Guide to monitor technology: resolutions, panel types, refresh rates

LCD diagram RGB subpixels Alternate 1280

Know your panels, know yourself

The overwhelming majority of computer monitors, laptop screens and tablets are based on TFT-LCD (Thin Film Transistor – Liquid Crystal Display) technology, but not all of them are equal. LCDs are divided by type, each having their own strengths and drawbacks. IPS panels provide improved color accuracy, better touchscreen performance and wider viewing angles. TN panels may look washed out by comparison, but they have the low response times and high refresh rates that make 3D action games come alive. High-contrast VA panels try to do it all, and come with the predictable compromise inherent in jack-of-all-trades solutions. Its horses for courses and you need to pick the ride that's right for you.

TN: Your father's flat screen

The most common LCD panels are based on TN, or Twisted Nematic designs. Since TN screens are made on a vast scale and have been for a while, they are pretty cheap. Online retailers stock an abundance of attractive 27-inch 1080p monitors with reasonable features for just a few hundred bucks. The price is nice, but the pixel density isn’t—and neither is the color quality or viewing angles, TN’s greatest weaknesses.

TN displays, like all TFT LCDs, work by passing light, such as an LED, through a pair of polarized screens, a color filter and liquid crystals that twist when current is applied to them. The more current applied, the more the liquid crystals twist and block light. Precise adjustments allow virtually any color or shade to be reproduced, but TN implementations have some limits.

Each pixel of an LCD display is made from a number of red, green and blue subpixels. Colors are made by mixing varying brightness levels for these pixels, resulting in a perceived solid color to the user. The problem with TN stems from its widespread adoption of a 6-bit per channel model, which limits output to only 64 shades per color, instead of the 256 shades available with an 8-bit per channel (for a total of 24-bit) implementation. TN compensates for this shortcoming with dithering, a pixel trick that uses alternating colors to produce a perceived third, but it's a poor substitute for proper 24-bit color reproduction. When combined with the inversion and washout that comes from narrow viewing angles, TN's elderly status in the LCD display world becomes clear.

TN Monitor

Color and contrast aren't the only important features in a monitor, however. For gamers especially, there's also refresh rate and response time, and when it comes to those, TN LCD screens still reign supreme.

Display responsiveness is measured by the milliseconds it takes for a pixel to change from one color state to another, frequently reported as the grey-to-grey or GTG speed. The higher this value, the more blur and smearing is apparent during rapid transitions. Use your eyes as a guide here and don't trust manufacturer's specifications, as no industry standard exists for measuring response time and hyperbole abounds.

TN's naturally low overhead and many years of development have resulted in ultrafast GTG times, usually well under the typical 5ms TFT-LCD average. There's also the matter of refresh rate, or how many times a second the screen redraws itself. A growing number of enthusiast model TN LCDs support 120Hz and 144Hz modes that help minimize the motion blur that affects 60Hz screens. Combined, these provide a crisp, lag-free experience especially well-suited to action games.

IPS: The professional's choice

IPS, short for In-Plane-Switching, was designed to overcome some of TN's shortcomings as a display technology. IPS screens also use liquid crystals, polarized filters and transmitters but the arrangement is different, with the crystals aligned for better color visibility and less light distortion. Additionally, IPS generally uses 8-bit depth per color instead of TN's 6-bit, resulting in a full 256 shades to draw upon for each color.

The differences are pretty dramatic. While TN displays wash out at shallow angles and never truly "pop" with color no matter how well they are calibrated, IPS panels have rich, bright colors that don't fade or shift when viewed from the sides. Moreover, pressing a finger on an IPS screen doesn't cause trailing distortions, making them especially useful for touchscreen applications.

While touted as the high end display technology of choice by giants such as Apple, the truth is that IPS screens come with drawbacks of their own. Due to their more complex construction and the additional transmitters and lighting required for each pixel, IPS screens tend to cost more than their TN counterparts. Part of the mark-up also comes from the popularity of IPS with design professionals. Manufacturers know they can charge these users more, so they do. In the last two years or so, the popularity of no-frills import IPS monitors from Asia has helped drive down prices and force big monitor brands like Dell to sell more reasonably priced IPS displays.

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IPS technology’s complexity also introduces additional overhead that reduces panel responsiveness. Most IPS displays clock in a few milliseconds slower than average, scoring roughly 8ms grey-to-grey, so blurring is common. That's not too much of a problem working in Photoshop, but it can be a disaster when gaming. Refresh rates aren't much better, with the vast majority of IPS displays rated for 60Hz. While many high end IPS monitors, such as the popular 2560x1440 27-inch Overlord Tempest, readily overclock in an unofficial capacity to 90Hz or more, that's not a feature that can always be counted on, and requires a monitor driver hack to achieve.

