You won’t be actually able to take 41MP photos using Nokia 808 PureView

by Arun Vishnu · Published March 1, 2012 · Updated March 1, 2012

Nokia announced the Nokia 808 PureView 41MP smartphone. It has a 41MP cam, but can you take a 41MP photo using 808? Answer is NO. So why they are saying it’s a 41MP cam?

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. 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.

The 808 defaults to a 5-megapixel resolution and the large sensor enables pixel oversampling(pixel binning) which combines several pixels into one superpixel. The technology means that taking typically sized shots (say, 5 megapixels) the camera can use oversampling to combine up to seven pixels into one “pure” pixel, eliminating the visual noise found on other mobile phone cameras. On top of that, you can zoom in up to 3X without losing any of the details in your shot – and there’s no artificially created pixels in your picture, either.

Confused? Ok let me explain. Do you know the difference between digital zoom and optical zoom?

Optical zoom is what I like to call true zoom. This function of a camera uses the lens within the camera to draw the image closer. Using the optics of the camera the image is bought forward much the same way as binoculars and other such instruments. When using optical zoom quality remains the same and the full resolution of the camera can be used on the zoomed image. Different levels of optical zoom can be achieved by changing the distances between the lens’. The motion of the front lens moving outwards on a camera is the lens achieving a greater level of zoom.

The idea behind digital zoom is that it takes a portion of the image and expand that image to the full size of the picture. What happens here is that the section of image that you are looking at becomes bigger, not closer. The image does look closer because it has been expanded however all that has happened is that the image quality has been reduced because it has been expanded with no new data for the image.

All camera phones has option to zoom, but since they don’t have a moving lens, they have only digital zoom. So what will happens when you zoom? They just magnify the image and the result will be a low quality/clarity image. But in Nokia 808, if you are taking photos in the default mode(5MP), you can zoom up to 3x without loosing the image quality. How this it is possible without a moving lens? Using the 41MP sensor and oversampling technology. When you zoom, 808 just reduces the number of pixels use to create a super pixel so you will not loose the quality like in other phones. 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.

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

The zoom function is completely silent — which is really important when shooting video.

You can use ‘Creative Shooting Mode’ to capture images at high resolution – 38 megapixels; then reframe, crop and zoom to find the best “picture within the picture” after the image has been shot and before saving it at convenient sizes for sharing and storage.

Depending on the aspect ratio you choose, it will use 7728 x 4354 pixels for
16:9 images/videos, or 7152 x 5368 pixels for 4:3 images/videos as is shown in Figure 1.

Actually you don’t need to take a 41MP image because 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? Nokia also says “It isn’t about shooting pictures the size of billboards! Instead, it’s about creating amazing pictures at normal, manageable sizes.”

If you rarely print your images or don’t need them larger than A3 size, 5Mpix is more than enough. In fact, you can get superb poster prints as large as 50 x 75cm (the size limit of most commercial printers) from very good quality 3Mpix images. Of course, if your needs are different, there is a higher resolution 8Mpix setting and a ‘full resolution’ mode on the Nokia 808 PureView. If you only ever view images on TV, PC or tablet, or upload to social sharing sites, we’ve provided an ideal 2Mpix lower-resolution setting. Oversampling is even greater here, and there’s an increased lossless zoom.

lens

The Carl Zeiss 5-element lens use in 808 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.

Oversampling eliminates Bayer pattern problems. For example, conventional 8MPix sensors include only
4Mpix green, 2Mpix red and 2Mpix blue pixels, which are interpolated to 8Mpix R, G, B image. With pixel
oversampling, all pixels become true R, G, and B pixels. What’s more, based on Nyqvist theorem, you
actually need oversampling for good performance. For example, audio needs to be sampled at 44 kHz
to get good 22 kHz quality.

The technology:

PureView Pro imaging specifications

41Mpix sensor with pixel oversampling
Lossless zoom: 3x for stills, 4x for full HD 1080p video
Carl Zeiss optics

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: 1.4 micron