Dr. Raymond Soneira of DisplayMate Technologies has made it his mission to suss out the best smartphone, tablet, HDTV, and multimedia displays from the worst with his Display Technology Shoot-Out series. Here, he tackles the differences between iPad 2 and iPhone 4 screens.
The display on the iPhone 4 has received widespread praise including the DisplayMate Best Mobile Display Award. But the LCD display on the iPad 2 has been the subject of many debates and rumors regarding its specs and performance, especially the resolution and Pixels Per Inch, which is only 132 ppi compared to the iPhone 4 Retina Display's 326 ppi. There is no question that a higher ppi is better, but the real question is whether the iPad 2 delivers good display performance when considering its price point and battery power constraints (and also availability in sufficient quantities for Apple).
In this article we will provide in-depth objective side-by-side comparisons of the displays based on detailed lab measurements and extensive viewing tests to set the record straight. The data and discussions are drawn from the individual dedicated articles in our Display Technology Shoot-Out series for each device: the iPad 2, iPhone 4 and iPhone 3GS. The older iPhone 3GS is included as a baseline to show how mobile displays have evolved since 2009.
As we show in Comparison Table below the display on the iPad 2 delivers almost identical performance to the impressive iPhone 4 Retina Display. Although the iPad has a higher pixel resolution than the iPhone 4, the screen is much larger so the number of Pixels Per Inch is only 132 ppi compared to the iPhone 4 Retina Display value of 326 ppi. Lower ppi makes the pixels more apparent, an effect called pixelation. The very high ppi is a major marketing feature for the iPhone 4, but it's actually something of an overkill (and primarily there for App compatibility) because existing anti-aliasing methods can successfully reduce noticeable pixelation at lower resolutions and ppi.
While the iPad 2 has excellent LCD display hardware, there are two significant shortfalls in the OS display software that Apple could easily fix with a software update that would notably improve the already excellent iPad 2 display performance.
The Current Anti-Aliasing Reduces Perceived Sharpness of Text and Graphics
Anti-aliasing makes images appear less pixelated and easier to read through the precise blending of adjacent pixel content in software. This is especially important for text and graphics on the iPad because of its much lower Pixels Per Inch than the iPhone 4. The anti-aliasing on the iPad 2 is far from state-of-the-art and degrades the perceived sharpness of text and graphics. You don't notice this same effect on the iPhone 4 because of its very high ppi, but the much lower ppi on the iPad needs good anti-aliasing to significantly improve perceived sharpness and rendering. This really stood out when I was reading the New York Times using Safari on the iPad 2 that was sitting right next to an Asus 1201N netbook (also running Safari) that has identical to the iPad 768 vertical pixel count, virtually identical screen height of 5.9 inches and 130 ppi. On-screen the articles were laid out in exactly the same way but the text and graphics looked substantially better on the netbook because of the sub-pixel anti-aliasing it uses (called ClearType in Windows, which is Microsoft's implementation of this technology). What's more, the IPS LCD display on the iPad is much better than the LCD on the Netbook so this result is even more striking. It's very hard to show this effect with a screen shot here because the camera, your display, and the jpg image processing all add their own anti-aliasing and other digital artifacts.
Anti-aliasing is done in iOS software so Apple could (or rather should) add sub-pixel anti-aliasing to the iPad, especially given the new high-speed processing enhancements that were added to the iPad 2, and it can be done even better on the iPad than with the generic software on the Netbook. It will make a big visual improvement and take some of the unwarranted pressure off the iPad's current ppi.
Automatic Brightness Controls Do Not Work Properly—and the Auto Brightness Bug
The Automatic Brightness controls on Smartphones and Tablets are (in principle) designed to appropriately set the screen brightness based on the current ambient light levels. This not only has a major impact on screen viewability and readability, eye comfort, and fatigue, but it plays a very important role in managing display power in order to maximize battery run time, something golden for all mobile displays. Unfortunately, Auto Brightness is very poorly implemented on all mobile devices including the iPhone 4 and iPad 2. This is examined in detail in our BrightnessGate article Smartphone Automatic Brightness Controls and Light Sensors are Useless. In addition, both the iPhone 4 and iPad 2 have an Auto Brightness Bug, where they lock onto the brightest ambient light sensor value that has been measured at any point starting from the time unit was awakened and hold that peak value even after the ambient light decreases substantially afterwards. This keeps the screen overly bright for the current conditions and wastes precious battery power.
Again, this is all done in the iOS software so Apple could (or rather should) fix Auto Brightness for all iOS devices.
Click to embiggen chart. For further details details, measurements, in-depth explanations and analysis see reference the links above at DisplayMate.
This article has been republished with permission from DisplayMate.com.
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 firstname.lastname@example.org.
About DisplayMate Technologies
DisplayMate Technologies specializes in advanced mathematical display technology optimizations and precision analytical scientific display diagnostics and calibrations to deliver outstanding image and picture quality and accuracy – while increasing the effective visual Contrast Ratio of the display and producing a higher calibrated brightness than is achievable with traditional calibration methods. This also decreases display power requirements and increases the battery run time in mobile displays. This article is a lite version of our intensive scientific analysis of smartphone and mobile displays – before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the deficiencies – including higher calibrated brightness, power efficiency, effective screen contrast, picture quality and color and gray scale accuracy under both bright and dim ambient light, and much more. Our advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. For more information on our technology see the Summary description of our Adaptive Variable Metric Display Optimizer AVDO. If you are a display or product manufacturer and want our expertise and technology to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.