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Mini Tablet Display Technology Shoot-Out

Amazon Kindle Fire HDX 7  –  Apple iPad mini Retina Display  –  new Google Nexus 7

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2013 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

 

 

 

Amazon

Kindle Fire HDX 7

Apple

iPad mini Retina Display

Google

new Nexus 7 (2013)

 

 

Introduction

A new generation of Mini 7 to 8 inch Tablets from three of the major manufacturers has just completed with the belated launch of the Apple iPad mini with Retina Display. Together with the Amazon Kindle Fire HDX 7 and new Google Nexus 7 (2013) they all should be, in principle, a notch down from the Large Size Flagship Tablets that we recently tested. But the Mini Tablets are growing rapidly in popularity and market share, so it’s a fiercely competitive category. As a result, they have some of the very highest technology displays with Quantum Dots, Low Temperature Poly Silicon, IGZO and/or high efficiency Backlight LEDs, all of which have a major impact on real image quality that we examine below.

 

The 7 inch tablet format was pioneered by the Barnes & Noble Nook Color, Amazon Kindle Fire, and (original) Google Nexus 7. After dismissing the smaller 7 inch tablets, Apple subsequently introduced in 2012 its own iPad mini, with a 7.9-inch 1024×768 display with a (surprisingly) much smaller Color Gamut and higher screen Reflectance than the existing models of the Kindle Fire and Nexus 7. A lot has happened to displays and display technology over the past year so this is much more than a rematch…

 

These new Mini Tablets all have higher than Full High Definition displays that have about 325 PPI Pixels Per Inch. At normal viewing distances a person with 20/20 Vision can’t resolve the individual pixels, so the displays appear to be perfectly sharp. With high resolution and sharpness taken care of (for now), there are many other equally important and even more challenging issues for Mini Tablets displays:

1. Picture quality as good or better than your HDTV (to entice you to watch downloaded content).

2. Excellent true color accuracy and accurate image contrast for high fidelity images of all viewed content.

3. Improved screen performance in high ambient light since Tablets aren’t used in the dark.

 

We’ll cover these issues and much more, with in-depth comprehensive display tests, measurements and analysis that you will find nowhere else.

 

Amazon provided DisplayMate Technologies with a production unit of the Kindle Fire HDX 7 to test and analyze for this Display Technology Shoot-Out article.

 

The Shoot-Out

To examine the display performance of the Amazon Kindle Fire HDX 7, the Apple iPad mini Retina Display, and the new Google Nexus 7 (2013) we ran our in-depth series of Mobile Display Technology Shoot-Out Lab tests. We take display quality very seriously and provide in-depth objective analysis and side-by-side comparisons based on detailed laboratory measurements and extensive viewing tests with both test patterns and test images. To see how far mobile displays have progressed in just three years see our 2010 Smartphone Display Shoot-Out and 2011 Tablet Display Shoot-Out, and for a real history lesson see our original 2006 Smartphone Display 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 below. The Comparison Table section summarizes the Lab measurements in the following categories:  Screen ReflectionsBrightness and ContrastColors and IntensitiesViewing AnglesDisplay White SpectrumDisplay Power ConsumptionRunning Time on Battery. You can also skip the Highlights and go directly to the Conclusions.

 

For additional background and information see our 2013 Flagship Tablet Display Shoot-Out, our 2012 Mini Tablet Display Shoot-Out, and our SID Tablet Display Technology Shoot-Out.

 

Overview of the Kindle Fire HDX 7

The Kindle Fire HDX 7 is Amazon’s 3rd generation LCD Tablet, and their displays have been improving by leaps and bounds since we first tested them back in 2011. Their Full Size Flagship Kindle Fire HDX 8.9 is the best performing Tablet display that we have ever tested, due in part to using the highest performance LCDs with Low Temperature Poly Silicon LTPS. But the Mini Kindle Fire HDX 7 that we test here is also incredibly innovative because it is the first Tablet display to use super high technology Quantum Dots, which produce highly saturated primary colors for LCDs that are similar to those produced by OLED displays. They not only significantly increase the Color Gamut to 100 percent but also improve the power efficiency at the same time. It’s a very impressive display with very impressive technology. More on these issues below.

 

Overview of the new Google Nexus 7

The new Google Nexus 7 (manufactured for Google by Asus) has a very impressive display that uses the highest performance LCDs with Low Temperature Poly Silicon LTPS, the same technology used in the iPhone 4 and 5, but on the new Nexus 7 with more than 3 times the screen area – it’s currently the second largest LTPS on a mobile display after the Kindle Fire HDX 8.9 mentioned above. The very high efficiency LTPS technology allows the new Nexus 7 display to provide a full 100 percent Color Gamut and at the same time produce the brightest Tablet display that we have measured so far in this Shoot-Out series. More on these issues below.

