Display Showdown Part Ia: Nexus One

SERIES OVERVIEW

This is Part I of a comprehensive multi-part article series with in-depth measurements and analysis for the displays on the Google Nexus One and the Apple iPhone 3GS. It is produced as a collaboration between DisplayBlog and DisplayMate Technologies. We will show you the good, the bad, and also the ugly unfinished rough edges and problems lurking below the surface of each of these displays. Each article will be introduced and discussed on DisplayBlog by me, Jin Kim, followed up with a detailed technical analysis and measurement data on the DisplayMate website by Dr. Raymond Soneira. There will be three parts to this series:

  • Part I: Google Nexus One (Part Ia, Ib, Ic, Id)
  • Part II: Apple iPhone 3GS (Part IIa, IIb, IIc, IId)
  • Part III: Detailed Point-For-Point Shoot-Out Comparison

Parts I and II will be rolled out and expanded in several stages over a period of about a week, so be sure to check each day for updates.

INTRODUCTION

There have been lots of excitement about the Nexus One’s OLED display. In this series of articles Dr. Raymond Soneira, President of DisplayMate Technologies, and I dive into a scientific analysis of the Nexus One display.

First, let’s go through some of the major websites touting the OLED display on the Nexus One:

The Nexus One is slim and curvaceous, and the OLED display is just stunning. –cnet

The 3.7-inch, 800×480 AMOLED screen is undoubtedly the best we’ve seen on an Android phone yet, delivering crisp and bright colours and much less glare than the LCD efforts found on HTC’s older Android handsets and, of course, the iPhone. As a result, your eyes won’t start going squiffy after a few hours squinting at it. –Electricpig

Even though the screen is the same size and same resolution as the Droid, it’s noticeably better. The colors are much more vibrant and the blacks are blacker, as evidenced by putting both side by side and hitting up various websites and loading various games. The pinks on Perez Hilton and the blues on Gizmodo just popped a lot more on the N1, and made the Droid (which was actually considered to have a great screen) seem washed out. The same feeling carries over when you compare the Nexus with the iPhone 3GS. And it’s pretty damn bright, compared to the other two phones. This is probably the best screen we’ve seen on a smartphone so far. – Gizmodo

Different users may have different initial impressions on placing the AMOLED side-by-side with a more traditional backlit LCD screen–Ars Deputy Editor Jon Stokes found the AMOLED to be a striking improvement, but to me it first came off as dark and underwhelming. However, upon extended use, I have to say, this is better. … The brightness gamut is excellent. … The OLED screen also has a much better viewing angle than a traditional LCD screen; this could be important for some car dock setups. Overall, I don’t think I’d trade this screen for the brighter Droid screen, or any other non-OLED screen. – Ars Technica

Although the Motorola Milestone has a screen with the same size as the Google Nexus One’s – 3.7 inches – and a few extra pixels (854×480, to the Nexus One’s 800×480) too, the Nexus One’s panel still outclasses it. That’s because it uses a different type of display, AMOLED, which many tip to be the next big thing in mobile. We’re not going to argue with them: it makes the Google Nexus One’s screen look absolutely glorious. Photos don’t quite do it justice, but take our word when we say the colours the screen produces are deeper and richer than on any previous Android phone. –Fonehome

The OLED screen on the Nexus One is spectacular–blacks looked inky black. Next to an iPhone and Motorola Droid, the colors on the Nexus One were vivid. – PCMag

As you can see everybody loves the OLED display in the Nexus One. This particular OLED display makes use of a special PenTile Matrix sub-pixel structure developed by Clairvoyante and now Nouvoyance. I had the pleasure of meeting Candice Brown Elliott, Founder and CEO of Nouvoyance, Joel Pollack, Sr. VP of Strategic Sales and Marketing, and Tony Botzas, Director of System Apps and Engineering, at their Cupertino location on February 3rd. The meeting was prompted by my post Nexus One Pentile Matrix OLED Display where I argued that the 3.7-inch OLED display in the Nexus One did not have a “resolution” of 800×480 but rather a much less 533×480. After two and a half hours I came out with a new-found appreciation for what Nouvoyance has achieved: Candice and her team have developed a deceptively elegant display system based on a deep understanding of human biology and psychology as they relate to vision. And in doing so has enabled a high-resolution OLED display requiring a simpler manufacturing process and lower costs.

