PureView zoom alive and well on non-Nokia phones. (Zooming losslessly on Android)

Did you know that many Android phones can do the same 'lossless zoom' trick as on the old Nokia 808 and Lumia 1020, i.e. smart cropping in on a high resolution sensor so that even when zoomed there's detail that's largely real and not interpolated, i.e. 'made up'?

Of course, you need a phone with a high resolution sensor in the first place and I'm lucky enough to have the ZTE Axon 7, with a 16:9 20MP sensor. Having taken several photos at default resolution, I looked at my snaps and thought "This is crazy, I don't need 15Megabyte 20MP photos - they're big and clumsy and something smaller would in almost all situations be better - I just don't need that insane detail."

Especially so when I zoomed in (say to 2x), at which point I had 20MP of digitally interpolated, slightly blocky 'detail'. It's all too much.

So I set the camera to take photos at 4MP in 16:9, a nice compromise between file size and resolution/detail. In fact, it's similar to what that old Nokia 808 and Lumia 1020 used to use.

I wonder.... what happens if I zoom now on this Android phone? Will the 4MP image simply get blown up and blockily zoomed, or will the phone be clever enough to 'smart crop' into that high resolution sensor, just as the 808/1020 used to?

So I did some tests. Here's a nice shot of some flowers, the original is at 4MP:


And here's a 1:1 crop from that image at blog resolution:


So a very tight crop and the resulting image is tiny, as you'd expect.

Now, using multi-touch on the Android phone's Camera UI, I zoomed in to '2x' and took the photo again:


A nice zoomed shot, but is this a genuine zoom, i.e. without loss? Let's now look at a 1:1 crop of the same detail as above:


This is quite a bit more detailed, as you'd expect.

Now, a 2x zoom is about near the limit for a 4MP photo smart-cropping into a 20MP sensor. There's a little resolution left over though, plus modern camera software is pretty good at a little interpolative digital zoom. So - why not push things and try for a full 3x zoom (incidentally, the same as the limit for those old Nokias with their 34 MP (at 16:9) sensors)?
Here's the same scene at 3x zoom in the Android phone's camera UI:


And again let's look at that central detail at 1:1 crop:


You're starting to see some processing now, some evidence of digital zoom techniques, but most of the detail here is real and I'm happy with the results.
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In all this I've been using Lineage OS (the successor to Cyanogen Mod on Android) on the ZTE Axon 7 and I appreciate that there are bazillion combinations of phone camera hardware and software in the Android world, so your mileage will most definitely vary. However, I do think that the idea presented here is worth investigating for many people.

Now, anyone who's been paying attention will pipe up with "Hang on, if the sensor is 20MP then why not just take all photos at this resolution and never zoom and then you'll always have maximum detail with no effort needed?"

And you'd be absolutely right, except that you're then back to the issue that your photos will all be 10MB or so and everything you ever share them with will have to do masses of downscaling in order to be able to show them at normal resolutions - a 20MP image is something in the order of 3000p, compare this to the typical 1080p computer or TV screen. Even a 4K display is still only 2160p.

For me, the compromise of setting the camera resolution low-ish and then knowing that I've got a genuine 2x lossless zoom in hand is just about right. You'd be amazed how arty you can get when you can zoom in and frame at capture time.*

* iPhone 7 Plus owners, over on iOS, need not apply, you've already got 2x optical zoom! And we're starting to see Android phones with similar arrangements.

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