The Monitor Guide - Specifications and Features Defined

1. Types of Monitors
   • LCDs Monitors Defined
   • CRTs Monitors Defined
2. LCD Technology
   • TFT Technology
3. LCD Panel Types
   • TN Panel Technology
   • VA Panel Technology
   • IPS Panel Technology
4. Monitor Specifications
   • Panel Size
   • Aspect Ratio & Resolution
   • Response Time
   • Contrast Ratio
   • Brightness
   • Refresh Rate
   • Back-lighting
   • Viewing Angles
   • Refresh Rate
   • Color Depth & Gamut
   • Pixel Pitch
   • Physical Specifications

TFT Technology and how a TFT Display Works

TFT stands for 'Thin Film Transistor' and describes the elements that actively control the pixels. For this reason, one speaks of so-called 'active matrix TFTs'. How are images produced? The basic principle is quite simple: a panel with many pixels is used, by which each pixel can emit any color. To this purpose, a back light is used which is normally comprised of a number of fluorescent tubes. In order to light a single pixel, all that needs to be done is for a small 'door' or 'shutter' to open to let the light pass through. The technology that makes this possible is of course more complicated and involved than the simple explanation above. An LCD is a Liquid Crystal Display. Liquid crystals can change their molecular structure and therefore allow varying levels of light to pass through them or they can block the light. Two polarization filters, color filters and two alignment layers determine exactly how much light is allowed to pass and which colors are created. The layers are positioned between the two glass panels. A specific voltage is applied to the alignment layer, creating an electric field - which then aligns the liquid crystals. Each dot on the screen (pixel) therefore requires three components, one for red, green and blue - just as for the tubes within CRT devices.

Currently, there is no alternative to TFT displays used in consumer monitors.

LCD Monitors Defined

This will be the primary focus of the guide. LCD stands for Liquid Crystal Display, and TFT stands for "Thin Film Transistor". These two terms are used commonly but refer to the same technology. Often the term TFT Display is used more when describing desktop displays, whereas LCD is more commonly used when describing TV sets.

CRT Monitors Defined

CRT stands for Cathode Ray Tube; while a minor sub point in this guide, it's important to note CRT monitors were used for decades and they still, in terms of picture quality, can be some of the best monitors on the market. Though size, cost of production, and energy consumption lead to their demise around the turn of the century.

TN Panel Technology

TN film (Twisted Nematic + Film) panels were the first panels to be used and are still widely implemented in many TFT’s today, especially mid to low end screens. This is due to the low manufacturing costs of TN panels. Traditionally they were not always very good at displaying blacks, but modern TN Film panels are actually improving in this regard. In fact many can compete with even VA matrices. There is also a problem with pixels dying and becoming a bright color rather than just completely going out (black). The main issue with TN Film panels is that they have restrictive viewing angles of up to a realistic range of about 140° horizontally, even though most are rated for 160° horizontally. Vertical viewing angles are very poor generally and suffer from a characteristic blackening of the image as you look from below. TN film panels traditionally offer the fastest pixel response times, and with the implementation of RTC (Response Time Compensation) & overdrive technologies; the grey to grey transitions have become even faster. Today, TN Film panels are used in the majority of gamer-orientated screens and are often used to break into new screen sizes, offering a cost effective way to provide larger screens without increasing the price too much. TN panels are generally sold at the 1080P or lower resolution, not breaking into higher domains.

VA Panel Technology

VA (Vertical Alignment) panels are the middle child of modern TFT’s. The early VA panels have been scrapped due to poor viewing angles, and in their place came the Multi-Domain Vertical Alignment (MVA) and Patterned Vertical Alignment (PVA) panels. These offer superior color reproduction compared with TN film, but not up to snuff with IPS displays. VA Panels have the advantages of both accurate black levels and above average viewing angles. There is a characteristic off-center contrast shift detectable from VA matrices, but not everyone will notice this or find it a problem. The wide viewing angles are achieved by having all the color elements of the panel split into cells or zones. These are formed by ridges on an internal surface of filters. The purpose of this design is to enable liquid crystals to move in opposite direction to their neighbors. It allows the observer to see the same shade of color irrespective of a viewing angle. There have been improvements to the MVA and PVA technologies, which has given birth to the Premium-MVA (P-MVA), Super-MVA (S-MVA), Advanced-MVA (AMVA), Super-PVA (S-PVA) and cPVA technologies. One of the main improvements in recent times has been in responsiveness, with overdrive playing a key role. MVA & PVA Panels are often used in consumer televisions for their good picture quality, viewing angles, and cheap cost compared to IPS.

