An attempt to explain the logic behind Nokia's 41 megapixel PureView 808 smartphone

Nokia's new PureView 808 smartphone has a camera sensor with no less than 41 megapixels, but Nokia is happy to refer to it as a 5 megapixel camera

Nokia is making waves at the Mobile World Congress in Barcelona this week because of its seemingly outrageous 41 megapixel camera phone, the PureView 808, launched at the event. I've covered this story and explained the technology rationale behind the PureView 808 and, with the reservation that I haven't seen or used one of these new smartphones yet, I have to say that the imaginative use of such a high resolution sensor does have theoretical logic on its side.

So I thought a simple demonstration of the principle of pixel binning, which is at the heart of the Nokia PureView 808, might be fun. Below is a section of a much larger image cropped for demonstration purposes. It's clearly noisy, with a reasonable level of grain. But if you click on the image you will open up the same image before it was reduced in size.



Click on the image to see the original, warts and and all, before it was shrunk

Although this is an artificial exercise I'm sure you can see that the process of reducing the size of an image, combining several pixels into one new pixel, or a 'super pixel' as Nokia calls them, much of the disturbing detail flaws, including chroma noise, in the original image are filtered out.

Most computer screens are limited to around 1920 pixels in width (the resolution of a 1080HD screen) and many are even smaller than that. If you re-size a modern camera image to fit onto the web you are doing the same thing, creating one new pixel out of several original pixels and in the process much unwanted detail in the form of noise becomes muted or disappears altogether.

Take our users' photo gallery - we recommend 800 pixel wide or tall images for best on-screen display. If your camera has a 12 megapixel sensor then that 800 pixels may well have been reduced from around 4000 original pixels, making one new pixel from five original ones. If you use the gallery you may have noticed that images that were marginal when examining them at pixel level can look rather better at screen resolution after re-sizing. Now you know why.

Nokia says that despite the PureView 808 having a 41 megapixel sensor, it was designed to deliver a really good quality 5 megapixel image. One of my best ever A3 prints came from a 3 megapixel camera, which is why I strongly believe that the quality of image pixels is often much more important than how many you have to start with. Nokia's theory that combining several pixels to make one better quality pixels does make a lot of sense. The PureView 808 has the best of both worlds - a marketing department's dream pixel count and a real-world ambition to deliver the best smartphone photo image quality by creating an image with less than the average number of pixels.

It all seems contradictory, but if you think about it - it does make sense. I just hope the final product lives up to the technology hype - I'm optimistic it will. And if it does, could this spark off a new generation of conventional cameras that employ even higher resolution sensors?