4K screens, with four times the resolution of high-definition television, are rapidly becoming more affordable. It is not just the large living room screen that will be ultra-high-definition. Phone and tablet displays will also reach 4K resolution, thanks to a new generation of processors. There is a prevalent view that higher definition offers diminishing returns, but it could soon become standard. Smaller screens, viewed at closer distances, will benefit from higher resolution, particularly for text and graphics.

Qualcomm predicts that by mid to late 2015 there will be a range of phones on sale with a resolution of 3840×2160 pixels. It believes that the mobile market will be a driving force behind 4K adoption, powered by processors such as its Snapdragon 805.

Many might question the need for such high resolution on a hand-held display. Some suggest that you need a screen of 60 inches or more across to benefit from 4K resolution at normal viewing distances.

Screen size and viewing distance determine the resolution at which it is no longer possible to discern individual pixels. This is dependent on human visual acuity.

Apple promoted the concept of the ‘retina’ display as one with a resolution such that it is not possible to discern individual pixels. An iPad mini with a 2048×1536 resolution display has a pixel density of 326 pixels per inch.

At a distance of around 10 inches, people with average vision can discern individual pixels at a density of up to about 340 pixels per inch, rising to around 570 pixels per inch for those with perfect vision.

However, the human vision system is not entirely explained by visual acuity. Another measure, known as vernier acuity, which distinguishes the relative alignment of two line segments, apparently shows that people can distinguish details five to ten times smaller than visual acuity would suggest.

This is because the image of a line stimulates many photoreceptors in the retina, which are then processed by the neural vision system in the brain.

This is particularly relevant for text and graphics. While 300 dots per inch in generally accepted as a reasonable resolution for photographs intended for print, text is generally rendered at much higher resolutions. Even entry-level laser printers offer 600dpi, while high-end printers range from 1200 to 2400dpi or more.

A study by Sharp, appropriately enough, concluded that many consumers can and do perceive differences in resolution far beyond 440 pixels per inch.

A 10-inch tablet with a resolution of 1920×1080, equivalent to high definition television, would have a pixel density of around 220 pixels per inch. The same size screen at a resolution of 3840×2160, or ultra-high-definition, would have a pixel density of around 440 pixels per inch, which may still be below the level that human vision can discern.

The resolution of phone and tablet displays has risen rapidly since these categories were first introduced. Premium products now pack more pixels than most laptops.

“Brands are finding it hard to differentiate their smartphone product lineup solely by increasing display resolution,” said Tina Teng, smartphones senior analyst for DisplaySearch. “However, that does not mean the trend toward higher resolutions is going to end.”

Sharp is developing a 4-inch screen with a resolution of 2560×1600 pixels, which works out at 736 pixels per inch. It is aiming to provide samples in 2015 for volume production in 2016.

DisplaySearch forecasts that smartphones with full high-definition or higher screens will account for a third of the market in 2015.

Shawn Lee, research director for DisplaySearch, commented: “While 4K UHD will not immediately become a mainstream display resolution, and there are many production challenges, we expect to see the first 4K UHD smartphones entering the market in 2015.”

DisplaySearch is forecasting shipments of over 100 million smartphones with ultra-high-definition screens in 2018.

Many believe that mobile devices, with 4K recording and viewing capabilities will drive the adoption of 4K. This is partly attributed to the shorter replacement cycles of phones and tablets compared to televisions.

That said, the price of 4K televisions is falling rapidly. The manufacturing cost of a 4K display will fall to that of an HD display today, as volumes rise.

DisplaySearch reports that manufacturers will ship 20 million 4K television panels in 2014, while overall television panel shipments are expected to reach almost 250 million.

There are still many challenges facing the broad adoption of 4K media, which needs more storage, greater bandwidth and higher processing capacity, without increasing power requirements.

The view that 4K only makes sense for very large screens, which is still prevalent among many television professionals, may need to be re-evaluated.

The perception of quality lies in the eye of the beholder. In the case of a handheld screen viewed relatively close, the benefits of higher resolution may be even more evident.