"When the 960×640 3.5-inch Retina Display was introduced with the iPhone 4, the rest of the smartphone industry had to do something about it. At the time most of the competition was at 800×480 on displays much larger. With the Retina Display Apple shifted the focus of attention on a smartphone display to resolution, specifically to a resolution threshold of about 300 ppi on a smartphone that’s used at a distance of about 12 inches.
Android OEMs and Google responded to the 3.5-inch 960×640 Retina display by improving the pixel format to 1280×720. But because Android renders text and graphics like desktop OSes (e.g. Windows, OS X) increasing resolution above 320 ppi means smaller UI elements. The display had to grow in size to compensate for shrinking UI elements. iOS renders the Retina display not by shrinking UI elements by one fourth but by doubling clarity and sharpness. Unless Google adds an additional “DPI level” beyond XHDPI, Android smartphones that match or beat the iPhone 4/4S in resolution will always be bigger, much bigger.""
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