Smartphone display terminology can be a little overwhelming. If you want to know what all the numbers and abbreviations attached to smartphone screens mean, this article is for you. Today we'll walk you through the major display types and considerations, as well as tell you what each screen type is best for, and what the key differences between the various screen resolutions are.
Steve Jobs may have been close enough to correct when he said there's no point in cramming higher pixel densities into smartphone displays if the human eye cannot perceive them, but there are subtleties to this argument that have been endlessly debated.
Display manufacturers are now doubling Jobs' magic number of 300 ppi on mobile devices, which would indicate that there are sufficient market forces that agree with them. But what does ppi even mean and why is 300 the magic number?
Key terms and concepts
When we talk about screens we normally talk about four key things: the display type, the diagonal measurement of the screen (in inches), definition (HD, Full HD, etc) and resolution (pixel density). The last two are closely related.
We can work out the definition of a display by looking at how many vertical and horizontal pixels make up the screen. So, just like any other rectangle, there's a vertical and horizontal measurement, it's just that it's measured in pixels rather than inches. Although this measurement relates to definition, it is frequently used interchangeably to discuss resolution.
The physical size of the display then lets us work out how many pixels are squeezed into one square inch: that's our pixels per inch (ppi) figure, which we refer to as resolution or pixel density. You can calculate your phone's ppi using a pixel density calculator or you can simply install CPU-Z and check the Device tab.CPU-Z
Pixels on paper
Using these terms and numbers, we can tell a lot about a display before we even see it, although to judge a screen's merits accurately, you really need to see it in person, because viewing angles, brightness, contrast, saturation and other factors also come into play.
For example, Apple measures pixels per degree, not pixels per inch as most Android manufacturers do, so even comparing numbers on paper is not always easy. But understanding what the names and numbers mean in the first place at least lets you get the jump on the finer details.
Definition and pixel density
Back in the stone age of smartphones – you know, around three years ago – devices had tiny screens with about eight pixels spread across the whole screen. OK, it wasn't quite that bad, but the advances in display technology and manufacturing processes have progressed in such leaps and bounds that many are left shaking their heads (and rubbing their eyes) when we start waxing lyrical about 4K displays.
We'll now take you through the numbers and measurements attached to each term and explain how everything fits together. There are plenty of resolutions and definitions below HD, but this is where we will start, because most smartphones these days are using at least an HD display.
HD stands for high definition. HD simply means a pixel measurement of 1,280 x 720 pixels. No matter how large the screen is, as long as the pixel measurement remains at this measurement, it's an HD display.
As you can probably tell, the smaller the HD screen the higher the pixel density and, theoretically, the better the picture. So simply having an HD display doesn't mean much, as it will produce a very different image on a 5-inch screen form a 10-inch screen (note: screen sizes are measured on the diagonal to take account of slightly different aspect ratios).
On a 4.3-inch screen, for example, the pixel density is 342 ppi. On a 4.7-inch screen, the pixel density drops to 312 ppi, but both are still HD displays. According to Apple, 300 ppi is the sweet spot, because that is roughly the point at which the human eye stops being able to discern individual pixels at a certain viewing distance (and on a certain sized screen).
Full HD is the next step up and is currently the standard for smartphone display definition, although 2K (QHD) has slowly been gaining traction on high-end devices since the Oppo Find 7 and LG G3, the first commercially available devices to have QHD screens.
Full HD measures 1,920 x 1,280 pixels. Again, the pixel density will depend on how large the screen diagonal. With smartphones at the 5-inch mark, the pixel density sits around 440 ppi, while on a 5.5-inch screen that number drops to 400 ppi.
QHD, Quad HD or 2K
QHD stands for Quad HD, which is four times the definition of standard HD. That means you can fit the same number of pixels as four HD displays into a QHD display of the same size. The pixel measurement for QHD is 2,560 x 1,440 pixels. A 5.5-inch QHD display has a pixel density of 538 ppi. For comparison, the pixel density of a 5.5-inch Full HD screen is 400 ppi.
Definitions are also often referred to by the smaller number of the pixel measurement, so HD will sometimes be called 720p, Full HD gets called 1,080p and so on. With QHD though, the 2K name comes from the fact that the bigger of the pixel measurements is over 2,000 pixels, which can admittedly be a bit confusing (and really ought to be referred to as 2.5K, if we were being entirely accurate).
