7 inch Tablet Display Technology Shoot-Out
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 first generation of 7 inch Tablets that launched in November of 2011
established an important new category with mass consumer appeal. They have only
about half the screen area of 10 inch Tablets, so they fill the large gap
between 4 inch Smartphones and the large Tablets. But in addition to being a
lot smaller and more portable than their 10 inch cousins, they were
considerably less expensive, with the original Amazon Kindle Fire pioneering a
$199 price that was considerably less than half the cost of existing Tablets.
With that size and price point they couldn’t simply be miniature 10 inch
Tablets. In particular, they can’t provide all of the same hardware and
functionality due to both size and cost constraints. This was incredibly
challenging, so the first generation displays came in near the bottom in
Brightness, Resolution, Color Gamut, Contrast, Calibration accuracy, Screen
Reflectance, and performance under high Ambient Lighting (to name just a few).
Still consumers bought them in droves, so millions were sold – and that always
guarantees a sequel…
Now in less than a year
a second generation of 7 inch Tablets has arrived – the Google Nexus 7 launched
in July and the Amazon Kindle Fire HD in September. There are many other
manufacturers making Tablets but these are the only models seeing significant
demand. As we’ll see, in this short period of time these mini Tablets have
evolved into first tier products with excellent displays that out perform most
full size higher priced Tablets. It shows how demand can drive the state-of-the
art very quickly. And they have become so successful that Apple can no longer
ignore them – so an iPad Mini is rumored to be coming in October – we’ll
analyze what is known about them so far.
The Shoot-Out
To compare the performance of the new Kindle Fire HD and Google
Nexus 7 we ran our in-depth series of Mobile Display Technology
Shoot-Out tests on them, together with the new
iPad and the iPad 2 to see how they all
compare. We take display quality very seriously and provide in-depth objective
analysis side-by-side comparisons based on detailed laboratory measurements and
extensive viewing tests with both test patterns and test images. For comparisons
with earlier “popular” Tablets see our 10 Inch Tablet Display
Technology Shoot-Out and for the comparisons with the original Amazon
Kindle Fire and Barnes & Noble Nook Tablet see our First Generation
IPS 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.
Comparison with iPads:
Our original plan for the Shoot-Out had been to compare
the displays on these inexpensive $199 Tablets to the $399 iPad 2 – even that
seemed rather unfair given the 2:1 price difference. But it didn’t take very
long to see that the Kindle Fire HD handily beat the iPad 2 in terms of picture
quality and accuracy, so we decided to upgrade the level of the Shoot-Out and
instead use the new iPad for the detailed display comparisons below. While the
display on the Kindle Fire HD does not beat the new iPad, it comes in a
relatively close second, and it even outperforms the new iPad in a number of
categories. That is a significant result all by itself – it shows how quickly
the competition and state-of-the-art is changing because the new iPad has one
of the most accurate displays in a consumer product that we have ever tested,
including high-end HDTVs. The display on the Nexus 7 did not perform as well as
the Kindle Fire HD as explained in detail below. We also discuss below how the
(rumored) upcoming iPad Mini is likely to fit in with these Tablets.
Sharpness:
The
display’s image sharpness depends on the pixel Resolution, while the visual
sharpness depends on the Pixels Per Inch PPI and the Viewing Distance (as well
as how good your vision is compared to 20/20 Vision). The Kindle Fire HD and
Nexus 7 have 1280x800 pixel displays, which exceeds the resolution needed for
viewing standard High Definition 1280x720 video content, one of their principal
marketing goals. They have 30 percent more pixels than the iPad 2 but only one
third of the number on the new iPad, which can display Full HD 1920x1080
content. For most photo and video content it is hard to visually distinguish HD
1280x720 from Full HD 1920x1080 because most photo and video images are
inherently fuzzy, with the sharpest image detail spread over multiple pixels.
