Google Nexus One OLED Display Shoot-Out

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2010 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

 

 

Series Overview

This is Part I of a comprehensive multi-part article series with in-depth measurements and analysis for the OLED and LCD displays on the Google Nexus One, the Apple iPhone 3GS and the Motorola Droid. 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 and display technologies. Each article will be introduced and discussed on DisplayBlog by Jin Kim, followed up with a detailed technical analysis and measurement data on the DisplayMate website. Part I deals with the Google Nexus One, Part II with the Apple iPhone 3GS, and Part III is a detailed point-for-point Shoot-Out comparison between the displays on Nexus One and the iPhone. Part IV deals with the Motorola Droid. The series continues with the Samsung Galaxy S and the Apple iPhone 4. Finally, there is a five way Smartphone "Super" LCD-OLED Display Technology Shoot-Out that compares all of the units simultaneously.

 

Introduction

There have been lots of articles and discussions about how beautiful and stunning the OLED display on the Nexus One looks, but no one has yet done anything more than superficial eye ball commentary. This article is an in-depth scientific analysis of the OLED display on the Nexus One.

 

The high resolution, high pixel density OLED display on the Nexus One is beautiful, even stunning on first view, but as we’ll see there are lots of issues, problems and artifacts lurking just below the surface, which we will explore in detail in this article. This is not altogether surprising since OLED displays are at the leading edge of display technology – they are still under development and still being perfected as a production display for use in consumer products.

 

The Nexus One display is distinctive and unusual in several respects: it is an Organic LED display, which is an emissive display technology, whereas most mobile devices have an LCD display, which uses a static backlight behind the panel. The screen is 3.7 inches diagonally and has a high-resolution high-density 800x480 pixel display with a screen Aspect Ratio of 1.67, which is higher than the iPhone’s 1.50, but lower than standard widescreen displays, which have an Aspect Ratio of 1.78.

 

Another unusual aspect of the Nexus One display is that it uses a PenTile pixel arrangement, where there are only two sub-pixels per pixel instead of the usual three, Red, Green and Blue, that are used in most display technologies. Every PenTile pixel includes a Green sub-pixel, but the Red and Blue sub-pixels appear in alternating pixels. In principle, that is only a minor issue because if Red or Blue isn’t available in a particular pixel, then the display driver can just use one from an adjacent pixel. But In practice, it makes things a lot harder for the software and makes it very likely that artifacts will creep into the on-screen images. Note that a 800x480 PenTile display only has two-thirds of the total number of sub-pixels found on an 800x480 LCD, so it won’t be quite as sharp as a typical 800x480 display.

 

Note that we are testing and evaluating the display on the Nexus One with whatever hardware, firmware, OS and software are provided by Google and HTC.

 

The inner details of the display technologies are very interesting, but our concern here is to evaluate the actual image and picture quality that they deliver, so we don’t really care how they do it, as long as they do it well. None-the-less with the measurements and analytical test patterns we will learn quite a bit about how they work.

 

FIGURE 1

Figure 1.  Revealing Screen Shots for the Google Nexus One and Apple iPhone 3GS.

Figure 1.  Revealing Screen Shots for the Google Nexus One and Apple iPhone 3GS.

The test patterns are 24-bit bmp at the native resolution of each display.

 

Results and Conclusions

The display was evaluated by downloading 24-bit native resolution 800x480 test patterns and 24-bit HD resolution test photos to the phone and using the main Nexus One Gallery Application to view and measure them. Note that we are testing and evaluating the display on the Nexus One with whatever hardware, firmware, OS and software are provided by Google and HTC.

 

Color Depth and Granularity:  Only 16-bits in the Browser and Gallery Applications

