LCD – For the Novice and the Expert
by Kristopher Kubicki on September 4, 2003 12:13 AM EST- Posted in
- Displays
Common LCD problems
What is ghosting?
Once upon a time, passive LCDs roamed the earth. Unfortunately, they were too slow and painful to look at for any extended period of time. 120ms response times assured anything over 7 frames per second left a lasting impression on your screen. Today, we have monitors that produce 16ms response times, although with the obvious sacrifice of color depth.Perhaps almost half of the people we talk to misinterpret ghosting. By definition from the VESA Flat Panel Display Manual, ghosting is actually the problem of interference over the signal, which results in an “echoed” image. However, misuse has somewhat skewed the word’s definition to also mean problems due to poor response times. To make matters more confusing, ghosting in the signal sense of the word and in the response sense are very hard to tell apart sometimes (especially if you don’t know what to look for).
We polled a few users in our forums that had “ghosting” problems. Three out of the five retracted their problem after we made them replace the analog signal cable with a DVI cable. Thus, we can infer that only two users really suffered from problems with the response time.
The new trend in LCD measurements is shifting to gray-to-gray response times, rather than black-to-white. As we mentioned earlier, black-to-white response times usually do not represent the most real world operations of LCDs. Part II of this LCD FAQ will deal most explicitly with response time issues, so we will not get too far into the subject here. As a simple word of advice, we encourage you to take a look at the LCD that you plan on buying in a store before you buy it online. Stay tuned for our Response Time follow up to this FAQ.
Other Image Problems
One of the other common types of interference on LCD screens has more to do with poor power supplies. Occasionally, an LCD will display an image, but seconds later, the image still persists. Below is an example:When the external brick overheats, we have noticed that its ability to produce clean signals degrades. Thus, the monitor does not properly modulate the signal. Our solution is to make sure your power supply is properly ventilated and not hot to the touch.
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Anonymous User - Friday, October 17, 2003 - link
I'd just like to bump #60. He asks some great questions - anyone have any answers?The 15" laptop 1600x1200 vs 19" desktop version has always bothered me. I wish I could buy my ThinkPad's display as a standalone device!
Anonymous User - Monday, September 15, 2003 - link
Thank you Kristopher for your informative article.I have been staring at a computer or TV monitor for over 25 years and between the CRT and aging, my eyes have been getting worst every year. I am interested in getting the best video quality monitor for under $1000 per monitor. After reading your article, I would assume that a CRT would be the best choice. However, I am in the market to purchase TWO monitors. This is so I can view two programs simultaneously or when a client comes over, rotate the second monitor for their viewing. I mostly stare at numbers, words and Internet images. Also, I prefer larger monitors (i.e. 19"+). Should I consider two CRTs, CRT as my primary and LCD as the secondary, or match monitors and save real estate with two LCDs? What models would you recommend?
Your suggestions are appreciated.
Michael
Anonymous User - Saturday, September 13, 2003 - link
Also, it seems that marketing is mostly centered on inches instead resolution. A bit too often this is also true for reviews which tend to place things like elegance of design, or number of USB ports or some such, above petty details like displayable desktop area.Is this just some braindead carryover from CRTs, or does the average consumer really not care about the number of pixels he gets?
Anonymous User - Friday, September 12, 2003 - link
One thing I'd like to know is why is that usual native resultion for 19" LCDs 1280x1024? Or more specifically, why do 17" and 19" LCDs generally have the same native resolution.I would have thought that the logical progression would have been (based on the resultions usually used on equivalent sized CRTs):
15" 1024x768
17" 1280x1024
19" 1600x1200
But no, you generally have to go up to 21" LCD to get a 1600x1200 native resolution. And it can't be a technical problem, because we have 15" notebook LCDs with 1600x1200 (and higher) resolution.
So, does anyone know why the LCD industry made the bonehead decision to standardize on having 17" and 19" LCDs have the same native resolution?
PS. And don't bother pointing out that there are a few 1600x1200 19" LCDs. I'm aware of these exceptions. I just don't understand why this isn't the standard.
rapsac - Thursday, September 11, 2003 - link
#58That is anybody's guess. No way to find out unless you buy one and open it up. Then use the panel# to get the specs at the panel manufacturer. (And wave your warranty goodbye like I did mine :( )
joramo - Tuesday, September 9, 2003 - link
Are this 16.7m color specifications true or is the same 18 bits AUO panel?ACER AL732 - 17"
Technical specifications
Display size 17"
Display type Active color matrix TFT
Display area 338 x 270 mm
Brightness 260 cd/m²
Resolution 1280 x 1024 pixels
Colour 16.7m (8-bits per color)
Pixel pitch 0.264 (H) X 0.264 (W)
Contrast ratio 450:1
Response rates Total: 16ms
Thx
KristopherKubicki - Monday, September 8, 2003 - link
#55: on the contrary, lg.philips actually informed us of the opposite. While technically the dithering does not impact the response time, electrical modulation does. This is a direct result of how many bits the signal is capable of.Kristopher
Anonymous User - Monday, September 8, 2003 - link
Are there any formal reviews on new substrates that offer 10-bit gamma correction? In particular, I am considering either the Sharp T1820 or the EIZO L695 (L685EX), and considering that their specs are fairly similar, I assume they are using the same substrate. Supposedly the 10-bit gamma correction is capable of displaying a 1024-step greyscale, which can help prevent banding in subtle gradiants.Unfortunately, neither of these LCDs are widely available for me to perform my own eye-testing. Ideally if someone can offer advice on whether this is an overpriced two-step-conversion technology (as with using an analog cable on an LCD), or if this truly offers discernable benifits, that would be great!
The Sharp T1820:
http://www.sharpsystems.com/tmplproduct_T1820.asp
The EIZO L695:
http://www.eizo.com/products/lcd/l695/contents.htm...
Also worth noting, EIZO CG18
http://www.eizo.com/products/lcd/cg18/contents.htm...
Please email: fhsieh@exeter.edu
Any information is appreciated!
Anonymous User - Monday, September 8, 2003 - link
ALL TN+film panels use dithering (or Frame Rate Control as they call it) to interpolate 24 bits colors with a 18 bits signal. These panels are either quoted as 262K colors (64³) or 16.2 millions colors (253³). This applies to ALL 15" monitors and almost ALL 17" monitors (including the Samsung model quoted as 16.7 millions in the article). However all 18" and higher monitors use panel driven with a 24 bits value.BTW, dithering has absolutely no impact on response time.
Anonymous User - Sunday, September 7, 2003 - link
Info on the Samsung X line fo monitors, in case anyone is interested.http://monitor.samsung.de/detail_tft_syncmaster.as...