How to observe and improve a PC Monitor’s responsiveness, and the factors that affect it
What is it that makes a great gaming monitor? The answers usually come from a general set of rules and factors like ‘a good resolution’ and ‘good image quality’. If we consult a gamer or a designer of some sort, they might even dip into details like the ‘Refresh rate’ or the ‘pixel resolution‘. However, for a layman, the answers to ‘what are the defining factors for a monitor’s motion performance’ can be tough to find. There is no defining solution for what affects a monitor’s ‘responsiveness’.
When it comes to Responsiveness, input lag plays a major role. Input lag is the lag or the difference (usually measured in milliseconds) between the Graphics card sending a frame to the monitor, and the monitor displaying that frame. This signal delay is small in nature, but a Low input lag leads to a ‘snappier’ feel while interacting with the display using an input device such as a mouse or a controller. 144hz Monitor.
Common causes of Input Lag
- Signal processing is done more extensively in some models than others. And sometimes, it results in a Signal Lag
- Sometimes, high-end displays use internal scalars to process the non-native resolutions. In some cases, the signal must pass through a Scalar even if there is no requirement of scaling it. This can result in a lag.
Solutions – best Gaming Monitor
- Running the monitor at its native display.
- Some manufacturers give their PC monitors a dedicated code that bypasses most of the Signal processing.
- In some PC displays, there is a ‘game preset’ or an ‘instant’ or ‘thru’ mode that can be activated through the On-screen display (OCD).
In order to measure the signal delay with accuracy, specialist equipment such as an photo diode and an oscilloscope is required. It helps determining just the signal delay rather than the overall latency. And SMTT (Small Monitor Test Tool) is a tool that is helpful in measuring the difference between the input lag and the display of choice. A stop clock is also used by users to measure the lag. Methods like these can help measure Input lag and give us a visual representation of what it is.
Methods like these give us a visual representation of the output of a display. As you can see in the image above. there is a visible lag as to when values are being changed. The result of such methods are also affected by the pixel transitions (the response time). The pixel response affects the ‘Visual latency’, not the ‘felt latency’ and sometimes, when it is included in some websites, users can refer to it as the Input lag. Here is what to keep in mind about the response time and the pure Signal delay:
- The response time primarily affects how the monitor ‘looks’.
- The Signal delay effects on how responsive the monitor ‘feels’.
Our job, is to focus on the former and it’s improvement in order to enhance the display and make the user feel more ‘snappy’ while using an input device.
Refresh rate is responsible for making a display look good and ‘fast’ in the eyes of the end user. It can be divided into two types – fixed and variable. 144hz display.
Fixed Refresh Rate
Under their native resolution, the majority of LCD monitors run at a refresh rate of 60Hz. What does that mean? It means that up to 60 individual frames of data can be displayed per second with a gap of 16.66ms between these frames. It is possible to alter this value to a degree, but the value must be pre-selected, as a normal monitor is not able to adjust its refresh rate on go.
However, there are a select few LCD screens which run in their native resolutions at a refresh rate of 120Hz and sometimes even as high as 144Hz. As you would expect, a refresh rate of 120Hz allows these monitors to display twice as much information, outputting up to 120 discrete frames per second with a 8.33ms gap between frames. Down below is a visual demonstration of these differences in value.
As we can see, the 60Hz monitor is showing a progression of one frame of information between Frame 1 (red dot) and Frame 2 (yellow dot). Now over the same 16.67ms time period, the 120Hz monitor has already progressed two frames, displaying ‘Frame 2’ after 8.33ms and moving on to ‘Frame 3’ (green dot). In practicality, what this means is that in the case of a 120Hz monitor, the ‘Visual fluidity’ of the scenes is increased and the level of blur is much reduced. The monitor also responds at twice the rate of a 60Hz monitor, to user commands and input updates like using a mouse – resulting in a superior performance and appearing ‘faster’ than a normal monitor would. This is coupled with a low input Lag to give you a faster motion visual performance.
