Apple iPad 2 and iPhone 4 LCD Display Shoot-Out
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
The display
on the iPhone 4 has received widespread praise including the DisplayMate Best Mobile
Display Award. But the LCD display on the iPad 2 has been the subject of
many debates and rumors regarding its specs and performance, especially the
resolution and Pixels Per Inch, which is only 132 ppi compared to the iPhone 4
Retina Display’s 326 ppi. There is no question that a higher ppi is better, but
the real question is whether the iPad 2 delivers good display performance when
considering its price point and battery power constraints (and also
availability in sufficient quantities for Apple). What has amazed and impressed
me about the iPad 2 is that Apple has included a first rate IPS LCD panel at a
very aggressive price point and not used a cheaper second or third tier LCD,
which is what most manufacturers do under these circumstances.
In this
article we will provide in-depth objective side-by-side comparisons of the
displays based on detailed lab measurements and extensive viewing tests to set
the record straight. The data and discussions are drawn from the individual
dedicated articles in our Display Technology Shoot-Out series for each device:
the iPad 2, iPhone 4 and iPhone 3GS. The
older iPhone 3GS is included as a baseline to show how mobile displays have
evolved since 2009.
As we show
in the Comparison Table below the display on the iPad 2
delivers almost identical performance to the impressive iPhone 4 Retina
Display. Although the iPad has a higher pixel resolution than the iPhone 4, the
screen is much larger so the number of Pixels Per Inch is only 132 ppi compared
to the iPhone 4 Retina Display value of 326 ppi. Lower ppi makes the pixels
more apparent, an effect called pixelation. The very high ppi is a major
marketing feature for the iPhone 4, but it’s actually something of an overkill
(and primarily there for App compatibility) because existing anti-aliasing
methods can successfully reduce noticeable pixelation at lower resolutions and
ppi.
While the
iPad 2 has excellent LCD display hardware, there are two significant shortfalls
in the OS display software that Apple could “easily” fix with a software update
that would notably improve the already excellent iPad 2 display performance.
The Current Anti-Aliasing Reduces Perceived Sharpness of Text and
Graphics
Anti-aliasing makes images appear less pixelated and
easier to read through the precise blending of adjacent pixel content in
software. This is especially important for text and graphics on the iPad
because of its much lower Pixels Per Inch than the iPhone 4. The anti-aliasing
on the iPad 2 is far from state-of-the-art and degrades the perceived sharpness
of text and graphics. You don't notice this same effect on the iPhone 4 because
of its very high ppi, but the much lower ppi on the iPad needs good
anti-aliasing to significantly improve perceived sharpness and rendering. This
really stood out when I was reading the New York Times using Safari on the iPad
2 that was sitting right next to an Asus 1201N Netbook (also running Safari)
that has identical to the iPad 768 vertical pixel count, virtually identical
screen height of 5.9 inches and 130 ppi. On-screen the articles were laid out
in exactly the same way but the text and graphics looked substantially better
on the Netbook because of the sub-pixel anti-aliasing it uses (called ClearType
in Windows, which is Microsoft’s implementation of this technology). What’s
more, the IPS LCD display on the iPad is much better than the LCD on the
Netbook so this result is even more striking. It’s very hard to show this
effect with a screen shot here because the camera, your display, and the jpg
image processing all add their own anti-aliasing and other digital artifacts.
Anti-aliasing is done in iOS software so Apple could (or
rather should) add sub-pixel anti-aliasing to the iPad, especially given the
new high-speed processing enhancements that were added to the iPad 2, and it
can be done even better on the iPad than with the generic software on the
Netbook. It will make a big visual improvement and take some of the unwarranted
pressure off the iPad’s current ppi.
Automatic Brightness Controls Do Not Work Properly – and the Auto
Brightness Bug
The
Automatic Brightness controls on Smartphones and Tablets are (in principle)
designed to appropriately set the screen brightness based on the current
ambient light levels. This not only has a major impact on screen viewability
and readability, eye comfort, and fatigue, but it plays a very important role
in managing display power in order to maximize battery run time, something
golden for all mobile displays. Unfortunately, Auto Brightness is very poorly
implemented on all mobile devices including the iPhone 4 and iPad 2. This is
examined in detail in our BrightnessGate article Smartphone
Automatic Brightness Controls and Light Sensors are Useless. In addition,
both the iPhone 4 and iPad 2 have an Auto Brightness Bug, where they lock onto
the brightest ambient light sensor value that has been measured at any point
starting from the time unit was awakened and hold that peak value even after
the ambient light decreases substantially afterwards. This keeps the screen
overly bright for the current conditions and wastes precious battery power. In
fact, from the Running Time on Battery entries in the Table
below, display brightness makes up to a 12.6 hour difference in the total
running time on battery – this is a big effect worth taking advantage of by
properly implementing Automatic Brightness!
Again, this
is all done in the iOS software so Apple could (or rather should) fix Auto
Brightness for all iOS devices.
