Digital Lossless Zoom explanation

Nokia has released their new Nokia Lumia 1020 phones and I want to shed some light on the technology they are trying to push with their latest mobile phones. It’s nothing new, I’ve been using it on my Olympus cameras for years and I’m sure others use it as well, but this is really the first time anyone has been using this technology in mobile phones (apart from its predecessor Nokia Lumia 808 of course). Other companies may use different names for it, I call it “Digital Lossless Zoom” or DLZ. Nokia calls it just “high resolution 3x zoom”…

What is the main benefit of DLZ?

Main benefit of DLZ is that you don’t really need mechanical lenses to do the zooming job, but you don’t lose the image quality either when zooming. All you need is a very high density optical sensor that can capture images at very high resolutions (or many many megapixels for regular Joe’s) As a result, this technology is ideal for mobile phones where you want compact dimensions (low thickness). Plus, since there aren’t any moving parts, power consumption is also lower and there is far lower chance of mechanical malfunction compared to traditional lenses.

Why is DLZ clever?

In the past, it was very problematic to make a very high density sensor that could capture 38 megapixels like these Nokia Lumia can (and still be able to stuff it in a tiny thin device like a mobile phone). But that is now history and we can now capture images a such high resolutions. So, sensor captures an image at incredible 38 megapixels. Reality is, for regular usage, most people will only ever going to need 8 megapixels tops. There are no portraits or family photos where you’d need more than that. Hell, even 5 megapixels is enough for most needs. And that’s where you can use DLZ to get zoom without using lenses to magnify things while still getting a decently sized output image.

What does “lossless” mean?

Term “lossless” is used for data manipulation where input and output data is exactly the same to the last bit on both ends. For example, photo captured in RAW is a perfect image, exactly what camera sensor has captured. If you have your camera set to store images in JPG and you have it set to Super quality (instead of Super Fine) in order to save space, that is called “lossy”, because you (irreversibly) sacrifice part of the data to save space. But if you save the same RAW image into PNG format (which is lossless), there will be no data loss and if you convert the PNG back into RAW, the original file and the converted one would be exactly the same in terms of quality. So, PNG is lossless, JPG is lossy. Easy enough right?

Similar logic works behind files archiving on computers. Whatever you compress in a RAR, ZIP or 7z archive, when you extract (unpack) the data, it will be the same as the initial data, you will just save the space. It’s all a question of practicality.

And the same goes for music. If you save an audio recording to MP3 (lossy audio encoder), you sacrifice part of the information to make the file smaller. But you can also use lossless compression (like APE or FLAC) and achieve slightly smaller savings, but you don’t sacrifice any quality.

The term “lossless” is used a bit differently in the case of Nokia Lumia zooming capability, but it just explains in one word, that you don’t sacrifice any quality in order to achieve the zooming capability. Which is what everyone want and the reason why everyone hate regular digital zoom…

Why all the negativity around digital zoom?

The reason behind it is in the fact that traditional “non-lossless” or “lossy” digital zoom is achieved by over-sampling the image (increasing the image resolution) and then cropping the desired part to achieve the zoom. And since you can’t get data out of thin air (except in CSI TV series where they can infinitely zoom any image till they get a super sharp zoomed reflection of a person standing 500 meters away from the point of the reflective object), you are interpolating it using various algorithms (like Bicubic resampling). This means that algorithms are predicting how pixels should look like in place where there were none of them before. Result is a zoomed image, but at very poor quality (lack of detail and excessive image softness).

How zoom works?

  • Original image at 38 megapixels (34 actually, because it’s 16:9😛 )

large-sensor-city-viewFull Resolution link:

  • Digital Zoom

Optical sensor captures an image at lets say native 5 megapixels. In order to achieve zoom, the image is over-sampled (increased) to lets say 15 megapixels using interpolation. Then you take a 5 megapixels rectangle and move it to where you want to make a zoom and then crop the image at that point, resulting in a final 5 megapixels big photo. Result is a zoomed 5 megapixel image at very low quality due to all the digital image processing done by image resizing algorithms (interpolation).


