If you go simply by the specs alone, the Redmi K20 Pro might seem like it has a better front camera compared to one on the OnePlus 7. At 20MP, it certainly has the resolution advantage over the 16MP camera on the OnePlus 7.
Of course, numbers don't tell everything and when it comes to actual image quality, the Redmi K20 Pro receives a sound beating from the OnePlus 7. The OnePlus 7 images have excellent detail with great looking skin tones, good dynamic range and a natural soft background due to the wider f2.0 aperture.
In comparison, the images from the Redmi K20 Pro are comically oversharpened to the point where any resolution advantage the camera may have had is now lost to all the ringing artifacts. The skin tones also look less accurate, even with all the beauty enhancements turned off. The dynamic range is also poorer.
It's worth remembering that while the OnePlus 7 images may look too soft in comparison, you can always add sharpening later if you desire. However, it's not easy to reduce the excessive sharpening in the Redmi K20 Pro images, which honestly look like they were shot at a much lower resolution than 20MP and then upscaled to 20MP, with the sharpening being added to hide that fact. We sincerely hope Xiaomi isn't up to such shenanigans and that the poor image quality is just a result of badly tuned software.
Both phones offer a portrait mode to blur the background. The Redmi K20 Pro also offers some additional effects for it, which replace the background with different patterns. These actually work surprisingly well most of the time but they do take a rather long time to process despite all the horsepower under the hood.
The actual edge detection is flaky on both devices and a bit of a hit or miss affair with neither being particularly good. The default background blur on the OnePlus 7 looks good, which is just as well since you can't adjust it. The default blur on the Redmi K20 Pro is a bit strong but you can adjust the fake aperture to control the blur.
Winner: OnePlus 7. No amount of megapixels, beauty modes or popup action can hide the fact that the Redmi K20 Pro just has a mediocre front camera.
Both, the OnePlus 7 and the Redmi K20 Pro are capable of videos in a multitude of resolutions and frame rates. Both phones can record videos in 4K at 60fps and both can do slow motion video. However, the Redmi K20 Pro has some key advantages, namely, being able to record videos using its telephoto and ultra-wide-angle lens, recording 960fps slow motion and being able to save videos in H.265 codec for smaller file sizes. The OnePlus 7 does have OIS though while the Redmi K20 Pro only has EIS.
Testing the 4K video at first, both phones are capable of good 4K 30 video. The Redmi K20 Pro in our tests produced more detailed videos with slightly better exposure while the OnePlus 7 had better white balance and more accurate colors. For our tripod test, we kept the stabilization feature on the Redmi K20 Pro disabled. The OnePlus 7 does not let you disable the EIS, which is why the video is slightly cropped in.
At 1080p, the difference in detail is even more stark. The Redmi K20 Pro captures excellent looking 1080p videos. The OnePlus 7, meanwhile, produces extremely soft-looking 1080p videos, which look more like upscaled 720p videos.
The Redmi K20 Pro can also shoot 4K and 1080p videos from its telephoto and ultra-wide-angle lens. We didn't see much difference between the 4K and 1080p videos from these lenses but this time that has more to do with how underwhelming the 4K is on these lenses. Still, both perform significantly better than the OnePlus 7, which has no telephoto or ultra-wide lens and can only do digitally zoomed videos, which, unlike its images, look pretty poor even in 4K.
In terms of stabilization, the OIS on the OnePlus 7 didn't make as big a difference as it did in low light photos. The EIS on the Redmi K20 Pro is quite capable and although it does add a bit of wobble to the image the overall stabilization is on par with the OnePlus 7. You can even turn it off if you have the phone placed on a tripod and gain some extra field of view, which is not possible on the OnePlus 7.
Winner: Redmi K20 Pro. The combination of different perspectives from the three lenses and excellent image quality makes the Redmi K20 Pro a better option for recording videos.