An absolutely shocking discovery is that the principal Browser and Gallery Applications in the Nexus One only use 16-bit color, so Red and Blue only have 32 possible intensity levels and Green only has 64 possible intensity levels. This is common on cheap low-end devices, but it is unacceptable for an expensive high-performance “Super Phone” that Google claims it to be. All screen colors are derived from intensity mixtures of the RGB primaries - with so few levels to work with the colors are coarse and inaccurate, which produces quite noticeable false contouring in many images and photos. Because Green has twice the number of levels as Red and Blue it has a finer intensity scale, which introduces combinations of Green and Magenta tints into images because Green can make intensity steps that Red and Blue cannot. Most computer, HDTV and mobile displays, including the iPhone, have at least 18-bit color and then often emulate full 24-bit color with dithering, providing 256 intensity levels for Red, Green and Blue, which produces a nice color and intensity scale without the ugly artifacts. Figure 1 shows the coarse intensity scale and the resulting false contouring in both a photograph and test pattern. Readers have sent in screen shots from an Astro Image Viewer Application that don’t show these artifacts and appear to be 24-bit color, so presumably Google will correct this shocking problem soon. The primitive 16-bit display interface should be eliminated. Google acknowledges these problems for all 2.1 Android phones including the Nexus One and Motorola Droid. The next major release of the Android OS will fix these issues and provide full 24-bit color and improved scaling. Click Here to Read the Google and Cooliris Statements.

 

Display Image Quality, Colors and Artifacts:  Lots of Shortcomings

The high resolution, high pixel density OLED display on the Nexus One is beautiful, even stunning on first view, but it has lots of color and gray scale accuracy errors and lots of display artifacts (which is anything that appears in any on-screen image that should not be there) and results from hardware, firmware or software processing errors. Some of these issues are unimportant for many phone functions. In particular, text, icons and menu graphics generated by the Android OS are all outstanding, very sharp, with excellent PenTile sub-pixel rendering. On the other hand, the accuracy of photographic images is severely impacted because of the poor factory display color calibration and the 16-bit interface in some of the main Android applications. The Gallery application also uses a laughably primitive scaling algorithm that is used to import images so they fit on the native 800x480 resolution of the display. It produces lots of dropped pixel content, color fringing, and moirés. See the NASA Photo in Figure 1 for an example. Note that this screen shot does not fully capture all of the incredible screen noise and artifacts. Google acknowledges these problems for all 2.1 Android phones including the Nexus One and Motorola Droid. The next major release of the Android OS will fix these issues and provide full 24-bit color and improved scaling. Click Here to Read the Google and Cooliris Statements.

 

The Measurements with Explanations and Interpretations:

The Measurements section below has details of all of the lab measurements and tests with lots of additional background information and explanations including the display’s Maximum Brightness and Peak Luminance, Black Brightness, Contrast Ratio, Screen Reflectance, Bright Ambient Light Contrast Rating, Dynamic Color and Contrast, Color Temperature and White Chromaticity, Color Gamut, Intensity Scale and Gamma, the variation of Brightness, Contrast Ratio and Color Shift with Viewing Angle, the Power Consumption and Light Spectrum of the display.

 

The Viewing Tests:  Gaudy Picture Quality

We compared the Nexus One side-by-side to a calibrated Professional Sony High Definition Studio Monitor using a large set of DisplayMate Calibration and Test Photographs. All of the photos on the Nexus One had way too much contrast and color saturation, to the point of appearing gaudy, particularly faces and well known objects such as fruits, vegetables, flowers, grass, even a Coca-Cola can. Photos that include very color saturated objects, such as a fire engine, were in some cases painful to look at. Many photos showed readily apparent color and intensity false contouring and image noise from excessive processing. These effects are similar to setting an HDTV to a Vivid picture mode and then turning up the Color and Sharpness Controls. The punchy and excessively vibrant looking images on the Nexus One may initially get lots of oohs and aahs, like in many of the early reviews, but after a while the gaudy looking images will become tiresome and unpleasant.

 

Factory Calibration and Quality Control:  Very Poor

OLED displays are at the leading edge of display technology – they are still under development and still being perfected as a production display for use in consumer products. That’s interesting, but they still need to be judged in comparison to LCDs, which are the dominant display technology in all current mobile devices. In that regard, if the Nexus One display were an LCD it would rank among the worst displays we have ever seen in a shipping product. Some of this is undoubtedly due to poor integration of the display hardware with the Android OS and software. Much of it, however, is simply due to very poor factory calibration and quality control, especially with the lack of any credible color and gray scale calibration. Most likely the display sub-assembly was just slapped in as-is into the phone, which is common in factories that are concerned with maximizing volume and minimizing production time and costs. That works fine for cheap displays in text-only based devices, but fails miserably for displays that are expected to deliver quality images for photo, video and web content, like the Nexus One…

 

Suggestions for Google:

1.       Eliminate the primitive 16-bit display interface and fix the Browser, Gallery and other applications.

 

2.       The White Point is too blue, lower it to D6500, which will improve color accuracy, slow the aging of the Blue OLED, reduce power consumption, and improve battery run time.

