Back to share more of our display measurement results from the new iPad. Side note before we jump in: this is a somewhat technical post, if you aren’t familiar with the general workings of an LCD, this great live teardown by Bill Hammack is worth watching: http://youtu.be/jiejNAUwcQ8
There are two ways to improve the color gamut performance of an LCD display: you can either make the backlight better or the color filters better. In both approaches, the goal is the same: to make red, green and blue light as pure as possible. The LCD display mixes these three primary colors to make all the other colors you see on screen, thus, the more pure the individual pimary colors are, the better all colors on screen are. Based on our measurements, it looks like Apple focused on the color filters for this new display, let’s take a closer look.
In the color spectrum chart below, you can see the result of some of the color filter changes that Apple made. Notice how the red peak (on the right, in the 600 nm range) has moved to a longer wavelength. This change in wavelength means reds on the new iPad will have a deeper hue, will be less orange and more distinctly red.
Another interesting thing to look at here is the blue peak at about 450 nanometers. In our last post, we noted that blue got the biggest boost with the new display. However, the blue peak did not change in wavelength or in shape, only amplitude (or brightness), which does not affect color. So what explains the dramatic improvement in blue seen on the new display?
The above spectrum isn’t telling the whole story. It was measured from a white screen, in other words a screen with all three primary colors turned on. We see very different results when looking at a screen with a blue image, where only the blue sub pixel filters are open.
This chart shows us only the light that is allowed to pass through the blue color filters. We can see the same blue peaks that we know from the white spectrum, but there’s also some extra light getting through – notice the two small tails to the right of the blue peak? That’s green light from the backlight leaking through the blue filter.
This means that when the iPad display needs blue light to make an image, some of that green comes along with the blue whether you want it or not. You will notice that the green blip is smaller on the new iPad, meaning less green is leaking through and a purer blue is displayed. Take a look at the comparison shot here and you can see how just a hint of that green leakage is making the iPad 2’s blue (on left) appear slightly aqua by comparison.
Blue color filter comparison: iPad 2 on left, new iPad on right
Leakage like this happens because its very difficult to make a truly perfect color filter and even harder to make one that is efficient enough for a mobile display. The reason is basic physics – a better color filter is narrower, allowing only the desired color through. However, the narrower you make the filter, the less light it lets through, and less light through means the display has to be driven harder to maintain brightness. This directly affects battery life, partially explaining the new iPad’s need for a larger battery. Based on our experience, we estimate that the color improvements alone in the new display probably cause it to consume about 20-30% more power than the iPad 2’s screen.
Perfecting the color performance of a display is a critical engineering challenge and worth highlighting because its one of those tiny details that Apple is so great at. Just making this small improvement in light leakage from iPad 2 to the new iPad accounts for a stunning amount of improvement in color performance and, most importantly, it makes for a richer user experience.
Last Friday Apple released an updated version of one of their hottest products, called simply “the new iPad.” Central to the update is a brand new display featuring significantly more resolution and color saturation. Since the resolution bit has been covered to death by others and we’re interested in color here we thought we’d take a closer look at Apple’s color saturation claims.
Using the new iPad, particularly next to an “iPad 2,” the reds and greens are noticeably better, but the blues in particular are quite striking. It actually makes the blue on the iPad 2 seem more ‘aqua’ than pure blue. The color data bears this out. According to our measurements, Apple has significantly increased the saturation in all three primaries, most notably in blue:
The key color claim that Apple made on stage at the iPad announcement was that the new iPad has 44% more color saturation. What they mean by that of course depends on the context. There are a couple of different color measurement standards that Apple could be gauging the performance of the new iPad against such as CIE 1931 or CIE 1976.
An easy way to think about these standards is a bit like the temperature measures that we are all familiar with, Celsius and Fahrenheit, in that they are different ways communicating the same information. Saying, “it’s 5 degrees warmer today” means something very different to users of each system and its much the same way with color spaces, only we’re talking about measuring how the eye perceives color, not how warm it is outside.
We should also note that when people in the display industry talk about color saturation as a percentage, it is common practice to refer to a color gamut standard within a CIE color space. There are many color gamut standards in use today including: NTSC, sRGB, Adobe RGB 1998, DCI-P3, and rec 709. Each of these standards is a subset of a CIE color space. They are typically used by content creators to ensure the compatibility of their work from device to device. For example, if I create an image in Adobe RGB, I would like to display it on a screen that can show all of the colors in Adobe RGB in order to make sure it accurately reproduces all the colors in my original shot.
