HD Super AMOLED versus Retina Display, and other screens (Smartphones Unlocked)

The Nokia Lumia 900 (right) has a clearer, brighter, less reflective AMOLED display than the HTC Titan II's LCD, thanks, in part, to a clever bit of screen design.

(Credit: Josh Miller/CNET)

When Raymond Soneira compares smartphone displays, he doesn't just stare at side-by-side screens, using his highly trained eye to detect differences in color temperature and contrast. He does that, make no mistake, but he also uses a suite of scientific tests that measure factors like brightness, color gamut, and reflection.

Ray Soneira, president of DisplayMate Technoligies.

(Credit: DisplayMate Technologies)

Soneira is the president, CEO, and founder of DisplayMate Technologies, a gold standard toolkit among manufacturers and display reviewers, CNET included. Holding a doctorate in theoretical physics, Soneira has spent 23 years fine-tuning the algorithms that analyze visual data on screens of all sizes, from smartphones to TVs. Mathematical models are a specialty of his; in past positions, Soneira has developed intricate tests for both AT&T Bell Labs and CBS (CNET's parent company), among others.

This mountain of experience and expertise is why I'm paying attention when Soneira tells me quite plainly over the phone, "Just about every single spec on displays is exaggerated."

And by "exaggerated," he suggests skewed, misleading, and sometimes utterly useless. Why? Because while a screen's resolution and other specs can indicate a certain level of performance, there are many more factors involved in determining a display's actual level of performance.

That's because what makes a smartphone screen great is a combination of factors like the physical screen materials, screen technologies (LCD versus OLED), pixel layouts (RGB variations), brightness, color accuracy, contrast ratio, reflectance, screen size, and pixel resolution.

Got all that? Good, now let's dive in.

The anatomy of a smartphone screen
Your smartphone screen is composed of several layers of material, starting from the bottom with the display's backing material. This "substrate" could range from the thin, pliable plastics of concept phones with flexible screens, to the tougher stuff of today's handsets.

On top of the substrate is the lighting element (like the backlight for LCD screens), which is then topped with a TFT (thin-film transistor) layer, which uses voltage-sipping transistors to keep the display's pixels shining until you refresh or change the image.

There's also the touch-sensitive panel; various films and filters that might reduce glare, for instance; and the cover glass, which might lay on top as a separate layer, or could be bonded to the touch layer. Gorilla Glass is one designer brand of cover glass.

An AMOLED display comes together.

(Credit: Wikipedia.org)

Why am I telling you this? Because the physical components can affect the screen's ultimate visual quality. For instance, screens with bonded cover glass remove trapped air you would otherwise have between the cover glass and lower layers. Removing that air can generally improve reading legibility by cutting down on some of the reflection you get when light pouring out from the screen bounces back to the display.

Lower-quality materials can also narrow the device's viewing angle and diminish the color, both of which make for a degraded experience overall.

LCD versus OLED
There are warring schools of thought surrounding which type of display technology is better: LCDs (which act as valves to allow varying amounts of the backlight through to the viewer) or AMOLED/OLEDs (a different approach that uses "active-matrix organic light-emitting diodes" to directly emit light). There are complex ins and outs, but in a nutshell, you can think about LCDs and OLEDs as follows:

LCD screens start with an always-on backlight; this technology requires light to create black, white, and colors. In general, high-end LCDs are known for producing the most accurate colors and grays, though their manufacturers sometimes intentionally calibrate LCDs to produce weaker red, blue, and purple shades in order to reduce the device's power consumption.

LCDs generally age slower, Soneira says, with the brightness and color balance holding up fairly well over thousands of hours of use.

OLED on the other hand, doesn't require any light to produce black, just white and colors. Therefore, it's considered battery-saving (since it requires no energy to create black) and can produce inky blacks. OLEDs are often considered brighter as well, creating punchy hues. As a side effect, OLED screens tend to oversaturate green. A more pressing problem, OLEDs also age more rapidly than LCDs, according to Soneira and other experts, which means that the red and blue colors deteriorate faster than green, which can further throw the color balance out of whack.

OLEDs can also be expensive to make, at least at their current stage of development, and in the past, limited production has caused some manufacturers, like HTC, to switch from AMOLED to LCD smartphone screens.