High
visual sharpness is necessary for rendering fine text and graphics without
pixelation and other visual artifacts. With 216 PPI the Kindle Fire HD and
Nexus 7 are significantly better than the 132 PPI for the iPad 2, but well
below the 264 PPI for the new iPad. The viewing distance where the Kindle Fire
HD and Nexus 7 become what Apple calls a “Retina Display” is 15.9 inches –
beyond that viewing distance people with 20/20 Vision cannot resolve the pixels
so the display appears perfectly sharp. For viewing distances less than 15.9
inches the pixels can be resolved by the eye, but anti-aliasing will reduce
their visibility. Since the viewing distance for 7 inch Tablets is around 12
inches their displays are not quite “Retina Displays” but they are still very
sharp and close to the visual resolution limit for most people (who also don’t
have 20/20 Vision).
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 first generation LCD Tablets have Color
Gamuts around 60 percent of the Standard Gamut, which produces somewhat subdued
colors. The original Kindle Fire and Nook Color Tablets have 55 percent, the
iPad 2 has 61 percent, but the new iPad pulled way ahead and has a virtually
perfect 99 percent of the Standard Color Gamut. The new Kindle Fire HD and the Nexus
7 both deliver an impressive 86 percent Standard Color Gamut, a major
improvement over almost all previous generation Tablets (and Smartphones).
While the Kindle Fire HD and Nexus 7 both have an 86
percent Color Gamut, they are actually rather different as discussed in detail
below. While the Nexus 7 has a very nice saturated Red that is close to the new
iPad Red, its Greens and Yellows are less saturated than even the iPad 2, which
is a significant step backward. On the other hand, the Kindle Fire HD has
Greens and Yellows that are slightly more saturated than the new iPad. These
were easy to see during the Viewing Tests. Just as important as the Color Gamut
is the Factory Display Calibration, which can ruin a excellent display if done
improperly…
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 does a virtually perfect Factory
Calibration for the new iPad, and Amazon has done an excellent Factory
Calibration for the Kindle Fire HD. It is probably more accurate with better
color than any display you own.
On
the other hand, the Factory Display Calibration on the Nexus 7 was severely
botched, which significantly degrades its picture quality. In spite of its good
Color Gamut, colors and contrast are washed out due to a compressed, convex,
and irregular Intensity Scale (sometimes called the Gray Scale). Bright images
look like over exposed photographs. We have discussed this in more detail in
this Display News article
– also see Figure 3
below for more information.
Nexus 7 Bugs:
The
Factory Display Calibration problem mentioned above for the Nexus 7 display
qualifies as a bug because it is a software or firmware problem rather than an
inherent hardware display issue. Depending on the display firmware this may or
may not be correctable with a software update.
The
Nexus 7 has another serious display bug: During testing we found that the
Brightness (Luminance) of the display decreases erratically by up to 15
percent. This is large enough to be occasionally noticeable and bring the Nexus
7 Maximum Brightness down to almost 300 cd/m2, which we classify as Poor for Maximum Brightness. We borrowed and tested
a second Nexus 7 unit and found identical behavior – so the effect is unlikely
to be due to a defective unit. In fact, we discovered it to be another software
bug. On the Nexus 7 the measured Luminance for a given image doesn’t change
over time – but it varies based on the user interactivity pattern and history.
For example, flipping to other images and then returning back to the original
image often results in a change in Luminance. This indicates that it is caused
by a software bug of some sort, possibly related to a faulty implementation of
Dynamic Backlight or Dynamic Contrast. This erratic behavior introduces some
uncertainties into the Nexus 7 measurements below. We believe the listed values
are correct as a result of many repeated measurements. It is likely that this
particular display bug can be fixed by Google with a software update.
Viewing Tests:
Using
our extensive library of challenging test and calibration photos, we compared
the Tablets to a calibrated professional studio monitor, and to the new iPad,
which has a virtually perfect Factory Calibration and Color Gamut. As expected
from the Lab measurements, the Kindle Fire HD produced beautiful picture
quality, much better than the iPad 2 and almost as good as the new iPad. The
only visually notable issue was that very deep reds, like in a fire engine,
were not as vibrant and have a slight shift towards orange.
