Tablet Display Technology Shoot-Out Apple iPad 2 – Motorola Xoom – Asus Transform

[blaggard]

Tablet Display Technology Shoot-Out
Apple iPad 2 – Motorola Xoom – Asus Transformer

Dr. Raymond M. Soneira[/h][h=3]President, DisplayMate Technologies Corporation
Copyright © 1990-2011 by DisplayMate Technologies Corporation. All Rights Reserved.
This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated
into any other work without the prior written permission of DisplayMate Technologies Corporation

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Introduction:
Tablets are essentially large portable displays – handheld screens designed for conveniently viewing content and images anywhere you want while untethered. For Tablets the display is the single most expensive and important hardware component because it determines the quality of the visual experience for every application on the Tablet. In this very hot ultra-competitive category an outstanding display is the single best way for manufacturers to make their Tablets stand out from the competition – particularly for Android based devices that have nearly identical OS. On the flip side, cutting corners, costs and quality for the display is a serious mistake because it results in sub-standard image and picture quality for everything that runs on the Tablet – we have one example here.

In all of the Display Technology Shoot-Outs we take display quality very seriously and provide in-depth objective side-by-side comparisons of the displays based on detailed lab measurements and extensive viewing tests. The data and discussions in this review article are drawn from the individual articles for each Tablet in our Display Technology Shoot-Out series starting with the iPad 2, the Motorola Xoom and Asus Transformer. We will be regularly adding the best new Tablet contenders – next up will be the Acer Iconia and Samsung Galaxy Tab 10.

Results Highlights:
In this Results section we provide short comparative Highlights for each Tablet display based on comprehensive lab measurements and extensive side-by-side visual comparisons using test photos, test images and test patterns. We first discuss some Common Issues and shortcomings and then make some objective display predictions (and suggestions) for the next generation of Tablets including an analysis of several popular rumors. The Comparison Table below summarizes the lab measurements in the following categories: Screen Reflections, Brightness and Contrast, Colors and Intensities, Viewing Angles, Display Backlight Power Consumption, and Running Time on Battery.

Common Issues:
First, all of these Tablets have large shinny mirror-like screens that are good enough to use for personal grooming. Think of it as one less thing you need to carry – but it’s actually a very bad feature that requires higher screen brightness and more battery power to offset the reflected light, and it also causes eye strain. The larger Tablet screen size makes it harder to position yourself and the screen to avoid bright reflections. Second, all of these Tablets have a reduced Color Gamut that leads to images with reduced color saturation. It’s an intentional tradeoff made to increase screen brightness, power efficiency and battery run time. Third, all of these Tablets have a sharp decrease in Brightness and Contrast with Viewing Angle. This is a significant issue only when multiple viewers are watching a Tablet but may also require a single viewer to carefully adjust the Tablet orientation. Fourth, all of the current 1280x800 Android 3.1 Tablets have only 1280x752 available pixels because 48 pixels are reserved for the system bar with the navigation buttons. Finally, Android 3.1 continues with a substandard Gallery viewer for photos and images that provides 16-bit color processed up to 24-bits with poorly implemented dithering. It’s about time that gets fixed…

Apple iPad 2
The iPad 2 has an excellent display, virtually identical in performance to the impressive iPhone 4 Retina Display, with a somewhat higher pixel resolution but a much lower pixel density of 132 ppi due to its much larger screen size. The iPad 2 IPS LCD display is fairly well calibrated and delivers bright images with excellent contrast, reasonably accurate colors and very good Viewing Angle performance with small color shifts but a large decrease in Brightness, which is the case even for the best LCDs. A major shortcoming is a reduced Color Gamut, but the iPad 2 improves on-screen image color saturation by steepening its intensity scale – a simple trick the other displays fail to implement.