Based on our measurements it looks like Apple is referring to the NTSC gamut within a color space. But which color space do they mean?
A 44% improvement within the CIE 1931 color space would give the new iPad the equivalent of the sRGB standard used by HDTV broadcasts, Blu-Ray and much of the web. Given the significance of achieving that standard, some thought Apple must have been trying to say “sRGB” without confusing consumers by describing the meaning of various color standards.
According to our data, this is not the case. The new iPad only manages about 26% more saturation over the iPad 2 when measured against the CIE 1931 NTSC color space. However, the unit we measured showed a 48% increase in saturation when measured in the CIE 1976 color space, so that must be Apples frame of reference.
Measurements and standards aside, the new display looks great. The improvement in color performance will greatly enhance the user experience, and as we discussed yesterday, show’s what Apple is betting on for the functionality of future devices.
In our next post we will explain exactly how Apple achieved this improved color performance and look at ways they can improve the next generation.
Which brings us to an immovable object meeting an irresistible force. Apple doesn’t make new devices which get worse battery life than the version they’re replacing, but they also don’t make new devices that are thicker and heavier. LTE networking — and, I strongly suspect, the retina display3 — consume more power than do the 3G networking and non-retina display of the iPad 2. A three-way tug-of-war: 4G/LTE networking, battery life, thinness/weight. Something had to give. Thinness and weight lost: the iPad 3 gets 4G/LTE, battery life remains unchanged, and to achieve both of these Apple included a physically bigger battery, which in turn results in a new iPad that is slightly thicker (0.6 mm) and heavier (roughly 0.1 pound/50 grams, depending on the model).
50 grams and six-tenths of a millimeter are minor compromises, but compromises they are, and they betray Apple’s priorities: better to make the iPad slightly thicker and heavier than have battery life suffer slightly.
This point can’t be understated. For Apple, the quality of the display, both in terms of resolution and color gamut, is so critical to the experience of using an iPad that they were willing to make some major tradeoffs. In this case they not only ended up with a slightly thicker, heavier device, they also used a significantly more expensive part. The end result is a stunning display that amplifies everything that was already great about the iPad 2 so it looks like a tradeoff worth making.
We took some color performance measurements of our new iPad this morning and we’ll be posting more details shortly.
If there is one thing we can take away from CES this year, it’s that displays with better color performance are on the horizon. Two of the largest attention getters at CES this year were new displays by Sony and LG. LG unveiled a 55″ OLED and Sony displayed a new “Crystal LED” technology. While both of these displays exhibited impressive performance, including a wider color gamut, the Sony TV was a prototype only, and the LG display is expected to be available later in the year at a hefty price.
As Hubert of Ubergizmo points out, these technologies offer great promise, however, cost will be their determining factor. OLED, which has been on the horizon for what seems like forever, still looks like it will not be available to the masses for quite a while, certainly not in large formats and not at a manageable price point for the consumer.
By contrast, QDEF, offers an affordable, consumer ready solution today. Display designers who are looking for the next new thing will find that they can have a screen with high brightness, deep color, high-DPI resolution and deep blacks in a display that’s as big as they want using QDEF with no increase in cost. This is because QDEF has been designed as a drop-in diffuser sheet replacement to leverage the billions of dollars of existing installed manufacturing capacity and two-plus decades of improvements to LCD performance. With QDEF, manufacturers can easily replace the diffuser sheet in their displays with a sheet of QDEF and gain over 100% of NTSC color performance.
I attended CES 2012 in Las Vegas earlier this month where I spent most of the week showing off a pair of QDEF-hacked iPads. Also found some time got to check out some other high color performance display technology and I’ll have more on that in a later post. For now, here’s a quick review of a couple QDEF coverage highlights from CES:
First up is a video interview I did with Bill Wong from Electronic Design. It was great to see these guys again and do a bit of deeper dive on the quantum dot nanotechnology that makes QDEF go:
I also ran into Jaymi Heimbuch of Treehuger about QDEF’s ability to improve the performance of LCD displays while using less energy and requiring far less capex than OLED:
The technology is as energy efficient as LED technology, which means it is way ahead of OLEDs right now which offer beautiful displays but not necessarily a constant energy savings. In other words, while the future of OLEDs may seem bright (and companies like Samsung are still pursuing OLED displays while others like Sony have dropped out of the race), the future of LEDs is already here and the technology from Nanosys can mean vast improvements without much effort.