Future Display Hardware Upgrades for Smartphones and Tablets
There are
quite a few things that Apple and other manufacturers can do to improve the
displays for their next generation of Smartphones and Tablets in order to stay
competitive in this extremely competitive category. We’ll cover this in Part II
(next week) on The Next
Generation of Smartphone and Tablet Displays. For example, we’ll discuss
ways to increase the LCD color gamut, examine IPS LCD versus OLED, display
power efficiency, Ambient Light Sensors, Automatic Brightness Controls, and the
appropriate screen resolution and ppi that takes into account performance,
cost, and power.
DisplayMate Display Optimization Technology
All of
these displays can be significantly improved and optimized on many different
levels through DisplayMate’s advanced mathematical display modeling and
scientific analysis. This article is a lite version of our intensive scientific
analysis of smartphone and tablet 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. 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.
Display Shoot-Out Comparison Table
Below we compare the
displays on the Apple iPad 2, iPhone 4, and iPhone 3GS based on objective
measurement data and criteria. The older iPhone 3GS is included as a baseline
to show how mobile displays have evolved since 2009. For
details, measurements, in-depth explanations and analysis see the Article Links below for the
individual dedicated articles for each device.
|
Categories
|
Apple
iPhone 3GS
Article Link
|
Apple
iPhone 4
Article Link
|
Apple iPad
2
Article Link
|
Comments
|
|
Display Technology
|
3.5 inch
LCD
Active
Matrix
|
3.5 inch
IPS LCD
Active
Matrix
|
9.7 inch
IPS LCD
Active
Matrix
|
Liquid Crystal Display and In Plane Switching.
All current displays have an Active Matrix.
|
|
Screen Shape
|
3:2 =
1.50
Aspect
Ratio
|
3:2 =
1.50
Aspect
Ratio
|
4:3 =
1.33
Aspect
Ratio
|
The iPad screen has the shape of 8.5x11
paper.
The iPhones have a wider screen that is
a
closer match to photos and video content.
|
|
Display Resolution
|
480 x 320
pixels
|
960 x 640
pixels
|
1024 x 768
pixels
|
The more Pixels and Sub-Pixels the
better
|
|
Pixels Per Inch
|
163 ppi
Good
|
326 ppi
Excellent
|
132 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
|
|
Hardware Color Depth
|
18-bit
color
|
24-bit
color
|
24-bit
color
|
24-bit color produces 16.8 Million screen
colors
|
|
Displayed Color Depth
|
18-bits
with
Dithering
to 24-bits
|
Full
24-bits
|
Full
24-bits
|
iPhone 4 and iPad 2 produce images with
relatively
smooth and artifact free colors and
intensities.
|
|
Viewing Tests
|
Subdued
Images
Photos and
Videos
have too little
color
and too
little contrast
|
Good
Images
Photos and
Videos
have too
little color
and too
much contrast
|
Good
Images
Photos and
Videos
have too
little color
and too
much contrast
|
The Viewing Tests examined the accuracy
of
photographic images by comparing the
displays
to a calibrated studio monitor and HDTV.
|
|
Suggestions and Conclusions
|
Suggestions
and
Conclusions
for
Apple
iPhone 3GS
|
Suggestions
and
Conclusions
for
Apple
iPhone 4
|
Suggestions
and
Conclusions
for
Apple
iPad 2
|
Part II of this article will be on what enhancements
the manufacturers need to implement for
the next
generation of displays in Smartphone and
Tablets.
|
|
Overall Display Assessment
|
Outdated
Display
|
Excellent
Display
DisplayMate Award
Best
Mobile Display
|
Excellent
Display
but it
needs
Driver
Updates
then a PPI
Upgrade
for the
next generation
|
Other than PPI resolution the iPad 2
display delivers
similar performance to the iPhone 4
Retina Display.
It needs a software update for anti-aliasing
and
another for the Auto Brightness Control,
then
higher PPI resolution for the next
generation.
|
|
Brightness and Contrast
|
|
Measured Maximum Brightness
is the Peak Luminance for White
|
Brightness
428 cd/m2
Excellent
------
No Apple
Brightness
Specs
|
Brightness
541 cd/m2
Excellent
-------
Apple
Advertises
500 cd/m2
typical
|
Brightness
410 cd/m2
Excellent
-------
No Apple
Brightness
Specs
|
Maximum Brightness is very important for
mobile
because of the typically high ambient
light levels.
All are very bright but the iPhone 4
exceeds
Apple’s advertised value – impressive!
|
|
Black Level
at Maximum Brightness
|
Black 3.1
cd/m2
Very High
|
Black 0.48
cd/m2
Very Good
for Mobile
|
Black 0.43
cd/m2
Very Good
for Mobile
|
Black brightness is important for low
ambient light,
which is seldom the case for mobile
devices.
|
|
Contrast Ratio
Relevant for Low Ambient Light
|
138
Poor
------
No Apple
Contrast
Specs
|
1,117
Very Good
for Mobile
------
Apple
Advertises
800
typical
|
962
Very Good
for Mobile
------
No Apple
Contrast
Specs
|
Only relevant for low ambient light,
which is seldom the case for mobile
devices.