Apple's iPhone 4/4S are a top-tier example of an LCD screen.

(Credit: Apple)

What is IPS?
What makes the two differing technologies more confusing is that there are multiple versions of each. For instance, IPS (in-plane switching) is a type of premium LCD technology that's touted for its wide viewing angle and clearer picture. LG uses IPS in the LG Optimus LTE, and Apple also lists it in the iPhone 4/4S and iPad specs (although Soneira mentions in one shootout that it's really a related technology called Fringe Field Switching, or FFS).

Soneira says that the cheaper versions of LCD technology found in the Motorola Xoom and Acer Iconia A500 tablets can account for their poor color saturation, narrow viewing angles, and increased reflection, the latter that impeded a clear view of the stuff on the screen.

So what about Super AMOLED?
The most common OLED smartphone screens also come with the prefix "Super." Don't let that throw you. Super AMOLED is simply Samsung's proprietary name and approach to making OLED smartphone displays.

Unfortunately, Samsung politely declined to participate in this story, so I can't share with you Samsung's in-house take on technical variances between its brand of AMOLED screens compared with others.

What I can elucidate is the main difference among the three Samsung AMOLED types: Super AMOLED, Super AMOLED Plus, and HD Super AMOLED -- and that difference comes down to subpixels.

PenTile matrix, RGBG

(Credit: Wikipedia.org)

Each screen pixel is actually composed of red, green, and blue subpixels that can turn on and off in combination to create any supported color combination (turn them all on at full blast to shine white). There are numerous ways to pattern the subpixels. Super AMOLED uses Samsung's PenTile layout, and its pattern of red, green, blue, green (RG-BG) subpixels.

PenTile, in fact, uses fewer red and blue subpixels as it does green. As such, PenTile also has fewer subpixels than the typical RGB layout found in LCDs and in other AMOLED screens, like the Nokia Lumia 900. Examine a PenTile screen closely and you might be able to detect a little more image granularity when you're looking at fine details and text. For the most part, though, your eyes fill in the blanks.

It was with great fanfare that Samsung trotted out its Super AMOLED Plus displays in early 2011, extolling the virtues of "50 percent more subpixels" on a total display. That's 12 subpixels per pixel rather than 8, Samsung says.

This might be a good time to address the fact that PenTile has multiple combinations and permutations that help reduce pixelation artifacts. So while you could count an eight-subpixel pattern (with four pixels in different subpixel combinations), Soneira maintains that there are still only two subpixels per pixel, either red-green or blue-green.

However you dice it, the increase led to crisper, smoother, brighter images since the larger subpixels also let in more light. The subpixel arrangement, which was simply an RGB pattern, is found on the Samsung Galaxy S II, Samsung Droid Charge, and Samsung Infuse 4G. Another by-product of Super AMOLED Plus' larger pixels is the need for a larger total screen size in order to achieve the same pixel count, like an 800x480-pixel resolution.

As for HD Super AMOLED, if you guessed it's a regular PenTile Super AMOLED display, but with a 1,280x720-pixel resolution, you'd guess right. You can find HD Super AMOLED on phones like the Samsung Galaxy Nexus, the Samsung Galaxy Note, and the Samsung Galaxy S III.

So why stop now?
With HD Super AMOLED, Samsung seems to have backed away from Super AMOLED Plus, with its RGB layout, and returned to Super AMOLED and its PenTile subpixel array -- a move that's disappointing some followers. Plenty of CNET readers and other smartphone enthusiasts have complained that Samsung isn't putting its best technology forward, reverting from the "Plus" screen in the Galaxy S II to the regular PenTile screen in Sammy's next flagship phone, the Galaxy S III.

Although Samsung didn't comment for this piece, an employee of Samsung America (but not Samsung Display) has said elsewhere that Samsung selected PenTile for its durability.

(Credit: Samsung)

In addition, Samsung calling the 1,280x720-pixel PenTile screen resolution "HD Super AMOLED" is a marketing exaggeration that can mislead consumers, says DisplayMate's Soneira, chiefly because of those fewer subpixels than a standard 1,280x720-pixel RGB high-definition display. While the naked eye may not notice the difference in photos and videos that are inherently fuzzy, the much smaller number of subpixels is noticeable in the presence of fine text and graphics, Soneira maintains, particularly if they're colored.

