iPad mini Display Technology Shoot-Out
Apple iPad mini – Amazon
Kindle Fire HD – Google Nexus 7
Dr. Raymond M. Soneira
President, DisplayMate Technologies Corporation
Copyright © 1990-2012 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 iPad mini has finally arrived – Apple’s much anticipated response to
the incredibly successful 7 inch Tablets pioneered by Amazon and Barnes &
Noble, and more recently by Google with its Nexus 7. So far they are the only
Tablets that have made a dent in Apple’s near monopoly on Tablets. At first
Apple declared them too small to be useful, but consumers clearly wanted
something more portable than a full size 10 inch Tablet, and also a lot less
costly. Millions were sold – and that got Apple’s attention. Over the past year
there have been increasingly credible accounts of a small iPad prototype being
developed by Apple, but there was no guarantee that it would turn into an
actual product until Apple’s official announcement.
In a short period of time mini Tablets have evolved into first tier
products with excellent displays. It shows how demand can drive the
state-of-the-art very quickly. Apple has made displays their most prominent
marketing feature because they determine the quality of the visual experience
for everything on a Tablet or Smartphone – including Apps, web content, photos,
videos, and its camera. So how good is the display on the iPad mini? And how
does it compare to the displays on the leading Amazon Kindle Fire HD and Google
Nexus 7 Tablets? And how does it compare to the displays on the full size iPads?
We’ll tell you here…
The Shoot-Out
To evaluate and analyze the display on the iPad mini we ran our comprehensive series of Mobile Display Technology
Shoot-Out tests and compared it to the Amazon Kindle
Fire HD and Google Nexus 7, and also to the iPad 2 and
new iPad 3. We take display quality very
seriously and provide in-depth objective analysis of side-by-side comparisons
based on detailed laboratory measurements and extensive viewing tests with both
test patterns and test images.
The discussions and analysis here deal primarily with the
iPad mini. For parallel in-depth discussions
and analysis of the Amazon Kindle Fire HD and Google Nexus 7 see our 7 Inch Tablet
Display Technology Shoot-Out. Our iPad Display Technology
Shoot-Out compares the iPad 2 and the new iPad 3. For earlier “popular” full size Tablets
see our 10 Inch
Tablet Display Technology Shoot-Out.
Results Highlights
In this Results section we provide Highlights of 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. 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,
Running Time on Battery. You can
also skip the Highlights and go directly to the Conclusions.
Sharpness and Resolution:
Pixel resolution has been the number one topic of
discussion for the iPad mini – both before and after launch. Many people were
expecting a Retina Display like the new iPad 3, but that would have required a
326 Pixels Per Inch display with more than 4 times the screen area of the
iPhone 5. That is currently out of the question for both cost and manufacturing
volume and yield since it would need to be Low Temperature Polysilicon. Given
that Apple has been sticking with either 1024x768 or 2048x1536 iPad displays
for compatibility reasons, that meant the iPad mini had to be 1024x768 with 163
Pixels Per Inch. But that’s now considered to be rather on the low side.
While screen Resolution gets lots of attention from both
consumers and marketers – it’s really only critical for providing visually
sharp text – but that applies for most applications running on a Tablet. The
$199 Amazon Kindle Fire HD and Google Nexus 7 both have considerably sharper
displays with 216 Pixels Per Inch, and they both delivered considerably sharper
text. We’ll discuss below how Apple can improve image sharpness on the mini
iPad.
Screen Reflectance:
The
screens on almost all Tablets and Smartphones are mirrors good enough to use
for personal grooming. Even in moderate ambient lighting the contrast and
colors can noticeably degrade from ambient light reflected by the screen,
especially objects like your face and any bright lighting behind you. So low
Reflectance is very important in determining real picture quality, especially
on the smaller and more portable Tablets. The lower the better… This article
shows how screen images degrade in bright Ambient Light.
Screen
Reflectance on the iPad mini is a surprisingly high 9.0 percent. On the Nexus 7
the Reflectance is a much lower 5.9 percent, while on the Kindle Fire HD it is
6.4 percent. As a result, the iPad mini reflects 53 percent more ambient light
than the Nexus 7 and 41 percent more than the Kindle Fire HD. That’s quite a
big difference… Screen visibility and readability in high Ambient Light depends
on both the Maximum Brightness and Screen Reflectance, which we evaluate with a
Contrast Rating for High Ambient Light. On the Kindle Fire HD it is 58 percent
higher than the iPad mini and 47 percent higher on the Nexus 7.