 

3.       Improve the factory display calibration to correct the large color and gray-scale tracking errors and the irregular and non-standard display contrast and Gamma.

 

4.       The color saturation of the display is way too high. You can trade this excess color saturation to boost the screen brightness by adjusting the software color calibration matrices. This will also improve the color accuracy of the display.

 

5.       Take full advantage of the OLED display: the ambient light sensor now just controls the screen brightness. You should also use it to control the gamma, color gamut, color saturation, and edge enhancement so that in low ambient light the display delivers beautiful and accurate image and picture quality, but as the ambient light increases slowly turn up these parameters to counter-balance the washed out appearance of the images in bright ambient light. Also add a display Vivid or Pizzazz control because some people prefer punchy images and pictures, while other people do not.

 

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. If you are a 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.

 

Nexus One Conclusion:  The Nexus One Display Looks Like a Prototype

The Nexus One OLED display has many spectacular qualities, but it is also loaded with lots of rough edges, hasty unfinished beta display drivers and Android software including principal applications like the Browser and Gallery, poorly implemented image processing, poor system integration together with sub-standard factory display calibration. It really looks and behaves like a prototype for a very nice future display, not a finished production display for a world class mobile device that Google markets it to be. It will be interesting to see the degree to which existing units will be corrected and improved with software updates.

 

 

The Measurements with Explanations and Interpretations

This section explains all of the measurements incorporated in the article. The display was evaluated by downloading 24-bit native resolution 800x480 test patterns and 24-bit HD resolution test photos to the phone and using the main Nexus One Gallery Application to view and measure them. Note that we are testing and evaluating the display on the Nexus One with whatever hardware, firmware, OS and software are provided by Google and HTC. 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 Automatic Brightness light sensor 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.

 

Konica Minolta CS-200

 

1.  Peak Brightness:  229 cd/m²  –  Poor, insufficient brightness for a mobile display

This is the maximum brightness that the display can produce, called the Peak White Luminance. 229 cd/m² is fine for normal indoor lighting but is quite low for a mobile device that will frequently be used in high ambient lighting environments. That makes the display hard to read, especially outdoors. And forget about seeing anything on-screen anywhere near sunlight…

 

2.  Black Level Brightness:  0.0035 cd/m²  –  Outstanding

The Black Level is the closest approximation to true black that the display can produce. Almost all displays wind up producing a visible dark gray on-screen instead of true black. This is a major problem for LCDs. The glow reduces image contrast and screen readability and can be distracting or even annoying in dark environments. It ruins the dark end of the display’s intensity/gray scale and washes out colors in the image. But note that in bright ambient lighting the Black Level is irrelevant because reflections off the screen dominate the screen background brightness. OLED is an emissive technology, so the Nexus One is able to produce very close to true black, which is absolutely stunning in dark ambient lighting. In fact, the Black Luminance was so low that the CS-200 was unable to measure it, so Konica Minolta loaned us their flagship CS-2000 Spectroradiometer to perform this measurement. The Nexus One black is so dark that we could only see it by eye in a totally black lab after waiting a few minutes for dark adaptation to set in.

 

3.  Contrast Ratio  –  Only Relevant for Low Ambient Light:  65,415  –  Outstanding

The Contrast Ratio is a measure of the full range of brightness that the display is capable of producing. It is the ratio of Peak Brightness to Black Level Brightness. The larger the Contrast Ratio the better, but it is only relevant for low ambient lighting because reflections off the screen dominate the display’s Black Level in bright ambient lighting. Note that any Contrast Ratio over 5,000 will not be visually significant except in fairly dark viewing environments with dark image content. Because the Nexus One OLED display produces an extremely dark black its Contrast Ratio is spectacularly large, the highest we’ve ever measured for a production display. Don’t confuse this true Contrast Ratio with the tremendously inflated Dynamic Contrast Ratios that are published by many manufacturers.