Asus Transformer
The Asus Transformer also has an IPS LCD like the iPad 2. It’s not as bright or as well calibrated as the iPad 2 but it still delivers very good performance including very good contrast, reasonably accurate colors and very good Viewing Angle performance like the iPad 2. But the Transformer screen has a 66 percent higher ambient light reflectance than the iPad 2. It has an 18-bit color display, but produces 24-bit color by using dithering (except in the Android Gallery viewer where there is 16-bit color with dithering as discussed above).

Motorola Xoom
The display on the Motorola Xoom is a lower performance LCD than on the other Tablets, compounded by poor factory calibration. Colors and color saturation were much worse than the other displays. The Xoom screen has 49 percent higher ambient light reflectance than the iPad 2 and the variation with Viewing Angle is awful. The Xoom also has a Dynamic Backlight that varies the screen brightness in a peculiar fashion – it slowly dims the screen based on the Average Picture Level down to about 60 percent and then just stops. It makes dim images dimmer – it’s counterproductive and just strange display behavior… The other Tablet displays have standard Backlights, which don’t vary the brightness with picture content.

And the Winner is…
For the current set of Tablets the iPad is the clear winner in every category, which is somewhat surprising considering it was the first Tablet to launch and the one that later competitors knew they had to beat – but as of yet none have succeeded. Next is the Asus Transformer, which delivers very good performance across the board and comes in a solid second, all the more impressive because it is $100 cheaper than the iPad 2 and $200 cheaper than the Motorola Xoom. And finally, the Motorola Xoom comes in a distant third and last place – it’s not a horrible display but definitely significantly below the display quality of the iPad 2 and Asus Transformer. This is all the more surprising because the Xoom is by far the most expensive Tablet, and Motorola previously included an outstanding display in the original Motorola Droid Smartphone – so they once knew how to deliver a great display. This time it seems they just settled for a cheap low-end poorly calibrated display. For details on all of the Tablets see the Comparison Table below.

What’s Coming Next
We will be regularly adding the best new Tablets to this Mobile Display Technology Shoot-Out series – next we’ll test the Acer Iconia and Samsung Galaxy Tab 10. We’ll also have a Display Shoot-Out between the Barnes & Noble Color Nook and the Amazon Color Tablet when it launches, plus a series for reflective Tablets with E-Ink, Pixel Qi and Mirasol displays.


The Next Generation of Tablet Displays
First we examine three popular Tablet rumors and then make some display predictions based on purely objective technical criteria.

Rumors:
There are lots of entertaining rumors regarding the next generation of Tablets and Smartphones – most are made up nonsense based on phony tips. Here is our objective technical analysis of three popular rumors:

First Rumor: The next generation Tablets will have OLED Organic LED displays. Right now this can be ruled out based on cost and insufficient production volume, especially in the case of the iPad. OLEDs are improving rapidly, but currently they have lower peak brightness and lower power efficiency than LCDs – both of which are very important for Tablets because of their relatively large screens. So, unlikely for the next generation, but undoubtedly coming in the near future…

Second Rumor: The next generation iPad will quadruple the number of screen pixels with a resolution of 2048x1536. This would undoubtedly be a great marketing move but it’s technically an overkill and comes with a large penalty in cost and performance – requiring significantly more processing power, more memory and battery power, plus lowering the display brightness efficiency. Hopefully display pixels will not follow the same path as the camera Mega Pixel wars – because like them more pixels lowers performance after reaching a certain point. Apple had to double the resolution on the iPhone 3GS because its 480x320 resolution was very low. The iPad is starting with a much higher 1024x768 so Apps hard coded for the iPad 1 and 2 can be rescaled easily by the OS up to the new iPad 3 resolution.

Third Rumor: An iPad Retina Display – to make the iPad 3 a Retina Display does not require the same pixels per inch (ppi) as the iPhone 4 Retina Display because it is typically held much further away from the eye, whose visual sharpness is based on angular rather than linear resolution. The iPad is typically held 15-18 inches away as opposed to the iPhone 4’s 12-15 inches. As a result, to meet the 300 ppi Retina Display specification made by Steve Jobs at WWDC for the iPhone 4, an iPad Retina Display would need only 240 ppi. So an iPad Retina Display could start anywhere above 1862x1397 pixels. That is still a major overkill that carries a significant performance and cost penalty – so it would be primarily a marketing ploy. See below for our recommendation.