Color Gamut and Color Accuracy:
While
the display PPI and pixel Resolution seem to get most of the attention, it is
the display’s Color Gamut together with the Factory Display Calibration (below)
that play the most important role in determining the Wow factor and true
picture quality and color accuracy of a display. The Color Gamut is the range
of colors that a display can produce. If you want to see accurate colors in
photos, videos, and all standard consumer content the display needs to closely
match the Standard Color Gamut that was used to produce the content, which is
called sRGB / Rec.709. Most of the previous generations of LCD Tablets and
Smartphones had smaller Color Gamuts around 60 percent of the Standard Gamut,
which produces somewhat subdued colors. But that’s been changing due to both
technology and competition.
While the iPad 2 and iPhone 4 had reduced 61-64 percent
Color Gamuts, the Amazon Kindle Fire HD and Google Nexus 7 both deliver a much
larger 86 percent Color Gamut, and the new iPad 3 and iPhone 5 have full 100
percent standard Color Gamuts. So it was a surprise and a major disappointment
for the iPad mini to arrive with an antiquated smaller 62 percent Color Gamut.
Factory Display Calibration:
The
raw LCD panel hardware first needs to be adjusted and calibrated at the factory
with specialized firmware and software data that are downloaded into the device
in order for the display to produce a usable image – let alone an accurate and
beautiful one. This is actually a science but most manufacturers seem to treat
it as if it were a modern art form, so few Tablets, Smartphones, and even HDTVs
produce accurate high quality images.
Apple
has been a leader in accurate display calibration – the new iPad 3 and iPhone 5
have among the best and most accurate factory calibrations we have ever
measured in a consumer product, including high-end HDTVs. The iPad mini follows
that tradition – it has an accurate White Point and a very accurate Intensity
Scale, except for a 5 percent compression near the Peak Intensity, which we
discuss in more detail below.
Viewing Tests:
Using
our extensive library of challenging test and calibration photos, we compared
the iPad mini to a calibrated professional studio monitor and to the new iPad
3, which has a virtually perfect Factory Calibration and Color Gamut.
In
spite of its smaller Color Gamut, the iPad mini delivered fairly accurate
picture quality and color accuracy. This is due to color management processing
that is generally absent from Tablets and Smartphones. However, the iPad mini
display is still unable to produce very saturated colors, like fire engine red,
which was not as vibrant and appeared with a noticeable shift towards orange.
Very saturated purples are also especially difficult to reproduce on LCD
displays with a reduced color Gamut. For example, the iPad mini appeared almost
identical to the iPad 2 in this screen shot comparing
the latter to the new iPad 3.
iPad mini Conclusions:
The iPad
mini is certainly a very capable small Tablet, but it does not follow in
Apple’s tradition of providing the best display, or at least a great display –
it has just a very capable display. What’s more, the displays on existing mini
Tablets from Amazon and Google outperform the iPad mini in most of our Lab
tests as documented below in the Shoot-Out Comparison Table.
Some of this results from constraints within the iPad product line, and some to
realistic constraints on display technology and costs, but much of it is due to
a number of poor choices and compromises.
Lower
Screen Resolution:
Many
people were expecting a Retina Display like the new iPad 3, but that would have
required a 326 Pixels Per Inch display with more than 4 times the screen area
of the iPhone 5. That is currently out of the question for both cost and
manufacturing volume and yield since it would need to be Low Temperature Polysilicon.
