Jump to content

LCD Buyers Guide


NIM

Recommended Posts

LCD Buyer's Guide

As of Thursday, Nov 23, 2006

News: Check out the new website!: lcdresource.com

My goal with this guide is to bring you the most accurate, practical, and up-to-date information possible on Liquid Crystal Displays. I hope you as a reader find said info helpful. Read on, and enjoy!

There won't be one question in here (that I can possibly answer) that I won't provide at least some kind of reply to, so if you have any concerns/suggestions/constructive criticism/need recommendations on what to buy, do not hesitate to ask! Everything is welcome. After all, that is the point of this thread.

We are in dire need of reviews, so if you own any LCD, no matter the size, please post the model and how you like it. Thanks!

------------------------------------

Table of Contents:

Criteria

Types of Panels

Aspect Ratios and Resolutions

Technologies

"Ghosting"

Backlight Uniformity/Leaking

Common Misconceptions

Color Reproduction

----------------------------------------------

1. Criteria

----------------------------------------------

Color gamut

"Color gamut" represents the range of colors that can be displayed using combinations of red, green, and blue subpixels. Certain monitors must emulate the colors (by dithering or frame rate control (FRC)) to display the full 24-bit of today's graphics adapters.

Black level (darkness of the color black)

LCDs require a source of light to display an image. Most today use cold cathode fluorescent lights (CCFLs), while more expensive ones use LED. With either technology, the crystals have a hard time blocking the light. How well they can do this is quantized by the black level. This measures how many nits (candelas per square meter) are emitted when black is displayed. Lower the better for black. For white, you'd want the highest value possible. The low black and the high white brightness values will produce a high-contrast display, and that's what you're looking for in terms of colors.

Response time

Response time measures how long it takes for one crystal cell to change its state from on to off. Some types of panels are faster than others in this category. The lower value of time (usually milliseconds) means a quicker change. A high response time can cause blurry/streaky effects in motion. A technology called ODC (overdriving circuit) can assist in reducing these effects.

Viewing angle

The viewing angle measurement denotes how far to each side it is that you can still make out an undistorted image. This varies among panels as well, as do all of the above. On TN panels, the colors will invert when viewed at an extreme angle. VAs will generally just decrease in brightness with little color shift. IPS panels exhibit the fewest effects when viewing from a different angle.

Input flexibility

Many monitors come with both a DVI (Digital Visual Interface) and VGA (Video Graphics Array) interface. DVI will deliver a perfect pictures in terms of geometry due to its digital nature. VGA, analog, can sometimes be noisy or blurry. Generally the difference is insignificant on LCDs 17" or smaller.

Ergonomics

LCDs can be very flexible with physical adjustments. These may include height adjustment, tilt, swivel, pivot, and rotate (portrait/landscape).

It shouldn't come as a surprise all measurements are biased when it comes to manufacturers' specifications.

----------------------------------------------

2. Types of Panels

----------------------------------------------

The most important thing to consider is the type of panel in the LCD.

(Please note that no guarantees are made regarding the accuracy of the scientific details on these panels.)

TN (Twisted Nematic): Without an ODC (overdriving circuit), this type of panel offers the fastest pixel response time. This does however come at the expensive of viewing angles and color fidelity. Out of all TFT-LCD panels, the TN type has the lowest contrast. It is also a 6-bit color depth panel, meaning dithering or frame rate control (FRC) must be employed to reach close to a full 8-bit depth. Pixels in their active state on a TN are black, while in their inactive, white.

(P-)MVA ({Premium} Multidomain Vertical Alignment): The liquid crystal (LC) cells on MVA panels are in their active state white, and in inactive black and are separated into four domains. This slightly improves viewing angle over TN-type displays (MVAs provide ~45 degrees). MVA panels also provide a high contrast ratio. Grayscale inversion is minimal on these displays. Response time is the second slowest in the industry without ODCs. MVAs and all derivatives hide details at a perpendicular viewing angle due to their multidomain nature.

PVA (Patterned-ITO Vertical Alignment): Developed by Samsung, PVA is very similar to MVA. Viewing angles are very similar and inversion is minimal at wide viewing angles. Samsung is not clear on the true color depth of these panels. These panels deliver the slowest response time.

S-PVA (Super Patterned-ITO Vertical Alignment): These types of panels deliver a full 8-bit color depth and have a structure split into eight domains. At wide viewing angles, they have less color shift and a lower black level than MVAs. According to Samsung, they have a higher contrast ratio and better response time than MVAs as well.

S-MVA (Super Multidomain Vertical Alignment): Likely similar to P-MVA from AU Optronics, Chi Mei Optoelectronics has developed the S-MVA type of panel. These also include multidomain, vertically-aligned liquid crystals so that the cells stay in the same shape at different positions, increasing brightness at wide viewing angles. According to CMO, S-MVA improves viewing angles from conventional MVA types to 80 degrees in all angles. Like other types of panels, response time has gradually improved on these as well.

