Evaluating the 173P+ Display Quality
PCSTATS evaluates LCD displays with Passmark
Monitor Test 2.2 and Pixel Persistence Analyzer
V1.011e. These software applications display a range of primary colours
and special monitor test patterns which enable an observer to diagnose a variety
of visual criteria, discover evidence of broken pixels, dithering readability,
ghosting, and other attributes.
Broken Pixels
What we class as a 'broken pixel' can
fall under any one of the following circumstances: pixels that are always on
(any colour), pixels that are always off, pixels which are unable to display a
primary colour or shade (red, green, blue), or pixels which only display white
or black. While many manufacturers may consider a few broken pixels acceptable,
PCSTATS believes the high cost of LCD displays should translate into a clear and
unblemished image that does not include a single conspicuous broken
pixel.
Ghosting and Pixel Persistence
One of the challenges in
testing LCD displays is quantifying the subjective examinations of ghosting in
comparison to the manufacturers' advertised pixel response times. Some LCD
displays boast 25ms pixel response times, others values as low as 8ms. The
question we face is determining the validity of these figures - are they
accurate measures of the time it takes a single pixel to turn on and return to
its original state (a full cycle), or is the value quoting a half a cycle, or
gray-to-gray transition? The tricks of the LCD industry are numerous when it
comes to shaving off milliseconds. As soon as we start seeing pixel refresh
times with an asterisk* behind the number, we know it's time to cut through the
PR-lingo and offer a better means of drawing comparisons.
With this in mind, PCSTATS has added Pixel
Persistence Analyzer V1.011e (PPA) to its LCD evaluation toolkit. PPA is a freely available program
which offers several specific tests for testing pixel persistence (a.k.a
"ghosting") in LCD displays. The PPA software interprets user adjustments to its
test screens, and returns numerical values for Gamma Factor, Transition Time,
scrolling text Readability and a couple other criteria.
As PCSTATS is specifically
interested in transition time (pixel responsiveness), we've adopted PPA's 'Chase
Test' for capturing snapshots of LCD ghosting in action. The program has clear
instructions on how to run the Chase Test to discover actual numerical pixel
response times for Red, Green and Blue colour patterns, but due to the
subjectiveness of the user interaction, consistency is difficult. The solution
we have opted for is to take a photo of the Chase Test pattern, allowing direct
monitor-to-monitor visual comparisons to be made. It's not a perfect solution,
but it is the best we've been able to come up with thus far for tackling this
sticky aspect of LCD monitor evaluation. These results do not validate the
manufacturers listed pixel refresh times, but rather illustrate the visual
ghosting differences between very quickly moving and static reference patterns.
Chase Test Settings
Frame Rate: 60fps
Rectangle Distance: 100 pixels
Tempo: 20
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Computer Hardware and Display Properties
Graphics card: Albatron Geforce 5950
Video Connection: DVI (analog does not maintain fixed 60fps frame rates, avoid)
Display Settings: 1280x1024 @ 32 bit
Display Frequency: 60Hz (required by PPA)
Colour Temperature: 6500 Kelvin
Operating System: WindowsXP SP2 |
For the PPA Chase Test, the
above test configuration is used for all three colour combinations; White/Blue
on Green, White/Yellow on Blue, and White/Red on Gray.
| LCD Monitor Model |
Pixel Refresh Time
(Mfgr. Spec.) |
Visible Ghosting Blocks From Solid Colour |
Ghosting Test Pattern: Green Sample (moving left to right) |
| Reference Geometry |
N/A |
0 |
 |
| Samsung 173P+ |
8ms* |
2 |
 |
| Samsung 192MP |
25ms |
4 |
 |
| Samsung 191T+ |
25ms |
4 |
 |
|
|
|
|
| LCD Monitor Model |
Pixel Refresh Time
(Mfgr.
Spec.) |
Visible Ghosting Blocks From Solid Colour |
Ghosting Test Pattern : Blue Sample (moving left to right) |
| Reference Geometry |
N/A |
0 |
 |
| Samsung 173P+ |
8ms* |
3 |
 |
| Samsung 192MP |
25ms |
4 |
 |
| Samsung 191T+ |
25ms |
4 |
 |
|
|
|
|
| LCD Monitor Model |
Pixel Refresh Time
(Mfgr.
Spec.) |
Visible Ghosting Blocks From Solid Colour |
Ghosting Test Pattern : Grey Sample (moving left to right) |
| Reference Geometry |
N/A |
0 |
 |
| Samsung 173P+ |
8ms* |
3 |
 |
| Samsung 192MP |
25ms |
5 |
 |
| Samsung 191T+ |
25ms |
5 |
 |
|
|
|
|
Ghosting Results?
It is pretty clear by looking at the three separate colour test patterns
that issues with ghosting are reduced on the 8ms (*gray-to-gray) Samsung 173P+
LCD monitor. The difference varies between 1-2 less visible ghosting blocks on
the 173P+, which is a little bit less than what we had anticipated before the
test was conducted against the 25ms panels. Of course, we're focusing on just
the following edge of the test pattern, the reduction also lessens the visual
effect on the leading edge.
Monitor Test Display Quality Observations
Brightness and Contrast: The Samsung 173P+ display exhibits
excellent shading under the gray scale test. The white scale bars are bright and
the black test background dark. Overall, the 173P+'s 1500:1 contrast
ratio translates into non-illuminated jet-black backgrounds, and bright
whites.
Colour Vibrancy: The three primary colour
test screens were vibrant and uniform from corner to corner.
Colour saturation was excellent, and there were zero dull or
broken pixels visible. There was no light leakage from the corners of the
display panel either.
Colour Shading: By displaying a static primary colour
transition from solid colour to black, it is possible to see one how well the
LCD panel handles colour shading. Limited to 16.7million colours, LCD screens
can suffer banding to some degree, where the slight transition from one shade to
another leads to a visible 'steped' appearance. The Samsung 173P+ performed very
well in this test, banding was not noticeable.
Non-native Resolution:
Native resolution is 1280x1024 pixels. Image dithering at a
non-native 1024x768 resolution was good, and without artifacts. For users
that prefer larger fonts, or need to run at a non-native resolutions the
173P+ handles text dithering gracefully.
Moire: When testing the Samsung 173P+ display on the Digital DVI
cable there was no visible background noise in any of the moire test patterns.
On Analog, autoadjust corrected moire lines in one pattern.
Gaming Tests: To
test out the real world action of fast paced FPS gaming on the Samsung 173P+ LCD
monitor we loaded up Quake 4 and put the Samsung screen through a couple of
rounds of alien-deamon fragging. The colours looked crisp, and I really liked
how the darker areas of the screen were actually black. On some inexpensive
LCD's, the backlight leaks through the darker areas of the screen which takes
away from the visual atmosphere the game otherwise creates. It's distracting and
kind of makes that $500 videocard pointless. Not so with the high 1500:1
contrast ratio of the Samsung 173P+ monitor.
As to the question of ghosting in the game... well it's a really subjective
observation. I'd have to say that it is not completely absent, even though the 173P+
panel boasts an 8ms gray-to-gray pixel response time. The effect is very minimal
if you can even spot it, and to be frank it is difficult to see unless one
is specifically looking for it. As for distracting visual elements, the blockiness
of movements in Quake 4 on an LCD is what stood out in our tests with the
game.
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