Given that Apple has been sticking with either 1024x768 or 2048x1536 iPad
displays for compatibility reasons, that meant the iPad mini had to be 1024x768
with 163 Pixels Per Inch. But that’s now considered to be rather on the low
side, especially given that the $199 Amazon Kindle Fire HD and Google Nexus 7
both have considerably sharper displays with 216 Pixels Per Inch. So Apple, the
inventor of Retina Display marketing, now has a significant competitive
shortfall on this very issue…
Improving
Screen Sharpness:
Apple
could have increased the iPad mini Screen Resolution in the same way as it did
for the iPhone 5 – simply having older Apps running Letterboxed inside a higher
resolution display, which would have been a great way to provide a higher Pixels
Per Inch display. iOS and newer Apps would have used the full higher Resolution
– that didn’t happen. While screen Resolution gets lots of attention from both
consumers and marketers – it’s really only critical for providing visually
sharp text – but that applies for most applications running on a Tablet. As we have pointed out a
number of times, the best way to increase visual text sharpness on any display
is by using Sub-Pixel Rendering, which Apple should now implement in order for
the iPad mini to become competitive on visual sharpness…
Viewing
Widescreen Content:
All
of the iPads have a 4:3 Aspect Ratio screen, rather than the 16:10 or 16:9
Aspect Ratios found on most other Tablets. One advantage of the iPad’s more
square 4:3 screen shape is that it lends itself better for use in both
Landscape and Portrait viewing modes. Another is that a 4:3 screen is often
better suited for reading because it has the same Aspect Ratio as content on 8.5x11
inch documents. But another major application for mini Tablets is viewing
widescreen video content with Aspect Ratios of 16:9 (and higher for many
movies). On the iPad mini 16:9 content is viewed Letterboxed with only 1024x576
Resolution, which is getting pretty close to Standard Definition video rather
than true High Definition 1280x720 video on most other mini Tablets like the
Amazon Kindle Fire HD and Google Nexus 7. A much better screen resolution
choice for the iPad mini would have been 1280x960, because it could then
deliver true HD video content, satisfactory Letterboxing for older 1024x768
Apps, plus much sharper text for reading…
Higher
Screen Reflectance:
The
iPad mini is the most portable of the iPads so it will often be used under
brighter ambient lighting than full sized Tablets. As a result it’s more
important for the mini to have a low Reflectance screen, otherwise reflections
from the higher ambient lighting will reduce screen visibility and wash out the
images and colors. Most displays are now coming with lower Reflectance screens.
The Amazon Kindle Fire HD and Google Nexus 7 managed to accomplish this, even
at their low price points, but the iPad mini comes with an unusually high
Reflectance – it reflects 53 percent more ambient light than the Nexus 7 and 41
percent more than the Kindle Fire HD. This is another poor choice and another
significant competitive shortfall…
Smaller
Color Gamut:
The previous generations of LCD Tablet and Smartphone
displays had smaller Color Gamuts in order to improve their screen Brightness,
Power Efficiency, and Battery Running Times. But that’s been changing due to
both technology and competition. Full standard Color Gamut displays not only
deliver more accurate and vivid colors, but are better in high ambient lighting
because the additional color saturation improves image contrast. While the iPad
2 and iPhone 4 had reduced 61-64 percent Color Gamuts the new iPad 3 and iPhone
5 have full 100 percent standard Color Gamuts. So it was a surprise and major
disappointment for the iPad mini to arrive with an antiquated smaller 62
percent Color Gamut, especially considering that the Amazon Kindle Fire HD and
Google Nexus 7 both managed to deliver considerably larger 86 percent Color
Gamuts. That’s another poor choice and another significant competitive
shortfall…
The
Next Generation of Tablet Displays:
Mini
Tablets fill an important need and will undoubtedly continue to grow in market
share, so it’s very important for manufacturers to understand how to optimize
their smaller displays in brighter ambient lighting environments to deliver
both top picture quality and long battery running time. See our new iPad 3 Shoot-Out
Conclusion for a discussion of the many improvements that are needed for
the next generation of both full size and mini Tablet displays.
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 help
manufacturers with expert display procurement and quality control so they don’t
make mistakes similar to those that are exposed in our Display Technology
Shoot-Out series. We can also 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.
Display Shoot-Out Comparison Table
Below we
compare the displays on the iPad mini, Amazon Kindle Fire HD, and
Google Nexus 7 based on objective measurement
data and criteria. Note that all of the tested Tablets were purchased
independently by DisplayMate Technologies through standard retail channels.