 

4.  Screen Reflectance:  15.5 Percent  –  Bad, Relatively High

The often overlooked Screen Reflectance is actually the most important parameter for a mobile display, even more important than Peak Brightness. The screen reflects a certain percentage of the surrounding ambient light, which adds to the screen background, washes out the image, and makes it harder to see what is on the screen. In high ambient lighting the Screen Reflectance can significantly reduce the visibility and readability of screen content. The lower the Screen Reflectance the better. The value for the Nexus One of 15.5 percent is relatively high for a mobile device and is among the highest that we’ve measured for mobile devices in the past. Lowering the Screen Reflectance increases the cost of a display, but it’s the easiest and best way to improve screen readability under bright ambient light. 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.

 

5.  High Ambient Light Contrast Rating:  15  –  Bad, Relatively Low

In the same way that the Contrast Ratio measures the screen contrast under low ambient lighting, the Contrast Rating specifies the relative screen contrast under high ambient lighting. It is the ratio of Peak Brightness to Screen Reflectance. The higher the value the better you’ll be able to see what’s on the screen when you are in a bright location. 15 is relatively low, so the Nexus One display is not good under high ambient lighting. For all mobile devices the High Ambient Light Contrast Rating is much more important than the Contrast Ratio.

 

6.  Dynamic Color and Dynamic Contrast:  Yes  –  But for Power Management

Some displays dynamically adjust the color, gray scale and contrast on every image that is displayed using an internal automatic image processing algorithm. The goal is to jazz up and “enhance” the picture by stretching and exaggerating the colors and intensity scale. It is similar to the Vivid mode found in many digital cameras and HDTVs. Since it alters and frequently distorts the image it is better left as an option for people who aren’t concerned with picture accuracy and fidelity. Since the Dynamic modes are generally triggered by changes in Average Picture Level, a very simple test for Dynamic Contrast is to separately measure the brightness of full screen Red, Green and Blue images and then compare them to White, which should equal their sum. If they don’t agree then there is Dynamic Color and Contrast processing. For the Nexus One, the measured Luminance for Red=81, Green=193 and Blue=18 cd/m². Their sum is 292 cd/m², which is 28 percent larger than the value measured for White, 229 cd/m², so the Nexus One employs some Dynamic Contrast. For the PenTile OLEDs this appears to be caused by intentional power management – similar in principle to Plasmas.

 

7.  Color Temperature and Chromaticity:  8870 degrees Kelvin  –  Whites are Too Blue

White is not a single color but rather falls within a range that is normally specified by a Color Temperature. For accurate color reproduction of most content, including photographs, images and web content it needs to be the industry standard D6500, which is how most professional photo and video content is color balanced. D6500 is the color of natural daylight and is similar to a Black Body at 6500 degrees Kelvin. 8870 Degrees is pretty far off and gives everything on the screen, including photographs, a noticeable bluish cast or tint, like Cool White fluorescent bulbs. Given the aging and efficiency problems with blue OLEDs, it is surprising to see a bluish tint on the Nexus One display, which means that the Blue OLED is being driven extra hard. Better to back it off and improve color accuracy, OLED aging, power consumption, and battery life all at the same time. The measured CIE Chromaticity Coordinates of the White Point are u’=0.1871 v’=0.4508. See the White Points in Figure 2 below.

 

8.  Color Gamut:  Much Larger than the Standard Gamut  –  Colors are Inaccurate and Over Saturated

The Color Gamut of a display is the range and set of colors that it can produce. The only way that a display will deliver good color and gray scale accuracy is if it is accurately calibrated to an industry standard specification, which for computers, digital cameras, and HDTVs is sRGB or Rec.709. It’s the standard for most content and necessary for accurate color reproduction. If the Color Gamut is smaller than the standard then the image colors will appear too weak and under-saturated. If the Color Gamut is greater than the standard then the image colors will appear too strong and over-saturated. The important point here is that a Color Gamut larger than the standard is also bad, not better. Wider gamuts will not show you any colors or content that are not in the original images, which are almost always color balanced for the sRGB / Rec.709 standard. Wider color gamuts simply distort and decrease color accuracy and should be avoided, except for some special applications.

 

Figure 2 shows the measured Color Gamut for the Nexus One and the iPhone 3GS alongside the Standard sRGB / Rec.709 Color Gamut in a CIE 1976 Uniform Chromaticity Diagram. The dots in the center are the measured White Points for the phones along with the D6500 Standard, which is marked as a white circle. The outermost curve are the pure spectral colors and the diagonal line on the bottom right is the line of purples. A given display can only reproduce the colors that lie inside of the triangle formed by its primary colors. Highly saturated colors seldom occur in nature so the colors that are outside of the standard sRGB / Rec.709 triangle are seldom needed and are unlikely to be noticed or missed in the overwhelming majority of real images. When a camera or display can’t reproduce a given color it simply produces the closest most saturated color that it can.