So while HD Super AMOLED is certainly HD by the definition of resolution, it's not necessarily as fine as other screens.

PenTile does have its pluses. It's cheaper to make than Super AMOLED Plus (Samsung can then pass the savings on to you) and it has some battery-saving efficiencies, since there are fewer subpixels that the battery has to power.

Pixel density
Pixel density can be a little bit slippery, depending on how you slice your pixels and subpixels. Generally speaking, though, the more pixels you have per inch, the better your picture. Apple's iPhone 4/4S may have a small 3.5-inch screen by today's standards, but its 960x640-pixel resolution still gives it a high pixel density of 326 pixels per inch. Compare that with the HTC One X, which has a 4.7-inch screen, a 1,280x720-pixel resolution, and a pixel density of 312 pixels per inch. Now compare both of those with the Samsung Galaxy Note, with its 5.3-inch screen, 1,280x800-pixel resolution, and 285 pixel density.

While pixel density is an important factor in the smoothness of the overall picture, it's just one facet of many. And when it comes to comparing smartphone pixel density with that of a tablet, you don't necessarily need the same high density. DisplayMate's Soneira explains here how fewer pixels can satisfy your eye when reading from a tablet you hold farther from your face than you would want from a smartphone, which has a smaller form factor and is often held closer.

Brightness and color
I've written in this article and others about themes of brightness, how good the iPhone 4/4S' screen is at reproducing natural color (especially in low-light photos), and at how vibrant and bright, but also overripe and candied, colors can look on an AMOLED display.

There are a few tricks you may want to be aware of when it comes to shopping and playing on demo devices. With any display, from smartphones to HDTVs, people's eyes are often drawn to the brightest and punchiest of the pack. However, oversaturated color gets tiring, and just looks cheap or fake when you're viewing something so familiar that your eye knows it's being fooled -- a video or photo of you or your dog, for instance. ("Hey, I'm not that orange!")

Some OLED devices do contain settings to dial down the juice, but you'll have to go hunting.

The same principles of eye candy apply to bright displays and promises of brightness. If you get your hands on a display device, adjust the screen brightness to the middle setting and see how you like it there.

LG has done some interesting marketing around brightness. Its "Nova" display describes its screens that can achieve 700 "nits" of brightness. That is really bright, but the trade-off you get on a phone like the LG Marquee is a lot of light, but less contrast and flatter color. You also get a voltage-thirsty setting that quickly drains your battery. It's a good idea to ratchet down the brightness for this one.

Reflection, the secret enemy
Even if your screen has high pixel density and great color reproduction, a highly reflective screen can mess up your view. Instead of reading your article, movie, or e-mail clearly, you may be dodging overhead lights, sun rays, and your own reflection to strain to see what's on the screen.

(Credit: iStockphoto)

As I mentioned above, the quality of the physical display materials can play a role in "reflectance." But manufacturers can also do something about it. In the Lumia 900, Nokia applies its ClearBlack filter above the touch layer on its (non-PenTile) AMOLED screen, but below the cover glass. ClearBlack works on LCDs, too.

The filter uses "circular polarization," which forces light to travel in a clockwise direction, then blocks off all the light that bounces back to the screen in a counterclockwise direction. The end result is reduced reflectance overall, and improved legibility both indoors and outdoors. In Soneira's test results, the Nokia Lumia 900's ClearBlack display was about about half as reflective as Apple's new iPad.

When asked if we'll see ClearBlack in many of Nokia's future phones, Markku Lamberg, Nokia's director of display and touch, told me this: "Nokia will continue to focus on outdoor legibility and other display related user experiences, with ClearBlack being one of the key technologies."

I'll take that as a yes.

iPhone 4S versus Samsung Galaxy Nexus
Holding these two phones side-by-side, it's easy to see in living color all the principles that go into display technology. There's the iPhone, with its IPS LCD display, its high pixel density, and cooler, toned-down colors.