The monitors with a high refresh rate are very popular among gamers and people who work with 3D structures. And when in the not so far away future, alternative technologies like the OLED will become mainstream, the demand of these monitors will just keep increasing.
Variable Refresh rate
The relationship between refresh rate and frame rate is as close as the relationship between a monitor and the rest of the system. In order to gain maximum benefit from the frame rate, one needs to keep the refresh rate high. In order to prevent the frame rate from exceeding the refresh rate, some users use ‘VSync’. In simple terms, this is done to ensure that the Graphic Processing Unit sends new frames to a monitor only when the monitor is ready to move onto its next refresh cycle. The GPU holds frames in this way and as a result, what happens is:
- An inherent delay takes place, which adds to the overall input lag. As the refresh rate increases , this ‘penalty’ becomes less severe. but it still exists.
- On some occasions, the frame rate falls below the monitor’s refresh rate-at which point, you can get a degree of stuttering. This happens because of a situation where the screen has finished drawing a frame and it is ready to move on to the next frame, but the GPU is not ready to send it. In such a scenario, the GPU sends the first frame to the monitor again (instead of sending a new one). This results in the monitor redrawing that frame-or a ‘stutter’.
Many gamers disable the ‘VSync’ in order to minimize Latency and Stuttering as much as possible. However, whenever the frame rate does not match the refresh rate, things are left to go out of sync. And this is something that happens quite often. Monitors typically refresh from ‘top to bottom’. In this scenario, a new frame is displayed only on the top half of the screen, whereas the bottom of the monitor is still displaying the old frame. The occurrence is distinct and distracting, and it is called ‘tearing’.
Tearing is what can lead some users to turn to VSync. However, NVIDIA came up with a solution. An alternative called as G-SYNC.
The chip displayed above has one function -to match the refresh rate of the display to frame rate of the content (for example, a game), in real time. This chip can only be used on a limited number of monitors and most of the time, it comes pre-installed into them.
Advantages of G-SYNC
- G-SYNC gives the user all the traditional benefits of having the VSync enabled without any problems that come along with it.
- This is a chip that automatically takes care of the refresh rate problem and yields better image quality and a smooth frame rate per second.
AMD also has a variable refresh rate technology by the name ‘FreeSync’. However, unlike G-Sync, the FreeSync technology do not require the type of specialist hardware that needs to be inside the monitor.
Advantages of FreeSync
- Newer iterations of FreeSync are designed to function over HDMI on specific monitors.
- This technology is getting wildly popular and there are more and more FreeSync monitors on the market like the BenQ XL2730Z and BL3201PT/PH.
The refresh rate is important for the display. But it is not the end of the story. In the diagram shown above, you might have seen that between one frame of the data and the next, there are literally blank spaces with nothing in between, that appear on the display. They appear on the display for a very short duration of time, but in case of some monitors, for example a 60Hz CRT, the monitor switches fro one frame to the next with a gap of 16.66ms where nothing is displayed on the screen. Hence, at lower refresh rates, users can notice that there is a ‘flickering’ on the monitor.
A majority of LCDs and some of the other non-CRT technologies use a technique called ‘sample and hold’ to display their images. In this process, a frame is held on the screen for the duration of the time of the ‘gap’ between frame 1 and frame 2, so that there is no visible flickering.
Drawing the Frame 2 on the LCD depends on the ‘Pixel Response Time’. In simple words, this is the time taken by the Pixel to turn from one color to the other. It is independent of the Color – however, it is affected by the shade’s intensity. For example, a transition from black to white, will typically take a different length of time as compared to a transition from ‘25% grey’ to white.
As not every Pixel transition will occur at the same speed, there is no standard unit of transition and the manufacturers commonly refer to Pixel response times as ‘grey to grey’ values with figures like 5ms and 2ms.
