In this edition of Primed, we'll be examining the different qualities and underlying technologies of several displays, starting with the ubiquitous TFT-LCD and moving through the nascent realm of glasses-free 3D and beyond. We'll also be addressing the importance of resolution and pixel density. Finally, we'll be scoping out a handful of upcoming technologies -- while some are thoroughly intriguing, others are just plain wacky. Go ahead... buy the ticket, take the ride, and join us after the break. It's Primed time.
Table of Contents
Introduction
LCD fundamentals
Display technologies explained
A 3D detour
Why resolution matters
The touchscreen
Looking forward
Wrap-up
Introduction |
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The most desirable phone displays today are variants of these two technologies. In the LCD camp, there's the Super LCD (S-LCD) and the IPS display -- with the latter as the basis for the Retina Display and the NOVA display. Likewise, the OLED territory is filled with options such as Super AMOLED, Super AMOLED Plus and ClearBlack. We'll discuss the important distinctions between these competing display types shortly, but first let's develop a fundamental understanding of how these brilliant creations work and how they came to be.
LCD fundamentals |
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The story of the LCD began in 1888 when cholesterol was extracted from carrots. Think we reached too far back? Not if you've ever wondered what liquid crystals are. You see, a botanist named Friedrich Reinitzer discovered this extract had two distinct boiling points and observed the molecule's ability to transmute from liquid to a crystalline structure in the interim. Even more shocking, the cloudy substance was able to reflect circularly polarized light and rotate the light's polarization. (This little tidbit will become important when we discuss how LCDs operate.) While liquid crystals appear throughout nature, it wasn't until 1972 -- when 5CB (4-Cyano-4'-pentylbiphenyl) was synthesized -- that they became commercially viable. A first of its kind, 5CB was chemically stable and entered its nematic phase at room temperature. While there's actually three phases of liquid crystals, we're most interested in the nematic one. This describes a state where molecules flow like liquid and self-align in a thread-like helix -- and coincidentally, are easily manipulated with electricity.
Now let's apply this knowledge to the modern TFT-LCD that you're familiar with. It's the basis for twisted nematic (TN) and in-plane switching (IPS) displays, and both technologies rely upon the thin film transistor (TFT) for the quick response time and image clarity that we take for granted. Fundamentally, the TFT is a matrix of capacitors and transistors that address the display pixel by pixel -- although at a blistering speed. Every pixel consists of three sub-pixels -- red, green and blue -- each with its own transistor, and a layer of insulated liquid crystals are sandwiched between conductive indium tin oxide layers. Shades are made possible by delivering a partial charge to the underlying LCs, which controls the amount of light that passes through the polarizing filter, thus regulating the intensity of each sub-pixel.
Display technologies explained |
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The most common LCD display is based on TN technology, which has been successful due to its relatively inexpensive production costs and fast refresh rates. Many of you will remember the shadow-trail that plagued early LCDs, and faster refresh rates reduce this effect and make the displays better suited for movies and games. Unfortunately, TN displays are famous for exhibiting poor viewing angles and most aren't capable of showing the entire 24-bit sRGB color gamut. In attempt to mimic the full range of 16.7 million colors, many screens implement a form of dithering to simulate the proper shade. Basic TN screens are hardly fantastic, but they're also good enough to survive the day without eliciting too many complaints.
Another technology that's gotten plenty of airtime is the Super LCD (S-LCD), which is a display that's manufactured by a joint-venture between Sony and Samsung. It employs an alternate method to IPS and TN that's known as super patterned vertical alignment (S-PVA). Here, the liquid crystals have varying orientations, which help colors remain uniform when viewed from greater angles. S-LCDs also feature improved contrast ratios over traditional TN displays, which exposes a greater amount of details in dark images. Further, these displays feature dual sub-pixels that selectively illuminate based on the brightness of the screen. As you can imagine, this provides power-saving benefits, along with refined control of colors on the screen.
You're most likely familiar with the active-matrix OLED (AMOLED), which relies on a TFT backplane to switch individual pixels on and off. Coincidentally, active-matrix displays consume significantly less power than their passive-matrix OLED (PMOLED) counterparts, which makes them particularly well-suited for mobile devices. These displays are typically manufactured by printing electroluminescent materials onto a substrate, and that relatively simplistic process suggests that OLEDs will ultimately become cheaper and easier to manufacture than LCDs. Shockingly, the most challenging step is the creation of the substrate itself, which remains a difficult and expensive endeavor. Currently, the limited supply and high demand of AMOLED screens has restricted their availability, and you're most likely to find them in high-end smartphones.
A 3D detour |
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Why resolution matters |
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So far, we've discussed the underlying technologies of mobile displays, but these options are merely one factor for consideration as you select your next phone. Screen resolution is another very important topic, as it determines the amount of content that can be displayed at any given time. Many of you are likely aware of this, but the physical size of a screen conveys nothing about the content that it can display. For example, a 4.5-inch screen with an 800 x 480 resolution actually displays less information than a 3.5-inch screen with a 960 x 640 resolution. These numbers are simply measures of the physical number of pixels positioned vertically and horizontally across the screen. Taking it a step further, the 800 x 480 screen is capable of displaying 384,000 pixels worth of information, while the 960 x 640 screen is capable of displaying 614,400 pixels worth of information. Put simply, a low-res screen simply can't convey the same amount of content as a high-res alternative.