For additional background and information see our 7 Inch Tablet
Display Technology Shoot-Out that analyzes the Amazon
Kindle Fire HD and Google Nexus 7 in
depth, and the iPad Display Technology Shoot-Out
that analyzes the iPad 2 and new iPad 3. For earlier “popular” full size Tablets
see our 10 Inch
Tablet Display Technology Shoot-Out.
|
Categories
|
Amazon
Kindle
Fire HD
|
Google
Nexus 7
|
Apple
iPad mini
|
Comments
|
|
Screen Diagonal Size
Display Technology
|
7.0 inches
IPS LCD
|
7.0 inches
IPS LCD
|
7.9 inches
IPS LCD
|
Liquid Crystal Display
In Plane Switching
|
|
Screen Shape
|
16:10 =
1.60
Aspect
Ratio
|
16:10 =
1.60
Aspect
Ratio
|
4:3 =
1.33
Aspect
Ratio
|
The iPad screen has the same shape as
8.5x11 paper.
|
|
Screen Area
|
22.0
Square Inches
|
22.0
Square Inches
|
29.6
Square Inches
|
A better measure of size than the
diagonal length.
|
|
Relative Screen Area
|
74 percent
|
74 percent
|
100 percent
|
Screen Area relative to the iPad mini.
|
|
Display Resolution
|
1280 x 800
pixels
|
1280 x 800
pixels
|
1024 x 768
pixels
|
The more Pixels and Sub-Pixels the
better.
|
|
Active Display Area
|
1280 x 800
pixels
|
1280 x 736
pixels
|
1024 x 768
pixels
|
The Nexus 7 reserves 64 pixels for a
navigation bar.
|
|
Pixels Per Inch
|
216 ppi
Very Good
|
216 ppi
Very Good
|
163 ppi
Relatively
Low
|
At 12 inches from the screen 20/20 vision
is 286 ppi.
See this on
the visual acuity for a true Retina Display
|
|
20/20 Vision Retina Display
down to this Viewing Distance
|
20/20
“Retina Display”
to 15.9
inches Viewing
|
20/20
“Retina Display”
to 15.9
inches Viewing
|
20/20
“Retina Display”
to 21
inches Viewing
|
For 20/20 Vision the minimum Viewing
Distance
where the screen appears perfectly sharp
to the eye.
|
|
Pixels Per Square millimeter
Text letters are 2D objects
|
72 ppmm2
|
72 ppmm2
|
41 ppmm2
|
Image elements like text letters are
seen as
2D objects drawn as a small area of
pixels.
|
|
Sub-Pixel Rendering
Improves Sharpness
|
No
Pixel
Rendering
|
No
Pixel
Rendering
|
No
Pixel
Rendering
|
Sub-Pixel Rendering improves visual
image
sharpness for text and graphics.
|
|
Small Text Readability
|
Very Good
|
Very Good
|
Somewhat
Fuzzy
|
Perceived visual sharpness reading small
text such
as on The New York Times website front
page.
|
|
Gallery / Photo Viewer Color Depth
|
Full
24-bit color
No
Dithering Visible
256
Intensity Levels
|
Dithered
24-bit color
False
Contouring
|
Full
24-bit color
No
Dithering Visible
256
Intensity Levels
|
Many Android Tablets and Smartphones
still have some
form of 16-bit color depth
in the Gallery Photo Viewer
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
Overall Assessments
This section summarizes
the results of all of the extensive Lab measurements and viewing tests
performed on all of the displays.
|
|
Viewing Tests
|
Very Good
Images
Photos and
Videos
have
accurate color
and
accurate contrast
|
Good
Images
Photos and
Videos
have
washed out
color and
contrast
|
Very Good
Images
Photos and
Videos
have good
color
and good
contrast
|
The Viewing Tests examined the accuracy
of
photographic images by comparing the
displays
to a calibrated studio monitor and HDTV.
|
|
Variation with Viewing Angle
|
Small
Color Shifts
with
Viewing Angle
Large
Brightness Shift
with
Viewing Angle
|
Small
Color Shifts
with
Viewing Angle
Large
Brightness Shift
with
Viewing Angle
|
Small
Color Shifts
with
Viewing Angle
Large
Brightness Shift
with
Viewing Angle
|
IPS LCDs have Small Color Shifts.
TN LCDs have Large Color Shifts.
