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Tablet Display Technology Shoot-Out
Apple iPad 2 – Motorola
Xoom – Asus Transformer
Acer Iconia – Samsung
Galaxy Tab
Dr. Raymond M. Soneira
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
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.
When
these 5 Tablets are viewed together side-by-side, the differences in their
displays are blatantly obvious – and they are blatant differences! This is
especially true for the Android Tablets because they all have identical 10.1
inch 1280 x 800 screens running virtually identical software. How could there
be such a large disparity in a highly competitive market? The price points
are all reasonably similar so that is not the primary factor. One major issue
is the manufacturers are all scrambling to get their products to market so
there isn’t enough time to properly engineer everything. But the biggest
factor is undoubtedly the explosive growth in the demand and volume of mobile
displays, so many existing and new factories don’t have the time and/or
expertise to properly manufacture and calibrate all the displays they are
producing.
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 Apple iPad 2, the Motorola Xoom,
the Asus
Transformer, the Acer Iconia,
and the Samsung
Galaxy Tab 10.1. We will be regularly adding the best new Tablet
contenders – Stay Tuned...
Results Highlights
In this
Results section we provide short comparative Highlights for each Tablet
display based on the comprehensive lab measurements and extensive
side-by-side visual comparisons using test photos, test images and test
patterns that are presented in later sections. We first discuss some Common Issues and Screen
Myths, 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 in the following
section 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 shiny mirror-like screens that are good
enough to use for personal grooming. Think of it as one less thing you need to carry –
seriously, 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
both yourself and the screen to avoid bright reflections. Second: all of these Tablets have a reduced
Color Gamut that produces images with less saturated colors. 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 these Tablets have an unsatisfactory
Ambient Light Sensor and Automatic Brightness Control, which wastes battery
power and causes eye strain – see the Recommendations below. Fifth: 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. Sixth: 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… Samsung to its credit has fixed
this on the Galaxy Tab. Finally: there was not a single bad pixel on any of
the tested units – congratulations to all! But most of the manufacturer
warranties state that bad pixels are entirely normal and not a defect, which
is not right… Asus is the only manufacturer to offer enclosed documentation
with a precise pixel defect policy, but it requires 2 adjacent bad pixels, or
up to a total of 8 bad pixels for replacement, which most consumers would
find highly objectionable.
Screen Myths
Most
people (and reviewers) seem to believe that the 10.1 inch screens (measured
diagonally) on the Android Tablets are larger than the 9.7 inch iPad screen –
but they are actually 5 percent smaller than the iPad in terms of the image
area of the screen, which is what really counts. This is due to both Aspect
Ratio geometry (the screen area decreases as the Aspect Ratio increases) and
the Android system bar, which reduces the image area.
The shape
of the screens are also significantly different: the iPad has an Aspect Ratio
of 4:3 = 1.33 (the ratio of width to height) and the Android Tablets all have
an Aspect Ratio of 16:10 = 1.60. But because of the
Android system bar the Aspect Ratio of the image area is larger, 1.70, which
is rather close to the HDTV 16:9 Aspect Ratio of 1.78. So Android Tablets are
very well suited for watching widescreen video in Landscape mode. However,
they are generally considered too narrow to be very useful in Portrait mode.
On the other hand, the iPad does not have a widescreen, but instead an Aspect
Ratio very close to standard 8.5 x 11 inch paper, so it is naturally very
good for reading lots of content in Portrait mode. In many cases it is also
better for reading content in Landscape mode because the iPad’s image height
is 5.8 inches while the Android Tablets have an image height of only 5.0
inches, so you can see more on the iPad before needing to scroll. On the
other hand, for watching 16:9 widescreen videos, the iPad image height is
only 4.4 inches, which is smaller than the Android height of 4.8 inches for
16:9 widescreen videos. So the best screen shape depends on your intended mix
of applications.
Tablet Highlights
For details and in-depth analysis see the Comparison
Table below.
Apple iPad 2 Highlights
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 that is also used by the Galaxy Tab, but the other displays
fail to implement this (and the Motorola Xoom does the reverse).
Asus Transformer Highlights
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 reflects 66 percent more
ambient light 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 Highlights
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, and the variation with Viewing Angle
is awful. The Xoom screen reflects 49 percent more ambient light reflectance
than the iPad 2. 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…
All of the other Tablet displays have standard Backlights, which don’t vary
the brightness with picture content (the Galaxy Tab makes it an option).