 

Overview of the iPad mini Retina Display

The iPad mini with Retina Display is Apple’s second generation Mini Tablet. The first generation iPad mini was disappointing because not only did it have a low resolution low PPI display, but its small 62 percent Color Gamut was the same as the older iPad 2, instead of the 100 percent Color Gamut on the iPad 3 and iPad 4 (and the new iPad Air). The new iPad mini with Retina Display has a high resolution high PPI display like the other two Mini Tablets that we test here. But shockingly, it still has the same small 63 percent Color Gamut as the original iPad mini and even older iPad 2. As a result, the iPad mini with Retina Display comes in with a distant 3rd place finish behind the innovative displays on the Kindle Fire HDX 7 and new Nexus 7. More on these issues below.

 

IGZO and LTPS

For the last two years one of the most talked about developments in display technology has been the introduction of IGZO (Indium Gallium Zinc Oxide). For both LCD and OLED displays, IGZO can be used to make the electronic circuitry in their Backplanes, which controls all of the pixels and sub-pixels. IGZO’s higher electron mobility allows the circuitry to be much smaller compared to traditional amorphous Silicon a-Si, which is currently what is used in most LCD displays. That allows the brightness and power efficiency of the display to significantly increase, which is very important. But the introduction of IGZO has been repeatedly delayed as the result of production and yield issues. Although all of the major display manufacturers are working on IGZO, Sharp has been the biggest advocate, and it is currently shipping some IGZO displays, including in the current iPads. LG is also shipping IGZO displays, including in its OLED TV, but not currently for the iPads.

 

This has created a production problem where Apple is using both IGZO and a-Si displays in the current iPads. The problem is that a-Si has much lower power efficiency than IGZO, so it uses much more power and also needs bigger batteries. So how can Apple use both display technologies in the same product? I’ve been told by using much higher performance (and cost) White LEDs in the Backlight of the a-Si panels, which equalizes the power efficiency for both types of displays in different ways. As a result, both types of displays can be engineered into the same Tablet and can provide comparable results for the consumer.

 

All of this reliance on IGZO is really bad planning… Right now there is a readily available display technology that has much higher performance than IGZO. It’s Low Temperature Poly Silicon LTPS, and it is used in all of the iPhones and in all of Samsung OLEDs (so it’s available in large quantities). Two innovative Tablet manufacturers, Amazon and Google, have significantly leapfrogged Apple by introducing Tablet displays using LTPS (in the Kindle Fire HDX 8.9 and the new Nexus 7), and they are significantly outperforming the IGZO and a-Si displays in the current iPads. Apple is now lagging in displays, an area where it was once the leader…

 

Quantum Dots

While IGZO has been getting most of the attention, a dark horse called Quantum Dots has emerged as a new and  truly revolutionary super high-tech advancement for LCD displays – and it is showing up for the first time in the Kindle Fire HDX 7, which we test here.

 

Quantum Dots are almost magical because they use Quantum Physics to produce highly saturated primary colors for LCDs that are similar to those produced by OLED displays. They not only significantly increase the size of the Color Gamut by 40-50 percent but also improve the power efficiency by an additional 15-20 percent. Instead of using White LEDs (which have yellow phosphors) that produce a broad light spectrum that makes it hard to efficiently produce saturated colors, Quantum Dots directly convert the light from Blue LEDs into highly saturated primary colors for LCDs. You can see the remarkable difference in their light spectra in Figure 4. Quantum Dots are going to revolutionize LCDs for the next 5+ years. To learn more about Quantum Dots read this from Nanosys. Congratulations to Amazon for leading the way and being the first to incorporate this revolutionary new display technology in Tablets! It will be interesting to see how rapidly other manufacturers adopt Quantum Dots. See Figure 1 and Figure 2 and the Colors and Intensities section for details.

 

Display Sharpness

These Mini Tablets all have almost exactly 326 Pixels Per Inch PPI (the same as the Retina Display iPhones). For 20/20 Vision the pixels are not resolved for viewing distances of 10.5 inches or more, which is less than the typical viewing distance of 12 inches or more. As expected, all were incredibly and impressively razor sharp, especially noticeable with text and graphics (and significantly sharper than the previous models).

 

Display Brightness

All of these Mini Tablets have fairly bright displays, with the Nexus 7 the brightest Tablet that we have measured so far in this Shoot-Out series, with an impressive Maximum Brightness of 572 cd/m2 (sometimes called nits). Part of this is due to its high performance and high efficiency LTPS LCD display discussed above. The Kindle HDX 7 has a very bright 494 cd/m2, and the iPad mini a much lower but still very good 414 cd/m2 (but the Nexus 7 is 38 percent brighter). Note that it is important to appropriately adjust the display brightness in order to preserve battery power and running time, and also to reduce eye strain from looking at too bright a display. See the Brightness and Contrast section for details.