If you ever doubted that video games are big business Activision’s recent sales record should be enough to convince you. On its way to reaching $1 billion in sales in just over two weeks with Call of Duty: Modern Warfare 3, Activision smashed every entertainment sales record.
Every entertainment sales record.
That means books, movies and video games. Over its lifetime the franchise has generated in the neighborhood of $6 billion in revenue, which puts it squarely into a Star Wars-level stratosphere as one of the most valuable entertainment properties ever.
What does this have to do with high gamut color display technology?
One of the potential hurdles to widespread adoption of high color gamut display technologies is a lack of content that’s optimized to take advantage of all those extra colors.
With Hollywood-sized blockbuster sales comes Hollywood-sized budgets to create rich new universes for gamers to explore. The expanded creative palette that high color gamut technology offers game developers is a perfect fit. What color is the blood of a martian supposed to be when it explodes and why limit it to a range of colors typically seen on earth?
Additionally, on the platform side, electronics manufacturers could take advantage of a push into high gamut displays to differentiate their entire hardware/software ecosystem. We already know that the current PlayStation™ hardware is capable of the xvColor high gamut standard. Pairing that with wide color games and a TV that can show it might prove a useful differentiator for any platform.
Videogames may just be the driving force that finally pushes high gamut displays into the mainstream.
Great infographic that describes the history of color in videogames from colored cellophane overlays to millions of colors. The end of the graphic just hints at the next evolution in color for video games- wider gamuts that will give designers a whole new palette of colors to work with:
This week I am featuring a guest blogger here– Jason Hartlove, CEO of Nanosys, the Palo Alto, CA-based maker of high color gamut-enabling display products. The following is a fairly in-depth, technical look at how and why Nanosys’ quantum dot phosphor technology improves LED LCDs just by changing the color content of the backlight. Note: a shorter version of this article originally appeared in the October 2011 print edition of LEDs Magazine.
LCD technology has made great progress in the past few years with innovations such as high resolution and 3D, yet color performance continues to lag. Displays on popular tablets can only express about 20 percent of the color a human eye can see; HDTV’s, only 35 percent. Surprisingly, color performance in displays has actually gone backwards since the days of CRTs.
Still, LED backlit LCDs have become the standard for the mobile devices and are fast becoming so for televisions due to their high resolution, low cost and thin form factors. According to Paul Semenza, Senior Vice President of DisplaySearch, a leading display market research firm, LED backlights will be used in 47.5% of LCD televisions and 98.4% of notebook PC displays shipped in 2011.
While new technologies with better color capabilities have emerged in recent years, such as discrete RGB LED, YAG with red phosphor and OLED, they face critical hurdles to mass adoption; primarily cost, scale and lower brightness. Until now, consumers have chosen cheaper, thinner and more efficient displays over a truly cinema-quality experience- but could they have it all?
What’s wrong with my current display?
To better understand the limitations faced by current TV and display makers, let’s take a look inside an LCD. For those who are not familiar, a typical LCD is made up of essentially two major parts: a light source, called the back light unit (or BLU) and a Liquid Crystal Module (or LCM). (See FIG. 1)
FIG. 1. LED LCD exploded diagram
Usually, when a display is operating, the BLU is on, providing a uniform, white sheet of light behind the LCM. The LCM contains millions of pixels, each of which is split into sub pixels, typically with two green sub-pixels, one red and one blue. By controlling the amount of time each sub-pixel is “open” or allowing light to pass through it, and making use of the human eye’s persistence of vision, any color that can be rendered from a combination of red, green and blue can be displayed at each pixel location. Since the quality or fidelity of those colors is a direct function of the sub-pixel color quality, how good is the quality of red, green and blue light coming from each sub-pixel?
The color of each sub-pixel is a function of two things; the quality of the light in the BLU, and the color filter at the sub-pixel. The color filter will separate its component color from the white light of the BLU, for example, the red color filter on the red sub-pixels will cut off the green and blue light. However, to make a high quality color of red, either the filter function needs to be very narrow, which results in substantial attenuation and loss of brightness, or the red spectra in the BLU white light should be narrow and well matched to the desired peak red color. The same is true for the green and blue sub-pixels as well.
Since making perfect color filters is not practical from either a cost or brightness perspective, why not make a better white light?
The problem is, the LED light source at the heart of the BLU is starving those filters of the colors that they really need to shine. Today, white LEDs are very good at producing some of the spectrum of light that we see as ‘white’ but not all. While there are a variety of approaches for making white light from LEDs, the conventional approaches all suffer some drawback for LCD displays.
