many pixels is questionable.

So instead of just bumping this one spec and expecting it to sell itself, they built a whole photo system around the idea. The 808 camera doesn’t take 41-megapixel photos; it collects 41 megapixels of data and uses all that data to create a very nice photo of a much smaller size. Imagine a photo around 8000×5000 pixels that isn’t particularly sharp; now shrink it down to something significantly smaller — maybe around 3000×2500 pixels (~8MP), just as an estimate. You do it intelligently, sharpening and de-aliasing and doing noise removal.

Here’s a rough estimate of the sizes (DPReview lists more specs):

They’re using 41 megapixels of raw material to give you 8 megapixels of product. And that 8 megapixel product is going to be significantly better than a “real” 8-megapixel image captured by a sensor a quarter the size of your pinky fingernail. Their camera really is better.

Of course, this comes with the standard caveat that independent testing must be done and what really matters is how it performs in everyday situations like dimly lit kitchens, restaurants, and out of the windows of cars. We’ll try it out ourselves, and will be sure to let you know if any more photographically-inclined authorities find out anything interesting.

The other shoe

And then there’s the handset itself. It’s chunky, it’s a weird shape, the camera sticks out the back. And it runs Symbian. Symbian! Why would Nokia do such a thing?

Because this project has been going on for five years, and five years ago the idea that Nokia and Symbian would be fighting for dear life wouldn’t quite have been believed. Nokia was still king of the world, iOS was just being born, and everyone was looking forward to Limo instead of Android.

They’re running it on Symbian because it was designed for Symbian, and it was too late to port the software and adapt the hardware to Windows Phone 7, which came along at the 11th hour, and at any rate the design spec for their Lumia phones would never have admitted a lens bump like the 808′s.

But they’re promising to bring the whole package to WP7 — which means Microsoft just got five years of Nokia R&D for free. It also means that if these guys play their cards right (a big “if”), WP7 could be the de facto gold standard for mobile photography in a year or two. When you consider how point and shoots are giving way to camera phones, and WP7 is aiming at the exact population that loves point and shoots, the pieces start looking very complementary indeed.

Nobody will buy the 808. It’s an evolutionary dead end. But the camera is a desirable trait that will be introduced to the Nokia-Microsoft hybrid soon — if either of these companies has any sense. Again, that’s a big if.

But this camera has restored some of my faith in Nokia and in mobile photography, something I trulydidn’t expect to happen any time soon, and not by them of all.

41MP Nokia 808 smartphone hints at pixel-binning future for small sensor cameras

Nokia has made the startling announcement that it has created a 41MP smartphone, the Nokia 808 PureView. Interestingly, in most shooting modes the camera will output 3, 5MP or 8MP stills, rather than offering its full resolution – promising greater quality and offering some clever features. And this isn’t a trade-show concept model, this is a product that will be offered to the public, though details of when and in which countries haven’t been announced. What’s interesting isn’t so much the pixel count as how it’s used, so we took a closer look.

The first thing to realize is that this isn’t a standard 1/3.2″ mobile phone sensor, it’s an unusual and remarkably large 1/1.2″ type (five times larger). In fact, it’s almost three times the size of the sensors in most compact cameras. As a result, its photosites are the same size as those in most 8.2MP cameraphone but the 808 doesn’t try to create an image of the same quality, 5 times bigger. Instead it oversamples the image and then pixel-bins down to a smaller size (though there is a special ‘creative’ shooting mode if you want the full resolution – 38MP at 4:3 aspect ratio, 36MP at 16:9).

Diagram showing the size of the Nokia 808 PureView’s 1/1.2″ sensor in comparison to those used in various compact cameras and mobile phones. A Four Thirds sensor is included for scale.

This pixel-binning means that noise (which occurs randomly) is averaged-out across multiple pixels (around 7-to-1 in the 5MP mode). The high native pixel count also means that it’s possible to effectively ‘zoom’ by cropping into the center of the image and reducing the number of pixels you average together. Consequently the 808 can offer a roughly 2.8x ‘zoom,’ while maintaining 5MP output, despite having a fixed lens. The image quality will drop (since the noise is no longer being averaged out), but it does mean you get a roughly 28-78mm equivalent zoom, without the need to have moving lens elements, making the process fast and silent. It also means the lens’ 15cm minimum focusing distance is maintained.

And, although the benefits of pixel-binning are lost as you magnify-in, because its photosites are the same size as contemporary 8MP phones, the resulting 5MP should offer the same pixel-level quality even at full magnification.

The same process allows 1080p video to be shot with a 4x cropping zoom.

Much like the Panasonic LX and GH cameras, the Nokia 808 uses an over-sized sensor to maximize the area used to offer different aspect-ratio images.

Despite the large sensor and comparatively large f/2.4 aperture, you won’t get much control over depth of field (it’ll be equivalent to setting an APS-C DSLR’s kit lens to 18mm f/5.6). The depth-of-field control is reduced still further when magnified-in, because it doesn’t gain the shallower depth of field that longer physical focal lengths usually bring. So, while it’s an improvement over most phones, we wouldn’t put much faith in the Nokia white paper’s talk of bokeh.

The interesting thing for us, though, is not the Panasonic-esque multi-aspect-ratio use of the sensor, nor the astonishing pixel count, it’s the idea of using that high pixel count to offer lower noise or non-interpolated digital zooming, while maintaining a constant image size. As Nokia’s blog points out:

‘5Mpix-6Mpix is more than enough for viewing images on PC, TV, online or smartphones. After all, how often do we print images bigger than even A4? [It] isn’t about shooting pictures the size of billboards! Instead, it’s about creating amazing pictures at normal, manageable sizes.’

And that’s something that might be interesting to see in future compact cameras – models that will concentrate on output of a sensible size so that the user can easily get the benefit of them oversampling the scene.

Click here to read Nokia’s blog post about the 808 PureView, which includes more detail about the phone’s other features.

And click here to read the company’s white-paper on the technology underpinning it.

Nokia 808 PureView lens and sensor specifications

  • Carl Zeiss Optics
  • Focal length: 8.02mm
  • 35mm equivalent focal length: 26mm, 16:9 | 28mm, 4:3
  • F-number: f/2.4
  • Focus range: 15cm – Infinity (throughout the zoom range)
  • Construction:
    • 5 elements, 1 group. All lens surfaces are aspherical
    • One high-index, low-dispersion glass mould lens
    • Mechanical shutter with neutral density filter
  • Optical format: 1/1.2”
  • Total number of pixels: 7728 x 5368
  • Pixel Size: 1.4um

Nokia’s sample images:

Nokia's sample images:

Nokia's sample images:

Nokia's sample images:

Nokia's sample images:

Nokia's sample images:

Nokia's sample images:

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