All LCDs have Large Brightness Shifts
|
|
Viewing the Screen with
Polarized Sunglasses
|
Extinction in
Landscape
View in Portrait
|
Extinction in
Landscape
View in Portrait
|
No Extinction But
Bluish Color Caste in
Landscape
|
Polarized Sunglasses are increasingly
popular,
which often makes the screen invisible
black for
certain orientations.
|
|
Overall Display Assessment
Lab Tests and Viewing Tests
|
Very Good Display
Very Good Calibration
|
Very Good Display has
Poor Calibration
Washed Out Images
Bugs that need Fixing
|
Good Display has
High Reflectance
Smaller Color Gamut
Very Good Calibration
|
Lab and Viewing Test Assessments
|
|
Major Display Weaknesses
|
Nothing Major But
Increase Color Temp
Increase Gamma
|
Poor Display
Calibration
|
Higher
Reflectance
Smaller
Color Gamut
|
Notable Display Weaknesses
|
|
Major Display Strengths
|
Display Calibration
Larger Color Gamut
|
Lowest Reflectance
Larger Color Gamut
|
Display Calibration
|
Notable Display Strengths
|
|
Current Overall Display Grade
|
A–
|
B–
|
B
|
Our Overall Assessments based on all
criteria
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
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.
The Kindle Fire HD and Nexus 7
significantly outperform the iPad mini with much lower Reflectance.
The iPad mini reflects 53 percent more
ambient light than the Nexus 7 and 41 percent more than the Kindle Fire HD.
|
|
Cover Glass
with Air Gap or Bonded to Display
See Figure 1
|
Cover Glass Bonded
No Air Gap
|
Cover
Glass Bonded
No Air Gap
|
Cover Glass
Bonded
No Air Gap
|
A Cover Glass with an Air Gap is easier
to
manufacture. Optical Bonding reduces
both
external and internal Reflections. See Figure 1
|
|
Average Screen Reflections
Percentage of Reflected
Light From All Directions
|
Reflects 6.4 percent
Very Good
|
Reflects
5.9 percent
Very Good
|
Reflects
9.0 percent
Relatively
High
|
Measured using an Integrating Hemisphere
that
produces a uniform anisotropic light
distribution.
|
|
Specular Mirror Reflections
Percentage of Light Reflected
See Figure 1
|
Reflects 7.6 percent
Very Good
|
Reflects 7.2 percent
Very Good
|
Reflects 12.1 percent
Poor
|
These are the most annoying types of
reflections.
Measured using a narrow collimated
pencil beam of
light reflected off the screen. See Figure 1
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
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.
All of the Tablets have comparable
Brightness and Contrast Ratio, but Contrast Ratio is only relevant for low
ambient light.
The iPad mini has a much lower Contrast
Rating for High Ambient Light than most Tablets in our Display Shoot-Outs.
|
|
Measured Maximum Brightness
is the Peak Luminance for White
|
Brightness
434 cd/m2
Very Good
|
Brightness
372 cd/m2
Good
|
Brightness
388 cd/m2
Good
|
Maximum Brightness is very important for
mobile
because of the typically high ambient
light levels.
|
|
Black Level
at Maximum Brightness
|
Black is
0.51 cd/m2
Very Good
for Mobile
|
Black is
0.40 cd/m2
Very Good
for Mobile
|
Black 0.46
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
|
851
Very Good
for Mobile
|
930
Very Good
for Mobile
|
843
Very Good
for Mobile
|
Measured in absolute darkness.
Only relevant for low ambient light,
|
|
Contrast Rating
for High Ambient Light
|
68
Very Good
|
63
Very Good
|
43
Relatively
Low
|
Visual Contrast in High Ambient Lighting.
Defined as Maximum Brightness / Average Reflectance.
|
|
Screen Readability in Bright Light
|
Very Good A–
|
Very Good A–
|
Good B
|
Indicates how easy it is to read the screen
under high ambient lighting. Very
Important!
See High
Ambient Light Screen Shots
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
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 Nexus 7 has a major problem with
its Intensity Scale due to a poor Factory Calibration. We have discussed this
in more detail in this Display News article. The
iPad mini suffers from the same problem of Peak Compression but on
a much smaller scale. See Figure 3
for more information.
The iPad mini is well calibrated but its
Color Gamut is at the low end of what we have seen in Tablets and Smartphones.
Some important issues regarding the
Color Gamut are explained in Figure 2
and the Intensity Scale in Figure
3.
|
|
White Color Temperature
|
6,380
degrees Kelvin
Close to
Standard
|
6,708
degrees Kelvin
Close to
Standard
|
6,711
degrees Kelvin
Close to
Standard
|
D6500 is the standard color of White for
most content
and necessary for accurate color
reproduction.
|
|
Color Gamut
See Figure 2
|
86 percent
of Std
Gamut Very
Good
See Figure 2
|
86 percent
of Std
Gamut Very
Good
See Figure 2
|
62 percent
of Std
Gamut Too
Small
See Figure 2
|
sRGB / Rec.709 is the color standard for
most
content and needed for accurate color
reproduction.