Then there's the Galaxy Nexus, with its larger 4.65-inch screen, 1,280x720 HD pixel resolution, and pixel density of roughly 316 pixels per inch. Colors on the AMOLED screen with the PenTile display, look rich and vibrant; they nearly leap off the screen. Blacks look inky, too, but the colors can cross the line to being overly saturated and unrealistic, especially the greens. Text is nice and legible, but not quite as crisp as on the iPhone.

Until I get my Samsung Galaxy S III in to review, I can only surmise a similar screen comparison as the Galaxy Nexus, since the screen specs on the S III and the Nexus are very close. The Galaxy S III, however, has a slightly smaller pixel density because of its larger 4.8-inch screen, and its steady 1,280x720-pixel resolution using the PenTile matrix.

I, too, would love to see how the Galaxy S III would look with the Super AMOLED Plus array's greater number of subpixels.

Who's getting it right?
According to DisplayMate's tests, and to CNET editors' own visual assessments, Apple, Nokia, and Samsung are the big winners -- Apple for its crystal clear Retina Display on the iPhone 4/4S phones and on the two newest iPads; and Samsung and Nokia especially for their lower screen reflectance on higher-end models like the Galaxy S and the Lumia 900, respectively.

Of course, Samsung and Nokia make a huge number of low-, mid-, and high-end models of smartphones and tablets, so budget devices made with less-expensive materials and technology won't perform as well as the higher-end models.

Noki Lumia 900 (center) compared with the iPhone 4S screen (above) and the Samsung Focus S (below), with brightness on full blast.

(Credit: Josh Miller/CNET)

Who's getting it wrong
HTC and Motorola LCD screens have performed poorly on DisplayMate's shootouts, especially when it comes to viewing angle and reflectance. CNET reviewers, including me, have also noted in reviews that their screens pale in comparison to others; chiefly to the iPhone's Retina Display and to the high-end AMOLED phones.

Soneira cited poor execution and cost as manufacturers' major obstacles. That isn't to say that HTC phones offer a poor viewing experience and that you should avoid them. Soneira's public tests (versus confidential ones that manufacturers commission) admittedly don't consider new phones like the HTC One X or HTC One S and both phones' screens look bright, colorful, and satisfying when they stand on their own.

Unfortunately, HTC chose not to participate in this story.

What needs to happen next
Ask DisplayMate's opinionated Soneira what he thinks should happen next in mobile display technology and he'll tell you in no uncertain terms. First, says Soneira, manufacturers need to work on color correctness, a topic worthy of its own lengthy story. It also boggles his mind that display-makers often miss the low-hanging fruit of reducing light reflectance since, in Soneira's words, "we don't just read screens in the dark." Antireflective coatings and glare-reducing layers should be relatively easy ways to help.

One of DisplayMate's tests compares the light spectra in Apple's backlit LCD screens with Samsung's Galaxy S smartphone AMOLED.

(Credit: DisplayMate)

In addition, the price of OLEDs needs to drop, and it will. Samsung and other suppliers that have heavily invested in the technology are seeing their R&D paying off. There are still some rough edges to the newer technology, but there's also great potential battery savings that won't sacrifice brightness and vibrant color.

"OLEDS have a bright future," Soneira told me. "Pun intended."

What this all means for you
The technical specs and side-by-side phone screen comparisons are interesting and important, but the way you feel about looking at a screen is the most important of all. I once purchased a phone whose keypad I hated (these were the flip-phone days), but whose screen color saturation and brightness overcame my reservations. Compared with the other choices in my price range, that phone possessed the screen I wanted to stare at every day.

So unless you're a total screen snob whom only specs can satisfy, my ultimate buying advice is this: stare at the screen long and hard, and hold it up next to other rival devices in the store. If you can live with it, if you never notice overly dull or artificial colors, or a distracting reflection, and if you feel you can read small text without bluriness or eye strain, then don't let the screen specs determine your purchasing path.

In most cases, the resolution of smartphone screens in the same class should be more or less comparable. Yet to get your best shot at the nicest picture that technology can produce, expect to bump yourself up to the pricier head of the class.

Smartphones Unlocked is a monthly column that dives deep into the inner workings of your trusty smartphone.

(Credit: Josh Long/CNET)