Due to its popularity, a lot of research has been done with IPS and many variants exist, including Samsung's popular PLS panels, mostly as subtle manufacturer variations or generational improvements on the technology, which has been around since 1996. PLS improves on IPS in a number of ways. Samsung claims it is cheaper, brighter, provides better viewing angles and allows for flexible displays, all of which are true—although critics claim PLS overclocks poorly and some panels use a TN-style 6-bit color space, much like LG's budget IPS variation eIPS. Most IPS implementations are more about patents than performance however, with little separating them in real world use.

VA: The middle man

In between the high speed of TN and the color richness of IPS sits a compromise technology, the VA, or Vertically Aligned, panel. VA and its variants take the IPS approach with 8-bit color depth per channel and a crystal design that reproduces rich colors but retains some of the low latency and high refresh speed of TN. The result is a display that's theoretically almost as colorful as IPS and almost as fast as TN.

VA panels have a few unique qualities, both positive and negative. They have superior contrast to both IPS and TN screens, often reaching 5000:1, and produce better black levels as a result. Advanced VA variants, such as the MVA panel used by Eizo in the Foris FG2421, support 120Hz officially and offer pixel latencies on par or better than IPS.

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Unfortunately VA has a few problems that are hard to ignore. First on the list is a TN-like color and contrast shift that occurs as viewing angles increase, which can make VA panels a tough pick for tasks that require accurate color reproduction. For gamers, there's another problem. While light-to-dark pixel transitions are speedy, darker color shifts have longer latencies which can result in blurring. VA panels aren't cheap, either. Still, if you want the best contrast ratios available in LCD technology, you won't find better than a good MVA panel.

Making the most of motion: Refresh rates, motion blur and strobed backlights

Most standard TFT-LCDs support a refresh rate of 60Hz, which means the screen is redrawn 60 times each second. While 60Hz may be sufficient for many desktop applications, higher refresh rates are desirable since they provide a smoother experience moving windows, watching video, and especially when gaming.

A refresh rate of 120Hz or even 144Hz alone isn't sufficient for blur-free gaming however, and closing that gap has been an area of focus for display makers in recent years. Much work has been done to supplement high refresh rates with additional features meant to reduce motion blur further. One method popular in gaming monitors is the inclusion of a strobed backlight, which disrupts eye tracking blur by cutting off the backlight for an instant, creating a CRT-like stable image. A strobed 120Hz display is more blur-free than a non-strobed 144Hz panel, but flickering the backlight understandably cuts down on the overall brightness of the image. Users with sensitive eyes can suffer from eyestrain and headaches induced from the flicker as well.

Tearing and synchronization

In addition to motion blur, another visual artifact that frustrates gamers is tearing. Tearing occurs on a monitor when a GPU sends a frame to the display before it's finished displaying the current one. This results in the lower part of the screen displaying one frame and the top part displaying the other, separated by a line across the image. Enabling V-Sync, which forces the graphics card to wait on the monitor for refresh, can reduce this problem, but V-Sync has issues of its own including increased input latency and rigid frame rate requirements.

To get around this, GPU manufacturers have introduced a pair of technologies that dynamically synchronize the monitor and GPU framerate, eliminating tearing without VSync's lag or heavy overhead. Nvidia calls their implementation G-Sync, and it requires a module built into the monitor as well as a newer, 650Ti or later graphics card. AMD has responded with the similar FreeSync, which doesn't require special hardware on the monitor's side other than support for the new Adaptive-Sync optional standard in the DisplayPort 1.2a specification, but does require a newer AMD graphics card (GCN 1.1 or later) to implement. These technologies are roughly comparable, with Nvidia's solution more readily available but more costly than AMD's alternative, which has only just begun to trickle out of development. Right now, the edge is with G-Sync.

Asus Gsync

Input latency

There's a final, mostly hidden factor that affects display responsiveness: input latency. Latency stems from the delay caused by post-processing done to the video signal after it leaves the GPU but before it's displayed on the monitor's screen. Few if any manufacturers actually list this figure, stressing GTG numbers instead, as latency has been getting worse due to feature bloat. This makes determining latency difficult, but there's a common sense guideline to selecting a display without excess input lag—more features mean more latency. If you've ever wondered why that great flat screen television is such a laggy gaming display for your rig, this is the reason.

Action gamers looking for competition-level, frame-accurate inputs are best served by displays with minimal onscreen menus, little to no post-processing of images and just a single port or two. This insures the video signal spends as little time bouncing around the monitor's scaling and processing hardware as possible and gets displayed without delay. This also means sacrificing some utility, but topping the leaderboards is worth it, right? Specially designed gaming monitors, such as the Asus VG248QE (0.7 ms input latency) and BenQ Xl2720T (1 ms input latency) can split the difference between these worlds.

The future is now

The flood of innovation in the display market shows no signs of abating, with TVs on one side and smartphones on the other, driving new technologies such as curved screens and desktop-grade OLED panels that promise speeds, contrast and color beyond anything seen so far. Those are all a few years out however, so when it comes to picking your next display, choose wisely, because the future is now.