In the above diagram, we can see that the transition occurring in the top row between a red dot (Frame 1) to Yellow is at the rate of “8ms grey to grey”. After 8ms, the completed yellow dot is displayed for the remaining duration(an extra 8.67ms) of that frame.
The bottom row shows this same transition but the response time value in this case is represented in value as “4ms grey to grey”. The finished Yellow dot (Frame 2) is there after only 4ms and then held for the remaining 12.67ms of the frame.
Hence, the shorter is the time spent in the transition phase, the less ‘trailing’ or ‘ghosting’ will be there on the display.
The use of a Voltage Surge
In the above example, the Red to Yellow transition would go no further until a new transition is called for in the next frame. Rapid response times such as this one are typically achieved on LCDs by using a ‘pixel overdrive circuit’. Voltage surges are applied to ‘push’ these pixels into the desired state more rapidly. This overdrive process is known as Response Time Compensation (RTC), or ‘Grey to Grey acceleration’, and is common these days in all the LCD panel types.
If the disparity between the speed of the accelerated transition and the native speed of a transition and is huge in value, then it can require an aggressive voltage surge to achieve the desired output. This invariably leads to a situation where the transition won’t just stop at the desired endpoint but will ‘overshoot’. The consequences of this overshoot include certain visible artifacts (known as RTC errors) such as ‘inverse ghosting’ and bright trails, which can be very distracting. Given below is an image to comprehend what it can look like.
Most grey to grey transitions normally take place between 4-10ms on all modern TN monitors. Using moderate overdrive, they can be pushed to as low as 2-3ms. With the use of moderate overdrive, some grey to grey response time values on IPS and PLS can fall to around 4-6ms (significantly reducing trailing). However, other transitions on IPS/PLS will remain closer to around 10ms unless the overdrive is extremely strong (with accompanying RTC errors). Now on most VA panels, the grey to grey transitions are ‘sluggish’ and they usually occur between 14ms to 30ms without overdrive. You can bring some of these transitions down to around 4ms with use of a moderate overdrive, while others will stubbornly remain well above 10ms.
In order to gain a better output, for all of these panel types ‘balance is key’.
CRTs vs. LCDs
If you are a long-term CRT user, you can tell that there was a slightly different ‘feel’ to gaming on a CRT as compared to modern LCDs. In modern LCDs, improved refresh rates and high response times decreased perceived blur and enhance the display experience.
But there is a catch.
It was noticed that some objects that remained sharp during brisk movements on a CRT seemed to be relatively blurry on an LCD. Why?
The answer lies in how these two displays process or sample the frames of information. A LCD takes the ‘sample and hold’ approach – displaying a frame and letting it sit on the screen till the other frame is ready to go, while an CRT uses an ‘impulsive’ approach, displaying frames one by one with nothing on the screen at the ‘gap durations’ between them.
In brief, we can see the dark phase in the first diagram where nothing is being displayed. On the other hand, we have the Frame hold in the diagram 2 where the Yellow dot is being held on the screen till the next frame is ready. On such a display, when your eyes are tracking the movement, they are being fed a continuous stream of information. Your eyes are at a lot of different positions throughout the screen refresh. The result is perceived motion blur – a blur that would persist even if the pixels were being transitioning at a very quick rate. As you can imagine, the Refresh rate also plays an important role in this process.
This increased smoothness in the LCDs comes largely down to a decrease in perceived motion blur. The frames are being held on the screen for a much shorter duration of time. Hence, a greater number of distinct frames is being fed to your eyes. Therefore, your eye movements are reduced. However, even in this case, the degree of eye movement is still larger than it is on a CRT. Following the ‘impulse-type approach’, a CRT flashes the information at you for an extremely brief period of time, followed by a blank screen (no information). As a result, your eyes aren’t spending much time at tracking motion – reducing the perceived blur significantly.
Pulse Width Modification Usage
The PWM is a method that is used for modulating the backlight brightness on some ‘Sample and Hold’ LCDs and OLEDs. Rather than using a varying direct current in order to modulate brightness, a PWM-controlled light source is flickered on and off rapidly to achieve a given degree of brightness.