 

Accurate 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. The iPad mini actually has an excellent and accurate calibration considering its small Color Gamut (below) because each unit receives individual display factory calibration. Each Kindle Fire HDX 7 also receives individual unit display calibration for the Color Gamut and White Point. For the Nexus 7 we don’t have any specific calibration information.

 

Intensity Scale and Accurate Image Contrast

The Intensity Scale (sometimes called the Gray Scale) not only controls the contrast within all displayed images but it also controls how the Red, Green and Blue primary colors mix to produce all of the on-screen colors. So if the Intensity Scale doesn't accurately follow the Standard that is used to produce virtually all consumer content then the colors and intensities will be wrong everywhere in all images. Unfortunately, many manufacturers are quite sloppy with the Intensity Scales on their displays.

 

The iPad mini has a virtually perfect Intensity Scale as the result of its detailed individual unit factory calibration. The Intensity Scale for the Kindle Fire 7 is a bit too steep, which increases the Image Contrast somewhat higher than it should be. That’s not always bad, because high ambient lighting winds up reducing Image Contrast, so the extra steepness can be beneficial. On the other hand, the Nexus 7 like all Nexus Tablets that we have tested, has a non-standard and too shallow Intensity Scale. That is always bad because it reduces precious Image Contrast, reduces Color Saturation, and introduces additional Color Errors. See Figure 3 and the Colors and Intensities section for details.

 

Color Gamut

The Color Gamut is the range of colors that a display can produce. In order to show accurate on-screen colors the display must match the Standard sRGB/Rec.709 Color Gamut that is used to produce virtually all consumer content. Note that consumer content does not include colors outside of the Standard Gamut, so a display with a wider Color Gamut cannot show colors that aren't in the original and will only produce inaccurate exaggerated on-screen colors – so in this instance, bigger than 100 percent is not better. The measured Color Gamuts for these Mini Tablets are shown in Figure 1.

 

The Kindle Fire HDX 7 and Nexus 7 both have Color Gamuts close to the sRGB/Rec.709 Standard, in the range of 97 to 103 percent, which is very good. However, the iPad mini Retina Display has a much smaller 63 percent Color Gamut, which is incredibly disappointing because it produces noticeably subdued image colors. In fact, it’s almost identical to the Gamuts on the much older iPad 2 and the original iPad mini. That is inexcusable for a current generation premium Tablet. It’s way below the Kindle Fire HDX 7 and 8.9, the iPad 3, iPad 4, iPad Air, and just about all current generation premium Tablets and Smartphones – see our Mobile Shoot-Out series. Compare the Color Gamuts in Figure 1 and in the Colors and Intensities section.

 

Absolute Color Accuracy

Getting very accurate screen image colors is very important and also very difficult because the display and calibration all need to be done extremely well at the factory. We have performed a set of detailed Lab spectroradiometer measurements of the Tablet displays to see how accurately they reproduce a set of 21 Reference Colors within the Standard sRGB/Rec.709 Color Gamut. The Reference Colors and the colors actually reproduced by the Mini Tablets are shown in Figure 2. The iPad mini is shown separately because its small Color Gamut results in very large errors within the plot.

 

The Color Accuracy Errors are examined in terms of JNCD (Just Noticeable Color Difference). The Kindle Fire has the best overall accuracy with an Average Color Error of 3.0 JNCD, which is Very Good. The Nexus 7 came in a close second at 3.1 JNCD, and the iPad mini came in a distant third with 6.6 JNCD. The Peak Color Accuracy Errors are much higher, particularly for the iPad mini, with 23.4 JNCD. The iPad mini does have some Color Management that improves the Color Accuracy for low saturation colors, but it can’t fix the higher saturated colors. See Figure 2 for a discussion of JNCD with plots of the Reference Colors and the actually reproduced colors, and the Colors and Intensities section for the numerical results.

 

Screen Reflectance and Performance in High Ambient Lighting

The screens on almost all Tablets and Smartphones are mirrors good enough to use for personal grooming. Even in moderate ambient lighting the sharpness and colors can noticeably degrade from light reflected by the screen, especially objects like your face and any bright lighting behind you. Screen Reflectance has been steadily decreasing. These Mini Tablets have around 6.5 percent Reflectance, ranging from 24 to 36 percent higher than the Flagship Kindle Fire HDX 8.9, which has the lowest Reflectance screen that we’ve measured for a Tablet. The iPad mini is the highest Mini Reflectance at 6.8 percent – considerably lower than the original iPad mini, which had 9.0 percent Reflectance, so this is a large improvement. This article has screen shots that show how screen images degrade from reflections in bright ambient light. See the Screen Reflections section for details.