Let’s get to the issue of whether the PenTile Matrix used in the Nexus One has a pixel format of 800×480 or not. The answer is complicated. And the reason is because we are dealing with the human visual system, which involves not just the biological functions of the eyes but the connections they have with the brain and how the two interact. I do not pretend to be an expert in this regard but the one thing I do know is that our visual system is brilliantly complex. We won’t get into that here.

What 800×480 really means is 800xRGBx480 and that in turn means there are 800 horizontal pixels and 400 vertical pixels and within each pixel there is a Red, Green, Blue sub-pixel. But how does 800×480 apply to a sub-pixel structure that is different? Therein lies the difficulty. Now we have to move away from discrete hardware specifications to vision.

The Video Electronics Standards Association (VESA) has a method to measure resolution especially when comparing displays with different sub-pixels. The VESA Display Metrology Committee has a definition for resolution in Section 303-7 of Flat Panel Display Measurements Standard Version 2.0:

… the number of alternate black and white lines that can be displayed with a stated minimum contrast modulation.

I would include: … that can be displayed and viewed … The minimum contrast modulation is 50%, but what in the world is contrast modulation?

… the difference between the white-line luminance and black-line luminance divided by the sum of the white-line luminance and the black-line luminance.

Hmm… I think the easiest way to think about this thing called resolution is this: the resolution is dependent on the number of black and white lines, either horizontal or vertical, with a certain level of contrast, meaning you need to be able to visually differentiate the black and white lines. So, let’s move from vision back to hardware specification: does the Nexus One’s PenTile Matrix OLED display have a resolution equivalent to a 800xRGBx480? The answer is: yes, it does.

The PenTile Matrix OLED display is the result of combining our understanding of vision biology and psychology. The result enables the manufacture of an OLED display sporting a resolution equivalent to the very best that LCD technology can offer and does not cost much more to manufacture. Unfortunately technology’s first generation is almost always wrought with imperfections. Samsung Mobile Displays (SMD) takes the brilliance of PenTile and makes it into a 3.7-inch OLED display. But that’s just the display. In the case of the Nexus One the SMD-manufactured OLED display is then integrated by HTC. Google’s Android smartphone OS is then mated to that hardware with software running on top of the OS. So how did Nouvoyance, SMD, HTC and Google do with the Nexus One? Let’s find out.

COLOR & IMAGE QUALITY

The PenTile Matrix OLED display used in the Nexus One uses 16-bit color. Most high-end smartphone displays make use of 18-bit color plus dithering to emulate 24-bit. The red and blue on the Nexus One have only have 32 possible intensity levels; the green has 64. Because screen colors are the result of mixing the red, green, blue the colors on the Nexus One are coarse, inaccurate, exhibit noticeable false contouring, and have a green & magenta tints in images. The iPhone’s TFT LCD makes use of 18-bit color plus dithering with 256 possible intensity levels for all three red, green, blue colors, resulting in smooth images and photographs.

The Nexus One has a high resolution, equivalent to a 3.7-inch 800xRGBx480 TFT LCD. Although resolution (pixel density) is much higher on the Nexus One compared to the 3.5-inch 480xRGBx320 pixel format on the iPhone 3GS, colors are over-saturated, grayscale was inaccurate and there are display artifacts, probably resulting from processing errors in hardware, firmware, software or all of them. Google and HTC decided to incorporate a fairly high-pixel count image sensor for the camera and it seems something wasn’t finely tuned enough. The Android OS seems to be employing some sort of pixel scaling to fit the entire OLED display resulting in poor image quality. As I have often said in previous posts any type of scaling, even when done well, deteriorates quality, but the initial scaling algorithm used in the Nexus One produces dropped pixel content, color fringing, and moirés.

The Nexus One was compared to a calibrated professional Sony studio monitor using a large set of DisplayMate Calibration and Test Photographs. All of the photos on the Nexus One exhibited gaudy color especially in common objects such as fruits, vegetables, flowers, grass and even a can of Coca-Cola. Color and intensity false contouring and noise from excessive processing were present in many of the photographs. Initially, the over-saturated images on the Nexus One might look punchy and vibrant but over time these images will certainly become unpleasant. A recommendation might be to make use of the ambient light sensor to control gamma, color gamut, color saturation, and edge enhancement in addition to display brightness.