- Some people are sensitive to the rapid flickering effect of a PWN controlled light source, and can suffer from visual discomfort.
- The flickering has some repercussions for how the ‘blur’ on moving objects is perceived on a display. The image essentially disappears very briefly when PWM-controlled light source flicks off and there can be visible fragmentation in the perceived blur when viewing the moving images. This fragmented blur is termed as ‘PWM artifact’.
LightBoost and Strobe Backlight
While the sampling methods of an LCD and a CRT are different, in order to decrease the perceived blur, modulating the backlight of an LCD monitor can be done, so that it would sample frames like an CRT.
The strobe backlights use an impulsive ‘on and off’ approach, ‘displaying’ and ‘not displaying’ frames on the LCD for the user.
Advantages of Strobe Backlights
- They decrease the perceived motion blur.
- The use of strobe backlights hides much of the Pixel transitioning process – including the Overdrive artifacts.
Sony ‘Motionflow’ – which involves the use of ‘Motion-Compensated Frame Interpolation’ (MCFI) technology is very popular among the users. It implements the creation of intermediate frames that are inserted between real frames to increase the overall refresh rate. Sony’s ‘Motionflow XR’ combines this MCFI technology with a strobe backlight for perfection in the display. Another model is the ‘Motionflow Impulse’, which uses a strobe backlight exclusively. The competition is not far behind as Samsung uses an alternative approach, called ‘Clear Motion Rate’ (CMR) which combines a strobe backlight on LCDs and strobe pixels on OLEDs with several other motion enhancements. One other great example is Panasonic using a strobe technology that they refer to as ‘Backlight Scanning’ (BLS) in some of their TV models.
This is something exclusively designed for PC users. Nvidia has created a low-latent strobe backlight solution for pc users that perfectly complements their 3D Vision 2 stereoscopic system.
The shutter glasses – an integral part of 3D Vision, have a left and a right lens that alternately opens and closes so that each eye can see a different frame (resulting in a 3D picture).
Nvidia’s LightBoost-compatible monitors have the ability to shut off their LED backlights in between frames and then momentarily pulse them on at a high brightness to display each frame of information/data. This ‘on-phase’ lasts for just a couple of milliseconds (if not less), and peaks at a brightness that exceeds the monitor’s usual ‘100% brightness’. For the remainder of the frame duration, the Off phase lasts; until a new frame needs to be shown and the next momentary brightness pulse occurs. Hence as the backlight itself acts as a shutter, this technology allows the shutter glasses to remain open for a longer duration of time, and let more light in.
Advantages of NVIDIA LightBoost
- In this case, the monitor is not sampling like an LCD, but like a CRT. The perceived motion blur is very less.
- It increases fluidity in output and 3D viewing can be done without any harm to your PC or the display.
- There is a rapid degradation in smoothness if the frame rate dips even slightly below what is needed to match the refresh rate.
- As it is designed for a 3D viewing environment only (with active shutter glasses) rather than direct 2D viewing, the OSD control of the image is shut off and image quality can be adversely affected in some cases if you view 2D.
Other Strobe backlight technologies for PC Monitors
Though the ones given above are the most popular technologies, here are some honorable mentions:
- Samsung’s SA750 and SA950 series (now discontinued) were 120Hz monitors that had a functionality integrated into it with its ‘Frame Sequential’ 3D mode that could set the backlight into a ‘strobe mode’ intended for 3D viewing. Additionally, it could also be used for 2D viewing with reduced motion blur.
- The EIZO FDF2405W and FG2421 are two high-end monitors using strobe backlight technology for 2D viewing. They implement ‘stroboscopic backlights’ and use a process called ‘Turbo 240’ on their gaming models to reduce motion blur and overcome some responsiveness limitations of their VA LCD panels.
How to measure motion Blur
The Static Photography Approach
There is a small tool in existence, called ‘PixPerAn’ (Pixel Persistence Analyzer).