  • Optical zoom

Optical sensor captures the image at the same native 5 megapixels. In order to achieve zoom, mechanical “contraption” of lenses in front of the sensor will move in such a way, that it will magnify the object/scenery you are pointing your camera at. There is no interpolation going on, all the magnification is done by the lenses. That’s why we call it “optical zoom”. And since lenses have nearly “infinite resolution” they don’t really make images any worse, apart from optical distortions which are often negligible compared to what digital zoom does to the photos. All the image quality boils down to the quality of the lenses as a result of it. But in general, even the worst optical lenses will do far (far) better than any digital zoom. End result is a 5 megapixel image with very good zoom quality as there are no digital resizing algorithms involved.


  • Digital Lossless Zoom (DLZ)

Optical sensor captures the image at its native 38 megapixels. Now, just like with Digital Zoom, you can take a 5 megapixels rectangle in size and move it anywhere on that massive 38 megapixels image and crop it (resulting in a maximal possible lossless digital zoom). The end result is a 5 megapixels photo with high quality zoom that can easily compete with the optical zoom at exactly the same end resolution of the final image.


  • Hybrid Digital Lossless Zoom (H-DLZ)

This is basically what i was using on my Olympus cameras. The capability was far lower than the one found on Nokia Lumia 1020, but it was there. The camera was 8 megapixels with 5x optical zoom. You could freely achieve 8 megapixels image with 5x optical zoom without any loss in quality. But if you wanted to achieve zoom higher than 5x, the camera sacrificed some of the megapixels in order to zoom even further. The end result was a 5 or 3 megapixels photo where i could zoom at things further and they still looked far better than any 8 megapixels photo that had digital zoom applied to it.


You may say, well, the last two images for optical and DLZ are exactly the same. Well, yes, they are! I used the same image to explain the point. End result between “optical zoom” and “digital lossless zoom (DLZ)” is exactly like this. Almost identical and 99% of people won’t be able to tell a difference. That’s why I think what Nokia is doing is a very clever idea that will keep our mobile phones slim while giving us the so much needed zooming capability on mobile phones, without making them look like casual cameras which are all fat and clumsy and they don’t belong on a mobile phone. Samsung Galaxy S4 Zoom model springs to mind, but if you look at it, all they did was stick a traditional lens on a Galaxy S4. It just looks silly and impractical. You can just as well strap a casual camera with some duct tape on a back of your normal Galaxy S4… I just wish MORE mobile phone makers would start using such method to achieve zoom on their mobile phones. While I admire modern Nokia phones in many ways, I’m just not sure about the Windows Phone OS. I’m more of an Android chap, so changing the entire way I use mobile phone now, is not something I want to do. But I would want it the other way around, either by Nokia joining the Android camp as well or Android vendors using the same DLZ method with huge sensors. Lets wait and see🙂

6 thoughts on “Digital Lossless Zoom explanation

  1. I switched from Android to Windows because my wife wanted an easy to use phone and she wanted us to have the same kind so she could use mine or hers as needed. I was very frustrated by her zeal and got a Windows phone. I do not plan on going back. Windows has been far better.


  2. Actually, Samsung does also use lossless digital zoom, and it is also possible to calculate that.

    You can calculate:
    1. How much zoom do i have to use to degrade the quality to X (mega)Pixels?
    2. How many megapixels will my output image be at X times zoom?
    3. X times zoom degrades the quality to Y pixels. What is the image’s resolution?

    I have got a Galaxy Note 3, and soon a Note 4 (but i love my Note 3, i just get a Note 4 because of HDR-Video and OIS-Camera), but i will write this example with an S3 with 3264 times 2448 pixels.
    At four times zoom, the maximum lossless image would be 816× 612 Pixels.

    The Note 4’s pointless EIGHT TIMES ZOOM does degrade the quality below 0.3 Megapixels.
    On a 5 MP Phone, 4x Zoom is enough to degrade the quality to approximite VGA-Resolution.

    2. How much zoom do i need to degrade the S5’s camera (5322×2988) to 2.5 MP?
    Just calculate √ ((5322×2988)/2.5)

    Maximum lossless digital zoom for 720p Video on an S5?
    √ ((5322×2988)/(1280×720))

    I hope, this made you smarter :·)


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