IPS Panel Technology

IPS (In Plane Switching) was introduced to try and improve on some of the drawbacks of TN Film. It was developed by Hitachi and was dubbed “super TFT”. They improved on viewing angles up to about 170H. This was done by controlling liquid crystal alignment slightly differently, but unfortunately, can affect response rate of the pixels. As such early models were not as good for gaming as TN panels. IPS panels were later developed into Super-IPS (S-IPS) panels by their main manufacturer now, LG.Display. Production costs have been lowered, which makes IPS Panels more widely used in the market. S-IPS offer perhaps the most accurate color reproduction available in the TFT panel market, and the widest viewing angles as well. They are also free of the off-center contrast shift which is evident on VA matrices, and as such are commonly the choice of graphics and color professional displays. Response times were traditionally behind those of TN Film and VA panel variants, but modern IPS panels using response time compensation (RTC) including the new generation of Horizontal IPS (H-IPS), Enhanced S-IPS (sometimes called E-IPS), Advanced Super IPS (AS-IPS), and "Economy" IPS (called e-IPS) panels can offer responsiveness to rival both.

Panel Size

Panel size is a simple topic, it refers to the physical size of a panel. While the bezel (outer edge) of the monitor will make it slightly larger than the actual panel size, it's no more than 1 to 2 Inches. Panel size is measured diagonally, corner to corner.

Aspect Ratio & Resolution

Aspect Ratio is related to the ratio of the image in terms of its size in correlation to the height vs the width. The aspect ratio can be determined by considering the ratio between horizontal and vertical pixels. Common aspect ratios are 4:3 and 16:9 which are both used for TV Broadcasting. 5:4 and 16:10 are less common aspect ratios used on computer monitors. It is argued that a 16:10 aspect ratio is better than a 16:9 aspect ratio.
The idea is that a 16:10 picture more accurately represents what the human eye can see. It can be argued that we all see things the same, with slight variances. The choice is up to you on what aspect ratio you would prefer. Though ergonomically speaking, and from experience; I would advise going for a 16:10 monitor over a 16:9 one.

Resolution is the number of distinct pixels in each dimension that can be displayed. The resolution of a TFT LCD is an important thing to consider. All LCD’s have a certain number of pixels making up their liquid crystal matrix, and so each LCD has a “native resolution” which matches this number. It is always advisable to run the LCD at its native resolution as this is what it is designed to run at and the image does not need to be stretched across the pixels. This helps keep the image at its most clear and at optimum sharpness. Some screens are better than others at running below the native resolution. You cannot run a LCD at a resolution of above its native resolution. Older applications and games that need to run at full screen, but do not support your resolution may show their age a bit more because of this. I would suggest running those games in "windowed" mode if you can, to maintain their image fidelity.

Response Time

Response time is the measured rise time (tR) and fall time (tF) of a pixel as it changes black > white > black. This is effectively the time it takes to change a pixel from one color to another and the total ‘response time’ should be quoted as the total of the tR + tF. Be wary of the figures manufacturers quote, as sometimes the "response time" can be quoted as just the rise time, and not the total response time.The faster this transition can change, the better, and with more fluid changes the images can change overall a lot faster. This helps reduce the effects of blurring / ghosting in games and movies which can result if response time is too slow. Generally, the lower the response time, the better. Different manufacturers have various ways of measuring their response time, so one 5ms panel might not be the same in real use to another 5ms panel for instance. Usually this comes from one manufacture using a figure that is Grey to Grey (G2G) or Black to White (B-W) instead of a full Black to White to Black.

Contrast Ratio

Contrast Ratio of a TFT is the difference between the darkest black and the brightest white. As a rule of thumb, the higher the contrast ratio, the better. On modern monitors you want to look for the "Static Contrast" which won't be more than 1000:1 on modern monitors. You will see most specification pages quoting dynamic contrast ratios, though in practice; these dynamic figures are not very useful. You'll want to pay attention to the only static figure.
AMVA Displays, a recent technology can offer up to 16,000:1 static contrast; though we do not know how long until these Displays make it into the consumer market.

Brightness

Brightness is a measure of the brightest white the TFT can display. Brightness is measured in Candela-per-square-metre (cd/m2). With current monitors you normally want to look for a monitor that has an OSD (On Screen Display) which can dynamically adjust the brightness of your monitor. Different lighting conditions in a room make this option important. Generally, laptops do feature backlight control as a method to help save battery life; it is still a relevant feature for desktop displays even though battery life is not a concern.

Backlighting

a There are 3 Primary Types of backlighting. CCFL (Cold Cathode Florescent Lamps) W-LED (White LED) and RGB-LED (Red, Green, & Blue LED.) Each has their own benefit and draw back.