Note that Too Large a Color Gamut is
visually
worse than Too Small.
|
|
Dynamic Contrast or Backlight
|
None
Excellent
|
Below 10
percent APL
Very Good
|
None
Excellent
|
Many manufacturers manipulate the
Intensity Scale
and Backlight based on image content.
That results
in inaccurate colors and images.
|
|
Intensity Scale and Image Contrast
See Figure 3
|
Very
Smooth
Contrast
is Excellent
See Figure 3
|
Irregular
and Convex
Saturation
and Clipping
See Figure 3
|
5% Peak
Compression
Contrast
is Very Good
See Figure 3
|
The Intensity Scale controls image
contrast needed
for accurate image reproduction. See Figure 3
|
|
Gamma for the Intensity Scale
Larger means more Image Contrast
See Figure 3
|
Gamma 2.16
Gamma is
Excellent
|
Gamma
1.70 to 2.44
Convex
Highly Variable
15% Peak
Compression
|
Gamma 2.15
Gamma is
Very Good
5% Peak
Compression
|
Gamma is the slope of the Intensity
Scale.
Gamma of 2.20 is the standard and needed
for
accurate image reproduction. See Figure 3
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
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 not an atypical viewing angle for Tablets. IPS
LCDs generally do well.
Note
that the Viewing Angle performance is also very important for a single viewer
because the Viewing Angle
varies
based on how the Tablet is held, and the angle can be very large if the
Tablet is resting on a table or desk.
All
of these Tablets have LCDs that perform very well with similar Viewing Angle
performance.
|
|
Brightness Decrease
at a 30 degree Viewing Angle
|
52 percent
Decrease
Falls to
208 cd/m2
Very Large
Decrease
|
53 percent
Decrease
Falls to
175 cd/m2
Very Large
Decrease
|
50 percent
Decrease
Falls to
194 cd/m2
Very Large
Decrease
|
Most screens become less bright when
tilted.
LCD brightness variation is generally
very large.
|
|
Contrast Ratio
at a 30 degree Viewing Angle
|
602
Very Good
for Mobile
|
662
Very Good
for Mobile
|
495
Very 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’)
= 0.0047
1.2 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.045
1.1 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.0037
0.9 times
JNCD
|
JNCD is a Just Noticeable Color Difference.
IPS LCDs have smaller color shifts with
angle.
|
|
Color Shifts for Color Mixtures
at a 30 degree Viewing Angle
Reference Brown (255, 128, 0)
|
Small
Color Shift
Δ(u’v’)
= 0.0069
1.7 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.0068
1.7 times
JNCD
|
Small
Color Shift
Δ(u’v’)
= 0.0067
1.7 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.
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
The Display Backlight power does not include the
power used by the LCD itself or by the display electronics.
Since the displays have different screen sizes and
maximum brightness, the values were also scaled to the
same screen brightness (Luminance) and screen area
in order to compare their relative Power Efficiencies.
The iPad mini falls in between the Nexus
7 and the Kindle Fire HD in Backlight Power Efficiency.
|
|
Display Backlight Power
at Maximum Brightness
|
2.1 watts
|
1.4 watts
|
2.3 watts
|
Lower power consumption is important for
energy
efficiency and improving running time on
battery.
|
|
Display Backlight Power Efficiency
same Peak Luminance 388 cd/m2
same 7.9 inch screen size area
|
2.5 watts
|
2.0 watts
|
2.3 watts
|
This compares the Relative Power
Efficiency
by looking at the same screen brightness
and
screen area.
|
|
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
|
|
Running Time on Battery
The running time on battery was determined with the
Brightness sliders at Maximum, 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. They all need a more convenient Manual
Brightness Control as described in the BrightnessGate article.
The Nexus 7 has the longest Running Time
at Maximum Brightness for any Tablet we have tested.
Since the display consumes the most
device power, the Running Times at lower Brightness settings will be longer.
|
|
Running Time
At the Maximum Brightness Setting
|
6.6 hours
|
9.1 hours
|
6.1 hours
|
Display always On at the Maximum setting
with
Airplane Mode and no running
applications.
|
|
Categories
|
Kindle
Fire HD
|
Nexus 7
|
iPad mini
|
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.
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