It's been half a year since Japan Display introduced its 543ppi smartphone screens - meaning it's about time rival screen maker Sharp upped the ante.

Sharp's newest innovation is a 600 pixel-per-inch, 5.5-inch smartphone LCD panel, which will be followed up by 7- to 9-inch versions for tablets, according to Japanese site Nikkei.

Naturally that beats Japan Display's 5.4-inch 1440 x 2560 display like paper on a rock (and might be about as useful).

Sharp is claiming these ultra-dense screens will enable 4K media playback, though that likely only applies to its tablets. As Android Authority points out, 4K on a 5.5-inch screen would require 800ppi, a milestone that has yet to be reached.

Screens get bigger, pixels get smaller

For comparison the iPhone 5S has a pixel density of 326ppi, the Samsung Galaxy S5 is 432ppi, the HTC One M8 sits at 441ppi and the Oppo Find 7 has a 538ppi QHD screen.

Whatever phones these displays find themselves in are going to look quite impressive, though some argue that at a certain point denser and denser screens don't make much of a visible difference.

Recently Japan Display also unveiled a 10.1-inch 4K tablet screen it said matches the battery life of less dense devices despite its ultra-dense display.

Of course for a larger-sized tablet screen "dense" means something like that display's 438ppi, which is 200 pixels-per-inch higher than the iPad Air's but still significantly lower than the best smartphone screens.

Beyond these ultra-high-density displays, Sharp is also reportedly keen to put its more efficient (but 300ppi-capped) LCD IGZO panels in more mid-resolution devices, a welcome focus for smartphone users who are OK with actually spying a pixel now and then.