Xiaomi Mix 4 Review: Number One For A Reason

Xiaomi Mix 4

Ben Sin

Ever since Xiaomi’s original Mi Mix attempted the idea of a “bezel-less phone” in 2016, phone brands, especially Chinese ones, have spent the last five years chasing the dream of a handset with a face that’s entirely screen. No buttons, no bezels, no notches.

In doing so, they found ingenious solutions to removing or relocating traditional smartphone components, such as the fingerprint sensor, buttons and earpiece. But the selfie camera proved to be a challenge to relocate or replace. Brands tried a myriad of different methods, such as housing the selfie camera in a pop-up or flip-over mechanisms. Xiaomi placed the camera at the bottom corner of the original Mi Mix. Other brands went as far as put an entire second screen on the back of the phone so users can simply use the rear cameras for selfies. None of these solutions were without compromises: the moving mechanical mechanisms meant those phones could not be water-proofed; and asking the user to flip the phone around or upside down for a selfie seems counterintuitive.

And so brands kept trying and now the latest take is here: putting the selfie camera underneath the screen and force the camera to simply shoot through the display panel. It’s a technology Oppo teased as a concept in 2019, ZTE rushed to the market in late 2020, and now Samsung and Xiaomi are almost simultaneously hitting the market with their implementations in August of 2021.

Considering it was Xiaomi’s original Mi Mix that spearheaded this “all screen” movement, it is perhaps not surprising that it is Xiaomi’s new Mix 4 that has pulled off the most convincing take—the only one so far that doesn’t appear to be a gimmick.

How the under-screen camera works

We must address the most pressing question first: how can a camera shoot through a display panel? Essentially, phone makers have to shrink the pixels in the section of the screen that covers the camera, the smaller pixels leave enough space between them for light information to pass through to the camera’s sensor.

A rendering of the smaller pixels in the Mix 4’s screen provided by Xiaomi


It’s a tech that requires a lot of tech hardware wizardry, because if pixels in a display panel are not uniform, it would usually show to the naked eye. And that’s exactly the case with ZTE’s and Samsung’s implementation so far. In both the ZTE Axon 20 (released September 2020) and the Samsung Galaxy Z Fold 3 (releasing this week), the under-screen selfie camera results in a flawed display that shows a clear, noticeable mark. The Xiaomi Mix 4 has no such problems. In the photo below, see how Samsung’s under-screen camera looks compared to the Xiaomi Mix 4’s.

Samsung’s under-screen camera (left) and Xiaomi’s (right).

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(To be fair: the above photo shows the absolute worse case—on a white page—of the mesh-like mark on Samsung’s screen. When displaying darker colors, it’s not as noticeable).

Xiaomi’s implementation of this under-screen technology, which the company has named “CUP” (camera under panel), uses transparent wiring technology underneath the panel to further make that part of the screen more seamless—for both the users’s eyes and also the camera sensor. Xiaomi claims it spent $77 million over five years in R&D to develop “CUP.”

The Xiaomi Mix 4’s under-screen camera is almost invisible.

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But of course, because the selfie camera is ultimately still shooting through multiple layers of glass, pixels, organic light diodes, and wiring, the image that passes through to the image sensor is not clean — akin to if we tried to look through a dusty or dirty window. In fact, when we preview the selfie in the camera viewfinder, the visuals look a bit soft on details and blurry.

This is where software processing comes in: Xiaomi’s post-image processing uses a proprietary algorithm that cleans up the shot with multi-frame HDR and defogging. In fact, if you snap a selfie and then immediately preview it, you can see the change happen in real time. The result is often impressive, with a final image that fixes most of the flaws shown in the camera viewfinder in real time.

Notice the visuals in the viewfinder (left) struggle with lighting and image sharpness; the final … [+] photo after post-image processing fixes most of those issues.

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It’s not perfect, however. The software tricks can only fix so much. If shooting in harsh lighting conditions, the photo will not be as good as a normal selfie camera. I’ll elaborate in the camera performance section further down.

Design, build, and hardware

All that money and time spent to develop an under-screen camera is so the Mix 4 can finally achieve the all-screen dream. The Mix 4 features an uninterrupted 6.67-inch 120Hz OLED screen. It is as close to just having the futuristic vision of just having a screen in your hand as it gets right now.

The Xiaomi Mix 4’s ceramic back.

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The Xiaomi Mix 4’s ceramic unibody build.

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The rest of the phone construction is equally impressive. The Mix 4’s entire back is crafted from a single piece of ceramic for a unibody vibe often not seen in phones. In other phones, there is a visible seam where the back plate meets the chassis; the Mix 4 has no such seam. The ceramic body has an anti-fingerprint, grippy texture that feels extra premium even when compared to other top flagships. The Mix 4 is my favorite 2021 phone to hold.

Under the hood, the Mix 4 is powered by the Qualcomm Snapdragon 888+, the newest chip from Qualcomm, and technically the most powerful in the Android space right now. There’s 12GB of RAM and a 4,600 mAh battery. All of these components are top notch.