4K or Ultra HD
You can probably see where this is going. Like 2K, the 4K name comes from the larger of the two pixel measurements, which are, technically speaking, 4,096 pixels in 4K and only 3,840 pixels in Ultra HD. So while these two terms are often used interchangeably, they are actually a little bit different.
Ultra HD is 3,860 x 2,160 pixels and 4K is 4,096 x 2,160. Both definitions frequently get shortened to 2,160p and the pixel difference is relatively marginal, but there is a difference. At one point, it seemed like we'd never see a 4K display in a smartphone, but then Sony released the Xperia Z5 Premium, which offered Ultra HD resolution on a 5.5-inch screen.
Sony refers to this display as 4K, but it actually uses the smaller measurement of Ultra HD, "not real" 4K definition. Nevertheless, the Z5 Premium has a pixel density of 806 ppi – far beyond what any sane person would consider necessary on a smartphone held 10 inches from your face – but the very least you can display the 4K video shot with the Z5 Premium on the Z5 Premium.
So what does this leave us with? A few trends: smartphone screens keep getting bigger and so does the definition of their screens. But as you can see in the explanations above, as we went from HD to Full HD to QHD the pixel densities increased too: from 342 ppi, to 441 ppi, to 538 ppi and now we're looking at 806 ppi.
Even though screens get bigger, the pixels get denser at a faster rate. This means image quality has improved dramatically because rapidly increasing pixel densities are appearing on screens that aren't significantly larger.
But at some point the battery demands and perception of ever-higher pixel densities has to find a balancing point. For many, this point is a 5.5-inch screen with Full HD resolution, and indeed, we have seen some manufacturers releasing 2015 phones with exactly these measurements.
Way back when the LG G3 was presented, LG made a compelling argument for why it chose to go with a QHD display. LG wanted to recreate in the digital world the best quality visuals available in the real world. So LG looked at the finest printing available – that found in high-quality art books – and discovered that in order to translate that into a smartphone screen they would need 540 pixels per inch. QHD just happened to fit the bill.
Of course, these kinds of resolutions mean nothing until the hard work is done to make them worthwhile: if your apps, user interface and web experience are all optimized for Full HD rather than QHD, then all those extra pixels are going to waste. Not to mention the additional strain on your battery to push all those extra pixels around your screen.
When we talk about the Galaxy S6, LG G4 or iPhone 6s, we're undoubtedly going to mention the type of display they use. There are many display types used in smartphones: LCD, IPS, TFT, OLED, AMOLED, Super AMOLED, Retina and so on. If reading that last sentence felt like reading Lord of the Rings (endless references to things with capital letters you know nothing about), then allow us to unravel the mysteries of smartphone screen types.
Note: The moiré effect visible in some photos is related to the mode of shooting, not the display type. (Fun fact: AMOLED screens are harder to shoot photos of than LCD because you get visible bands in pictures taken at certain shutter speeds.)
LCD means Liquid Crystal Display. As you can probably figure out, LCD is made up of an array of liquid crystals that get illuminated by a back-light. Because LCDs don't require much energy to power a screen, the technology is very popular in portable devices.
LCDs also tend to perform quite well in direct sunlight, as the entire display is illuminated from behind, so they are ideal for smartphones. However, this back-lighting means that blacks tend to appear gray and LCDs therefore have less contrast than some other display technologies.
There are two main types of LCD: TFT and IPS. TFT stands for Thin Film Transistor, an advanced version of LCD that uses an active matrix (like the AM in AMOLED). Active matrix means that each pixel is attached to a transistor and capacitor individually.
The main advantage of TFT is its relatively low production cost and increased contrast when compared to traditional LCDs. The disadvantage of TFT LCDs is more excessive energy consumption than some other LCDs and less impressive viewing angles and color reproduction.
IPS stands for In-Plane Switching and it is a further improvement on TFT LCDs. To summarize very roughly: the way the crystals are electrically excited is different and the orientation of the crystal array is rotated.
This orientation change improves viewing angles, contrast ratio and color reproduction. Energy consumption is also reduced compared to TFT LCDs. Because IPS LCDs tend to be better than TFT LCDs, they are also more expensive when put on a smartphone.