Don’t confuse our measured objective
values with
the often inflated manufacturer Contrast
specs.
|
|
Screen Reflectance
of Ambient Light
|
Reflects
9.2 percent
Good
|
Reflects
7.0 percent
Very Good
|
Similar to
iPhone 4
Measurement
coming
with Part II
|
Reflectance is the most important spec
for mobile
because of the typically high ambient
light levels.
|
|
Screen Bright Contrast Rating
for High Ambient Light
|
Bright
Contrast 47
Very Good
|
Bright
Contrast 77
Excellent
|
Similar to
iPhone 4
Measurement
coming
with Part II
|
Indicates how easy it is to read the
screen
under high ambient lighting. Very
Important!
Defined as Maximum Brightness / Reflectance
|
|
|
|
White Color Temperature
|
6,977
degrees Kelvin
Close to
D6500
|
7,781
degrees Kelvin
White
Slightly Too Blue
|
6,991
degrees Kelvin
Close to
D6500
|
D6500 is the standard White for most
content
and necessary for accurate color
reproduction.
|
|
Color Gamut
See Figure 1
|
Color
Gamut Too Small
60 percent
of Std
See Figure 1
|
Color
Gamut Too Small
64 percent
of Std
See Figure 1
|
Color
Gamut Too Small
61 percent
of Std
See Figure 1
|
sRGB / Rec.709 is the color standard for
most
content and needed for accurate color
reproduction.
Too Large is visually worse than Too
Small.
|
|
Picture Color Saturation
|
Saturation
Very Low
Subdued
Colors
|
Saturation
Too Low
Subdued
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 2
|
Poor -
Very Low
and
Concave
|
Good
Contrast
Too High
|
Good
Contrast
Too High
|
The Intensity Scale controls image
contrast needed
for accurate image reproduction. See Figure 2
|
|
Gamma for Intensity Scale
See Figure 2
|
Poor -
Less than 1.90
Gamma Too
Low
|
Good 2.68
Gamma Too
High
|
Good 2.66
Gamma Too
High
|
Gamma of 2.2 is the standard and needed
for
accurate image reproduction. See Figure 2
|
|
Viewing Angles
|
|
Brightness Decrease
at a 30 degree Viewing Angle
|
63 percent
decrease
to 161
cd/m2
Very Large
|
57 percent
decrease
to 235
cd/m2
Very Large
|
58 percent
decrease
to 171
cd/m2
Very Large
|
Screens become less bright when tilted.
LCD brightness variation is generally
very large.
|
|
Contrast Ratio
at a 30 degree Viewing Angle
|
44
Extremely
Low
|
556
Very Good
for Mobile
|
564
Very Good
for Mobile
|
A measure of screen readability when the
screen
is tilted under low ambient lighting.
|
|
Color Shift
at a 30 degree Viewing Angle
|
Large
Color Shift
Δ(u’v’)
= 0.0418
10 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.0096
2.4 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.0100
2.5 times
JNCD
|
JNCD is a Just Noticeable Color Difference.
IPS LCD has a smaller color shift with
angle.
|
|
Display Backlight Power Consumption
|
|
Display Backlight Power
at Maximum Brightness
|
0.81 watts
|
0.42 watts
|
2.7 watts
Larger
Screen
|
Lower power consumption is important for
energy
efficiency and improving running time on
battery.
|
|
Display Backlight Power Efficiency
same Peak Luminance 410 cd/m2
same 3.5 inch screen area
|
0.78 watts
|
0.32 watts
|
0.34 watts
|
This compares the Relative Power
Efficiency of the
iPad 2 and iPhones by looking at the
same screen
brightness and screen area. The iPad 2
and iPhone 4
have the highest efficiencies we have seen
- higher
than other LCDs and much higher than
OLEDs.
|
|
Running Time on Battery
|
|
Running Time
At Maximum Brightness Setting
|
Not
Available
|
7.8 hours
|
7.2 hours
|
Display always On at the Maximum setting
with
Airplane Mode and no running
applications.
|
|
Running Time
At Middle Brightness Slider Setting
|
Not
Available
|
12.3 hours
|
11.8 hours
|
Display always On at the Middle slider
setting with
Airplane Mode and no running
applications.
|
|
Running Time
At Minimum Brightness Setting
|
Not
Available
|
17.9 hours
|
19.8 hours
|
Display always On at the Minimum setting
with
Airplane Mode and no running
applications.
|
|
Categories
|
Apple
iPhone 3GS
Article Link
|
Apple
iPhone 4
Article Link
|
Apple
iPad 2
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: Display Technology Shoot-Out Article
Series Overview and Home Page
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