If the OLED display was judged in comparison to LCDs used in smartphones, it would rank among the worst we have ever seen in a shipping product. The poor integration among display hardware, the Android OS and software in addition to sub-standard factory color and grayscale calibration are to blame. For a high-end smartphone like the Nexus One that require high performance in regards to rendering photographs, video and web content this lack of quality control is surprising and not acceptable.

The OLED display in the Nexus One looks like a prototype and these are the reasons why:

  • Rough edges
  • Buggy display drivers
  • Poor image processing
  • Poor system integration
  • Low quality factory display calibration

Google, HTC, and Samsung Mobile Display has delivered a high-end “superphone” with the Nexus One incorporating an unique display using the PenTile Matrix OLED display system. But they have a lot of work ahead of them to make sure the next version (the Nexus Two?) addresses all of these problems in the display.

DISPLAY TEST RESULTS

This section explains all of the measurements incorporated in the article. All measurements were made using DisplayMate Multimedia Edition for Mobile Displays to generate the analytical test patterns together with a Konica Minolta CS-200 ChromaMeter, which is a Spectroradiometer. All measurements were made in a perfectly dark lab to avoid light contamination. All devices were tested with their backlight set for maximum brightness with the light sensor-based automatic brightness control turned off, and running on their AC power adapter with a fully charged battery, so that the battery performance and state was not a factor in the results. For further in-depth discussions and explanations of the tests, measurements, and their interpretation refer to earlier articles in the DisplayMate Multimedia Display Technology Shoot-Out article series and the DisplayMate Mobile Display Shoot-Out article series.

Peak Brightness: 229 cd/m²

Peak white luminance is the maximum brightness of the display. In the case of the Nexus One it was 229 cd/m². This level is adequate for normal indoor ambient light settings but will make it difficult to read outdoors.

Black Level Brightness: 0.0035 cd/m²

Almost all displays exhibit a dark gray instead of true black and LCDs are especially prone to this. Since OLED is an emissive technology the display on the Nexus One produces black that is very close to true black and was too low to measure with the CS-200, so Konica Minolta loaned us its flagship CS-2000 Spectroradiometer, which measured the black level brightness at just 0.0035 cd/m². In a dark ambient setting the Nexus One’s OLED display looks ridiculously amazing.

Contrast Ratio: >45,800:1

At greater than 45,800:1 the Nexus One’s OLED display exhibited an incredible contrast ratio, the highest DisplayMate has ever measured. Any contrast ratio over 5,000:1 is only visually significant with dark image content in dark ambient light settings.

Screen Reflectance: 15.5%

The screen reflectance on the Nexus One was a relatively high 15.5% and among the highest that we’ve measured for mobile devices. This is not good. Screen reflectance is the most important specifications for a mobile display. The display reflects a certain percentage of the surrounding ambient light that adds to the screen background and washes out the display. The higher the screen reflectance the harder it is to see the display. This becomes more problematic in high ambient light environments. The screen reflectance measurements were done in accordance with VESA FPDM 308-1, Reflectance with Diffuse Illumination, using an integrating hemispherical dome and a calibrated diffuse white reflectance standard.

High Ambient Light Contrast Rating: 15

Contrast rating measures display contrast in high ambient environments and is the ratio of peak brightness to screen reflectance. Higher values mean the display is easier to see in bright environments. The Nexus One’s contrast rating is a low 15, which means the OLED display is difficult to see in high ambient light environments.

Dynamic Color and Dynamic Contrast: Colors Blown by 28%

Dynamically adjusting color and contrast based on an internal automatic image processing algorithm is a good idea but extremely difficult to do right. Dynamic color and contrast control frequently distorts images and at the least this should be an option that can be turned off if the results are not satisfying. On the Nexus One dynamic color and contrast control seems to be implemented and blows out color by 28%.

WHAT’S UP NEXT

In the next several days Dr. Raymond Soneira and I will be adding more interesting results from the Measurements and Test Pattern Tests for the Nexus One:

  • Part Ib: Color Temperature and Chromaticity, Color Gamut, Intensity Scale and Gamma
  • Part Ic: Brightness Decrease with Viewing Angle, Contrast Ratio Shift with Viewing Angle, Color Shift with Viewing Angle
  • Part Id: RGB Display Power Consumption, OLED and LCD Spectra

For screen captures, more technical and in-depth explanations please visit DisplayMate.