IPS (In-Plane Switching): The IPS panel was pioneered by Hitachi to fix the problems that plague the VA and TN types. Like TN, most IPSes contain only a single domain, although DD-IPS (dual domain IPS) does exist. This technology sports the least distortion at wide viewing angles. Two transistors per each pixel are needed, so brighter backlighting is crucial and power consumption is higher than competing technologies, but response time benefits greatly from this. Color depth varies. One disadvantage is that a purple-black is now introduced in black colors at different viewing angles.

S-IPS (Super In-Plane Switching): LG Philips LCD improved on IPS with their S-IPS technology. These offer a lower black level, higher contrast ratio, lower response time, and a wider viewing angle than traditional IPS technology. Color depth on S-IPS panels is 8-bit. The purple-black tinting still applies to wide viewing angles, but orange and red hues are greatly reduced versus other technologies at wider viewing angles.

AS-IPS (Advanced/Enhanced Super In-Plane Switching): These type of panels are LG Philips LCD's third generation of IPS technology. This is mainly just a wieldy moniker for improvements in the front-end driving electronics, including ODC to reduce response time, and a dynamic contrast ratio technology, raising contrast up to 1600:1. The diagonal viewing angle is also increased to 178 degrees, from 170 on S-IPS panels. AS-IPS panels very often include much brighter backlights than S-IPS types.

A-MVA (Advanced Multidomain Vertical Alignment): This is a new panel from AU Optronics promising contrast ratio and viewing angle performance comparable to Samsung's 8-domain S-PVA panels. These should be capable of true 8-bit color. Still, it is unknown if ODC will force them to dither.

Still confused? Check out the Matrix of all Matrices.

----------------------------------------------

3. Aspect Ratios and Resolutions

----------------------------------------------

Aspect ratio is a proportion representing width divided by height. Common aspect ratios are listed below.

5:4 (1280x1024 for 17" and 19"): Squarest of all the listed, thus maximum area.

4:3 (1600x1200 for 20.1")

16:10 (1680x1050 for 20.1", 1920x1200 for 24"): Resolution of most "widescreen" monitors

16:9 (1280x720, 1920x1080): True widescreen. No LCD monitors that I know of incorporate this HDTV resolution with one exception, this Westinghouse 37", but this is more of a TV due to its size. 16:10 is the commonly used one for monitors because it's a good compromise between productivity (Word documents anyone?) and movie watching.

As for scaling quality, it first depends on if you tell your graphics card to do it, or your monitor. If you find your monitor's scaling is sub par, you can engage your graphics card's scaler. In addition there are a number of scaling modes, like 1:1 and fixed aspect ratio scaling. Many monitors deliver OK scaling when viewing photos, however text clarity can easily suffer. Games may not look very pleasing at lower resolutions.

----------------------------------------------

4. Technologies

----------------------------------------------

Overdrive (Response Time Accelerator)

Most commonly called ClearMotiv (ViewSonic), MagicSpeed (Samsung), Over Driving Circuit (LG.Philips LCD), and Response Time Compensation (X-Bit Labs). All of the above technologies bump the voltage to increase the speed of the transition (among other things in the case of ClearMotiv). When it goes too far (an overshoot), there can be noise, especially noticeable in subtle transitions or the dithering of TN panels. Tom's Hardware Guide does however have a rating for this overshoot phenomenon. X-Bit Labs has also cracked down on it in their recent reviews.

"Widescreen" (16:10 AR)

Usually widescreen means 16:9, but LCD monitor manufacturers use the moniker widescreen to refer to a 16:10 ratio instead, a compromise between desktop real estate and movie watching. While it may sound great at first, there are a lot of things to consider. Is widescreen all it's cracked up to be?

The main problem with widescreen is the resolution itself. As you may know, LCDs can not change their resolution without a loss of quality, and most of the time it's a significant loss of clarity. CRTs can do this much better because they inherently have a Gaussian distribution of the pixels, and in the end it yields much better quality. Think of it like analog zoom vs. digital zoom.

This means in order to get a good image on a widescreen monitor, you must run it at its native resolution, or deal with black bars on the edges. I'd say 75% of today's games still require you to edit a configuration file manually to achieve the widescreen resolution. Fortunately, many people have already done the grunt work for you. Here's a site that will help you configure your game to work with your widescreen LCD: Widescreen Gaming Forum

But, not all games can support widescreen, even through the configuration file. For these, you'll have to settle with the black bars or scaling.

X-Brite/OptiClear/Acer CrystalBrite

These are special contrast-increasing coatings. Note, Samsung's MagicBright/MagicColor and BenQ's SensEye are not necessarily related to these, they are internal panel technologies. Anyhow, many people prefer the higher contrast of these coatings and say they look beautiful. One small note of concern is they could increase glare, but that'll depend on the ambient lighting surrounding you.

