Samsung Galaxy Tab 10.1 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
Series
Overview
This is part of a
comprehensive article series with in-depth measurements and analysis for the
LCD and OLED displays in state-of-the art Smartphones and Tablets. 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, and then demonstrate how the displays can be improved by using
images that have been mathematically processed to correct color and imaging errors
on Tablets and Smartphones so you can compare them to the originals.
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Introduction
A key element in the success of all Tablets and Smartphones is
the quality and performance of their display. There have been lots of
articles comparing various smartphone LCD and OLED displays and
technologies, but almost all simply deliver imprecise off-the-cuff remarks
like “the display is gorgeous” with very little in the way of serious
attempts at objective or accurate display performance evaluations and comparisons
– and many just restate manufacturer claims and provide inaccurate
information, performance evaluations and conclusions. This article objectively
evaluates the display performance of the Samsung Galaxy Tab 10.1 LCD Tablet
Display based on extensive scientific lab measurements together with
extensive side-by-side visual tests.
The Samsung Galaxy Tab 10.1 has a high performance
Plane to Line Switching PLS LCD display with a White LED backlight. The
screen is 10.1 inches diagonally and has a high-resolution 1280x800 pixel
display with a screen Aspect Ratio of 1.60, which is significantly larger
than the iPad 2, which has an Aspect Ratio of 1.33, but less than a
widescreen HDTV, which has an Aspect Ratio of 1.78.
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.
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FIGURE 1
Figure 1. Revealing Screen Shots for
the Samsung Galaxy Tab.
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Samsung Galaxy Tab: Intensity Scale Ramps
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Samsung Galaxy
Tab: NASA Photo - Sunset on Mars
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Figure 1. Revealing Screen Shots for
the Samsung Galaxy Tab.
The test patterns and photos are 24-bit color
bitmaps at the native resolution of each display.
Results and Conclusions
The Samsung Galaxy Tab
display was evaluated by downloading 24-bit native resolution 1280x752 test
patterns and 24-bit HD resolution test photos to the tablet. Note that while
the LCD screen has 1280x800 pixels only 1280x752 are available for applications
because 48 pixels are reserved for the Android 3.1 system bar with the
navigation buttons. Note that we are testing and evaluating the display on the
Samsung Galaxy Tab with whatever hardware, firmware, OS and software are
provided by Samsung and Google Android.
Color
Depth and Granularity: Excellent Artifact Free 24-bit Color
The Galaxy Tab provides full on-screen 24-bit color,
which has 256 possible intensity levels for each of the Red, Green and Blue
sub-pixels that are used to mix and produce all of the on-screen image colors.
It’s the same as what is found on most monitors and HDTVs. When done properly, as
on the Galaxy Tab, it produces a nice color and intensity scale with few
visible artifacts. Note that Samsung to its credit has fixed the 16-bit color
limitation of the Gallery on Android 3.1 by overwriting the Android images with
full 24-bit color images. Figure 1 shows the smooth intensity scale for both a
photograph and test pattern that are visibly free of all but minor artifacts on
the Galaxy Tab.
Display
Image Quality, Colors and Artifacts: Very Good except for Very High Color Saturation
The image and picture quality on the Samsung Galaxy Tab
are fairly good across the board, including text, icons, and menu graphics. In
the important category of images, pictures and photographs from external
sources, whether they be from digital cameras or web content, are rendered
quite well, except that there is way too much color saturation due to the very
high color gain used during image signal processing.
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, Backlight Power Consumption, and Light Spectrum of the display.
The
Viewing Tests: Too Much Image Contrast and Color Saturation
We compared the Samsung Galaxy Tab side-by-side to the
other Tablets and 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 Galaxy Tab had too much contrast and excessive very high
color saturation.
Factory
Calibration and Quality Control: Very Good Except for Color Saturation
The
overall factory calibration and quality control for the Samsung Galaxy Tab
display is very good. It was very well calibrated, except that the color gain
was set extremely high resulting in excessive color saturation. The color and
gray-scale tracking are very good, which means that the Red, Green and Blue
primaries have been carefully calibrated and balanced.
Suggestions for Samsung:
The
Samsung Galaxy Tab has an all around excellent display, but here are some
suggestions on how to make it better: its only major shortcoming is excessive
color saturation due to the very high color gain used during image signal
processing. This could be fixed easily with a software update by adding a color
picture control that lets users adjust the color to their liking. Otherwise the
Galaxy Tab out-performed the other displays in most test categories. The
accompanying iPad
2 and iPhone 4 LCD Shoot-Out includes some suggestions for the OS driver
software to further improve the Galaxy Tab image quality by using better
sub-pixel anti-aliasing. The Automatic
Brightness Controls and Light Sensors article includes
some important suggestions for correcting the Automatic Brightness control,
which is very important for screen readability, viewing comfort and preserving
battery power.