 

Viewing Angle Performance

While Tablets are primarily single viewer devices, the variation in display performance with viewing angle is still very important because single viewers frequently hold the display at a variety of viewing angles, plus they are large enough for sharing the screen with others. All of these Tablets have displays with high performance IPS or FFS LCD technology, so they were expected to show very little color shift with viewing angle, and our Lab measurements confirmed their excellent Viewing Angle performance, with no visually noticeable color shifts. However, all LCDs, do have a strong decrease in brightness (Luminance) with Viewing Angle, and these Mini displays all showed, as expected, more than a 50 percent decrease in brightness at a modest 30 degree Viewing Angle. See the Viewing Angles section for details.

 

Viewing Tests

The big differences in Color Gamut between the Kindle Fire HDX 7 and Nexus 7, and the much smaller Gamut in the iPad mini Retina Display were quite obvious and easy to see in the side-by-side Viewing Tests. The Kindle Fire had the best color accuracy and overall picture quality, with slightly too much Color Saturation and Image Contrast due too a slightly too steep Intensity Scale. The Nexus 7 was a close second, primarily as the result of too shallow an Intensity Scale. The iPad mini Retina Display came in a very distant 3rd place finish with significantly undersaturated colors – particularly noticeable are reds that appear too orange, together with greens and blues that appear weak and washed out. See Figure 1 and Figure 2 and the Colors and Intensities section for quantitative details.

 

Display Power Efficiency

We measured the Power Consumption of all three displays. The Relative Power Efficiency (for the same Luminance and screen area) is highest for the Nexus 7, which has the highest performance and most efficient LTPS Low Temperature Poly Silicon LCD. Second is the Kindle Fire HDX 7, which has a Backlight using Quantum Dots that increases the power efficiency by 20 percent while at the same time increasing the Color Gamut by up to 50 percent as discussed above.

 

The iPad mini Retina Display has the lowest Power Efficiency of the tested Mini Tablets. It uses 30 percent more display power than the original (Non-Retina) iPad mini. But that means there has been a significant enhancement in its power efficiency (from either IGZO or high performance White LEDs as discussed above), because the jump up to Retina Display from the iPad 2 to iPad 3 resulted in more than a 100 percent display power increase. See the IGZO discussion above and our iPad 3 Display Shoot-Out for more information on LTPS, IGZO and a-Si power efficiency. See the Display Power Consumption section for details.

 

 

Conclusions:   Two Very Impressive Tablet Displays and One Disappointment…

These Mini Tablets include some of the most impressive and innovative displays and display technologies, which is perhaps not that surprising given how popular and competitive this mobile category has become.

 

First, they all have high resolution displays, with more pixels than your 50 inch HDTV, but on a 7-8 inch screen, which is certainly impressive. With about 325 Pixels Per Inch, at normal viewing distances a person with 20/20 Vision can’t resolve the individual pixels, so the displays all appear to be perfectly sharp.

 

Even more impressive is that the Kindle Fire HDX 7 and new Google Nexus 7 displays also deliver a full 100 percent Color Gamut, with color accuracy and picture quality that is probably better than most HDTVs, laptops, and monitors. They accomplish this in two very different ways…

 

The new Google Nexus 7 has a very impressive display that uses the highest performance LCDs with Low Temperature Poly Silicon LTPS. The very high efficiency LTPS technology allows the new Nexus 7 display to provide a full 100 percent Color Gamut and at the same time produce the brightest Tablet display that we have measured so far in this Shoot-Out series.

 

Most impressive of all is the Kindle fire HDX 7 –  the first Tablet display to use super high technology Quantum Dots, which produce highly saturated primary colors that are similar to those produced by OLED displays. They not only significantly increase the Color Gamut to 100 percent but also improve the power efficiency at the same time. Instead of using White LEDs (which have yellow phosphors) that produce a broad light spectrum that makes it hard to efficiently produce saturated colors, Quantum Dots directly convert the light from Blue LEDs into highly saturated primary colors for LCDs. You can see the remarkable difference in their light spectra in Figure 4. Quantum Dots are going to revolutionize LCDs for the next 5+ years. To learn more about Quantum Dots read this from Nanosys. Congratulations to Amazon for leading the way and being the first to incorporate this revolutionary display technology in Tablets! It will be interesting to see how rapidly other manufacturers adopt Quantum Dots. This level of display competition and excellence is great to see! Consumers will come to appreciate and then demand this new high level of display performance excellence, which will hopefully spur other manufacturers into improving their display performance in order to remain competitive.

