What is lossless zoom and how does it work in the Lumia 1020 and Xperia Z1?

Smartphone cameras have been improving at a rapid pace, and while the field owes credit to many, it is Nokia, and as of late -- Sony -- that are at the helm. Every year, we're treated to larger sensors, more and bigger pixels, larger apertures, OIS, and more features than we can count. But one thing has been missing for a long while now, and that's proper zoom. After all, many a situation necessitate that you either get closer, or miss the shot, and in those cases you're pretty much done for if you have to rely on the traditional digital zoom. Sure, the objects do appear closer, but the price is often a prohibitive loss of detail, as the images are upscaled to the desired resolution with no regard to the actual resolution. Well, thanks to the giant sensors on the Nokia Lumia 1020 and Sony Xperia Z1/Z1 Compact, zoom is no longer a problem. But instead of opting for bulky and noisy zoom lens (Galaxy S4 Zoom), they both rely on their massive resolution in order to get what we call 'lossless' zoom. 


So what's lossless zoom, then? In simple terms, it means that zooming into a scene will only result in a negligible loss in quality. Think of it this way: if your camera shoots a picture in a RAW format, the resulting file will contain all the available information for the photo. But the file will be larger, which is why formats, such as JPEG are common -- they reduce the size of the file, but also the quality of the picture. JPEG is irreversibly 'lossy'. On the other hand, a format like PNG is considered 'lossless' -- information about your photo won't be sacrificed at the alter. Digital to lossless zoom is what JPEG is to PNG. But how does it work in practice? 

Starting with the Nokia 808 PureView, the fabled Finnish manufacturer has been increasing its lead in the camera department ever since. Equipped with a humongous 41-megapixel sensor, the 808 PV is a beast to this date. As you can guess, much of the underlying tech behind the newer, Lumia 1020, was inherited from the 808. Lossless zoom is one of them. Some of you probably don't know this, but despite its massive sensor, the Lumia 1020 typically snaps 5-megapixel photos. Those are not comparable to your everyday 5-megapixel shooter, though, as they have been 'oversampled', meaning that you get 5 million 'super pixels'. These are created by combining information from neighboring pixels, and melding it into one, high-definition pixel. In result, stills are less blurry and noisy, and they're not as prone to artifacts.  

 

But back to zoom -- it's only lossless because there is such an abundance of pixels, as we said -- 34MP/38MP in 16:9/4:3 aspect ratios, respectively. So, instead of upscaling when the level of zoom exceeds the set resolution, the Lumia 1020 can zoom up to x4 in Full HD, without any considerable loss in clarity. As there are less and less extra pixels available as you crank up the zoom, the level of oversampling goes down as you zoom farther and farther, until it reaches zero at x6 zoom in 720p, for example. No further lossless zooming is possible at that point, as the level of zoom will go beyond the capabilities of the sensor, and it'll have to upscale the shots, sacrificing detail. Best of all, since only the central part of the optics is being used during zooming, optical and geometric distortions, and vignetting, are all minimal. 

We've talked quite a bit about Nokia, but that's only because the Sony Xperia Z1 and Z1 Compact and their 20.7-megapixel G Sensor goes for much the same approach. And while the Z1 snaps 8-megapixel shots by default, the massive resolution still allows it crank up the zoom up to x1.8 times, without any significant loss in clarity. So not as impressive, nor as potent, but still a noteworthy feature. 

At the end of the day, while it's good to have the technical side of this down (especially if you're a self-proclaimed photography buff), all you really need to remember is that these two cameraphones will let you zoom into your chosen scene without any considerable drops in performance. 

reference: Nokia [1], [2], Sony