It can be used to analyze pixel responsiveness. The image below shows a photograph taken using PixPerAn on the Samsung S27A750D, which is a 120Hz LCD. The settings used for response time is ‘Faster’. Because the backlight is constantly lit up, this can fairly represent the pixel response behavior at any given time.
The ‘woven’ trail that can be seen behind the original image indicates the presence of some mild overdrive artifacts. Now, given below are the images taken after we activate the ‘frame sequential’ strobe backlight mode.
As we can see, the first image is when the strobe backlight is off and the second one is when it is on and very briefly pulsing to a brightness exceeding anything possible with ‘Frame Sequential’ disabled. It can be observed that the trailing is very faint and is essentially hidden along with any other overdrive artifacts.
The Pursuit Photography Approach
It is absolutely possible to give an accurate representation of what the eye see in terms of motion blur and the imperfections in pixel responsiveness by using this technique. By moving the camera at a steady speed, matching the pace of action on the screen, we can give an accurate representation of what our eyes see during observing movement on the monitor. The images below were captured with the ‘UFO Motion Test’ for ghosting running at 960 pixels/second, with the UFOs moving from left to right. The middle row of the test ( with a medium cyan background) was used. This is a practical approach that allows accurate analysis of both perceived blur and pixel response behavior.
Three monitors were used in the test. Down below is a synopsis.
- The ‘reference’ monitor (always shown first in each row of pictures) is the Samsung S27A750D. It has a 120Hz refresh rate and the ability to use 3 main backlight operating modes. First picture in the first row shows this monitor set to 60Hz and at a response time setting of ‘Faster’. Here, brightness is set at ‘100’ so that it’s DC-regulated. The pixel responsiveness that we can observe is fast enough for optimal 60Hz performance and there is no noticeable overshoot. In this case, the considerable blurring of the UFO image is purely down to eye movement and is captured accurately by the pursuit camera.
- The next image in this row shows the same monitor now set with a brightness of ’50’ (causing the backlight to operate using PWM at a cycling frequency of 180Hz). We can notice the ‘fragmented trailing’ here, with the UFO appearing to be broken up with 3 distinct repetitions.
- The third image shows the Dell U3415W, which doesn’t provide pixel transitions consistently fast enough for an optimal 60Hz performance. That is the reason why we can see not only the blur caused by eye movement (as with the reference screen) but also some additional trailing.
- The first image here shows the S27A750D operating at 120Hz, having the response time set to ‘Fastest’, and brightness to ‘100’. These settings allow the monitor to perform pixel transitions fast enough for an optimal 120Hz performance (less than 4ms). Additionally, it ensures that the backlight uses DC dimming for a fair comparison with the remaining pictures on row 2. We can see that the UFO is considerably sharper as compared to when this monitor was operating at 60Hz. This reflects that the doubled refresh rate reduces eye movement, in turn reducing perceived blur. We can see a faint ‘shadowy’ trail, which is a small amount of overshoot that resulted from these heavily accelerated pixel transitions.
- The second image on this row has the ‘BenQ XL2730Z’ monitor set to use its ‘High’ AMA (Advanced Motion Acceleration response time), and maximum 144Hz refresh rate settings. We can see a fairly similar overall motion blur to the fast 120Hz reference. We can also notice a bit of extra trailing here, most notably a kind of ‘vapor trail’ behind this yellow UFO cockpit., which is a bit of overshoot.
- The final picture on this row demonstrates the amount and type of overshoot that can occur if a monitor is using exceptionally aggressive Pixel acceleration. In this case BenQ’s ‘Premium’ AMA solution on the XL2730Z is used. Palpable inverse ghosting can be observed, with the colors of the UFO appearing to be inverted for the trail.
- The first image in this row has the S27A750D monitor set to its ‘Frame Sequential’ setting, which causes the backlight to strobe at 120Hz.