Recommendations:
Here are a few generic recommendations for the next generation(s) of Tablets: There are quite a few things that manufacturers (including Apple) can do to improve their Tablet displays to stay competitive in this extremely competitive category. For advanced and proprietary recommendations and optimizations, manufacturers should contact DisplayMate Technologies.

First Recommendation: Reduce the Screen Reflectance using an anti-reflection screen coating together with a surface haze layer to cut down on mirror reflections. It will then be necessary to eliminate the air gap between the LCD and cover glass by optically bonding them together.

Second Recommendation: Based on the above discussion for an iPad Retina Display, a good technical and marketing compromise for Tablet resolution is 200 ppi. A 1600x1200 9.7 inch iPad display works out to 206 ppi. For the 10.1 inch Android Tablets 1792x1120 works out to 209 ppi. Image sharpness can be considerably enhanced even further with sub-pixel anti-aliasing, but even without it the Tablet displays will appear very sharp at 200 ppi.

Third Recommendation: Carefully increase the display Color Gamut and image color saturation by managing the light spectrum of the Backlight and the Intensity Scale Gamma.

Fourth Recommendation: The Ambient Light Sensors and Automatic Brightness Controls on all Smartphones and Tablets are very poorly implemented. That wastes precious battery power and also causes eye strain. See our BrightnessGate article, which also proposes an improved display User Interface.

DisplayMate Display Optimization Technology
All Tablet and Smartphone displays can be significantly improved using DisplayMate’s advanced scientific analysis and mathematical display modeling and optimization of the display hardware, factory calibration, and driver parameters. This article is a lite version of our intensive scientific analysis – before the benefits of our DisplayMate Display Optimization Technology, which can correct or improve all of these issues. If you are a display or product manufacturer and want to significantly improve display performance for a competitive advantage then Contact DisplayMate Technologies.

Tablet Display Shoot-Out Comparison Table:
Below we compare the displays on the Apple iPad 2, Motorola Xoom and Asus Transformer based on objective measurement data and criteria.
For details, measurements, in-depth explanations and analysis see the Article Links below for the individual dedicated articles for each device.