Another component of screen resolution is pixel density, which is the total number of pixels within a physical constraint. It's calculated in pixels per inch (ppi), which is fundamentally a measure of how tightly pixels are squeezed together. This element was somewhat of an afterthought until Apple introduced the Retina Display, but it has important ramifications for the overall crispness of text and images. While the iPhone 3GS came with a 3.5-inch screen with an HVGA resolution, the iPhone 4 kept this same screen size yet boosted its resolution to 960 x 640. The result was a massive increase in pixel density, which grew from 163ppi in the iPhone 3GS to a staggering 326ppi with the iPhone 4. Of course, these numbers are merely academic until you examine the impact that a high pixel density has upon the overall legibility of small text and clarity of images. As you'd expect, other manufacturers aren't letting Apple have all the fun in the pixel density war, and we're seeing particularly exciting developments from Toshiba and Samsung (more on that a bit later).
Now, take the diagonal resolution (in our case, 933 pixels), and divide that by the display size (4-inches). If you've done the math properly, you'll see this particular display has a pixel density of 233ppi. While most smartphones on the market today feature perfectly acceptable pixel densities, this little tidbit could come in handy if you're looking for the clearest possible display.Diagonal resolution = square root of [ (width x width) + (length x length) ]
Using the example of a 4-inch display with a WVGA resolution, your equation should look like the following:
Diagonal resolution = square root of [ (800 x 800) + (480 x 480) ]
Diagonal resolution = square root of [ 640,000 + 230,400 ] = square root of 870,400
Diagonal resolution = 933 pixels
The touchscreen |
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Now that we've examined display technologies and screen resolution, let's take a brief moment to discuss touch screens, which are crucial elements for modern smartphones. The dominant touchscreen technology is known as capacitive touch, which receives feedback from your body's ability to conduct electricity. When you place a finger on the display, the screen's electrostatic field becomes distorted, and the change in capacitance is registered by the underlying sensor. From there, software is used to react to your input. The beautiful part about a capacitive touchscreen is its ability to register multiple points of contact at the same time, which enables multi-touch functionality such as pinch-to-zoom.
Another type of touchscreen on the market today is known as the resistive touchscreen. It's generally less expensive to produce and responds to physical force. While there are multiple elements to a resistive screen, the most important are two electrically conductive layers that are separated by a narrow space. When you press on the display, the two layers come into contact with one another, which registers as a change in current. Unfortunately, these added layers reduce the overall brightness of the display and increase the amount of glare reflected from the screen. You'll generally find resistive touch screens in lower-end smartphones because they don't support multi-touch, although a few individuals appreciate its ability to receive input from a stylus, gloved fingers or fingernails.
Looking forward |
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Hopefully we've given you a solid overview of the current state of mobile displays, but as you'd expect in an industry that's rapidly evolving, there's plenty of exciting possibilities on the horizon. Here's a few gems that are sure to whet your palate for the future.
Full HD resolution and crazy pixel density
Transparent displays
Manufacturers are finding a new take on our mobile phones being a window to the world, as transparent displays are now coming into the fray. TDK began production of a see-through OLED earlier this year, and while we'd be shocked to see this novelty crop up in smartphones, it's sure to give some added intrigue to the feature phone segment. Whether it can actually save SMS fiends from walking into oncoming traffic is still debatable.
Flexible displays
Electronic ink
Take one quick look at your smartphone's power consumption and it's painfully obvious that the display is the primary culprit. With projects such as Mirasol and E Ink Triton leading the way, we're hoping to see a day when color "electronic ink" becomes useful for smartphones. In addition to requiring only a fraction of the power of its illuminated brethren, these displays offer full visibility in direct sunlight. Of course, the need for a light source is a given, and current refresh rates would make for lousy gaming and video playback, but these alternatives are getting better with each new announcement. For those needing maximum battery life at all costs, these displays can't come soon enough.
Wrap-up |
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While we're steering clear of crowning one display technology as king of the mobile empire, hopefully you've got enough information to make that decision for yourself. Granted, the quality of a screen is only one factor to consider when choosing a phone that's best suited for your needs, but it's an important consideration nonetheless. While LCDs typically deliver sharper and brighter images, more accurate colors, and perform better in direct sunlight, they cannot match the vibrant colors and excellent contrast ratios of their AMOLED counterparts. No matter which side of the fence you're sitting upon, you're certain to make a good decision by choosing one of the newer technologies. We've seen a dramatic improvement in mobile displays throughout the past few years, and if your budget allows, we wholeheartedly recommend that you leave older displays in the past -- where they belong. At the end of the day, your eyes will surely thank you for the consideration.