The main camera system consists of a triple lens array covering the wide, ultra-wide and zoom focal lengths, they’re very good cameras, but not Xiaomi’s best offering. More on this later.

Overall, the Mix 4 is an exceptionally crafted, elegant handset.

The Mix 4 comes in three colors



The Xiaomi Mix 4 runs Android 11, with the company’s MIUI software on top. Because the Mix 4 is only selling in China for now, the software does not come with Google apps, but they can be installed easily via Xiaomi’s own app store (or any other side-loading method of your choosing). Once installed, the phone behaves normally like any other internationally released Android phone.

Xiaomi’s software is colorful, lively and full of whimsical animation. I am a fan. For the most part, it offers everything Google intended Android to offers, plus more customization. I do have one gripe: the one-hand mode still only works with on-screen button navigation and not swipe gesture navigation. Considering the latter is the standard in smartphones, this essentially means the phone doesn’t really have a one-hand mode.

Camera performance

Xiaomi’s under-screen camera is clearly the best version of this technology right now, as selfies produced are noticeably better than selfies captured by Samsung’s and ZTE’s under-screen camera.

However, if we’re comparing against a “normal” selfie camera—one not covered by layers of stuff, then the Mix 4’s photos fall short.

In good lighting conditions—daytime photos—the gap in quality isn’t that wide. A Mix 4 selfie will look almost as good as selfies captured by a new iPhone or Samsung. In the below shot, the Mix 4’s image has softer details and weaker dynamic range than the iPhone 12 Pro’s photo, but it’s still a very good selfie considering it is shooting against backlight.

Mix 4 selfie (left), iPhone 12 Pro selfie (right).

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But in harsh lighting conditions such in low light situations, the Mix 4’s selfies are noticeably inferior to any modern smartphone selfie photo.

Galaxy S21 Ultra selfie (left), Mix 4 selfie (right).

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Moving to the other side, the Mix 4’s main camera system consists of a triple lens array: a 108-megapixel main shooter, 8-megapixel Periscope 5x zoom lens, and a 13-megapixel ultra-wide. While the ultra-wide shooter can be a bit soft on details, the main camera is excellent, producing Instagram-worthy shots like these.

A photo sample captured by the Mix 4’s main camera.

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Mix 4 main camera sample.

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Mix 4 main camera samples.

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The 5x zoom lens is not quite at the absolute best tier (Samsung Galaxy S21 Ultra, Huawei P40 Pro Plus, or Xiaomi’s own Mi 11 Ultra), but still really good and much better than anything an iPhone can do.

1x, 10x, and 30x zoom shots taken from the same spot.

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Overall performance

The Mix 4 overall performs exceptionally. The Snapdragon 888+ is the best possible chip for an Android phone right now, and the phone zips around with ease no matter how much I push it. Battery life could be better, as the 120Hz screen eats a lot of power—on a weekend day out around town in which I used the phone often for photos, videos and social media, the Mix 4 drained about 12% of battery per hour, meaning it did not last even 10 hours outside. But that’s very heavy usage—a more normal person’s use case should be able to get 12-14 hours.

The Mix 4’s cameras are very good.

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The good news is the Mix 4 includes s 120W charging brick in the box. Charging at this speed is surreal, as a 10-minute top up will add roughly 40% of battery. So as long as you have time for even a five, six minute charge in the middle of the day, the phone should be guaranteed to last you an entire 15-hour day outside.

The Mix 4 also supports wireless charging up to an insane 100W speed provided you buy Xiaomi’s official charger (for comparison, the iPhone charges wirelessly at 15W).

I also want to mention the Mix 4’s haptics and speakers, both are superb and among the best in the industry. These are two areas that Xiaomi has really nailed in the last two years.


I know there will be people who find the entire premise of under-screen cameras to be overkill and unnecessary, especially since Android flagships today are already almost entirely screen, with only a small hole drilled into the screen to accommodate the selfie camera. For some, willingly sacrificing selfie camera quality just to gain an extra 0.5% of screen space is ridiculous.

The Mix 4’s uninterrupted display.

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But here’s the thing, the Mix 4 isn’t made for them. It’s instead made for those who don’t take selfies much or those who obsess about the smallest of things, like design symmetry. These people exist, too, I still hear from readers who complain about the iPhone’s notch.

And best of all, the Mix 4 is relatively inexpensive compared to its peers. Selling only in China helps, but the Mix 4 starts at 4,999 yuan, which is around $770. This is for a phone with a cutting-edge new camera technology, the best possible processor in Android, tip top flagship level screen, haptics, speakers, and an almost flagship level cameras.

Xiaomi recently overtook Samsung to become the world’s No. 1 phone brand by market share (a.k.a. phones sold). It’s not hard to see why: the company consistently puts out the premium phones at a more attractive price point than everyone else.

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