 

FIGURE 2

Figure 2.  CIE 1976 Uniform Chromaticity Diagram showing the Color Gamut and White Points for the Nexus One and iPhone 3GS

 

Both displays perform poorly with reference to the standard Color Gamut, which is the black triangle in Figure 2. The Nexus One has much too large a color Gamut and the iPhone has much too small a color Gamut. As a result the Nexus One produces images that have significantly too much color saturation and the iPhone produces images that have significantly too little color saturation. This applies to all external content viewed on those displays, including web content, such as images, photos and videos. This was easy to see in the viewing tests where we compared the displays side-by-side to a calibrated Professional Sony High Definition Studio Monitor using a large set of DisplayMate Calibration and Test Photographs. All of the Nexus One photos had way too much color, to the point of appearing gaudy, particularly faces, and well known objects such as fruits, vegetables, flowers, grass, and even a Coca-Cola can. Photos with very saturated objects such as a fire engine, were in some cases painful to look at. Google should be able to correct and reduce the excessive color saturation by modifying the display color transformation matrix to blend the Nexus One native Red, Green and Blue primaries so that they match the sRGB / Rec.709 Standard primaries.

 

9.  Intensity Scale and Gamma:  Poor, Too Steep, Too Irregular, and Non-Standard

The display’s intensity scale not only controls the contrast within an image but it also controls how the Red, Green and Blue primary colors mix to produce all of the on-screen colors. So if it doesn’t obey the industry standard intensity scale then the colors and intensities will be wrong everywhere on-screen because virtually all professional content and all digital cameras use the sRGB / Rec.709 standard, so it’s necessary for accurate image, picture and color reproduction. The standard intensity scale is not linear but rather follows a mathematical power-law, so it is a straight line on a log-log graph. Its slope is called Gamma, which is 2.2 in the standards. In order to deliver accurate color and intensity scales a display must closely match the standard. Figure 3 shows the measured (Transfer Function) Intensity Scale for the Nexus One and iPhone 3GS alongside the industry standard Gamma of 2.2, which is a straight line.

 

FIGURE 3

Figure 3.  Intensity Scale for the Nexus One and iPhone 3GS

 

Both displays perform poorly with respect to the standard intensity scale, which is necessary in order to accurately reproduce images and pictures for most content. Over most of the range the Nexus One has too steep an intensity scale, which reproduces images with too much contrast and increases the saturation of most colors. Above 70 percent signal Intensity the reverse is true, the convex shape reduces contrast, so images with a lot of very bright content will appear somewhat washed out. (If that’s hard to see on this plot, note that it covers a range of 1000:1 in brightness.) It’s also very irregular and bumpy, which worsens the false contouring from the substandard 16-bit color depth used by the Nexus One. Both of these effects are due to poor quality control and/or poor factory calibration. It could also be due to a problem in the PenTile sub-pixel rendering. Gamma is the slope of the intensity scale, which should be a constant 2.2 like the straight line in Figure 3. In the central 20 to 80 percent signal range the Gamma for the Nexus One is 2.55, which is noticeably too steep and produces too much image contrast. Continuing below 25 percent signal intensity it takes a very steep dive. In the high 75 to 100 percent signal intensity range the Gamma is 1.82, which is incredibly low, producing low contrast and somewhat washed out images in this range. It may be possible for Google to correct this through proper factory calibration by modifying the display Look Up Tables, but there may be more fundamental issues causing this problem.

 

10.  Brightness Decrease with Viewing Angle:

28 percent decrease in 30 degrees  –  Surprisingly large for an OLED

A major problem with many displays, especially LCDs, is that the image changes with the viewing angle, sometimes dramatically. The Peak Brightness, Black Luminance and Contrast Ratio generally change with viewing angle (in addition to color, see below). Some display technologies are much better than others. A pure OLED display should not show any viewing angle effects, however, the Nexus One shows a surprisingly large variation in Brightness with viewing angle, undoubtedly due to the touchscreen layer and anti-reflection absorption layer that are on top of the OLED layer. At a moderate 30 degree viewing angle the Peak Brightness of the Nexus One fell by a surprisingly large 28 percent to 166 cd/m², which is definitely into unacceptable dim screen territory.