CCFLs (Cold Cathode Florescent Lamps) are extensively used as backlighting for computer and television LCDs. These Lamps originally did not have the same power to add to the color gamut as they do today; but by no means were they a bad solution.
More recent displays have started to utilize a newer generation of CCF lamps, offering a widened gamut and typically a coverage of the NTSC color space of 92 - 97%. There is a difference in practice, however, as diffusional layers can alter the final image. Usually they produce very pure and deep red and green colors that typically, you can notice in normal use, though the blue spectrum did not get as much of a boost from the new lamps. If you switch the lamps in an older monitor to newer lamps, only the saturation of those colors that didn’t fit within the old monitors’ gamut are improved in reality.

White-LED (W-LED) The LED's are placed in a line along the edge of the matrix, and the uniform brightness of the screen is ensured by a special design of the diffuser. The color gamut is still limited to around 68% NTSC but are cheaper to manufacturer and so are being utilized in more and more screens, even in the more budget range. They do have their environmental benefits as they can be recycled, and they have a thinner profile making them popular in super-slim range models and notebook PC's.


RGB LED backlighting consists of an LED backlight based on RGB triads, each triad including one red, one green and one blue LED. With RGB LED backlighting the spectrum of each LED is rather wide, so their radiation can’t be called strictly monochromatic and they can’t match a laser display, yet they are much better than the spectrum of CCFL and W-CCFL backlighting. LED backlighting is not common yet in desktop monitors, and their price tends to put them way above the budget of all but professional color enthusiast and business users. We will probably see more monitors featuring LED backlighting over the coming years, and these models are currently capable of offering a gamut covering > 114% of the NTSC colour space.

Viewing Angles

Viewing angles are quoted in horizontal and vertical fields and often look like this in listed specifications: 170/160 (170° in horizontal viewing field, 160° in vertical). The angles are related to how the image looks as you move away from the central point of view, as it can become darker or lighter, and colors can become distorted as you move away from your central field of view. Because of the pixel orientation, the screen may not be viewable as clearly when looking at the screen from an angle, but viewing angles of TFT’s vary depending on the panel technology used.As a general rule, the viewing angles are IPS Panels have the best viewing angles, with VA panels coming in second; TN Film Panels usually are in the rear. Some newer TN Film Panels can have viewing angles close to VA Panels; though many manufacturer quoted specs are inaccurate or exaggerated. In reality, IPS and VA panels are the only technologies which can truly offer wide viewing fields and are commonly quoted as 178/178. VA panels can sometimes show a colour / contrast distortion as you move slightly away from a central point. While most people do not notice this anomaly, others find it distracting. IPS panels do not suffer from this.

Refresh Rate

TFT screens do not refresh in the same way as a CRT screen does, where the image is redrawn at a certain rate. A TFT monitor will only support refresh rates coming from your graphics card between 60Hz and 75Hz (ignoring modern 120Hz monitors for a moment). Anything outside this will result in a "signal out of range" message or similar. The “recommended” refresh rate for a TFT is 60hz, a value which would be difficult to use on a CRT. The “maximum” refresh rate of a TFT is 75hz, but usually if you are using a DVI connection the refresh is capped at 60hz anyway.

One thing which some people are concerned about is the frames per second (fps) which their games can display. This is related to the refresh rate of your screen and graphics card. Vsync is an option on most video cards which synchronizes the frame rate of your graphics card with the operating frequency of your graphics card (i.e. the refresh rate). Without vsync on, the graphics card is not limited in it's frame rate output and so thus output as many frames as possible by the card. This can often result in graphical anomalies including 'tearing' of the image, which is when the screen and graphics card are out of sync and the picture appears mixed as the monitor tries to keep up with the demanding frame rate from the card. To avoid this annoying symptom, vsync needs to be enabled.

With vsync on, the frame rate that your graphics card is determined by the refresh rate you have set in your OS. Capping the refresh rate at 60hz in your display settings limits your graphics card to only output 60fps. If you set the refresh at 75hz then the card is outputting 75fps. What is actually displayed on the monitor might be a different matter though. You can measure the internal frame rate of your system using programs like 'fraps' and also some games report your frame rate. Remember, the frequency of the monitor is still being scaled down to 60Hz by the interface chip. If you are worried about frame rate in fast games then it is a good idea to try the refresh rate at 75Hz and see if you think it looks better. A lot of it could be based on placebo effect though, and if you have a decent graphics card which can handle a constant 60fps it might look just as good as if it were outputting 75fps.