A YAG based white LED (i.e. Yttrium-Aluminum-Garnet phosphor pumped by an GaN blue source), produces a spectrum rich in blue with a broad yellow component. This light has very weak green and red content, and the spectra is widely distributed from aqua-marine through green, yellow, orange and red (see FIG. 2 below). When this light is filtered into the component RGB colors by the sub-pixels, the result is not accurate enough to produce the quality of color we see when we look at the natural world as illuminated by daylight.
FIG. 2. Spectrum of a conventional white LED (GaN + YAG) backlight, which does not provide a good match with red, green and blue color filters in the liquid-crystal module (LCM).
So, an ideal light source for an LED LCD BLU would therefore be something in between daylight and two-color white. For vibrant colors, it would need to generate lots of energy across all of the red, green and blue wavelengths used by the filters. But, for efficiency’s sake, it should also not spend energy producing light between R, G and B because we just won’t see that light after its passed through the filters.
So how do we do THAT?
To solve the problems described above, what we need is a new class of material, not found naturally occurring anywhere on Earth, that can be tuned to emit light at just the right wavelengths for our displays and do so very efficiently. Fortunately, nanotechnology researchers have been working on designing just such a material for decades, building it literally one atom at a time, and Nanosys, a company in Palo Alto, California has perfected the art. Called “Quantum Dots”, the tiny, nanocrystal phosphors they make are a bit bigger than a water molecule but smaller than a virus in size.
Unlike conventional phosphor technologies such as YAG that emit with a fixed spectrum, quantum dots can be fabricated to convert light to nearly any color in the visible spectrum. Pumped with a blue source, such as the GaN LED, they can be made to emit at any wavelength beyond the pump source wavelength with very high efficiency (over 90% quantum yield) and with very narrow spectral distribution of only 30 – 40nm full width at half maximum (FWHM).
The real magic of quantum dots is in the ability to tune (at the fabrication stage) the color output of the dots, by carefully controlling the size of the crystals as they are synthesized so that their spectral peak output can be controlled within 2 nanometers to nearly any visible wavelength.
This capability makes quantum dots stand out against emerging iterations of YAG phosphor technology such as red phosphor doped YAG, which adds some red-emitting phosphor to the green-yellow emitting YAG to boost color performance. This idea is similar to quantum dot technology in that it attempts to engineer a spectrum of white light by combining materials with different emission spectra. However, these crystalline phosphor materials are still fundamentally limited by their atomic structure and therefore cannot be precisely tuned to match either existing color filter or manufacturers desired specifications. This leaves display manufacturers with a system that still results in light and efficiency losses due to the relatively wide FWHM output of the phosphors and poor conversion efficiencies and stabilities of red phosphors.
With quantum dot technology, display designers will have the ability to tune and match the backlight spectrum to the color filters. This means displays that are brighter, more efficient, and produce truly vibrant colors.
FIG. 3. Spectrum from a Nanosys quantum-dot enhancement film (QDEF). The film contains green- and red- emitting phosphors and is stimulated by a blue GaN LED.
How does it all come together?
Engineering the quantum dots to precise display industry specifications isn’t enough on its own to revolutionize the way LCDs are experienced. The dots need to be easily integrated into current manufacturing operations with minimal impact on display system design if they are to be widely adopted. To do this, Nanosys spent a lot of time working with major display manufacturers to get the packaging just right so that it would be a simple, drop-in product that did not require any line retooling or process changes. The end result is called Quantum Dot Enhancement Film or QDEF.
FIG. 4. The quantum-dot enhancement film (QDEF) is designed to replace the diffuser in an LCD backlight unit (BLU) and is placed between the BLUE and the liquid-crystal module (LCM). The QDEF contains red- and green-emitting quantum dots and is illuminated by blue LEDs in the BLU.
Designed as a replacement for the an existing film in LCD backlights called the diffuser, QDEF combines red and green emitting quantum dots in a thin, optically clear sheet that emits white light when stimulated by blue light. (Of coursesome of that blue is allowed to pass through to make the B in RGB at the LCM). So manufacturers who’ve invested billions in plant and equipment for LCD production can simply slip this sheet into their process, change their ‘white’ LEDs to blue (the same LEDs but without the phosphor) and start producing LCD panels with the colors and efficiencies of the best OLEDs, at a fraction of the cost.
Nanosys is currently shipping production samples to display manufacturers and is on track to begin producing at commercial volumes by the end of 2011.