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.
Samsung Galaxy
Tab Conclusion: Excellent Mobile Display
With
the new Galaxy Tab 10.1, Samsung has delivered the first Android Tablet with an
impressive, potentially outstanding display, but then ruined it by turning up
the color level to obnoxious levels – apparently in an effort to overcompensate
and blatantly standout from the other mobile LCD displays that have subdued
color. But in the case of color, too little is a lot better than too much. The
Galaxy Tab display has a PLS (Plane to Line Switching) LCD, which is Samsung’s
version of IPS, and it performs comparably to IPS – sometimes a bit better and
sometimes not. It’s an impressive mobile display with a lot better standout
performance than all of the other Android Tablets – except in one very
important category… If you like to watch your HDTV with the Color Saturation
control set to maximum then you will be right at home with the Galaxy Tab
because Samsung has turned the color obnoxiously high with no way to lower it.
It’s tolerable for images that don’t have much color to begin with, but it
hurts to look at images that have strong color content. Moderation rather than
the sledge hammer approach to color would have resulted in an outstanding
display. This could be fixed easily with a software update by adding a color
picture control that lets users adjust the color to their liking.
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 1280x752 test
patterns and 24-bit HD resolution test photos to the Samsung Galaxy Tab. Note
that while the LCD screen has 1280x800 pixels only 1280x752 are available for
applications because 48 pixels are reserved for the Android 3.1 system bar with
the navigation buttons. Note that we are testing and evaluating the display on
the Samsung Galaxy Tab with whatever hardware, firmware, OS and software are
provided by Samsung and Google Android. 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: 464 cd/m2 –
Excellent brightness for a Mobile Display
This is the maximum brightness that the display
can produce, called the Peak White Luminance. 464 cd/m2 is about as
bright as you’ll find on any current mobile display. It’s fine for just about
everything except direct sunlight, although it may be too bright for
comfortable viewing under dim ambient lighting. If you find that to be the
case, turn down on the Galaxy Tab’s Automatic Brightness, which uses a light
sensor to adjust the Peak Brightness settings. Since that can be used to
decrease the power used by the backlight it will also increase the battery run
time.
2. Black Level Brightness: 0.51 cd/m2
– Very Good for a Mobile Display
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. The Samsung Galaxy Tab’s value of 0.51 cd/m2 is higher
than the other Tablets (primarily because of its very high Peak Brightness) but
still reasonably dark for a mobile display in typical ambient lighting. Note
that if you decrease the screen Brightness with the (Backlight) Brightness
Control, the Black Brightness will also decrease proportionally by the same
amount, so in dimmer ambient lighting the Black Brightness can be reduced
significantly if desired.
3. Contrast Ratio – Only Relevant for Low
Ambient Light:
916 –
Very Good for Mobile
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. The very best LCDs now have (true) Contrast Ratios
of 1,500 to 2,000 so the 916 value for the Samsung Galaxy Tab is very good for
a mobile device. Don’t confuse the true Contrast Ratio with the tremendously
inflated values that are published by many manufacturers.
4. Screen Reflectance of Ambient Light: 8.2 Percent – Relatively Low
The often overlooked
Screen Reflectance is actually the most important parameter for a mobile
display, even more important than Peak Brightness. This is especially true for
the large 10.1 inch Samsung Galaxy Tab display. 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 Samsung Galaxy Tab is among the lower
values we have measured for mobile device. 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. Bright Ambient Light Contrast Rating: 57 – Very Good
In the same way that the
Contrast Ratio measures the screen contrast under low ambient lighting, the
Bright 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. The Contrast Rating for the Samsung Galaxy Tab is 57,
higher than all of the other Tablets but not as high as some Smartphones. For
all mobile devices the High Ambient Light Contrast Rating is much more
important than the Contrast Ratio.
6. Dynamic Color and Dynamic Contrast: No – Which is Good
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 generally 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 Samsung Galaxy Tab, the measured Luminance for Red=111,
Green=289 and Blue=83 cd/m2. Their sum is 483 cd/m2,
which is fairly close to the measured 464 cd/m2 White Luminance.
7. Color Temperature and Chromaticity: 8380 degrees Kelvin –
White is Too Blue Compared to D6500
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 set to 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. The Samsung Galaxy Tab’s White Point is reasonably far
from D6500 – see the White Points in Figure 2 below. The measured CIE
Chromaticity Coordinates of the Samsung Galaxy Tab White Point are u’=0.1980
v’=0.4455.