120Hz Monitors and LCD TV's
You will see more mentions of higher refresh rates from both LCD televisions and monitors nowadays. It's important to understand the different technologies being used though and what constitutes a 'real' 120Hz and what is 'interpolated':

Interpolated 120Hz and above - These technologies are the ones commonly used in LCD TV's where TV signal input is limited to 50 / 60 Hz anyway (depending on location). To help overcome the issues relating to motion blur on such sets, manufacturers began to introduce a technology to artificially boost the frame rate of the screen. This is done by hardware processing inside the monitor which adds an intermediate and interpolated (guessed and calculated) frame between each real frame, boosting the frames from 50/60FPS to 100/120FPS. This technology does offer a noticeable improvement in practice and is controlled very well. Some sets even have 240Hz and 360Hz technologies which operate in the same way, but with further interpolation and inserted frames.

True 120HZ technology - to have a true 120Hz screen, it must be capable of accepting a full 120Hz signal output from a device (e.g. a graphics card). Because TV's are limited at the moment by their input sources they tend to use the above interpolation technology, but with the advent of 3D TV and higher frequency input sources, this should change. Desktop monitors are a different matter though as graphics cards can obviously output a true 120Hz if you have a decent enough card. Some models can accept a 120Hz signal but need different interfaces to cope (e.g. dual-link DVI). These monitors were also introduced with the development of 3D gaming so will no doubt become more and more mainstream. These offer obvious advantages in terms of gaming where a frame rate of >60fps can be properly displayed. It also helps improve any motion blur and produce smoother movement. It can also help reduce RTC related artifacts and overshoot which is an added bonus.

Color Depth & Reproduction

Color Depth is like Accuracy
Color Reproduction is Precision

The color depth of a TFT monitor is related to how many colors it can produce. The more colors available, the better the color range can potentially be.The color depth of a panel is determined really by the number of possible orientations of each sub pixel (red, blue and green). These different orientations basically determine the different shade of grey (or colors when filtered in the specific way via RGB sub pixels) and the more "steps" between each shade, the more possible colors the panel can display.

8Bit Color Depth allows a total of 16.2 million reproducible colors. This is the most common color depth to find on most monitors on store shelves right now, no matter what the panel type is. Some early TN Panels were only 6bit, but that is not the case anymore.

10-bit color depth is capable of 1024 shades per sub-pixel, but is typically only used for very high-end graphics cards. This allows for a massive 1.07 billion colors and a 30-bit (10-bit per sub pixel = 10 + 10 +10 = 30) color depth. These are currently only available in some high end IPS panels. In theory, the more steps per sub pixel, the more detail can be shown and this is important where gradients are common or subtle differences need to be seen. For a 10-bit panel to be truly utilized, you need an entire 10-bit "journey" though.
10-bit color depth is only usable with a DisplayPort connection currently.

Pixel Pitch

The pixel pitch of a TFT is related to the distance between pixels. Pixel pitch is normally listed in the manufacturers specification. Generally you need to consider that the 'tighter' the pixel pitch, the smaller the text will be, and potentially the sharper the image will be. To be honest, monitors are produced with a sensible resolution for their size and so even the largest pixel pitches return a sharp images and a reasonable text size. Some people do still prefer the larger-resolution-crammed-into-smaller-screen option though, giving a smaller pixel pitch and smaller text. It's down to choice and ultimately eye-sight. If 2 monitors are 24" and offer resolutions of 1920x1200, then the pixel pitch will always be the same. (Exception is if a monitor is listed as 24" but only has a 23.6" viewable screen.)

Physical Specifications

VESA Mounting is the most standard mount system for monitors. If you are looking for a monitor that you'll add to a rack of monitors, or buy a different stand for, you'll usually want to make sure it features VESA mounting.

DVI is "Digital Video Interface," and one of the oldest standards used on current monitors. It supports resolutions up to 2650x1600 @ 60Hz in Dual Link mode, 1920x1200 @ 120Hz in Dual Link Mode, and 1920x1200 @60hz in Single Link mode.

Dual Link & Single Link are physical definitions, so a single link connection cannot be made into a dual link connection with something like software, but must be implemented at the hardware level.

HDMI is "High-Definition Media Interface." Originally developed for use with TV's and receivers as a way to transmit audio & video over one cable, it has since evolved to carry more high fidelity signal, and even ethernet functions. HDMI is a proprietary standard, built on the foundation laid by DVI. DVI & HDMI signals can be interchanged with adapters at relative ease.

DisplayPort is a new generation connection standard. Currently in terms of fidelity and features, it stands at the king of the hill offering the most features, and the highest fidelity video signal (10-Bit Color Depth.) Active adapters are needed for conversion to HDMI, DVI, or VGA.

In a perfect world, your monitor will have many connections; though most do not usually need that many inputs. If you have the option, using a DisplayPort monitor (as they are typically IPS displays right now) and a video card which supports DisplayPort is the best option for you.

Color Gamut

In color reproduction, the gamut, or color gamut, is a certain complete subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device. Color Gamut is based on the CIE Scale.

Color Gamut is usually unlisted by manufacturers and is not considered a "important" feature to most.