HDCP

High-Bandwidth Digital Content Protection. This will be mandatory for playing Blu-Ray/HD-DVD discs on Vista (or any other OS). You won't need it to boot into Windows though (not even Vista). HDCP can be used through the DVI port or through the HDMI port. It's hardly anything to worry about for computer monitors (very few have it), but you should definitely consider it for multimedia monitors and TVs.

Hi-FRC (pdf)

This is a new form of FRC (temporal "dithering") developed by Chi Mei Optoelectronics that makes up for the colors lost in conventional FRC (3 tones, (256-3)^3=16.2M). When a color value of 1 is requested, it is remapped to 0.25, 2 to 0.5, 3 to 0.75, and then 4-255 are created by the regular FRC method. The end result is 16.7M colors.

----------------------------------------------

5. "Ghosting"

----------------------------------------------

Maybe you've looked at LCDs before, and find the colors great, the viewing angles good, but one thing you are especially worried about with your future purchase is the response time. There's a fundamental problem in explaining how good or bad the level of ghosting is. This may be the only way I can relate it to you: if you've ever used an aperture grille CRT and seen its faint lines but still love it regardless, the same thing will probably happen to you with response time.

Obviously the first week you get it, that's the first thing you're going to look for, because for most gamers it's the obvious disadvantage. So you bring your LCD home, plug it in and play some Battlefield 2 on it, then turn around a bit, and you can see some smearing. At that point, you're probably already thinking of returning it and thinking you'll never be able to live with it. In reality, once you take your focus off scrutinizing the ghosting and start playing your game, you will find it to be an extremely small obstruction, if it is any problem at all. In the end, that's all that matters. It's also worth noting some people may not even be able to see it if they look for it. Unless you have a panel with an atrocious response time like 25 ms. (min), then it will be a minor issue. That said there are some people who may be especially sensitive to it.

----------------------------------------------

6. Backlight Uniformity/Leaking

----------------------------------------------

Unfortunately, this can vary a lot per unit. If uniformity is bad, some places on the panel will be slightly brighter than others. This still occurs today, especially in cheaper monitors. However even more expensive ones have their share of duds, such as the VP191b/VP930b, which many users have had leaking issues with, along with some of the Dells. But like I said, this will vary per unit. The majority of the time, this is not a problem.

----------------------------------------------

7. Common Misconceptions

----------------------------------------------

An IPS or VA panel is always 8-bit

Just because the crystals themselves have the ability to twist that accurate does not necessarily mean the driving electronics can support it. Don't rely on this. For instance, the Samsung 970P and ViewSonic VP930b use a form of dithering/FRC.

16.7 million colors is a connotation for a dither-free 8-bit panel

You cannot count on this measurement to be true among manufacturers.

A lower-listed response time on the specifications is always faster

This is very untrue. Manufacturers can measure the response time any way they so desire. Gray to gray, white to black and back to white, only the rise time, only the fall time, or any combination of those. One manufacturer's "20 ms." can be another's "4 ms." Beware. For example, the Samsung 940B is rated as 8 ms., but it reaches 35 ms. most of the time.

Contrast ratios

Usually the contrast ratios are grossly overrated on spec sheets and there's no telling if they're using the standard ANSI method.

Viewing angles

This is yet another inflated spec. 160/160 can mean 80/80 up/down and 80/80 left/right or 40/120 up/down and 90/70 left/right. You can't tell. Some manufacturers will list their method as CR>5 or CR>10, this means it maintains a contrast ratio>x at y angle. But there will still be immense distortion on some panels, particularly TN. It does not take that in to account.

Bigger is better

When you compare a 17" to a 19" which both have a 5:4 1280x1024 resolution, the 19" only has bigger dot pitch. This means your display will be grainier in general, though text will be bigger for the visually-impaired. Unfortunately, manufacturers are mostly only spending R&D on 19" panels nowadays, and some are even cheaper than their 17" counterparts.

----------------------------------------------

8. Color Reproduction

----------------------------------------------

6-bit LCDs can truly only produce 262,144 colors ((2^6)^3). Thus they must implement a dithering or frame rate control technique to simulate up to 16.7 million colors. These techniques still don't reproduce colors as good as 8-bit panels that don't use the dithering. More primitive forms of dithering can only reach 16.2 million colors (253^3=16,194,277). True 8-bit PVA and IPS panel LCDs can produce 16,777,216 (16.7 million) real colors ((2^8)^3). And to recap: not all PVA and IPS panels are driven by "true" 8-bit electronics, so they could still use dithering! As another precaution, LCDs do tend to have problems reproducing skin/subtle tones vibrantly.

Source: Anandtech Forums

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...