8. Color Gamut:
Much Smaller than the Standard Color Gamut –
But 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 Gamuts for the Tablets 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 Point for the Samsung
Galaxy Tab
The LCD Tablets all perform poorly with reference to the
standard Color Gamut, which is the black triangle in Figure 2. They have much
too small a color Gamut. As a result they produce images that have
significantly too little color saturation. This applies to all external content
viewed on the 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. On
most of the LCD Tablets, the photos looked somewhat pale, flat, washed-out and
under-saturated. On the Galaxy Tab Samsung has turned up the Color Saturation
by increasing the Color Gain in the same way as coan be done on all TVs and
many monitors.
9. Intensity Scale, Image Contrast and Gamma: Too Steep, Too Much
Image Contrast, 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 Galaxy Tab alongside the
industry standard Gamma of 2.2, which is a straight line.
FIGURE 3
Figure 3. Intensity Scale for the
Samsung Galaxy Tab
The Samsung Galaxy Tab has a slightly irregular Intensity
Scale with respect to the Standard intensity scale, which is needed in order to
accurately reproduce images and pictures for most content. Gamma is the slope
of the intensity scale, which should be a constant 2.2 like the straight line
in Figure 3. The Gamma for the Galaxy Tab, like the iPad 2, is too steep with
respect to the Standard intensity scale, which is needed in order to accurately
reproduce images and pictures for most content. Gamma is the slope of the
intensity scale, which should be a constant 2.2 like the straight line in
Figure 3. The Gamma for the Galaxy Tab is 2.32 rising to 2.77 which is too high
compared to the standard.
10. Brightness Decrease with Viewing Angle: 52 percent Decrease in
30 degrees – Bad, Very Large
A major problem with many displays, especially
LCDs, is that the image changes with the viewing angle, sometimes dramatically.
The Peak Brightness, Black Luminance, Contrast Ratio and color generally change
with viewing angle (see below). Some display technologies are much better than
others. At a moderate 30 degree viewing angle the Peak Brightness of the
Samsung Galaxy Tab fell by 52 percent to 224 cd/m2, which is an
incredibly large decrease, but is better than all of the other Tablets.
11. Black Level and Contrast Ratio Shift with
Viewing Angle:
At a moderate 30 degree viewing angle the Black
Level Brightness decreased somewhat to 0.43 cd/m2, but the Contrast
Ratio still fell considerably to 518. This behavior is typical for LCDs.
12. Color Shift with Viewing Angle: Excellent, Barely
Visible Shift
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 the primary colors
shifted by a maximum of Δ(u’v’) = 0.0048, which is 1.2 times the Just
Noticeable Color Difference. A much more challenging test is to use mixtures of
primary colors. Reference Brown (255, 128, 0) is a good indicator of color
shifts with angle because of the unequal drive levels and roughly equal
luminance contributions from Red and Green. For the Reference Brown color
mixture the color shift was Δ(u’v’) = 0.0034, which is just 0.8 times
JNCD. These values are so low that the Samsung Galaxy Tab barely shows any
detectable color shift with angle.
13. RGB Display Power Consumption: Poor, Relatively High
The power consumed by LCD
displays is independent of the brightness and color distribution of the images
– it only depends on the Brightness setting of the Backlight that illuminates
the LCD from behind. The Automatic Brightness option allows the ambient light
sensor on the Galaxy Tab to adjust the backlight brightness and power setting
as the ambient light changes. This not only improves visual comfort but can
also increase the battery run time. We turned off Automatic Brightness for the
tests. It is possible to indirectly determine the power used by the display by measuring
the AC power used by the Samsung Galaxy Tab with different backlight settings.
Table 1 lists the Measured
Relative Power, the Measured Luminance, and the Relative Luminous Efficiency,
which is just the Measured Luminance divided by the Measured Relative Power,
and normalized to 1.0 for White, which has the highest total efficiency.
Table 1. Samsung Galaxy
Tab LCD Display Power Consumption
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Maximum Backlight
Full Screen
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Black
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Peak Red
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Peak Green
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Peak Blue
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Peak White
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Measured Relative Power
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4.7 watts
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4.7 watts
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4.7 watts
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4.7 watts
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4.7 watts
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Measured Luminance
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0.51 cd/m2
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111 cd/m2
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289 cd/m2
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83 cd/m2
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464 cd/m2
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Relative Luminous Efficiency
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0.0011
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0.24
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0.62
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0.18
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1.00
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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 their spectra
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 Galaxy S Smartphone OLED with the spectra of the
LCD Tablets. The spectra for White, which is the sum of the Red, Green and Blue
primaries is shown in Figure 4 for the LCD Tablets as well as the Samsung
Galaxy S OLED.
FIGURE 4
Figure 4. RGB Spectra for the LCD
Tablets and also for the Samsung Galaxy S OLED
As
expected the OLED RGB spectra are relatively narrow because of their high color
saturation. The LCD RGB spectra are a filtered broadband spectrum. The
backlights for the LCD Tablets are white LEDs, which consists of a Blue LED
with a yellow phosphor.
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: 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