 

And finally… the iPad mini with Retina Display unfortunately comes in with a distant 3rd place finish behind the innovative displays on the Kindle Fire HDX 7 and new Nexus 7 because it still has the same small 63 percent Color Gamut as the original iPad mini and even older iPad 2. That is inexcusable for a current generation premium Tablet. The big differences in Color Gamut between the Kindle Fire HDX 7 and Nexus 7 and the much smaller 63 percent Gamut in the iPad mini Retina Display were quite obvious and easy to see in the side-by-side Viewing Tests. See Figure 1 to compare the widely disparate Color Gamuts and Figure 2 to see the very large  Color Errors that result. This all appears to be due to incredibly poor planning. Instead of moving up to the higher performance (and cost) Low Temperature Poly Silicon LCDs, Apple chose to continue gambling on IGZO, which has resulted in both production shortages and inferior products.

 

Two innovative Tablet manufacturers, Amazon and Google, have significantly leapfrogged Apple by introducing Tablet displays using LTPS (in the Kindle Fire HDX 8.9 and the new Nexus 7), and they are significantly outperforming the IGZO and a-Si displays in the current iPads. Apple was once the leader in mobile displays, unfortunately it has fallen way behind in both Tablets and Smartphones. This should be a wakeup call…

 

What’s Next…

There is still tremendous room for improvement and innovation in display technology, which I have covered in recent articles on super high density 440+ PPI displays, curved and flexible displays, OLED mobile displays and OLED TV displays.

 

The most important developments for the upcoming generations of mobile displays will come from improvements in their image and picture quality in ambient light, which washes out screen images, resulting in reduced readability, image contrast, and color saturation and accuracy. The key will be in dynamically changing the display’s color management and intensity scales in order to automatically compensate for reflected glare and image wash out from ambient light. See this article on display performance in ambient light. The displays and technologies that succeed in implementing this new strategy will take the lead in the next generations of mobile displays…

 

 

DisplayMate Display Optimization Technology

All Smartphone and Tablets 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, prototype development, and production 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.

 

Amazon

Kindle Fire HDX 7

Apple

iPad mini Retina Display

Google

new Nexus 7 (2013)

 

 

Display Shoot-Out Comparison Table

Below we compare the displays on the Amazon Kindle Fire HDX 7, the Apple iPad mini Retina Display, and the new Google Nexus 7 (2013) based on objective Lab measurement data and criteria. For additional background and information see our Flagship Tablet Display Shoot-Out, our 2012 Mini Tablet Display Shoot-Out, and our SID Tablet Display Technology Shoot-Out.

 

 

Categories

Amazon

Kindle Fire HDX 7

Apple

iPad mini Retina

Google

new Nexus 7

Comments

Display Technology

7.0 inch

IPS LCD

a-Si Backplane

Quantum Dots

7.9 inch

IPS / FFS LCD

IGZO / a-Si Backplane

 

7.0 inch

IPS LCD

LTPS Backplane

 

Liquid Crystal Display

In Plane Switching  /  Fringe Field Switching

Low Temperature Poly Silicon

Indium Gallium Zinc Oxide

amorphous Silicon

Screen Shape

16:10 = 1.60

Aspect Ratio

4:3 = 1.33

Aspect Ratio

16:10 = 1.60

Aspect Ratio

The iPad screen has the same shape as 8.5x11 paper.

The Kindle and Nexus have a shape about half way between 8.5x11 paper and Widescreen TV.

Screen Area

22.0 Square Inches

29.6 Square Inches

 22.0 Square Inches

A better measure of size than the diagonal length.

Relative Screen Area

100 percent

135 percent

100 percent

Screen Area relative to the Google Nexus 7.

Display Pixel Resolution

1920 x 1200 pixels

2048 x 1536 pixels

1920 x 1200 pixels

Screen Pixel Resolution.

Total Number of Pixels

2.3 Mega Pixels

 3.1 Mega Pixels

2.3 Mega Pixels

Total Number of Pixels.

Pixels Per Inch

323 PPI

Excellent

326 PPI

Excellent

323 PPI

Excellent

Sharpness depends on the viewing distance and PPI.

See this on the visual acuity for a true Retina Display

20/20 Vision Distance

where Pixels are Not Resolved

10.6 inches

or more

10.5 inches

or more

 10.6 inches

or more

For 20/20 Vision the minimum Viewing Distance

where the screen appears perfectly sharp to the eye.

At 12 inches from the screen 20/20 Vision is 287 PPI.

Appears Perfectly Sharp

at Typical Viewing Distances

Yes

Yes

Yes

Typical Viewing Distances are 12 inches or more.

