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Regarding the 41 megapixel sensor on the Nokia 808 PureView

Nokia has just announced the Symbian-based 808 PureView at MWC and as you may already know it has a stonking 41 megapixel sensor. In this post I’ll try to explain briefly how the 41 megapixel sensor makes sense and that how Nokia is not out of its mind. 

In a regular digital camera, the number of “pixels” on the sensor are equivalent to the number of pixels that are found in the final image. That is, each of the pixels on the sensor ends up contributing one pixel to the image. 

In low light conditions, not enough light reaches the pixels on the sensor, which results in noise being visible on the final image. Also, as you add more pixels to a sensor without making it larger, the pixels on the sensor become physically smaller and are hence able to capture less light, resulting in noisy images. 

To take care of this situation, phone manufacturers these days use larger sensors and aperture to get in more light on their high resolution sensor. 

What Nokia has done here is use a 41 megapixel sensor, that despite its high resolution count, isn’t exactly that much larger than most phone camera sensor. Which means that the individual pixels on the sensor are even smaller. So how does it all work? 

It’s simple. What Nokia is doing here is called pixel binning, where they combine multiple pixels on the sensor to create one pixel in the final image. In case of the 808, they are using eight physical pixels on the sensor to create one pixel in the final image. So if you divide the 41 megapixels of the sensor by eight, you get 5 megapixels, which is what the actual resolution of the final image will be. 

So how is this better? The answer is in front of you. When you look at an image on your phone or your PC without zooming it 100%, you are recreating a similar effect as pixel binning. That is, you are using multiple pixels of the final image to fill up a single pixel on your phone’s display or your monitor. Because of this images look sharper and noise-free when zoomed out but when you zoom in at 100%, those things become visible. 

Because Nokia is using the information from 41 megapixel to create a 5 megapixel image, the images will have a lot more detail in them and the noise, although present in the original 41 megapixel image, won’t be visible in the final 5 megapixel image because, to put it simply, it has been zoomed out. 

You can try this effect out right now on your PC. Take an extremely high resolution image and downsize it to a much lower resolution, say, VGA. That image will look much sharper and will be more detailed than the one shot natively at VGA resolution. 

So even though 41 megapixels sounds crazy at first, there is a method to this madness. 

Update 1: One major thing I forgot to mention before is zooming. Most phones these days have digital zoom, which basically takes existing pixels and performs a 200% (2x) zoom on them, resulting in a mess, which gets worse as you continue zooming. On these phones, you are operating on a 1:1 scale, that is each pixel of the sensor contributed one pixel to the final image, so there aren’t many (or any) pixels to spare for zooming.

On the 808, the camera uses eight pixels to produce one pixel in the final image, which means there are plenty of pixels to spare. The camera can crop a small portion of the main image and then zoom it and even then each of the pixels in the final image will be made up of several pixels on the sensor. In fact, there are so many pixels on the 808 that you can zoom up to 3x without seeing a drop in quality. If you do that you will still have two pixels on the sensor making up one pixel in the final image. The quality won’t be great anymore but it will still be a lot better than conventional digital zoom.

For something without optical zoom, this is the best way to zoom on a camera. This is digital zooming done right. 

Update 2: You also have the option of using higher resolutions wherein the pixel binning effect is toned down as you go up. The max resolution is 38 megapixels, where I assume no amount of pixel binning is taking place. I saw a few samples at that resolution and they look pretty good but they’re all in bright sunlight. I’m assuming low light performance at that resolution won’t be so great, in which case it would be best to dial down the resolution. Also, zooming with either not be available or be of poor quality at that resolution. 

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