Xiaomi kept more or less everything on its latest flagship device similar to what we have seen on Xiaomi Mi Mix 2, however, cameras on its latest flagship device are updated and are now even better. Phone comes with a dual rear camera setup, having two 12 MP Sony sensors with an f/1.8 and f/2.4 aperture respectively. One of those lenses is a wide-angle lens and other is a telephoto for depth measuring.
Reason for this combination of lenses is to deliver a mix of wide angle and telephoto, which means this camera is able to zoom while limiting overall loss of quality in images. Both lenses can also use their offset positions from one another to map and identify depth, which can then be used to apply software-produced soft backgrounds, just like you would typically find in a portrait shot. Xiaomi Mi Mix 2S cameras have larger pixels compared to many competitors (1.4um, not 1.25um like older Xiaomi Mi Mix 2). That clearly improves quality, particularly in low-light, plus Xiaomi has included hardware level multi-frame noise reduction and 24 million focusing points on sensors themselves to enhance autofocus.
Autofocus works well but not as fast as on some smartphones available in market, such as Huawei P20 Pro. A touch on screen will select focus but it needs to be faster in order to rival best of best and truly be a flagship. Xiaomi has implemented four-axis Optical Image Stabilization on its cameras, and instead uses artificial intelligence to perform clever tricks such as 'on-the-fly translation', online currency conversion and intelligent background blurring (bokeh effect). Bokeh effect is actually also possible from front camera, which means you can create bokeh-effect selfies too.
As for results, Xiaomi's Mi Mix 2S deliver shots that have detailed colors, ample sharpness and even low light shots are not filled with image noise. Sometimes, there's noise or extra saturation in photos which prevent it from being cleanest result you'll see from a flagship camera phone, while even daylight shots have some presence of grain within them. Camera interface is largely unchanged from previous years, but there's a new AI feature that automatically sets up ideal shooting mode for a particular shot. AI-assisted feature is similar to what we've seen from likes of Huawei, and it works by gauging lighting conditions and subject to offer optimal shooting mode. It works seamlessly, and you see a clear difference with this feature, once again in low-light conditions. To my surprise, however, this mode does not really say much about what it's doing. Other major manufacturer implementing AI in their cameras is Huawei, but its AI system tells you which mode it has selected based on what it thinks it's looking at. This makes those camera phones easier to use generally more intelligent. I personally like Xiaomi Mi Mix 2S having such a mode, but it should've been designed to give more information to users like its Huawei counterpart does.
Xiaomi Mi Mix 2S is first phone in China to support Google's ARCore platform. This adds Augmented Reality capabilities similar to Google Pixel phones. There are tons of apps and games that enable AR functionality on phone to have fun with. Phone is also capable of shooting videos up to 4K at 30 fps, which is inferior to Apple iPhone X's 4K at 60 fps. Even at 1080p you don't get option to shoot at 60 fps which is quite disappointing. Videos coming out of this phone are good, however. OIS helps in stabilization and that could be a reason why Xiaomi decided to ditch 60 fps as OIS doesn't work at that frame rate. Dynamic range is good, and camera doesn't perform bad even in low light while shooting videos but once you compare videos taken from this phone to those taken from competitors, you clearly see difference in quality and that's something Xiaomi really needs to work on.
For selfies, Xiaomi Mi Mix 2S has a 5 MP front-facing camera with an f/2.0 aperture that sits in a very awkward position below screen. When triggering selfie mode in camera app, it actually tells you to rotate phone 90 degrees in order to capture selfies like you would with any other smartphone. Selfies come out sharp, and bokeh selfies aren't bad either. However, it is certainly not the best selfie camera out there, as Apple iPhone X takes sharper selfies with better edge detection when using portrait mode.
It is a success, although Xiaomi really needs to polish things more to make it a truly great camera. Loading time is not as instant as on other flagships, for example, while scrolling between modes. Short Video, Video, Photo, Portrait, Square, Panorama, Manual should switch instantly to be extra quick. Once during my test, when in Manual mode, interface of Panorama Mode was showing even when I was using Manual Mode and such little blunders differentiate a phone from being a top flagship device.