Photo Viewer Color Depth

Full 24-bit color

No Dithering Visible

256 Intensity Levels

Full 24-bit color

No Dithering Visible

256 Intensity Levels

Full 24-bit color

No Dithering Visible

256 Intensity Levels

Many Android devices still have some form

of 16-bit color depth in the Gallery Photo Viewer.

The Nexus 7 and Kindle Fire do not have this issue.

 

Overall Assessments

This section summarizes the results of all of the extensive Lab measurements and viewing tests performed on the displays.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Viewing Tests

in Subdued Ambient Lighting

Very Good Images

Photos and Videos

have accurate color

and slightly high contrast

Good Images

Photos and Videos

have reduced color

and accurate contrast

Very Good Images

Photos and Videos

have accurate color

slightly reduced 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

All three displays have Small Color Shifts

and a Large Brightness decrease with

Viewing Angle, which is typical for

high performance LCDs.

Overall Lab Assessment

Lab Tests and Measurements

Very Good Display

Very Good Display

But

Small Color Gamut

Very Good Display

These Mini Tablets all tested very well,

except for the intentional Small Color Gamut

of the iPad mini.

Absolute Color Accuracy

Very Good Accuracy

Good Accuracy

Small Color Gamut

Very Good Accuracy

See Figure 2 and Colors and Intensities for details.

Image Contrast Accuracy

Very Good Accuracy

But Image Contrast is

Slightly Too High

Excellent Accuracy

Close To Perfect

Good Accuracy

Reduced Image Contrast

See Figure 3 and Brightness and Contrast for details.

Overall Display Calibration

Lab Tests and Viewing Tests

Very Good Calibration

Very Good Calibration

But

Small Color Gamut

Very Good Calibration

But

Reduced Image Contrast

The Kindle Fire and Nexus 7 are very well

calibrated, which was easy to see in both

the Lab Tests and the Viewing Tests.

Overall Display Assessment

Very Good  A

Good  B

Small Color Gamut

Very Good  A

Reduced Image Contrast

The displays on the Kindle Fire and Nexus 7

Mini Tablets are both all around Very Good.

 

The iPad mini has a Small Color Gamut that

performs well below the other Mini Tablets.

 

Screen Reflections

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. Many Tablets still have greater than 10 percent reflections that 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 continue to reduce the mirror reflections with anti-reflection

coatings and matte or haze surface finishes.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Average Screen Reflection

Light From All Directions

Reflects 6.3 percent

Very Good

Reflects 6.8 percent

Very Good

Reflects 6.2 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.

Relative Brightness of the

Reflected Ambient Light

102 percent

 110 percent

100 percent

Relative Brightness of the Reflected Ambient Light

expressed as a percentage of the lowest amount.

Mirror Reflections

Percentage of Light Reflected

 7.1 percent

Very Good

 8.4 percent

Good

 6.9 percent

Very Good

These are the most annoying types of reflections.

Measured using a narrow collimated pencil beam

of light reflected off the screen.

 

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.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Measured Maximum Brightness

Peak Luminance for White

Brightness 494 cd/m2

Excellent

Brightness 414 cd/m2

Very Good

Brightness 572 cd/m2

Excellent

This is the Brightness for a screen that is entirely

all white with 100% Average Picture Level.

Relative Maximum Brightness

86 percent

72 percent

Much Lower

100 percent

Relative Maximum Brightness expressed as

a percentage of the Brightest display.

 

Dynamic Black Level

at Maximum Brightness

For Full Screen Black Only

0.33 cd/m2

Very Good for Mobile

0.43 cd/m2

Very Good for Mobile

0.43 cd/m2

Very Good for Mobile

Dynamic Brightness can reduce or even turn off

the Backlight during Full Screen Black.

True Black Level

at Maximum Brightness

For Typical Screen Content

0.44 cd/m2

Very Good for Mobile

0.43 cd/m2

Very Good for Mobile

0.43 cd/m2

Very Good for Mobile

This is the True Black Level for most images

rather than the Dynamic Black on a full screen.

True Contrast Ratio

Relevant for Low Ambient Light

1,123

Very Good for Mobile

963

Very Good for Mobile

1,330

Very Good for Mobile

Only relevant for Low Ambient Light levels,

which is seldom the case for mobile devices.

 

Contrast Rating

for High Ambient Light

78

Very Good

61

Very Good

92

Very Good

Depends on the Screen Reflectance and Brightness.

Defined as Maximum Brightness / Average Reflectance.

See this SID article for a detailed explanation.

Relative Contrast Rating

for High Ambient Light

85 percent

Somewhat Lower

 66 percent

Much Lower

100 percent

Best

Relative Contrast Rating for High Ambient Light

expressed as a percentage of the highest value.

