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Introduction

We've talked recently about the roadmaps for high refresh rate displays and panels in the monitor market, spanning across various panel technologies and screen sizes. One interesting sector was in the TN Film market where high refresh rate screens of 120Hz and 144Hz have been available for many years, originally being the only choice in the LCD monitor market for high frame rate gaming. While other panel technologies like IPS and VA have more recently ventured in to the 120Hz/144Hz refresh rate market themselves, TN Film is again pushing the boundaries this year with the arrival of native 240Hz refresh rate support. This doubles the potential frame rate support from the original 120Hz panels from many years ago, going back to 2009 in fact. If you refer to the previously mentioned roadmap article you will see that it is AU Optronics who, as a panel manufacturer, are pushing the refresh rate for this new generation of TN Film panel, with options being produced in 24.5" and 27" sizes. The first to go in to production was the 24.5" panel variants which have quickly been adopted by some of the main gaming display manufacturers. Acer, Asus, BenQ and AOC have all got equivalent 24.5" models (often referenced as 25" in size for ease) coming out to compete in the ever-popular gamers sector.

We have already reviewed recently the AOC offering, their AGON AG251FZ which combined one of these new panels with support for AMD FreeSync variable refresh rates and a whole range of gaming features. Now we have with us another option, produced by Asus and this time paired with NVIDIA G-sync instead. The new PG258Q forms part of their popular ROG Swift branded gaming range of screens, and this model also offers some impressive gaming features of its own including the aforementioned 240Hz native refresh rate, along with a 1ms G2G response time, G-sync and even ULMB (Ultra Low Motion Blur) support which was not available on the AOC model. We will see how it compares to the AOC equivalent, as well as against some of the other Asus gaming screens we've tested over the years.

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Specifications and Features

The following table gives detailed information about the specs of the screen:

The PG258Q offers a limited range of connectivity options given the use of a G-sync module, with only DisplayPort 1.2a and HDMI offered. DisplayPort is needed to support the refresh rate up to 240Hz, including G-sync support from compatible NVIDIA graphics cards (30- 240Hz range). The digital interfaces are HDCP certified for encrypted content and the video cables are provided in the box for both video connections.

The screen has an external power supply and comes packaged with the power cable and power brick you need. There are also 2x USB 3.0 ports available and a headphone socket on the back underside of the screen. There are no further extras here such as integrated speakers, mic connections or light sensors.

Below is a summary of the features and connections of the screen:

OSD Menu

Above: OSD control buttons on the back right hand side of the screen. Click for larger version

Power Consumption

In terms of power consumption the manufacturer lists typical 'on' usage as <65W which they stats is "measuring a screen brightness of 200 nits without audio/ USB/ Card reader connection". They also list <0.5W usage in standby. We carried out our normal tests to establish its power consumption ourselves.

We tested this ourselves and found that out of the box the screen used 26.6W at the default 80% brightness setting. Once calibrated the screen reached 17.5W consumption, and in standby it used only 0.5W. We have plotted these results below compared with other screens we have tested. The consumption is comparable to the other screens in this 24 - 25" size range we have tested as you might expect (comparing the calibrated states).

Panel and Backlighting

Panel Part and Colour Depth

The screen features an AU Optronics Q250HTA00 TN Film technology panel which is capable of producing 16.7 million colours. This is achieved through a 6-bit colour depth with additional Frame Rate Control (FRC). The panel part is confirmed when dismantling the screen as shown below. This is an unusual designation for an AUO panel, which suggests it perhaps might be a custom-made part for Asus:

Screen Coating

The screen coating is a medium anti-glare (AG) offering. It isn't a semi-glossy coating, and isn't as light as some modern IPS type panels either. It's in keeping with other TN Film panels we've tested. Thankfully it isn't a heavily grainy coating like some old IPS panels feature, although there is some graininess noticeable. It retains its anti-glare properties to avoid too many unwanted reflections of a full glossy coating, but does not produce an too grainy or dirty an image that some thicker AG coatings can. There were some slight cross-hatching patterns visible on the coating as well but only if you looked very closely.