The 'good' news about LCD screens is that their energy consumption isn't affected by the on-screen colors. On an LCD screen you can use bright colors, white or dark themes and not have to worry about one or the other consuming more battery life. LCDs also usually have higher brightness levels than other display types and typically last longer than AMOLED screens.
AMOLED stands for Active Matrix Organic Light-Emitting Diode. While this may sound complicated it actually isn't. We already encountered the active matrix in TFT LCD technology, and OLED is simply a term for another thin-film display technology.
OLED is an organic material that, like the name implies, emits light when a current is passed through it. As opposed to LCD panels, which are back-lit, OLED displays are 'always off' unless the individual pixels are electrified.
This means that OLED displays have much purer blacks and consume less energy when black or darker colors are displayed on-screen. However, lighter-colored themes on AMOLED screens use considerably more power than an LCD using the same theme. OLED screens are also more expensive to produce than LCD.
Because the black pixels are 'off' in an OLED display, the contrast ratios are also higher than LCD screens. AMOLED displays have a very fast refresh rate too, but on the down side are not as visible in direct sunlight as back-lit LCDs. Screen burn-in and diode degradation (because they are organic) are other factors to consider.
On the positive side, AMOLED screens can be made thinner than LCDs (because they don't require a back-lit layer) and they can also be made flexible. This is why we've seen Samsung bending the AMOLED display on the Galaxy S6 Edge and LG using a Plastic OLED (P-OLED) on its flexible G Flex 2.
Difference between AMOLED and Super AMOLED
Super AMOLED is the brand name given by Samsung to its range of superior smartphone displays, which, like IPS LCDs, improve upon the basic AMOLED recipe. Super AMOLED displays reduce the thickness of the screen by integrating the touch response layer with the display itself.
Super AMOLED displays handle sunlight better than AMOLED displays and are also better on power consumption. As the name implies, Super AMOLED is simply a better version of AMOLED. It's not all just marketing bluster either: Samsung's displays are regularly voted as the technically best smartphone displays around.
Retina is another marketing term, this time from Apple. A Retina display is not defined by any particular characteristic, other than that it is supposedly of sufficient resolution that the human eye can't discern pixels at a normal viewing distance.
This measurement obviously changes depending on the size and resolution of the display. Apple popularized the Retina concept with the iPhone 4, which had a 960 x 640 pixel resolution on a 3.5-inch IPS LCD screen, resulting in 330 pixels per square inch (ppi).
Considering a 5.5-inch QHD display (fairly common on high-end Android phones these days) has 534 ppi, you can see that not everyone agrees that there's no point going above 330 ppi. Back in mid-2014, Samsung's Galaxy S5 LTE-A shipped with a massive 577 ppi and, as mentioned above, the Z5 Premium has 806 ppi.
Contrary to Steve Jobs' belief in the immutable law of Retina, Apple, under Tim Cook, has finally capitulated on pixel density. The iPhone 6 Plus, Apple's first large-screened iPhone, bumps the display resolution to Full HD, so its 5.5-inch screen has a pixel density of 401 ppi.
Which display type is better?
As we have seen, each term is not restricted to one manufacturer: AMOLED is not always Samsung and Retina is not always Apple (although no one else uses the term). iPhone IPS LCD displays are currently manufactured by LG, Samsung has built displays for the iPad and not all Samsung devices are AMOLED either. As is probably clear from our explanations above, it is not simply a case of which display is better: it's a trade-off between pros and cons.
All of this is to say two things: numbers and technical data are important when comparing the screens on two smartphones, but the real-world performance of these displays is just as important. It is impossible to gauge a display on paper, you really need to see it in real life to know if it is too cool or warm for you, whether you like its saturation, brightness or contrast levels, what its viewing angles are like, and so on.
Don't fall into the trap of believing the marketing hype. Analyze the displays for yourself, ask other users on the forum, or if a device is not yet available, seek the advice of sites whose opinion you trust.
Lastly, be aware of your usage habits and select a display accordingly: if you are a couch potato by night and are desk-bound all day, then the daylight viewing benefits of LCDs are probably not so important to you. If you're an outdoors type, then maybe they are.
If you're crazy about squeezing every drop of life out of your battery or are simply obsessed with eye-popping color and contrast, then take a look at AMOLED. In some ways the grass will always be greener because not every display type can satisfy all preferences, but you can still make informed choices that will tick as many boxes as possible for you.
Do you have any questions about display types and resolution? Let us know in the comments.