Screen Viewability

in High Ambient Light

Very Good  A

Very Good  A

Very Good  A

Indicates how easy it is to view the screen

under high ambient lighting. Depends on

both the Screen Reflectance and Brightness.

See High Ambient Light Screen Shots

 

Colors and Intensities

    

Figure 1

Color Gamuts

Click to Enlarge

 

Figure 2

Color Accuracy

Click to Enlarge

 

Figure 3

Intensity Scale

Click to Enlarge

 

The Color Gamut, Intensity Scale, and White Point determine the quality and accuracy of all displayed images and all

the image colors. Bigger is definitely Not Better because the display needs to match all the standards that were used

when the content was produced. For LCDs a wider Color Gamut reduces the power efficiency and the Intensity Scale

affects both image brightness and color mixture accuracy. See the above Figures for detailed explanations.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

White Color Temperature

Degrees Kelvin

See Figure 1

 

6,904 K

Close to Standard

 

See Figure 1

6,885 K

Close to Standard

 

See Figure 1

7,106 K

Slightly Too Blue

 

See Figure 1

 

D65 with 6,500 K is the standard color of White

for most Content and needed for accurate color

reproduction.

See Figure 1 for the plotted White Points.

 

Color Gamut

Percent of Standard Gamut

Measured in the dark at 0 lux

See Figure 1

 

97 percent

Fairly Close to Standard

 

See Figure 1

63 percent

Gamut Too Small

 

See Figure 1

103 percent

Fairly Close to Standard

 

See Figure 1

sRGB / Rec.709 is the color standard for most

content and needed for accurate color reproduction.

 

Note that Too Large a Color Gamut can be visually

worse than Too Small.

 

Absolute Color Accuracy

Average Color Error

for 21 Reference Colors

See Figure 2

Average Error 3.0 JNCD

Very Good

 

See Figure 2

Average Error 6.6 JNCD

Good

 

See Figure 2

 Average Error 3.1 JNCD

Very Good

 

See Figure 2

JNCD is a Just Noticeable Color Difference.

 

See Figure 2 for the definition of JNCD.

 

Average Errors below 3.5 JNCD are Very Good.

Absolute Color Accuracy

Largest Color Error

for 21 Reference Colors

See Figure 2

Largest Error 5.4 JNCD

Very Good

 

See Figure 2

Largest Error 23.4 JNCD

Poor

 

See Figure 2

 Largest Error 6.5 JNCD

Very Good

 

See Figure 2

JNCD is a Just Noticeable Color Difference.

 

See Figure 2 for the definition of JNCD.

 

Largest Errors below 7.0 JNCD are Very Good.

This is twice the limit for the Average Error.

 

Dynamic Brightness

Luminance Reduction with

Average Picture Level APL

0 percent

Excellent

0 percent

Excellent

 0 percent

Excellent

This is the percent Brightness reduction with APL

Average Picture Level. Ideally should be 0 percent.

Intensity Scale and

Image Contrast

 

See Figure 3

Smooth but Too Steep

Contrast Somewhat High

See Figure 3

Very Smooth

Contrast is Excellent

See Figure 3

Smooth but Concave

Contrast is Somewhat Low

See Figure 3

The Intensity Scale controls Image Contrast needed

for accurate image reproduction. See Figure 3.

Gamma for the Intensity Scale

Larger has more Image Contrast

 

See Figure 3

Average 2.43

Varies 2.17 to 2.61

Somewhat Variable

Somewhat Too High

 Gamma is 2.22

Excellent

Straight and Constant

Close to Perfect

Average 2.01

Varies 1.86 to 2.15

Concave and Variable

Gamma Too Low

Gamma is the slope of the Intensity Scale.

Gamma of 2.20 is the standard and needed for

accurate image reproduction. See Figure 3.

 

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 Smartphones and Tablets.

 

Note that the Viewing Angle performance is also very important for a single viewer because the Viewing Angle varies

based on how the display is held. The angle can be very large if resting on a table or desk.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Brightness Decrease

at a 30 degree Viewing Angle

58 percent Decrease

Very Large Decrease

 57 percent Decrease

Very Large Decrease

57 percent Decrease

Very Large Decrease

All LCDs appear much less bright when tilted.

LCD decrease is generally greater than 50 percent.

True Contrast Ratio

at a 30 degree Viewing Angle

732 Portrait

     603 Landscape

Very Good for Mobile

623 Portrait

    470  Landscape

Very Good for Mobile

719 Portrait

     502 Landscape

Very Good for Mobile

A measure of screen readability when the screen

is tilted under low ambient lighting.

