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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KristopherKubicki - Thursday, September 4, 2003 - link
#16 - very interesting. Thank you for this information as I will pass it on to others.#19 - Sorry James (whips himself with a wet noddle.) Next time I do something like this I will spend a little more time talking about the BL.
#20 - Im a big Local H fan, but the subtitle actually is derived from an old excellent Stanely Kubrick movie. http://www.imdb.com/title/tt0057012/
#21 - We have had some troubles obtaining Hyundai and LG.Philips based monitors. Fujitsu and Samsung (and AUO I guess) kind of dominate the Us market. I will see if I cant get some more for our internation readers.
#22 - That would be the contrast ratio. However, as we have mentioned before, this measurement seems to vary so much from manufacturer to manufacturer, that it becomes almost useless.
Thanks for all the positive feedback!
Cheers,
Kristopher
Anonymous User - Thursday, September 4, 2003 - link
A point that usually isn't addressed when talking about LCD displays (perhaps it's just me) is the intensity of the colors. I don't care how many variations of pastel an LCD is capable of, the colors just look washed out to me. Is there a measurement that quantifies this?Anonymous User - Thursday, September 4, 2003 - link
Yeah, I was reading the article and immediately wondered why Hyundai is not cited as panel manufacturer.I am the VERY HAPPY owner of an Hercules Prophetview 920DVI Black Edition, second generation (same panel as the Hyundai Q17, 20ms response time). I bought it because of an excellent THG review, based on other input as well, based on its great look, based on its price at that time and based on the panel replacement policy by Hercules that seems (not a single dead pixel, yet...) better than others.
Also, as can be seen in several reviews online and as I personally experienced at a LAN where a buddy brought his Hitachi CML174, the response time in games feels a little better on my 20ms than on his 16ms...
Just a single annoyance, maybe due to my R8500LE DVI output, is that, in Quake3, when there is a lot of 'shiny' light/reflection (as in the second solo level, the fire wall/column when getting inside, and having to choose left or right), there is a lot of tearing/banding, especially visible on these shiny/reflective surfaces...
Does not appear on the theoretically slower 172T on a R9700Pro.....
Anonymous User - Thursday, September 4, 2003 - link
This has nothing to do with actual LCD's but I loved the Local H reference in the article subtitle.Matt
Anonymous User - Thursday, September 4, 2003 - link
Glad to see the article Kristopher, but how could you have a whole article about LCD's without discussing the all important BACKLIGHT.When you look at a modern active matrix LCD you're basically staring straight into a fluorescent bulb--the backlight. The appearance of the substrate can be significantly affected by the quality of the backlight, and when you're using the LCD to perform everyday work like word processing or working in a spreadsheet then 90 percent of the screen is pure white and all you're really seeing IS the backlight.
In that situation the experience using the LCD is highly dependent on characteristics of the backlight--such as the flicker rate of the fluorescent backlight or any anomalies in the backlight's spectrum of colors.
It's true that these factors are usually glossed over by mainstream PC magazines I was expecting Anandtech to cover these issues.
James
Anonymous User - Thursday, September 4, 2003 - link
When I got my monitor. I though it had few dead pixels but in reality it was a little specks of something on the screen, In which case whipping it fixed the "dead pixels".Anonymous User - Thursday, September 4, 2003 - link
I have been looking at getting an LCD for a little while now and found this artical to be very interesting. One thing I would like to comment on is you talk about large screen LCD monitors and how there is a lack of a choice. This is true but one thing I have been looking at is getting a Samsung LCD HDTV Monitor. These have a 16ms response time and reach the larger sizes and have PC hook ups in DVI and a regular 15 pin connector. Of course all of this is assuming that price is no option, as these screens are expensive. Samsung already has a 32inch screen that looks great, model LTN325W, and is gonna be putting out a 26 inch mondel, LTN265W in near future. I wonder how these screens would stack against the LCD monitors you discussed.rapsac - Thursday, September 4, 2003 - link
One important conclusion is missing in the article:On page 10 in the list of brands with the same panel you can see that the # of colors change from manufacturer to manufacturer. Fact is that this specific panel only uses 18bit color info, resulting in 262200 colors. All companies that state more colors LIE.
The controllers they use for these panels use some form of interpolation to fake more colors, but this will never result in as good a picture as with 24 bit panels.
Also, the interpolation is based on FRC (frame rate control); hereby the pixels get different color info each refresh. This results in visible noise (look at any Acer/BenQ from closeby, chances are you'll see it straight away) and it will also completly ruin the response times as more than 1 refresh is neccesary to give the pixel its color.
I have had a lengthy discussion with BenQ about this. The only result is that they promised to state the #colors of models with interpolation to 16M instead of 16.7M, at least this gives the end user a means to detect a 262k panel with interpolation.
Anyway, I've been screwed by BenQ with a 15" FP567 and whenever I see a LCD review I try to warn ppl. Acer and Benq (and lots of other brands) use these 262k panels in almost all their cheap models, so watch out and demand that you can return it if the specs are completly false.
Anonymous User - Thursday, September 4, 2003 - link
Its a shame that this article did not point out the Hyundai panels. I have an L70S with a 16ms response time, and the picture quality is very good, and I can't perceive any "ghosting." The big downside to this monitor is the lack of DVI. Has anyone else had good experiences with the Hyundai panels?PrinceGaz - Thursday, September 4, 2003 - link
Excellent article.@#13: "A good article.I my self use CML174.
Made a lot of difference to my eyes compared to CRT."
Were you by any chance running your CRT at the default refresh-rate of 60hz? Thats the usual reason people claim they cause eye-strain (often because they don't know how to change it). For the price of a new LCD display, you could get a larger high-quality CRT monitor capable of running at 85hz or higher (ideally 100hz) and you'd be amazed how much better it is than any LCD. On the other hand you could just increase the refresh-rate on the old one and save some cash.
Myself I use the 22" CRT Mitsubishi DiamondPro 2070SB with a 20" visible display at 1600x1200 @ 100hz and the picture is fantastic. Theres no LCD available which could come close to it especially for gaming. Unless you need to take it to a LAN party :)