Acer Iconia Highlights
The Acer
Iconia A500 also has a lower performance LCD like the Motorola Xoom, but it’s
better in a few decisive categories and is much better calibrated. Of
particular noteworthiness, it was the definitive leader in Contrast Ratio,
with more than double that of any other tested Tablet because of its very
dark black. We triple checked this with some special DisplayMate test pattern
measurements to make sure that it wasn’t due to a Dynamic Backlight. But it
really has a true very dark black, which is quite noticeable in a dark room.
Unfortunately the black brightness increases rapidly with Viewing Angle. The
Iconia also had a nicely calibrated intensity scale, but it would actually
have been better off with a steeper intensity scale in order to increase
color saturation in the same fashion as the iPad 2 and Galaxy Tab.
Samsung Galaxy Tab 10.1 Highlights
The
Galaxy Tab display has a PLS (Plane to Line Switching) LCD, which is
Samsung’s version of IPS, and it performs comparably to IPS – sometimes a bit
better and sometimes not. It’s an impressive mobile display with a lot better
standout performance than all of the other Android Tablets – except in one
very important category… If you like to watch your HDTV with the Color
Saturation control set to maximum then you will be right at home with the
Galaxy Tab because Samsung has turned the color obnoxiously high with no way
to lower it (see below). It’s tolerable for images that don’t have much color
to begin with, but it hurts to look at images that have strong color content.
Moderation rather than the sledge hammer approach to color would have
resulted in an outstanding display. This could be fixed easily with a
software update by adding a color picture control that lets users adjust the
color to their liking – see our Third
to Fifth Recommendations below.
And the
Winner is…
While the
iPad 2 display easily outperformed all of the previous Android Tablets, with
the new Galaxy Tab 10.1, Samsung has delivered the first Android Tablet with
an impressive, potentially outstanding display, but then ruined it by turning
up the color level to obnoxious levels – apparently in an effort to
overcompensate and blatantly standout from the other mobile LCD displays that
have subdued color. But in the case of color, too little is a lot better than
too much… As a result the iPad 2 still delivers the best color picture
quality and accuracy of all of the Tablets, even though its colors are somewhat
subdued. As things stand, based on all of the display tests, the iPad 2 and
Galaxy Tab 10.1 are reasonably close in performance in most categories, so
it’s almost a tie, but the Galaxy Tab is ahead more often than the iPad 2, so
the Galaxy Tab is the Winner, by a nose… But should Samsung or Android add a
color picture control to the Galaxy Tab with a software update as we describe
below, then the Galaxy Tab would be the decisive Winner, by a lot. Of course,
Apple could do the same… What is also impressive is that the iPad 2 is still
delivering top display performance close to what many predict is the end of
its product cycle, with lots of interesting predictions for the Next
Generation, which we discuss and analyze below.
Coming in
a solid third place is the Asus Transformer, which delivers very good display
performance across the board, all the more impressive because it is $100 less
expensive than the iPad 2 and Galaxy Tab, and $200 less than the Motorola
Xoom. Next is the Acer Iconia A500, which has a display that is somewhat
similar in performance to the last place Motorola Xoom, but is better in a
few decisive categories and is much better calibrated. It’s $50 less
expensive than the iPad 2 and Galaxy Tab but $50 more than the Asus
Transformer. And finally, the Motorola Xoom comes in last place – like the
Acer Iconia it’s not a horrible display but definitely significantly below
the display quality of the iPad 2, Galaxy Tab, 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, which still delivers the best picture quality of any mobile
display we have ever tested – 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 – Stay Tuned... 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 predictions that are
based on purely objective technical criteria – but note that marketing and
other issues are major factors in what will appear in the future
generation(s) of Tablets.
Rumors:
There are
lots of entertaining rumors regarding the next generation of Tablets and
Smartphones – most are made up nonsense based on phony tips. We don’t have
any inside information on what’s coming, so here is some purely 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 (which is sounding more and more likely) 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 could 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 resolution rather than linear
ppi 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 – but in this very competitive market it is undoubtedly coming
sometime soon... 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. This will
significantly improve screen visibility under bright ambient lighting and
result in longer battery running time.
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: The display User Interface on both the iPad and Android
Tablets simply has a simple Brightness Control. The display needs a Pizzazz
picture control that simultaneously adjusts the color and image contrast
based on user visual preferences – similar in concept to the Sound Equalizer
for audio found on most mobile devices (but not as complicated). And the external
volume controls found on all mobile devices should also allow for easy
tweaking of the display brightness.
Fourth Recommendation: Carefully increase the display Color Gamut and color
saturation by managing the light spectrum of the Backlight and the Intensity
Scale Gamma.
Fifth 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. They should also be
used to adjust the picture control discussed above in order to partially
compensate for washed out images under bright ambient lighting. 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. We can improve the performance of any specified set of display
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.
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