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 - Friday, September 5, 2003 - link
#42 - this will be addressed in Part II =)Kristopher
Anonymous User - Friday, September 5, 2003 - link
Very nice article. Easy to read, fun and very informative.However, as someone here stated earlier, the reference to how some companies manage to get more than the 262000 colours with the 16ms AUO substrate is missing. It seems that they do this by alternating two colours, which would in effect mean the actual total rise and fall time for that one colour is more than 16 ms. But perhaps this is to be discussed in the follow-up to the article? I'm really interested in reading about the grey-grey times for the panels, so I'll be looking forward to part II.
AbRASiON - Friday, September 5, 2003 - link
Wouldn't touch one until it beats a CRT in every single way - periodFor work yes, sure right now, one res all day, no games, no worries.
For home, multiple resolutions, more dos boxes - linux sessions (ok I don't have any but if I did) - games which I don't have a strong enough video card for native resolution etc etc.
also the stupid ghosting / shading effect of the high refresh (16ms is too high)
Until it beats a CRT in every single way - I'm not going over - EVEN IF CRT's end up costing more.
Plus CRT's are getting better, my 22" Philips (100hz 1600x1200) is only like 45cm deep - quite short really considering.
virtualgames0 - Thursday, September 4, 2003 - link
I think you missed a big issue with LCD image problems that I have commonly observed. Most LCDs are very dim, and almost all of them I've seen are nowhere close to comparable to a CRT, the only ones I've seen that were comparable was the NEC.Another problem I have commonly observed is that the majority of LCDs have very visable "gate lines(as you called it in the artlce), so then you can see that every pixel is seperated, and it makes everything look pixelated, and it feels like you're trying to look through that mesh...
spikemike - Thursday, September 4, 2003 - link
I'm not 100% sure but i believe a 1280x1024 LCD monitor is actually built in a 5:4 ratio. So the pixels are still square.n0d3 - Thursday, September 4, 2003 - link
What I missed, and I'm sure it will be coverd in an update, was something more about resolutions. Here's why.Today, people seem to be using 'weird' or 'odd' resolutions a lot, basically because it seems better to have bigger numbers. For instance, 1280x960 is not acceptable (The drivers for my old Connect3d radeon 9000 did NOT support this resolution) however 1280x1024 is just fine. This strikes me as odd because monitors still use a 4:3 ratio. A lot of resolutions conform to this 'standard' 640x480 800x600 etc etc. But in the higher range they seem to 'cheat' a lot more. From what I can understand, this would cause a distorted display. This is very true for CRT's but LCD's seem to be heading that way asweel, wich is something I Don't get. I say this because it is always recommended to use an LCD at it's own resolution, wich is the amount of pixels on the substrate. I can hardly imagine that they would produce non 4:3 screens, allthough ofcourse it is possible.
Some more info on this would be greatly appreciated since I could be wrong about this and tell people wrong things : )
P.S. and yes, I know that if your monitor is capable of going up really high in resolution the distortion on lower resolutions should be minimal, nevertheless, it is deffinatly there.
Anonymous User - Thursday, September 4, 2003 - link
Thanks for a very informative article.I have a Samsung 172T and I have to say the image quality is outstanding. I don't play a lot of FPS games, but for varied use including games and video,using DVI, there are no significant motion blur problems. This monitor is head and shoulders above comparable units I've seen, at least for general use. The price of this unit has dropped significantly since I bought mine almost a year ago. (It may be discontinued).
Been an Anandtech reader since 1996. Keep up the great work!
spikemike - Thursday, September 4, 2003 - link
I'm still not sure if you have it quite right, each subpixel can be independently controlled, you can get 16 shades of blue 16 shades of green and 16 shades of red, giving you 12bit color or 4096 total colors, the red blue and green do not depend on each other, red can be full on, blue can be "1/2" on and green can be off. The main problem was the lack of color, slow response times, and the fact that the information would "bleed" into the column, having one off pixel in a whole column of on pixels would decrease the over all brightness of that columnKristopherKubicki - Thursday, September 4, 2003 - link
#33, I clarified the article a little to apply to both the EE folks and just the casual reader ;)Kristopher
spikemike - Thursday, September 4, 2003 - link
oops i meant posts 29 and 30 were mine