4K Is Not UHD

In a recent post on high-resolution screens for smartphones I used the term 4K for describing the resolution of mobile screens with 3840 x 2160 pixels and was quickly and rightly reprimanded by an observant reader paying attention to detail. Indeed, I had fallen prey to marketing lingo. Strictly speaking 4K is a standard defined by industry consortium DCI (Digital Cinema Initiatives) that defines a resolution standard of 4096 x 2048 pixels used in the production and projection of movies. That’s slightly more than Ultra High Definition’s 3840 x 2160 pixels. UHD also defines double the basic resolution at 7680 x 4320 pixel too. Both share a common 16:9 aspect ratio, and 4K UHD and 8K UHD are terms used to distinguish between the two.

Marketers fromTV manufacturers often substitute 4K UHD with the more punchy 4K, opening terrain for confusion. True 4K has as slightly different aspect ratio of 256:135, which equates to 16:8.44. In other words, watching a 4K movie on UHD TV means either having narrow black bars on the top and bottom sides if you squeeze a full 4K frame onto the UHD screen, or losing small parts of the left and right edges of a frame if the 4K film is to fill the complete UHD screen. Most of us are familiar with this behaviour from previous formats. No big deal.

4K versus UHD

4K	4K UHD	8K UHD
4096 x 2048	3840 x 2160	7680 x 4320
4096 x 2048	3840 x 2160	7680 x 4320
16 : 8.44	16 : 9	16 : 9

Megapixels shots that make UHD sense

A further common fallacy in the multimedia industry is comparing pixels from cameras with those of screens.

Pixels describing a camera’s resolution are counted differently from those specifying a display’s resolution.

In the display world a single pixel consists of three separate RGB (red, green, blue) light sources. In other words, a single pixel on a screen can represent any given colour. Contrast this to the world of cameras, or more accurately image sensors. Each pixel in an image sensor captures one of the three RGB components that represent a colour. But it’s not as simple as dividing the megapixel count of a camera by three to arrive at the best display resolution. In short, cameras use a variation of the RGB model that takes the pecularities of the human eye into consideration and gives green twice as many detectors as red and blue to achieve better luminance resolution. The RGB pixel ratio 1:2:1 of image sensors means you need to divide the camera’s megapixel number by four when figuring out the best screen resolution to display a photo.

For example, take a 4K UHD display resolution with its count of 3840 x 2160 = 8.3 megapixels. Mutiplying that number by four means a 33.2 megapixel camera starts making sense when viewing captured shots on a 4K UHD TV.

In the past camera and smartphone vendors instigated a megapixel race to lure customers into buying their latest high-resolution devices. This marathon seemed nonsensical in a small-screen or High-Definition (HD) world. Ultimately many other parameters govern the overall quality of a snapshot, like the physical size of each “pixel” in an image sensor to name but one.

As more and more 4K UHD TVs are finding their way on to retailer’s shelves, the megapixel madness in smartphones and digital cameras of previous years begins to make sense. Favouring a smartphone with more than 16 camera megapixels is a serious consideration for hi-res aficionados on the way to their next phone replacement spree.

4K on Mobile - splash, bang or thud?

The new year has just begun and the mobile industry is bracing for the splash of 4K displays in the smartphone market. Will smartphones with Ultra-High-Definition (UHD - the acronym denoting 4K resolution) become a runaway success? They promise a four times higher resolution than the current high-end of small screen technology. They also require four times the amount of data to transfer and a lot more processing muscle to handle the extra workload in tasks such as compression and image enhancement .

 
Rumours have it that Samsung’s Galaxy Note 5 (to be released mid 2015) will feature a 4K screen resolution of 2160 x 3840 pixels on a 5.9 inch display delivering an astonishing pixel density of 746 ppi (pixels per inch). What does this all mean and does it make sense, or is it just one more superlative being added to the spec list of megapixels, octacores etc. to dazzle the consumer?

10-fold increase in 4K smartphone unit shipments

Not if you believe Qualcomm, the Nr. 1 chip supplier in the mobile handset world with a market share of over 50 % for baseband modems in cell phones according to Forward Concepts . A quick look at 4K support in their Snapdragon 805 system-on-chip reveals an unshakeable commitment and formidable investment in this latest display technology.