- The second image in this row shows the XL2730Z monitor, using the AMA setting ‘High’ and having ‘Blur Reduction’ enabled,/ operating at a refresh rate of 144Hz. These settings force the backlight to strobe at 144Hz.
As you can see, the final row is there to simply demonstrate the effects of introducing a strobe backlight into the equation. It has a massive impact on lowering the perceived motion blur and it reinforces responsiveness. In both of these cases, we can see that the UFO is far more distinct than on any of the other rows of images, showing sharp details.
The Numbers Approach
As demonstrated above, we have the UFO Motion test that gives us a good visual demonstration of some of the concepts affecting a PC monitor’s responsiveness. But these tests are also helpful in trying to quantify the differences between them. We can use this test to calculate a value known as ‘Moving Picture Response Time’. Put simply, the ‘MPRT’ denotes the overall level/value of perceived motion blur, taking into account the eye movement associated with lower values that indicate less motion blur.
MPRT is designed to denote the total visual responsiveness, the refresh rate and to sample the monitor’s behavior. This test allows you to employ a wide range of pixel transitions, ranging to white (grey 100%) from black (grey 0%) with 25%, 50% and 75% grey steps in between. Pixel responses that are particularly slow can increase MPRT values slightly as well; though trailing may be visible in such cases that go beyond the scope of perceived blur due to eye movements.
The graphical representation in the image below that represents the MPRTs for a range of PC monitors. The Moving Picture Response Times given for each display below are an average, including transitions between every grey level that is available in the test (0, 25, 50, 75 and 100). These transitions are done both ways (for example, white to black and black to white both are tested). The monitors below include a range of different refresh rates (60Hz, 72Hz, 120Hz and 144Hz) as well as panel types (TN, VA, IPS and PLS). Models that operate on ‘sample and hold’ methodology are given blue bars, whereas those that use strobe backlights have green bars.
The graph above shows that all 60Hz displays that use ‘sample and hold’ have MPRT values of around 16.67ms. The 120Hz Samsung display has an MPRT value of 8.33ms, which is half as of the 60Hz displays. The VG248QE and PG278Q displays both have MPRTs of 6.94ms at 144Hz. These figures mirror the delay between frames, stressing the importance of refresh rate as a dominant limiting factor in the perceived fluidity on any ‘sample and hold’ monitor. The monitors with IPS panels (for example, the AOC q2963Pm and Dell P2414H) typically have pixel response times of around 6-8ms. Nonetheless, they aren’t outperformed by the ASUS VG248QE, when it is set to the same refresh rate (60Hz), despite the ASUS having very good pixel response time of around 2ms. Interestingly enough, when the AOC q2963Pm is over clocked to 72Hz, the MPRT decreases despite the monitor making no adjustments to its pixel response times whatsoever. All of these facts indicate that Refresh Rate is the main influence on the MPRT, as it is the main influence on the level of motion blur for these displays. The result? We going back to establish that the Refresh rate is a crucial factor in affecting a PC monitor’s responsiveness.
If you want to judge the responsiveness of a monitor, hard work is mandatory as manufacturers usually give us very little to go by. The specifications that are provided to us have the ‘grey to grey response time’, and these response time values are significant. But as we have established in the article, the reason for why you must look beyond the single value specified by the manufacturer is that there are a lot of factors affecting a PC monitor’s responsiveness.
Other than Response time, the Refresh Rate is also a big factor to consider. Additionally, these two intertwine, forming a key part of how well your monitor will handle motion. Another important factor is ‘Input lag’, primarily affecting how a monitor ‘feels’ in response to a user’s input.
The point is, the manufacturers don’t usually specify all of these factors. What can get more confusing as a buyer, is that some of these terms are thrown around quire loosely and finding accurate information can be difficult. Therefore, before you spend your hard earned money on a monitor, it is essential to do some research and observe all of these factors closely. A good monitor requires certain values that you should be on the lookout for. And with all of these factors covered in this article, we hope that your search ends here.