Images
on the Nexus 7 were noticeably washed out in both color and image contrast –
especially bright images. For example, this was rather noticeable in
photographs of faces, which are often the center of attention and brightly lit,
and the eye is especially critical when faces are rendered improperly. Another
important issue was that Greens and Yellows were especially weak and under
saturated, even much more than the iPad 2, which has a much smaller Color Gamut
but a more saturated Green primary.
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. The lower
the better… This article
shows how screen images degrade in bright Ambient Light.
Screen
Reflectance on the iPad 2 is 8.7 percent and on the new iPad it is 7.7 percent.
However, on the Nexus 7 the Reflectance is an impressive much lower 5.9
percent, while on the Kindle Fire HD it is 6.4 percent – both are significant
improvements over the iPads. For comparison, the iPad 2 reflects 47 percent
more ambient light than the Nexus 7 and 36 percent more than the Kindle Fire
HD. Screen visibility and readability in high Ambient Light depends on both the
Maximum Brightness and Screen Reflectance. The Kindle Fire HD has the highest
measured Contrast Rating for High Ambient Light of any Tablet that we have
tested in our entire Shoot-Out series, and the Nexus 7 is a close second. Both
are much better than either the iPad 2 or the new iPad.
The Rumored iPad Mini?
There are credible rumors that sometime in October Apple
will announce an iPad Mini with a 7.85 inch 160 PPI screen and solution of
1024x768 pixels. Given that Apple generally does a good job with their
displays, how is it likely to compare and compete with these existing Tablets?
Color Gamut: It’s very likely
that the iPad Mini will have a 100 percent Color Gamut like the new iPad ,
which is 14 percent greater than the Kindle Fire HD and Nexus 7. Pixels Per Inch: The Kindle Fire HD and Nexus 7 have
216 PPI, considerably greater than the predicted 160 PPI for the iPad Mini or
the 132 PPI for the iPad 2, but considerably less than the 264 PPI for the new
iPad. Screen Resolution: The Kindle Fire HD and
Nexus 7 have1280x800 resolution with a 16:10 Aspect Ratio, considerably greater
than the iPad Mini’s predicted 1024x768 with a 4:3 Aspect Ratio. Video Resolution: When looking at standard 16:9 HDTV
widescreen content, the Kindle Fire HD and Nexus 7 deliver Standard HD 1280x720
Resolution, considerably greater than the 1024x576 Resolution predicted for the
iPad Mini. Screen Area: The iPad Mini is
predicted to have an area that is 34 percent larger than the Kindle Fire HD and
Nexus 7. However, for 16:9 content the area is only 6 percent larger.
An Updated Shoot-Out:
When
the iPad Mini becomes available we will do another complete 7 inch Tablet
Shoot-Out with the iPad Mini instead of the new iPad. We’ll also check to see
if Google has corrected the Calibration and Brightness problems noted above
with a software update.
Conclusion: An Impressive Second
Generation…
The
first generation of 7 inch Tablets that launched in 2011 established an
important new category with mass consumer appeal. This second generation of 7
inch Tablets has resulted in impressive improvements in display quality, now
rivaling the top performing and most expensive large format Tablets, including
the new iPad. The 7 inch Tablets have only about half the screen area of 10
inch Tablets, so they are much easier to carry around and fill the large gap
between 4 inch Smartphones and the large Tablets. Amazon and Google are also
positioning them to sell video content, subscriptions, and consumer goods. This
is the justification for being able to sell them at the incredibly low $199
price point, with close to zero margin. The displays need to produce beautiful
picture quality in order to encourage consumers to purchase lots of content.