Smart Phone Display Trend – Source: IHS DisplaySearch, 2015 IHS DisplaySearch expect a 10-fold increase in annual shipments of 4K displays on smartphones by 2017. A modest 6 million units are forecast to ship this year (2015).

Why the 4K smartphone market differs from its TV counterpart

Most of us have witnessed how TV formats battled in moving from PAL/NTSC to high-definition HDTV and the time it took for content and broadcasting in this format to become common. Seers from the mobile world expect the change to 4K to be a completely different kettle of fish. Uptake of this superior technology will be swift . The premise is that mobile devices such as smartphones don’t need to wait for 4K content to become available on a large scale as they are already equipped with cameras and codecs that generate 4K video which can be shared with like-minded. The breakthrough will be further fueled by the fact that consumers buy new mobiles every other year. That’s a very different replacement cycle to PCs or TVs, driving down the cost of high resolution handsets at a much quicker rate. 

Your best viewing distance

 The proposition of enjoying an immersive cinematic experience, viewing an image in fine detail, or simply reading crisp text are undeniably attractive. Does 4K on a handheld deliver on this promise and improve the user experience compared to lower resolution displays? Image quality is an extremely subjective experience and its perception depends on a multitude of factors, not the least of which being the condition of your eyesight. Objectively speaking however, a higher resolution always makes perfect sense the closer you get to the screen or the bigger the screen gets. At some point your eyesight will notice the edges of rasterized text or displayed objects. But how close is close and how big is big? Smartphones are getting bigger by the day - sometimes that small hand can barely hold newer models. In addition, the phone, or shall we call it phablet (phone + tablet) , is at most an arm’s length away from your eyes, usually viewed less than elbow’s length away or some 40 cm / 16 inches. Experts from the display market rely on a simple but reliable rule of thumb for the “best” viewing distance based on screen resolution and size for 16:9 aspect ratios:

• for UHD (2160 x 3840) it’s 1.5 x height of the display
• for Full HD (1080 x 1920) it’s 3 x height of the display

Even the best-sighted of us will no longer be able to distinguish differences to the next lower-resolution display beyond this measure.

So, how does this translate to the latest phablets?

 

	Screen Diagonal	Screen Size	Resolution In pixels	Pixels-per-Inch (PPI)	Best Viewing Distance (landscape)
SAMSUNG Galaxy Note 5 **	15 cm 5.9 "	13.1. x 7.4 cm 5.2 x 2.9 "	3840 x 2160 UHD	746	11 cm 4.3 "
SAMSUNG Galaxy Note 4	14.5 cm 5.7 "	12.6 x 7.1 cm 5.0 x 2.8 "	2560 x 1450 WQHD	515	16 cm 6.3 "
Apple iPhone 6 Plus	14 cm 5.5 "	12.2 x 6.9 cm 4.8 x 2.7 "	1920 x 1080 Full HD	401	21 cm 8.3 "
Apple iPhone 6	12 cm 4.7 "	10.4 x 5.9 cm 4.1 x 2.3 "	1334 x 750	326	31 cm 12.2 "

       ** estimated release is mid 2015

As the table suggests, a cinema quality movie on a 4K smartphone will deliver a better user experience if viewed from a distance of less than 11 cm / 4.3  inches (landscape mode). That’s really close in front of the eyes. Of course, zooming ever further into a hi-res photo by pinching the touchscreen remains an attractive side benefit of 4K content on 4K displays. The “best viewing distance” matches Qualcomm’s affirmation on the average person being able to immediately appreciate the superior quality of a 344 ppi display if viewed closer than 10 inches (25 cm). However note, 344 ppi is not even Full HD resolution.

Notwithstanding, the mobile future is 4K

In the mid nineties when browsing the Internet and Search were at their genesis, I remember contending with technology peers that the future of the medium would remain text-based, more than enough for the emerging knowledge-based, networked society at the time. My rationale was that pictures, let alone videos, would never break through because of bandwidth and cost considerations. How wrong could I have been! As the saying goes “a picture says more than 1000 words”. And if a picture actually sells more than 1000 words, the dynamics of retail and commerce will drive adoption for certain. So, with this in mind and unencumbered by conventional wisdom, 4K on smartphones are destined to break in and break through, even if their added value may not be apparent to the mobile user at first glance.