Less than a year after the first generation of smaller tablets gained traction, a second generation of 7-inchers has arrived -- the Google Nexus 7 launched in July and the Amazon Kindle Fire HD in September. There are many other manufacturers making small 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 outperform most full-size higher-priced tablets. But which is best?
DisplayMate's visual wizard Raymond Soneira put the Kindle Fire HD and Nexus 7 through a fierce battery of tests to determine who has the best, brightest 7-inch tablet display once and for all. Here's what he found.
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. For the comparisons with the original Amazon Kindle Fire and Barnes & Noble Nook Tablet see our First Generation IPS Tablet Display Technology Shoot-Out.
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 summarises the lab measurements in the following categories: Screen Reflections, Brightness and Contrast, Colours 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 tablets to the 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 (rumoured) upcoming iPad Mini is likely to fit in with these tablets.
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 per cent 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 artefacts. With 216ppi the Kindle Fire HD and Nexus 7 are significantly better than the 132ppi for the iPad 2, but well below the 264ppi 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).
Colour Gamut and colour Accuracy
While the display pixel density and pixel resolution seem to get most of the attention, it is the display's colour gamut together with the Factory Display Calibration (below) that play the most important role in determining the Wow factor and true picture quality and colour accuracy of a display. The colour gamut is the range of colours that a display can produce. If you want to see accurate colours in photos, videos, and all standard consumer content the display needs to closely match the Standard Colour Gamut that was used to produce the content, which is called sRGB / Rec.709. Most of the first generation LCD tablets have colour gamuts around 60 per cent of the Standard Gamut, which produces somewhat subdued colours. The original Kindle Fire and Nook colour tablets have 55 per cent, the iPad 2 has 61 per cent, but the new iPad pulled way ahead and has a virtually perfect 99 per cent of the Standard Colour Gamut. The new Kindle Fire HD and the Google Nexus both deliver an impressive 86 per cent Standard Colour Gamut, a major improvement over almost all previous generation tablets (and smartphones).
While the Kindle Fire HD and Nexus 7 both have an 86 per cent colour 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 colour gamut is the Factory Display Calibration, which can ruin an excellent display if done improperly.
Factory Display Calibration
The raw LCD panel hardware first needs to be adjusted and calibrated at the factory with specialised 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 colour 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 colour gamut, colours and contrast are washed out due to a compressed, convex and irregular Intensity Scale (sometimes called the grey scale). Bright images look like over exposed photographs. We have discussed this in more detail in this Display News article -- also see Figure 3 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 per cent. This is large enough to be occasionally visually noticeable and can bring the Nexus 7 Maximum Brightness down to almost 300cd/m2, which we classify as Poor for Maximum Brightness. We borrowed and tested a second Nexus 7 unit and found identical behaviour -- 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 behaviour 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.
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 colour 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 colour and image contrast — especially bright images. For example, this was rather noticeable in photographs of faces, which are often the centre 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 colour gamut but a more saturated green primary than the Nexus 7.
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 colours 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 per cent and on the new iPad it is 7.7 per cent. However, on the Nexus 7 the Reflectance is an impressive much lower 5.9 per cent, while on the Kindle Fire HD it is 6.4 per cent -- both are significant improvements over the iPads. For comparison, the iPad 2 reflects 47 per cent more ambient light than the Nexus 7 and 36 per cent 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 Rumoured iPad Mini?
There are credible rumours that sometime in October Apple will announce an iPad Mini with a 7.85-inch 160ppi screen and a Resolution 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 7-inch tablets?
Colour Gamut: It's very likely that the iPad Mini will have a 100 per cent colour gamut like the new iPad 3, 14 per cent greater than the Kindle Fire HD and Nexus 7.
Pixels Per Inch: The Kindle Fire HD and Nexus 7 have 216
, considerably greater than the predicted 160ppi for the iPad Mini or the 132ppi for the iPad 2, but considerably less than the 264ppi for the new iPad.
Screen Resolution: The Kindle Fire HD and Nexus 7 have 1280x800 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 per cent larger than the Kindle Fire HD and Nexus 7. However, for 16:9 content the area is only 6 per cent 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 rivalling 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 a low 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 HD 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 colour accuracy. While the new iPad's 264ppi screen is significantly sharper for reading text and viewing finely detailed computer graphics, the Kindle Fire HD's 216ppi screen is still very sharp and its 1280x800 screen exceeds the resolution needed for viewing standard HD 1280x720 video content, one of its principal marketing goals. Like the new iPad, the Kindle Fire HD has better picture quality and colour 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 per cent erratic variation in screen Brightness, sometimes bringing the Nexus 7 Maximum Brightness down to almost 300cd/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 434cd/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 issues, 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 rumoured 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 rumoured 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.
Display Shoot-Out Comparison Table
Here 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. You can click for full view either here or on the chart itself.
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.
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 PhD in Theoretical Physics from Princeton University, spent five years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another five years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested and installed colour 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 [email protected].
DisplayMate Technologies specialises in advanced mathematical display technology optimizations and precision analytical scientific display diagnostics and calibrations to deliver outstanding image and picture quality and accuracy — while increasing the effective visual Contrast Ratio of the display and producing a higher calibrated brightness than is achievable with traditional calibration methods. This also decreases display power requirements and increases the battery run time in mobile displays. This article is a lite version of our intensive scientific analysis of smartphone and mobile displays — before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the deficiencies — including higher calibrated brightness, power efficiency, effective screen contrast, picture quality and colour and grey scale accuracy under both bright and dim ambient light, and much more. Our advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. For more information on our technology see the Summary description of our Adaptive Variable Metric Display Optimizer AVDO. If you are a display or product manufacturer and want our expertise and technology to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.