White Point Color Shift

at a 30 degree Viewing Angle

Small Color Shift

Δ(u’v’) = 0.0033

0.8 times JNCD

Small Color Shift

Δ(u’v’) = 0.0020

 0.5 times JNCD

Small Color Shift

Δ(u’v’) = 0.0035

0.9 times JNCD

JNCD is a Just Noticeable Color Difference.

See Figure 3 for the definition of JNCD.

Primary Color Shifts

Largest Shift for R,G,B

at a 30 degree Viewing Angle

Small Color Shift

Δ(u’v’) = 0.0118 for

3.0 times JNCD

Small Color Shift

Δ(u’v’) = 0.0051 for

1.3 times JNCD

Small Color Shift

Δ(u’v’) = 0.0026 for

0.7 times JNCD

JNCD is a Just Noticeable Color Difference.

See Figure 3 for the definition of JNCD.

Color Shifts for Color Mixtures

at a 30 degree Viewing Angle

Reference Brown (255, 128, 0)

Small Color Shift

Δ(u’v’) = 0.0045

1.1 times JNCD

Small Color Shift

Δ(u’v’) = 0.0032

0.8 times JNCD

Small Color Shift

Δ(u’v’) = 0.0047

1.2 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. See Figure 3 for the definition of JNCD.

 

 

 

Figure 4

Display Spectra

Click to Enlarge

 

Display Power Consumption

The display power was measured using a Linear Regression between Luminance and AC Power with a fully charged battery.

 

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 Relative Power Efficiency of the displays is highest for the Nexus 7, which has an LTPS Low Temperature

Poly Silicon LCD Backplane, next is the Kindle Fire HDX 7, which has Quantum Dots, and lowest is the iPad mini.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Maximum Display Power

Full White Screen

at Maximum Brightness

2.3 watts

3.3 watts

 1.8 watts

This measures the display power for a screen

that is entirely Peak White.

Relative Power Efficiency

same Luminance 414 cd/m2

same 7.9 inch screen area

 2.6 watts

3.3 watts

1.7 watts

This compares the Maximum Power Efficiency

by scaling to the same screen brightness and

same screen area as the iPad mini.

 

Running Time on Battery

The running time on battery was determined with the Brightness sliders at the Maximum setting, in Airplane Mode,

with no running applications, and with Automatic Brightness turned off.

 

This determines the how the display can affect the Running Time on Battery.

 

Note that Automatic Brightness can have a considerable impact on running time but we found poor performance

in our BrightnessGate analysis of Ambient Light Sensors and Automatic Brightness. We plan on retesting several

new models in the near future.

 

 

Kindle Fire HDX 7

iPad mini Retina

new Nexus 7

Comments

Running Time on Battery

At Maximum Brightness Setting

 Not Yet Available

Not Yet Available

 Not Yet Available

Display always On at the Maximum setting with

Airplane Mode and no running applications.


 

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.

 

DisplayMate Display Optimization Technology

All Smartphone and Tablet 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, prototype development, and production 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.

 

About DisplayMate Technologies

DisplayMate Technologies specializes in proprietary sophisticated scientific display calibration and mathematical display optimization to deliver unsurpassed objective performance, picture quality and accuracy for all types of displays including video and computer monitors, projectors, HDTVs, mobile displays such as smartphones and tablets, and all display technologies including LCD, OLED, 3D, LED, LCoS, Plasma, DLP and CRT. This article is a lite version of our intensive scientific analysis of Smartphone and Smartphone mobile displays – before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the display deficiencies. We offer DisplayMate display calibration software for consumers and advanced DisplayMate display diagnostic and calibration software for technicians and test labs.

 

For Manufacturers we offer Consulting Services that include advanced Lab testing, analysis and evaluations, confidential Shoot-Outs with competing products, calibration and optimization for displays, improving the User Interface for the entire display system, plus on-site and factory visits. We help manufacturers with expert display procurement, prototype development, optimization, and production quality control so they don’t make mistakes similar to those that are exposed in our Display Technology Shoot-Out series. See our world renown Display Technology Shoot-Out public article series for an introduction and preview. DisplayMate’s advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. If you are a display or product manufacturer and want to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.

 

Article Links:  2013 Flagship Tablet Display Shoot-Out

Article Links:  2012 Mini Tablet Display Shoot-Out

Article Links:  SID Tablet Display Technology Shoot-Out

 

Article Links:  Tablet Displays Under High Ambient Lighting Shoot-Out

Article Links:  Automatic Brightness Controls and Light Sensors

 

Article Links:  Mobile Display Shoot-Out Article Series Overview and Home Page

Article Links:  Display Technology Shoot-Out Article Series Overview and Home Page

 

 

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