The
display on the Kindle Fire was the decisive winner of these two leading 7 inch
Tablets. It is much better than the iPad 2 and almost as good as the new iPad
in overall picture quality and color accuracy. While the new iPad’s 264 PPI
screen is significantly sharper for reading text and viewing finely detailed
computer graphics, the Kindle Fire HD’s 216 PPI screen is still very sharp and
its 1280x800 screen exceeds the resolution needed for viewing standard High
Definition 1280x720 video content, one of its principal marketing goals. Like
the new iPad, the Kindle Fire HD has better picture quality and color accuracy
than most HDTVs, laptops, and monitors, so it could wind up being your most
accurate display for viewing photos, videos and web content. Mobile displays
are often viewed under reasonably high Ambient Lighting. The Kindle Fire HD has
the highest measured Contrast Rating for High Ambient Light of any Tablet that
we have tested in our Shoot-Out series, which is impressive.
The
Nexus 7 actually has an LCD display that is similar in performance to the
Kindle Fire HD, but a poor (and sloppy) Factory Calibration has degraded its
native panel performance. Depending on the display firmware this may or may not
be correctable with a software update. A second problem is a bug that causes a
15 percent erratic variation in screen Brightness, sometimes bringing the Nexus
7 Maximum Brightness down to almost 300 cd/m2, which we classify as Poor for Maximum Brightness. It is likely that this
particular display bug can be fixed by Google with a software update. On the
other hand, the Kindle Fire HD has a (stable) Maximum Brightness of 434 cd/m2
that is much brighter than the Nexus 7 and among the Brightest Tablets we have
tested. If both Nexus 7 problems are fixed with a software update, then the
Nexus 7 display will be much closer in performance to the Kindle Fire HD. But
in addition to these, the Nexus 7 has a Green primary that is much less
saturated than even the iPad 2, which is quite noticeable and a step backward.
This also significantly lowers the saturation of Yellows that lie between Green
and Red. This can’t be fixed in software, but even so, the Nexus 7 could still
become a very good display if the other display software and firmware issues
are fixed.
Of
course, the big question is how the rumored iPad Mini will affect the 7 inch
Tablet category, and how will the Kindle Fire HD and Nexus 7 be impacted by its
expected introduction in October? If the display predictions in our Rumored
iPad Mini section above come true, then there are enough pluses and minuses
between them that they should all be able to coexist as far as display
performance and picture quality are concerned.
While
these Tablet displays are all very good, there is still plenty of Room for
Improvement. See the new iPad Shoot-Out
Conclusion for a discussion of the many improvements that are needed for
the next generation of 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 Amazon Kindle Fire HD and Google Nexus 7 with the new iPad
based on objective measurement data and criteria. Note that the tested Tablets
were purchased independently by DisplayMate Technologies through standard
retail channels.
For
additional background and information see the iPad Display Technology Shoot-Out
article that compares the iPad 2 and the new iPad.
When the iPad Mini is launched we will add it to the 7 inch
Tablet Shoot-Out.
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Categories
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Amazon
Kindle
Fire HD
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Google
Nexus 7
|
Apple
new iPad
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Comments
|
|
Display Technology
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7.0 inch
IPS LCD
|
7.0 inch
IPS LCD
|
9.7 inch
IPS LCD
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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
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22.0
Square Inches
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22.0
Square Inches
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45.2
Square Inches
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A better measure of size than the
diagonal length.
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Relative Screen Area
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49 percent
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49 percent
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100
percent
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Screen Area relative to the new iPad.
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Display Resolution
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1280 x 800
pixels
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1280 x 800
pixels
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2048 x 1536
pixels
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The more Pixels and Sub-Pixels the
better.
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Active Display Area
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1280 x 800
pixels
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1280 x 736
pixels
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2048 x
1536 pixels
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The Nexus 7 reserves 64 pixels for a
navigation bar.
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Pixels Per Inch
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216 ppi
Very Good
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216 ppi
Very Good
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264 ppi
Excellent
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At 12 inches from the screen 20/20 vision
is 286 ppi.
See this on
the visual acuity for a true Retina Display
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|
20/20 Vision Retina Display
down to this Viewing Distance
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20/20
“Retina Display”
to 15.9
inches Viewing
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20/20
“Retina Display”
to 15.9
inches Viewing
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20/20
“Retina Display”
to 13.0
inches Viewing
|
For 20/20 Vision the minimum Viewing
Distance
where the screen appears perfectly sharp
to the eye.