What does it look like?
The result is stunning color. A QDEF-enabled display can express over 60% of the spectrum a human eye can detect, compared with 20% for todays LED backlit LCD’s. This means that browsing through photos on your tablet will be more like holding a stack of high quality, professional prints in your hand and watching a movie on the big screen in your living room is more akin to attending a private screening at a Hollywood studio.
Comparison shot showing two 47" TVs with QDEF on the right and a YAG based display at left. While your display can't display the true difference in color it is possible to see that the frog on the left is just not as green (looks kind of yellow-ish by comparison)
LED backlit LCD TVs have established market dominance and tablet computers –which predominantly use LCDs– sales are expected to eclipse 100 million units over the next few years. Color is likely to be the next big differentiator in what is an increasingly cutthroat consumer display market as more players enter the market and alternative technologies are further developed.
Higher color performance displays will allow developers and content creators to create a stunning new visual experience for consumers. Display makers who can bring user experience closer to reality without sacrificing efficiency or cost will be able to establish a dominant market share.
You’d be surprised at how often these two terms are used interchangeably in describing display performance. In fact, their recent misuse by a top display executive at a major consumer electronics company was one of the chief inspirations for this blog.
Basically, it boils down to this:
More bits means more colors can be displayed
More gamut means more colors can be displayed
Got it yet?
While factually accurate, the statement above clearly illustrates the source of many a gamut vs bit depth misconception. Let’s dig a little deeper and define these terms.
First you should understand the simplicity with which modern displays create the color picture you are currently looking at. Digital displays create all the colors you see by mixing just three primary colors, much like you did while finger painting in grade school. So, red plus green equals yellow, red plus blue is magenta and all three primaries combined creates white.
So, what is bit depth? Bit depth refers to the number of bits that your computer uses to describe a specific color to your screen. A typical modern display has “8-bit” color depth, which is a shorthand way of saying “8 bits of data per primary color.” Since 8 bits translates into 256 distinct values, your computer can call for 256 distinct hues of red, green and blue.
While ‘256’ does not sound like a lot of colors – it’s actually quite impressive. Mixing 256 reds with 256 greens and 256 blues (256 x 256 x 256), in a massive expansion of the finger painting analogy from above, creates nearly 16.8 million possible colors. Not too bad, right?
Well, you might ask, how many different colors can I actually see? Turns out a number of studies have been conducted on this, and most researchers agree that humans can detect anywhere between 7-10 million unique colors (see: http://physics.info/color/). This means that even a measly 8-bit display should have plenty of color accuracy headroom above and beyond the performance of your eyes.
So, a more accurate way to describe bit depth would be: more bits mean that a higher number of distinct colors can be displayed.
If bit-depth refers to the number of distinct colors that can be displayed, where does that leave gamut? Perhaps the easiest way to think about gamut is as a measure of the range of colors that a display can show. Your 8-bit display may be able to show 16.8 million colors but that doesn’t tell you much about which colors. You see, not all reds, greens or blues are created equal. When your computer calls for a specific color of deeply saturated red, for example, what you actually see is limited by the physical capabilities of the systems in your display.
How is gamut measured?
Color gamut performance is measured by a variety of standards, typically defined by groups like the National Television System Committee (NTSC) as a way of maintaining consistent color, from capture, to broadcast to end viewer. Creative professionals like graphic designers and Hollywood cinematographers rely on these standards to make sure that their work looks how they intended it to across a variety of screens and print media. The most common gamut standard, developed by the NTSC in 1953 in anticipation of color television, which is typically referred to as simply “NTSC,” covers about 50% of what your eye can see. 58 years and a couple generations of IPads later, we must be able to do better than that, right?
The above diagram, called a “CIE Diagram” (CIE stands for Commission Internationale de l'Éclairage or International Commission on Illumination) is an abstract, two-dimensional (missing luminance) mathematical chromaticity model. In layman’s terms, what you are looking at is the full range of colors that humans can perceive, represented by the horseshoe shape and the subset of colors that HDTVs can display, inside the triangle. Note that the deepest reds, greens and blues are out of reach for HDTV.
Putting it all together
Now we can put the two definitions together to clarify the oversimplification from the introduction:
More bits means more distinct colors can be displayed, within a range of colors that is defined by the display’s gamut
For a really in depth look at how color is displayed on your screen check out Steve Patterson’s very informative, much more in depth post on this topic over at photoshopessentials.com.