Categories	Apple iPad 2 Article Link	Motorola Xoom Article Link	Asus Transformer Article Link	Comments
Display Technology	9.7 inch IPS LCD	10.1 inch LCD	10.1 inch IPS LCD	Liquid Crystal Display and In Plane Switching.
Screen Shape	4:3 = 1.33 Aspect Ratio	16:10 = 1.60 Aspect Ratio	16:10 = 1.60 Aspect Ratio	The iPad screen has the same shape as 8.5x11 paper. Android Tablets have an active screen similar to HDTVs.
OS Version for the Tests	iOS 4.3	Android 3.1	Android 3.1	The current OS versions available during testing.
Display Resolution	1024 x 768 pixels	1280 x 800 pixels 1280 x 752 active	1280 x 800 pixels 1280 x 752 active	The more Pixels and Sub-Pixels the better. Android 3.1 Tablets reserve 48 pixels for Buttons and Status.
Pixels Per Inch	132 ppi Good	149 ppi Good	149 ppi Good	At 12 inches from the screen 20/20 vision is 286 ppi. Best human vision is about 20/10 vision or 572 ppi. See this on the visual acuity for a true Retina Display
Display Color Depth	Full 24-bit color	Full 24-bit color	18-bit color with dithering to 24-bit color	The iPad 2 produces images with relatively smooth and artifact free colors and intensities.
Photo Viewer Color Depth	Full 24-bit color	16-bit color with poor dithering to 24-bit color	16-bit color with poor dithering to 24-bit color	Android 3.1 continues with a poor Gallery viewer that provides 16-bit color with poorly implemented dithering.
Overall Assessments This section summarizes the results of all of the extensive lab tests and viewing tests performed on all of the Tablets. For details, measurements, in-depth explanations and analysis see the Links for the individual dedicated articles for each Tablet. The iPad 2 had the best display overall. The Asus Transformer was a very good second. The Motorola Xoom was a distant third and poorest display.
Viewing Tests	Good Images Photos and Videos have too little color and too much contrast Small Color Shifts with Viewing Angle	Subdued Images Photos and Videos have too little color and too little contrast Large Color Shifts with Viewing Angle	Good Images Photos and Videos have too little color and good contrast Small Color Shifts with Viewing Angle	The Viewing Tests examined the accuracy of photographic images by comparing the displays to a calibrated studio monitor and HDTV. In side-by-side visual comparisons all viewers rated the iPad 2 the Best, the Asus Transformer “Very Good” and the Motorola Xoom the “Worst.”
Suggestions and Conclusions	Suggestions and Conclusions for Apple iPad 2	Suggestions and Conclusions for Motorola Xoom	Suggestions and Conclusions for Asus Transformer	Our Conclusions and Suggestions for improving each of the displays.
Overall Display Assessment	Excellent 1st Gen Display But needs major updates for the next generation	Mediocre Display The Most Expensive	Very Good Display The Least Expensive	The iPad 2 had the best display overall. The Asus Transformer was a very good second. The Motorola Xoom was a distant third and decidedly worst.
	Apple iPad 2	Motorola Xoom	Asus Transformer
Screen Reflections Figure 1. Screen Reflection Photos Click to Enlarge All of these screens are large mirrors good enough to use for personal grooming – but it’s actually a very bad feature… We measured the light reflected from all directions and also direct mirror (specular) reflections, which are much more distracting and cause more eye strain. The 10 – 15 percent reflections can make the screen much harder to read even in moderate ambient light levels, requiring ever higher brightness settings that waste precious battery power. Hopefully manufacturers will reduce the mirror reflections with anti-reflection coatings and haze surface finishes.
Average Screen Reflection Light From All Directions	8.7 percent	13.0 percent	14.4 percent	Measured using an Integrating Hemisphere. The Motorola Xoom and Asus Transformer reflect over 50 percent more light than the iPad 2.
Mirror Reflections Percentage of Light Reflected	10.8 percent	13.6 percent	15.1 percent	These are the most annoying types of reflections. Measured using a narrow collimated pencil beam of light reflected off the screen.
	Apple iPad 2	Motorola Xoom	Asus Transformer
Brightness and Contrast The Contrast Ratio is the specification that gets the most attention, but it only applies for low ambient light, which is seldom the case for mobile displays. Much more important is the Contrast Rating, which indicates how easy it is to read the screen under high ambient lighting and depends on both the Maximum Brightness and the Screen Reflectance. The iPad is decidedly the Best in Brightness, Contrast Ratio and Contrast Rating for High Ambient Light.
Measured Maximum Brightness is the Peak Luminance for White	Brightness 410 cd/m2 Excellent	Maximum 408 cd/m2 Dynamic Backlight reduces it to 257 cd/m2	Brightness 325 cd/m2 Good	Maximum Brightness is very important for mobile because of the typically high ambient light levels. Dynamic Backlight on the Motorola Xoom curiously reduces brightness with Average Picture Level.
Black Level at Maximum Brightness	Black is 0.43 cd/m2 Very Good for Mobile	Black is 0.56 cd/m2 Dynamic Backlight Black is 0.35 cd/m2	Black is 0.42 cd/m2 Very Good for Mobile	Black brightness is important for low ambient light, which is seldom the case for mobile devices. Dynamic Backlight also reduces the Black Level.
Contrast Ratio Relevant for Low Ambient Light	962 Very Good for Mobile	729 Very Good for Mobile	769 Very Good for Mobile	Only relevant for low ambient light, which is seldom the case for mobile devices. Defined as Maximum Brightness / Black Brightness.
Contrast Rating for High Ambient Light	47 Very Good	20 - 31 Good	23 Good	Indicates how easy it is to read the screen under high ambient lighting. Very Important! Defined as Maximum Brightness / Average Reflectance.