Backlight Type and Colour Gamut

The screen uses a White-LED (W-LED) backlight unit which is standard in today's market. This helps reduce power consumption compared with older CCFL backlight units and brings about some environmental benefits as well. The W-LED unit offers a standard colour gamut which is approximately equal to the sRGB colour space. Anyone wanting to work with wider colour spaces would need to consider wide gamut CCFL screens or the newer range of GB-r-LED type (and similar) displays available now. If you want to read more about colour spaces and gamut then please have a read of our detailed article.

Backlight Dimming and Flicker

We tested the screen to establish the methods used to control backlight dimming. Our in depth article talks in more details about a common method used for this which is called Pulse Width Modulation (PWM). This in itself gives cause for concern to some users who have experienced eye strain, headaches and other symptoms as a result of the flickering backlight caused by this technology. We use a photosensor + oscilloscope system to measure backlight dimming control with a high level of accuracy and ease. These tests allow us to establish

1) Whether PWM is being used to control the backlight
2) The frequency and other characteristics at which this operates, if it is used
3) Whether a flicker may be introduced or potentially noticeable at certain settings

If PWM is used for backlight dimming, the higher the frequency, the less likely you are to see artefacts and flicker. The duty cycle (the time for which the backlight is on) is also important and the shorter the duty cycle, the more potential there is that you may see flicker. The other factor which can influence flicker is the amplitude of the PWM, measuring the difference in brightness output between the 'on' and 'off' states. Please remember that not every user would notice a flicker from a backlight using PWM, but it is something to be wary of. It is also a hard thing to quantify as it is very subjective when talking about whether a user may or may not experience the side effects.

100%                                                  50%                                                  0%
   
Above scale = 1 horizontal grid = 5ms

At 100% brightness a constant voltage is applied to the backlight. As you reduce the brightness setting to dim the backlight a Direct Current (DC) method is used, as opposed to any form of PWM. This applies to all brightness settings from 100% down to 0%. The screen is flicker free as a result which is great news.

Contrast Stability and Brightness

We conducted these tests in the default settings. The brightness control gave us a very good range of adjustment, although there was a limitation at the lower end certainly. At the top end the maximum luminance reached 488 cd/m² which was a lot higher than the specified maximum brightness of 400 cd/m² from the manufacturer. There was a good 371 cd/m² adjustment range in total, and so at the minimum setting you could reach down to luminance of only 116 cd/m². This is still very high really and while it should be an adequate level for typical day to day work, it doesn't give you any option for those wanting to work in darkened room conditions with low ambient light. A setting of 1% in the OSD menu should return you a luminance of around 120 cd/m² at default settings in this preset mode. It should be noted that the brightness regulation is controlled without the need for Pulse Width Modulation, using a Direct Current (DC) method for all brightness settings between 100 and 0% and so the screen is flicker free.

We have plotted the luminance trend on the graph above. The screen behaves as it should in this regard, with a reduction in the luminance output of the screen controlled by the reduction in the OSD brightness setting. This is a linear relationship as shown.

The average contrast ratio of the screen was good for a TN Film panel at 995:1. This was very stable across the brightness adjustment range as shown above. Note that this was in the default screen settings.

Testing Methodology

An important thing to consider for most users is how a screen will perform out of the box and with some basic manual adjustments. Since most users won't have access to hardware colorimeter tools, it is important to understand how the screen is going to perform in terms of colour accuracy for the average user.

We restored our graphics card to default settings and disabled any previously active ICC profiles and gamma corrections. The screen was tested at default factory settings using our new X-rite i1 Pro 2 Spectrophotometer combined with LaCie's Blue Eye Pro software suite. An X-rite i1 Display Pro colorimeter was also used to verify the black point and contrast ratio since the i1 Pro 2 spectrophotometer is less reliable at the darker end.