 

11.  Black Level and Contrast Ratio Shift with Viewing Angle:  Not Visually Significant

The Black Level and Contrast Ratio also vary with Viewing Angle, but since they are both spectacular for the Nexus One their variation is of no visual significance.

 

12.  Color Shift with Viewing Angle:  Surprisingly Large for an OLED

Colors generally shift with viewing angle whenever the brightness shifts with viewing angle because the Red, Green and Blue sub-pixels each shift independently and vary with intensity level. At a moderate 30 degree viewing angle Red shifted the most, by Δ(u’v’) = 0.0262, which is 7 times the Just Noticeable Color Difference. This was visually noticeable as a shift towards orange. Green shifted the least at Δ(u’v’) = 0.0107 and Blue shifted by 0.0169. These are surprisingly large for an OLED, again, undoubtedly due to the touchscreen layer and anti-reflection absorption layer that are on top of the OLED layer.

 

13.  RGB Display Power Consumption:  Relatively High  –  Not a Green Display…

Unlike LCDs, the power consumed by OLEDs varies with the brightness of the individual Red, Green and Blue sub-pixels, so the power consumption varies with the brightness and color distribution of each image. When the display is all black, the OLED display effectively uses no power, although the drive circuits still consume some. Maximum power is used when the display shows Peak Intensity White over the entire screen because all OLED sub-pixels are at their maximum brightness. It is possible to indirectly determine the power used by the display by measuring the AC power used by the Nexus One with different test patterns. The average power used when the screen is all black is used as the baseline and is subtracted from the power measured for the other states.

 

Table 1 lists the Measured Relative Power for full screen Black and Peak Red, Green, and Blue. The second row lists the Measured Luminance, and the third row is the Relative Luminous Efficiency, which is just the Measured Luminance divided by the Measured Relative Power, and normalized to 1.0 for Green, which has the highest efficiency.

 

Table 1.  Nexus One OLED Display Power Consumption

 

The Blue OLED uses the greatest amount of power but produces by far the least amount of brightness, resulting in less than 10 percent of the Green OLED’s Luminous Efficiency. Lowering the White Point from the bluish 8870 degrees Kelvin to the standard D6500 degrees Kelvin would not only improve the picture quality and accuracy, but it would also reduce Blue OLED aging, improve the overall power efficiency, and increase battery run time because it would lower the drive level for the Blue OLEDs. So Google, get with it and go Green…

 

14.  OLED and LCD Spectra:  Very Interesting

The spectra of an LCD display is just the spectrum of the backlight filtered through the individual Red, Green and Blue sub-pixel filters within the panel. OLEDs are emissive devices so the spectra of the Nexus One is just the sum of the individual Red, Green and Blue OLED spectra, modified slightly by the touchscreen layer and anti-reflection absorption layer through which their light must pass. We thought it would be very useful and interesting to compare the spectra of the Nexus One with the spectra of the iPhone 3GS, so we asked Konica Minolta to loan us their flagship CS-2000 Spectroradiometer to perform the measurements. The spectra for White, which is the sum of the Red, Green and Blue primaries is shown in Figure 4 for both the Nexus One and iPhone 3GS.

 

FIGURE 4

Figure 4.  RGB Spectra for the Nexus One and iPhone 3GS

 

As expected the OLED RGB spectra are relatively narrow because of their high color saturation. The iPhone LCD RGB spectra is a filtered broadband spectrum. The backlight for the iPhone is a white LED, which consists of a Blue LED with a yellow phosphor.

 

Special Thanks to Jay Catral of Konica Minolta for visiting the DisplayMate Lab and bringing the CS-2000 Spectroradiometer to measure the Spectra and the very dark Black Luminance of the Nexus One. And Special Thanks to Konica Minolta Sensing for loaning us the CS-2000 and sending Jay Catral.

 

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:  Google Nexus One OLED Display

Article Links:  Samsung Galaxy S Super OLED Display

Article Links:  Apple iPhone 3GS LCD Display

Article Links:  Motorola Droid LCD Display

Article Links:  Apple iPhone 4 LCD Display

 

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

 

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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