	Apple iPad 2	Motorola Xoom	Asus Transformer
Colors and Intensities Figure 2. Color Gamuts Click to Enlarge Figure 3. Intensity Scales Click to Enlarge Figure 4. Color Differences Click to Enlarge The Color Gamut, Intensity Scale, and White Point determine the quality and accuracy of all displayed images and all the image colors. Bigger is definitely Not Better because the display needs to match all the standards that were used when the content was produced. For LCDs a wider Color Gamut reduces the power efficiency and the Intensity Scale affects both image brightness and color mixture accuracy. The Motorola Xoom was the worst performer.
White Color Temperature	6,991 degrees Kelvin Close to D6500	7,557 degrees Kelvin White Slightly Too Blue	6,570 degrees Kelvin Very Close to D6500	D6500 is the standard White for most content and necessary for accurate color reproduction.
Color Gamut See Figure 2	Color Gamut Too Small 61 percent of Std See Figure 2	Color Gamut Too Small 55 percent of Std See Figure 2	Color Gamut Too Small 56 percent of Std See Figure 2	sRGB / Rec.709 is the color standard for most content and needed for accurate color reproduction. Note that Too Large is visually worse than Too Small.
Picture Color Saturation	Saturation Too Low Subdued Colors	Saturation Too Low Weak Colors	Saturation Too Low Subdued Colors	Picture Color Saturation depends on Both the Color Gamut and the Intensity Scale Gamma.
Intensity Scale and Image Contrast See Figure 3	Good Contrast Too High	Contrast Irregular Typically Too Low	Good Contrast Varies	The Intensity Scale controls image contrast needed for accurate image reproduction. See Figure 3
Gamma for Intensity Scale See Figure 3	Good 2.66 Gamma Too High	Poor 1.68 – 2.43 Gamma Very Irregular	Good 2.10 – 2.23 Gamma a Bit Irregular	Gamma of 2.2 is the standard and needed for accurate image reproduction. See Figure 3
	Apple iPad 2	Motorola Xoom	Asus Transformer
Viewing Angles The variation of Brightness, Contrast, and Color with viewing angle is especially important for Tablets because of their large screen and multiple viewers. The typical manufacturer 176+ degree specification for LCD Viewing Angle is nonsense because that is where the Contrast Ratio falls to a miniscule 10. For most LCDs there are substantial degradations at less than ±30 degrees, which is a small angle. The Motorola Xoom was by far the worst performer.
Brightness Decrease at a 30 degree Viewing Angle	58 percent Decrease Falls to 171 cd/m2 Very Large Decrease	52 percent Decrease Falls to 196 cd/m2 Dynamic Backlight Falls to 124 cd/m2 Very Large Decrease	58 percent Decrease Falls to 135 cd/m2 Very Large Decrease	Screens become less bright when tilted. LCD brightness variation is generally very large.
Contrast Ratio at a 30 degree Viewing Angle	564 Very Good for Mobile	105 Poor - Very Low	438 Good for Mobile	A measure of screen readability when the screen is tilted under low ambient lighting.
Primary Color Shifts at a 30 degree Viewing Angle	Small Color Shift Δ(u’v’) = 0.0100 2.5 times JNCD	Small Color Shift Δ(u’v’) = 0.0124 3.1 times JNCD	Small Color Shift Δ(u’v’) = 0.0110 2.8 times JNCD	JNCD is a Just Noticeable Color Difference. IPS LCDs have a smaller color shift with angle.
Color Shifts for Color Mixtures at a 30 degree Viewing Angle Reference Brown (255, 128, 0)	Small Color Shift Δ(u’v’) = 0.0047 1.2 times JNCD	Large Color Shift Δ(u’v’) = 0.0435 11 times JNCD	Small Color Shift Δ(u’v’) = 0.0056 1.4 times JNCD	JNCD is a Just Noticeable Color Difference. Reference Brown is a good indicator of color shifts with angle because of unequal drive levels and roughly equal luminance contributions from Red and Green.
	Apple iPad 2	Motorola Xoom	Asus Transformer
Display Backlight Power Consumption The power used by the Backlights were measured. Since the displays have different screen sizes and maximum brightness the values were also scaled to the same screen brightness and screen area in order to compare their relative power efficiencies. Although not a big surprise it was nice to see that all had essentially identical power efficiencies from their LCD optics and LED backlights.
Display Backlight Power at Maximum Brightness	2.7 watts	2.6 watts	2.1 watts	Lower power consumption is important for energy efficiency and improving running time on battery.
Display Backlight Power Efficiency same Peak Luminance 325 cd/m2 same 10.1 inch screen area	2.2 watts	2.1 watts	2.1 watts	This compares the Relative Power Efficiency by looking at the same screen brightness and screen area.
	Apple iPad 2	Motorola Xoom	Asus Transformer
Running Time on Battery The running time on battery was determined with the Brightness sliders set for maximum, middle and minimum brightness with the Tablet in Airplane Mode with no running applications and with Auto Brightness turned off. Note that Auto Brightness can have a considerable impact on running time but we found abysmal performance for both the iPhone and Android Smartphones in our BrightnessGate analysis of Ambient Light Sensors and Automatic Brightness.
Running Time At Maximum Brightness Setting	7.2 hours	6.1 hours	5.9 hours	Display always On at the Maximum setting with Airplane Mode and no running applications.
Running Time At Middle Brightness Slider Setting	11.8 hours	data soon	data soon	Display always On at the Middle slider setting with Airplane Mode and no running applications.
Running Time At Minimum Brightness Setting	19.8 hours	data soon	11.1 hours	Display always On at the Minimum setting with Airplane Mode and no running applications.
Categories	Apple iPad 2 Article Link	Motorola Xoom Article Link	Asus Transformer Article Link	Comments