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Gallery / Photo Viewer Color Depth
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Full
24-bit color
No
Dithering Visible
256
Intensity Levels
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Dithered
24-bit color
False
Contouring
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Full
24-bit color
No
Dithering Visible
256
Intensity Levels
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Most Android Tablets and Smartphones still
have some
form of 16-bit color depth
in the Gallery Photo Viewer
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|
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Kindle
Fire HD
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Nexus 7
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new iPad
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|
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Overall Assessments
This section summarizes
the results of all of the extensive Lab measurements and viewing tests
performed on all of the displays.
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Viewing Tests
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Very Good
Images
Photos and
Videos
have
accurate color
and
accurate contrast
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Good
Images
Photos and
Videos
have
washed out
color and
contrast
|
Very Good
Images
Photos and
Videos
have
accurate color
and
accurate contrast
|
The Viewing Tests examined the accuracy
of
photographic images by comparing the
displays
to a calibrated studio monitor and HDTV.
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Variation with Viewing Angle
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Small
Color Shifts
with
Viewing Angle
Large
Brightness Shift
with
Viewing Angle
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Small
Color Shifts
with Viewing
Angle
Large
Brightness Shift
with
Viewing Angle
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Small
Color Shifts
with
Viewing Angle
Large
Brightness Shift
with
Viewing Angle
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IPS LCDs have Small Color Shifts.
TN LCDs have Large Color Shifts.
All LCDs have Large Brightness Shifts
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Viewing the Screen with
Polarized Sunglasses
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Extinction in
Landscape
View in Portrait
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Extinction in
Landscape
View in Portrait
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Extinction in
Portrait
View in Landscape
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Polarized Sunglasses are increasingly
popular,
which often makes the screen invisible
black for
certain orientations.
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Overall Display Assessment
Lab Tests and Viewing Tests
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Very Good Display
Very Good Calibration
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Good Display has
Poor Calibration
Washed Out Images
Bugs that need Fixing
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Excellent Display
Excellent Calibration
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The Nexus 7 display can be significantly
improved
if Google fixes the two software and
firmware bugs
that we identified.
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Current Overall Display Grade
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A–
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B–
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A
|
If Google fixes the two software and
firmware bugs
we identified the Nexus 7 Display Grade
will go up
to B+ due to the Color Gamut issues we
identified.
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|
|
Kindle
Fire HD
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Nexus 7
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new iPad
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|
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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 new iPad with much lower Reflectance.
The new iPad reflects 31 percent more ambient light
than the Nexus 7 and 20 percent more than the Kindle Fire HD.
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|
Average Screen Reflection
Light From All Directions
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Reflects 6.4 percent
Very Good
|
Reflects
5.9 percent
Very Good
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Reflects
7.7 percent
Very Good
|
Measured using an Integrating
Hemisphere.
The best value we have measured is 4.4
percent
and the current worst is 14.8 percent.
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|
Mirror Reflections
Percentage of Light Reflected
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7.6 percent
Very Good
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7.2 percent
Very Good
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9.9 percent
Good
|
These are the most annoying types of
reflections.
Measured using a narrow collimated
pencil beam of
light reflected off the screen.
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|
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Kindle
Fire HD
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Nexus 7
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new iPad
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|
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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 Nexus 7 Maximum Brightness is lower than many
Tablets plus it has a Bug that causes the Brightness to decrease
erratically by up to 15 percent down to
almost 300 cd/m2, which we classify as Poor for Maximum
Brightness.
See Nexus 7 Bugs under Highlights for more details.
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|
Measured Maximum Brightness
is the Peak Luminance for White
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Brightness
434 cd/m2
Very Good
|
Brightness
372 cd/m2
Good
|
Brightness
421 cd/m2
Very Good
|
Maximum Brightness is very important for
mobile
because of the typically high ambient
light levels.
