re: Why is resolution a measure of quality for smartphone screens, but not cameras?

That's not entirely correct, unless you equate resolution to quality.

For instance, this picture was taken with a 20mp camera, and the native resolution is 5184x3426 at 300dpi. However, the purposes of screen resolution, it's been converted for the web to 92 dpi.


This one is taken with a iPhone and the resolution is 3264 x 2448 again converted to 92dpi



For web purposes the resolution's irrelevant because it's downsized so dramatically.

For printing purposes, the megapixels are irrelevant because each camera has a different sensor size...The iPhone is a 4mm sensor, and the 1Dx has a 34x26mm sensor. consequently, you will inherently get a higher quality photo print from a lower mega pixel full frame sensor than you will from a larger mp micro 4/3 or APS-C compact sensor.