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Apple iPad 2 and iPhone 4 LCD Display Shoot-Out

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2011 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 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). What has amazed and impressed me about the iPad 2 is that Apple has included a first rate IPS LCD panel at a very aggressive price point and not used a cheaper second or third tier LCD, which is what most manufacturers do under these circumstances.

 

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.

 

Results Highlights

As we show in the 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. In fact, from the Running Time on Battery entries in the Table below, display brightness makes up to a 12.6 hour difference in the total running time on battery – this is a big effect worth taking advantage of by properly implementing Automatic Brightness!

 

Again, this is all done in the iOS software so Apple could (or rather should) fix Auto Brightness for all iOS devices.

 

Future Display Hardware Upgrades for Smartphones and Tablets

There are quite a few things that Apple and other manufacturers can do to improve the displays for their next generation of Smartphones and Tablets in order to stay competitive in this extremely competitive category. We’ll cover this in Part II (next week) on The Next Generation of Smartphone and Tablet Displays. For example, we’ll discuss ways to increase the LCD color gamut, examine IPS LCD versus OLED, display power efficiency, Ambient Light Sensors, Automatic Brightness Controls, and the appropriate screen resolution and ppi that takes into account performance, cost, and power.

 

DisplayMate Display Optimization Technology

All of these displays can be significantly improved and optimized on many different levels through DisplayMate’s advanced mathematical display modeling and scientific analysis. This article is a lite version of our intensive scientific analysis of smartphone and tablet 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. 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.

 

Display Shoot-Out Comparison Table

Below we compare the displays on the Apple iPad 2, iPhone 4, and iPhone 3GS based on objective measurement data and criteria. The older iPhone 3GS is included as a baseline to show how mobile displays have evolved since 2009. For details, measurements, in-depth explanations and analysis see the Article Links below for the individual dedicated articles for each device.

 

Categories

Apple iPhone 3GS

Article Link

Apple iPhone 4

Article Link

Apple iPad 2

Article Link

Comments

Display Technology

3.5 inch

LCD

Active Matrix

3.5 inch

IPS LCD

Active Matrix

9.7 inch

IPS LCD

Active Matrix

Liquid Crystal Display and In Plane Switching.

All current displays have an Active Matrix.

Screen Shape

3:2  =  1.50

Aspect Ratio

3:2  =  1.50

Aspect Ratio

4:3  =  1.33

Aspect Ratio

The iPad screen has the shape of 8.5x11 paper.

The iPhones have a wider screen that is a

closer match to photos and video content.

Display Resolution

480 x 320 pixels

960 x 640 pixels

1024 x 768 pixels

The more Pixels and Sub-Pixels the better

Pixels Per Inch

163 ppi

Good

326 ppi

Excellent

132 ppi

Good

At 12 inches from the screen 20/20 vision is 286 ppi.

Best human vision is about 20/10 vision or 572 ppi.

See this on the visual acuity for a true Retina Display

Hardware Color Depth

18-bit color

24-bit color

24-bit color

24-bit color produces 16.8 Million screen colors

Displayed Color Depth

18-bits with

Dithering to 24-bits

Full 24-bits

Full 24-bits

iPhone 4 and iPad 2 produce images with relatively

smooth and artifact free colors and intensities.

Viewing Tests

Subdued Images

Photos and Videos

have too little color

and too little contrast

Good Images

Photos and Videos

have too little color

and too much contrast

Good Images

Photos and Videos

have too little color

and too much contrast

The Viewing Tests examined the accuracy of

photographic images by comparing the displays

to a calibrated studio monitor and HDTV.

Suggestions and Conclusions

Suggestions and

Conclusions for

Apple iPhone 3GS

Suggestions and

Conclusions for

Apple iPhone 4

Suggestions and

Conclusions for

Apple iPad 2

Part II of this article will be on what enhancements

the manufacturers need to implement for the next

generation of displays in Smartphone and Tablets.

Overall Display Assessment

Outdated Display

Excellent Display

DisplayMate Award

Best Mobile Display

 Excellent Display

but it needs

Driver Updates

then a PPI Upgrade

for the next generation

Other than PPI resolution the iPad 2 display delivers

similar performance to the iPhone 4 Retina Display.

It needs a software update for anti-aliasing and

another for the Auto Brightness Control, then

higher PPI resolution for the next generation.

 

Brightness and Contrast

Measured Maximum Brightness

is the Peak Luminance for White

Brightness 428 cd/m2

Excellent

------

No Apple

Brightness Specs

Brightness 541 cd/m2

Excellent

-------

Apple Advertises

500 cd/m2 typical

Brightness 410 cd/m2

Excellent

-------

No Apple

Brightness Specs

Maximum Brightness is very important for mobile

because of the typically high ambient light levels.

 

All are very bright but the iPhone 4 exceeds

Apple’s advertised value – impressive!

Black Level

at Maximum Brightness

Black 3.1 cd/m2

Very High

Black 0.48 cd/m2

Very Good for Mobile

Black 0.43 cd/m2

Very Good for Mobile

Black brightness is important for low ambient light,

which is seldom the case for mobile devices.