About the Author:
Dr. Raymond Soneira is President of DisplayMate Technologies Corporation of Amherst, New Hampshire, which produces video calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers. See www.displaymate.com. He is a research scientist with a career that spans physics, computer science, and television system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from Princeton University, spent 5 years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested, and installed color television broadcast equipment for the CBS Television Network Engineering and Development Department. He has authored over 35 research articles in scientific journals in physics and computer science, including Scientific American. If you have any comments or questions about the article, you can contact him at dtso.info@displaymate.com.

About DisplayMate Technologies:
DisplayMate Technologies specializes in advanced mathematical display technology optimizations and precision analytical scientific display diagnostics and calibrations to deliver outstanding image and picture quality and accuracy – while increasing the effective visual Contrast Ratio of the display and producing a higher calibrated brightness than is achievable with traditional calibration methods. This also decreases display power requirements and increases the battery run time in mobile displays. This article is a lite version of our intensive scientific analysis of smartphone and mobile displays – before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the deficiencies – including higher calibrated brightness, power efficiency, effective screen contrast, picture quality and color and gray scale accuracy under both bright and dim ambient light, and much more. Our advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. For more information on our technology see the Summary description of our Adaptive Variable Metric Display Optimizer AVDO. If you are a display or product manufacturer and want our expertise and technology to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.

Article Links: Apple iPad 2 LCD Display
Article Links: Motorola Xoom LCD Display
Article Links: Asus Eee Pad Transformer LCD Display
Article Links: Smartphone "Super" LCD-OLED Display Technology Shoot-Out
Article Links: Smartphone Automatic Brightness Controls and Light Sensors are Useless
Article Links: Mobile Display Shoot-Out Article Series Overview and Home Page
Article Links: Display Technology Shoot-Out Article Series Overview and Home Page


Source: http://www.displaymate.com/Tablet_ShootOut_1.htm

[Geko]

A colleague had an asus transformer. He said the tablet was very good. But the screen was awful. He sent it back and is waiting to test the Samsung tab 10.1 when it launches in a month or 2.