4K is 3840*2160 = roughly 8.3 megapixels.

That's at a 16:9 video ratio though. There are no phone camera sensors out there with a 16:9 ratio. That would be useless for taking still photographs.

Most DSLR/mirrorless cameras have a 3:2 ratio, whereas smartphone cameras tend to have a 4:3 ratio.

If you want to make a smartphone camera sensor that can do 3840 pixels across that can shoot 4k, the 4:3 sensor would need to be 2880 pixels tall. So 3840*2880 = 11.1MP would be the bare minimum size for a smartphone camera that can shoot 4K.

In practice you'd want something larger than that, so you can do DCI 4K (which is a bit higher resolution) and do things like gyroscopically assisted electronic image stabilization (which benefits from a few extra pixels around the border). The iPhone can probably implement video stabilization that rivals GoPro's HyperSmooth stabilization.

Hmm, had in mind DCI which consider quite larger than UHD 4K, but yes, it's still ~ 9MP.

> YouTube, since 2010,[51] and Vimeo allow a maximum upload resolution of 4096 × 3072 pixels (12.6 megapixels, aspect ratio 4:3)

I guess it really depends on the aspect ratio you're going for.

https://en.wikipedia.org/wiki/4K_resolution#Video_streaming

I've never personally seen that resolution used, nor called "4K". If you're going to lump together a resolution with 50% more pixels under the same umbrella term then IMO "4K" is meaningless and we need more granular terminology.

Yeah, and now if something doesn't have enough to do 4k there's:

a) nothing stopping them from faking it, plenty of crappy hardware will record files in an upscaled resolution (see webcams especially for this)

b) you probably don't want a larger version of the output of that device anyways.

I mean even a 130 dollar phone has a 13 megapixel camera. https://www.amazon.com/BLU-Android-Factory-Unlocked-Display/...