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|
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 0.48
cd/m2
Very Good
for Mobile
|
Black brightness is important for low
ambient light,
which is seldom the case for mobile
devices.
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|
Contrast Ratio
Relevant for Low Ambient Light
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851
Very Good
for Mobile
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930
Very Good
for Mobile
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877
Very Good
for Mobile
|
Only relevant for low ambient light,
which is seldom the case for mobile
devices.
Defined as Maximum Brightness / Black
Brightness.
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|
Contrast Rating
for High Ambient Light
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68
Very Good
|
63
Very Good
|
55
Good
|
Defined as Maximum Brightness / Average Reflectance.
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Screen Readability in Bright Light
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Very Good A–
|
Very Good A–
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Good B+
|
Indicates how easy it is to read the
screen
under high ambient lighting. Very
Important!
See High
Ambient Light Screen Shots
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|
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Kindle
Fire HD
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Nexus 7
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new iPad
|
|
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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 – also
see Figure 3
for more information.
Some important issues regarding the
Color Gamut are explained in Figure 2.
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White Color Temperature
|
6,380
degrees Kelvin
Close to
Standard
|
6,708
degrees Kelvin
Close to
Standard
|
7,085
degrees Kelvin
Somewhat
Too Blue
|
D6500 is the standard color of White for
most content
and necessary for accurate color
reproduction.
|
|
Color Gamut
See Figure 2
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Very Good
86 percent
of Std
See Figure 2
|
Very Good
86 percent
of Std
See Figure 2
|
Excellent
99 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 a Color Gamut is
visually
worse than Too Small.
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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.
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|
Intensity Scale and Image Contrast
See Figure 3
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Very
Smooth
Contrast
is Excellent
See Figure 3
|
Irregular
and Convex
Saturation
and Clipping
See Figure 3
|
Very
Smooth
Contrast
is Perfect
See Figure 3
|
The Intensity Scale controls image
contrast needed
for accurate image reproduction. See Figure 3
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|
Gamma for the Intensity Scale
Larger means more Image Contrast
See Figure 3
|
Good 2.16
Gamma is
Excellent
|
1.70 to
2.44
Gamma is
Poor
Convex
Highly
Variable
|
Outstanding
2.20
Gamma is
Perfect
|
Gamma is the slope of the Intensity
Scale.
Gamma of 2.20 is the standard and needed
for
accurate image reproduction. See Figure 3
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|
|
Kindle
Fire HD
|
Nexus 7
|
new iPad
|
|
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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 IPS Tablets
perform very well and have very 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
|
57 percent
Decrease
Falls to
182 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
|
526
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’)
= 0.0046
1.2 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’)
= 0.0073
1.8 times
JNCD
|
JNCD is a Just Noticeable Color Difference.
Color Shifts for non-IPS LCDs are about 10
JNCD.
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
|
new iPad
|
|
|
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 Nexus 7 is 24 percent more Power Efficient than
the Kindle Fire HD and has double the Efficiency of the new iPad.
|
|
Display Backlight Power
at Maximum Brightness
|
2.1 watts
|
1.4 watts
|
7.0 watts
|
Lower power consumption is important for
energy
efficiency and improving running time on
battery.
|
|
Display Backlight Power Efficiency
same Peak Luminance 434 cd/m2
same 7 inch screen size area
|
2.1 watts
|
1.7 watts
|
3.5 watts
|
This compares the Relative Power
Efficiency
by looking at the same screen brightness
and
screen area.
|
|
|
Kindle
Fire HD
|
Nexus 7
|
new iPad
|
|
|
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.
|
|
Running Time
At the Maximum Brightness Setting
|
6.6 hours
|
9.1 hours
|
5.8 hours
|
Display always On at the Maximum setting
with
Airplane Mode and no running applications.
|
|
Categories
|
Kindle
Fire HD
|
Nexus 7
|
new iPad
|
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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and Smartphone displays can be significantly improved using DisplayMate’s
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