Contrast Ratio

Relevant for Low Ambient Light

138

Poor

------

No Apple

Contrast Specs

1,117

Very Good for Mobile

------

Apple Advertises

800 typical

962

Very Good for Mobile

------

No Apple

Contrast Specs

Only relevant for low ambient light,

which is seldom the case for mobile devices.

 

Don’t confuse our measured objective values with

the often inflated manufacturer Contrast specs.

Screen Reflectance

of Ambient Light

Reflects 9.2 percent

Good

Reflects 7.0 percent

Very Good

Similar to iPhone 4

Measurement

coming with Part II

Reflectance is the most important spec for mobile

because of the typically high ambient light levels.

Screen Bright Contrast Rating

for High Ambient Light

Bright Contrast 47

Very Good

Bright Contrast 77

Excellent

Similar to iPhone 4

Measurement

coming with Part II

Indicates how easy it is to read the screen

under high ambient lighting. Very Important!

Defined as Maximum Brightness / Reflectance

Colors and Intensities     

Figure 1.  Color Gamuts

Click to Enlarge

        

Figure 2.  Intensity Scales

Click to Enlarge

 

White Color Temperature

6,977 degrees Kelvin

Close to D6500

7,781 degrees Kelvin

White Slightly Too Blue

6,991 degrees Kelvin

Close to D6500

D6500 is the standard White for most content

and necessary for accurate color reproduction.

Color Gamut

See Figure 1

Color Gamut Too Small

60 percent of Std

See Figure 1

Color Gamut Too Small

64 percent of Std

See Figure 1

Color Gamut Too Small

61 percent of Std

See Figure 1

sRGB / Rec.709 is the color standard for most

content and needed for accurate color reproduction.

Too Large is visually worse than Too Small.

Picture Color Saturation

Saturation Very Low

Subdued Colors

 Saturation Too Low

Subdued Colors

Saturation Too Low

Subdued Colors

Picture Color Saturation depends on both the

Color Gamut and the Intensity Scale Gamma.

Intensity Scale and Image Contrast

See Figure 2

Poor - Very Low

and Concave

Good

Contrast Too High

Good

Contrast Too High

The Intensity Scale controls image contrast needed

for accurate image reproduction. See Figure 2

Gamma for Intensity Scale

See Figure 2

Poor - Less than 1.90

Gamma Too Low

Good 2.68

Gamma Too High

Good 2.66

Gamma Too High

Gamma of 2.2 is the standard and needed for

accurate image reproduction. See Figure 2

 

Viewing Angles

Brightness Decrease

at a 30 degree Viewing Angle

63 percent decrease

to 161 cd/m2

Very Large

57 percent decrease

to 235 cd/m2

Very Large

58 percent decrease

to 171 cd/m2

Very Large

Screens become less bright when tilted.

LCD brightness variation is generally very large.

Contrast Ratio

at a 30 degree Viewing Angle

44

Extremely Low

556

Very Good for Mobile

564

Very Good for Mobile

A measure of screen readability when the screen

is tilted under low ambient lighting.

Color Shift

at a 30 degree Viewing Angle

Large Color Shift

Δ(u’v’) = 0.0418

10 times JNCD

Small Color Shift

Δ(u’v’) = 0.0096

2.4 times JNCD

Small Color Shift

Δ(u’v’) = 0.0100

2.5 times JNCD

JNCD is a Just Noticeable Color Difference.

IPS LCD has a smaller color shift with angle.

 

Display Backlight Power Consumption

Display Backlight Power

at Maximum Brightness

0.81 watts

0.42 watts

2.7 watts

Larger Screen

Lower power consumption is important for energy

efficiency and improving running time on battery.

Display Backlight Power Efficiency

same Peak Luminance 410 cd/m2

same 3.5 inch screen area

0.78 watts

0.32 watts

0.34 watts

This compares the Relative Power Efficiency of the

iPad 2 and iPhones by looking at the same screen

brightness and screen area. The iPad 2 and iPhone 4

have the highest efficiencies we have seen - higher

than other LCDs and much higher than OLEDs.

 

Running Time on Battery

Running Time

At Maximum Brightness Setting

Not Available

7.8 hours

7.2 hours

Display always On at the Maximum setting with

Airplane Mode and no running applications.

Running Time

At Middle Brightness Slider Setting

Not Available

12.3 hours

11.8 hours

Display always On at the Middle slider setting with

Airplane Mode and no running applications.

Running Time

At Minimum Brightness Setting

Not Available

17.9 hours

19.8 hours

Display always On at the Minimum setting with

Airplane Mode and no running applications.

Categories

Apple iPhone 3GS

Article Link

Apple iPhone 4

Article Link

Apple iPad 2

Article Link

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.

 

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.

 

 

Article Links:  Apple iPad 2 LCD Display

Article Links:  Apple iPhone 4 LCD Display

Article Links:  Apple iPhone 3GS LCD Display

 

Article Links:  Smartphone "Super" LCD-OLED Display Technology Shoot-Out

Article Links:  Smartphone Automatic Brightness Controls and Light Sensors are Useless

 

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

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

 

 

Copyright © 1990-2011 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

 


                                                                                                                                                                                                                                                                                                                   
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