Nokia's PureView 808 smartphone 41 megapixel camera steals the show
Click on an thumbnail to open the original Nokia PureView JPEG image (up to almost 14MB per image)
Nokia's deserved camera reputation
This week the massive Mobile World Congress trade show is on in Barcelona. This is where the majority of new mobile phone handsets are launched each year. It's also where the network operators and technology infrastructure providers unveil their latest products and innovations. Super fast G4 mobile broadband was expected to be the hot topic this year but that ailing Finnish company, Nokia, has stolen all the limelight and it's not actually phone functionality that's causing a storm, it's the camera section of Nokia's new PureView 808 smartphone, complete with 41 megapixel sensor and Carl Zeiss optics. If that's not enough, Nokia has released some sample images that appear to justify claims that the PureView 808 is capable of taking some very impressive photos. You can follow links from thumbnails to these sample images below. For smartphone experts another big surprise is that the PureView 808 handset runs Nokia's old Symbian operating system, eschewing the company's more recent focus on Microsoft's Windows Phone platform.
Click on an thumbnail to open the original Nokia PureView JPEG image (up to almost 14MB per image)
Nokia's deserved camera reputation
Nokia has earned a reputation for installing rather good cameras, branded with Carl Zeiss optics, in their smartphones since the remarkable Nokia N95 back in 2007, which in my opinion was the first camera phone to produce respectable photographic results. The Nokia N8 launched in 2010 was lauded by camera magazines and is probably still the best performing camera in a smartphone even after the recent launch of the Windows platform Nokia Lumia 800, which has a good camera but not a match for the N8's. So, in a way, I'm not surprised by Nokia's continued emphasis on camera quality with the new Nokia PureView 808 launched this week at the Mobile World Congress. But does Nokia meet our expectations or has the company gone megapixel mad?
If you read more respectable articles about sensor resolution, you may have noticed advice that can be summarised as "it's not how many pixels your camera has but how good those pixels are." It's certainly advice that I subscribe to. But does this invalidate Nokia's strategy of cramming 41 million pixels into a relatively small sensor? Nokia actually answers this question quite convincingly. For a start, the PureView 808's sensor is on the large size for even a dedicated compact camera, and a giant among sensors used in most smartphones. It's a 1/1/2" format sensor, 250% larger in area than the sensor used in the Nokia N8. But that was a 12 megapixel part, so the PureView 808 sensor's pixel pitch is actually smaller as there are 341% more pixels in an area 250% larger. For argument's sake, let's give Nokia the benefit of the doubt and assume that pixel quality two years on is the same as that of the N8. But this still doesn't explain why Nokia more than tripled the pixel resolution for the PureView 808.
It's not about pixels for pixels' sake
The PureView 808 sensor has 41 million pixels in total, though not all are actually used. If you use a 4:3 aspect ratio frame, which most compact cameras use, the maximum pixel count is 38 million (7152x5368) and if you use the widescreen 16:9 aspect ratio the pixel count is 34 million (7728x4354). Nokia's sensor is a rare multi-aspect ratio type. The two supported frame aspect ratios use the maximum number of vertical or horizontal pixels; for the 4:3 format all the vertical pixels are used and in the wide screen format all the horizontal pixels are used. This arrangement was pioneered by Panasonic Lumix for its DMC-GH1 and GH2 Micro Four Thirds cameras and so avoids inefficient wastage of the sensor area when changing the aspect ratio of the frame.
Have 41 megapixels but use them cleverly to make a really good 5 megapixel image
Nokia proposes that we use several sensor pixels to build a single image pixel. It's the reverse of interpolation as we usually see it, where additional image pixels are invented from fewer sensor pixels resulting in a large image file but reduced image quality. Although the Nokia PureView 808 has 41 megapixels, Nokia says ignore that - assume your PureView 80's camera is a good quality 5 megapixel one. That means around 8 sensor pixels will contribute to a single image pixel. And, Nokia says, by doing this you get great quality at a lower but more than adequate resolution, even in low light. It also means you can improve the quality of digital zooming.
Combining several sensor pixels to make one image pixel is called pixel 'binning'. Nokia also call it over-sampling. This technique has been used for many years as a way of reducing image noise at high ISO sensitivities. Noise is function of errors in individual pixel values and if you combine enough pixels to make one image pixel you can reduce the impact of severely bad individual pixels. Nevertheless, for most photographers the idea of pixel binning is counter-intuitive. But Nokia argues that for most of us a good quality 5 megapixel image is perfectly adequate for a high quality smartphone. I agree - as long as the quality of those pixels is good. Pixel-binning promises this, but for Nokia it also has another important benefit; endowing the PureView 808 with a good quality zooming function without the bulk, complexity and expense of incorporating zoom optics.
Making digital zoom work a lot better?
There is a function we take for granted with 'proper' cameras and that is the ability to zoom the lens in and out. Zoom lenses are complicated items of optical and mechanical design and they are large and bulky. Digital zooms are dismissed by many for being a lame alternative to optical zooms and with poor results to boot. The Nikon N8 only offered a 2x digital zoom because any greater and image quality would suffer noticeably. If you zoom 2x digitally you effectively crop out 75% of the frame and that, in the case of the N8, leaves you with only 3 megapixel image. With the PureView 808 there are lots more pixels, so at 2x zoom you will have around 10 megapixels to play with or 2 sensor pixels to 1 image pixels. By 2.5x zoom you are at 5 megapixels and that reaches 1 sensor pixel to 1 image pixel. And that's the zooming limit - there is no up-scaling or interpolation that would result in reduced image quality. The comparable zoom range using 4:3 frame mode is 28-70mm.
Nokia also makes some good points comparing its take on digital zoom compared with the traditional optical zoom. There are no motors rearranging the optics as in a zoom lens so zooming is silent. As the zoom crops to the centre of the sensor through its range, the central area of the frame gets sharper and geometric distortion is much lower. Vignetting is also absent near the centre of the frame. Nokia's lens works at f/2.4 and that doesn't have to reduce through the zoom range like most conventional zoom lenses, so shutter speeds are kept at usable levels and Nokia even claims that a combination of a relatively large sensor and a wide aperture can result in nice bokeh, or defocussed backgrounds, something you would normally only expect with a much bigger camera and lens.
Much of the benefits outlined for still photography with Nokia's PureView technology also apply to video movie mode as well. You can record at 1280x720 (720HD) and between 20 and 30 frames per second and with a 4x lossless digital zoom.
Are Nokia's claims believable?
I think they are - at least plausible. I don't see any major flaws in the technology argument but will of course reserve judgment for when I get my hands on a sample PureView 808. The full resolution samples provided by Nokia do look remarkably good, but I don't think Nokia would distribute poor samples in the first place. You can see blue channel noise in the sky areas but many compact cameras exhibit this trait and even some larger ones. Pixel-binning down to 5 megapixels is bound to fix that. But by 2.5x zoom there is no more pixel binning so noise will be more evident. So I expect the best image quality to be at the widest zoom setting that uses all the sensor area. Nokia would say that at 2.5x zoom, although image quality will not be quite as hot, that it will still seriously out-perform any other smartphone camera and that is certainly my expectation.
I certainly like Nokia's thinking and I really do hope that their thinking turns into great results. I can't wait to find out!
Nokia PureView 808 camera 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: 1.4 microns
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