Targets for these tests are as follows:

• CIE Diagram - validates the colour space covered by the monitors backlighting in a 2D view, with the black triangle representing the displays gamut, and other reference colour spaces shown for comparison

• Gamma - we aim for 2.2 which is the default for computer monitors

• Colour temperature / white point - we aim for 6500k which is the temperature of daylight

• Luminance - we aim for 120 cd/m², which is the recommended luminance for LCD monitors in normal lighting conditions

• Black depth - we aim for as low as possible to maximise shadow detail and to offer us the best contrast ratio

• Contrast ratio - we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present

• dE average / maximum - as low as possible. If DeltaE >3, the color displayed is significantly different from the theoretical one, meaning that the difference will be perceptible to the viewer. If DeltaE <2, LaCie considers the calibration a success; there remains a slight difference, but it is barely undetectable. If DeltaE < 1, the color fidelity is excellent.

Default Performance and Setup

Default settings of the screen were as follows:

Asus ROG Swift PG258Q - Default Settings

   

Initially out of the box the screen was set in the default Racing Mode Game Visual preset and with the gamma option set to 2.2. With a very high default 80% brightness setting out of the box the screen was overly bright and uncomfortable to use, so you will definitely need to turn that down. You could tell the screen was using a standard gamut backlight as well with the naked eye, and the colour balance and temperature felt pretty good, although the image did appear a little washed out and perhaps a little too cool.

We went ahead and measured the default state with the i1 Pro 2. The CIE diagram on the left of the image confirms that the monitors colour gamut (black triangle) is fairly equal to the sRGB colour space. There is some modest over-coverage in blues and greens but not by anything significant. Default gamma was recorded at 2.0 average in this mode, leaving it with a moderate 10% deviance from the target. Remember this is a gaming screen, where a lower gamma like this is often desirable for gaming uses. There are a couple of other gamma settings in the OSD menu which affords you some further control. We measured those modes as well and found that the 1.8 setting delivered an average gamma of 1.6 (27% deviance from the target), while the 2.4 mode returned an average of 2.3 and only a small 3% deviance from the target. We will look at some optimal settings in a moment. White point was measured at a slightly cool 6121k, being 6% out from the 6500k we'd ideally want for desktop use.

Luminance was recorded at an extremely bright 437 cd/m² which is far too high for prolonged general use. The screen was set at a default 80% brightness in the OSD menu but that is easy to change of course to reach a more comfortable setting without impacting any other aspect of the setup. The black depth was 0.44 cd/m² at this default brightness setting, giving us a decent (for a TN Film panel) static contrast ratio of 990:1. Colour accuracy was moderate out of the box with an average dE of 3.0 measured. Testing the screen with colour gradients showed smooth transitions in all shades, with some slight gradation evident in darker tones.

We thought it might be useful to provide some recommended OSD settings for the screen to show what is possible even without a calibration device and proper ICC profiling of the display. A simple change in the OSD menu to gamma mode 2.4 returned a better setup for gamma, reducing the 10% deviance we'd seen out of the box to only 5% now. The adjustments to the RGB controls brought the white point in line, now at 6519k with 0% deviance from our target. You need to adjust the brightness control all the way down to 1% to achieve a lower, more comfortable luminance. The contrast ratio is impacted a little by the change to the gamma mode, and the lowering of the RGB controls. It was now measured at 892:1 which was still decent enough for this panel technology.

Calibration

We used the X-rite i1 Pro 2 Spectrophotometer combined with the LaCie Blue Eye Pro software package to achieve these results and reports. An X-rite i1 Display Pro colorimeter was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.

Asus ROG Swift PG258Q - Calibrated Settings

   

We stuck to the optimal OSD settings we'd identified before, including the 2.4 gamma mode and the slightly tweaked RGB values. All these OSD changes allowed us to obtain an optimal hardware starting point and setup before software level changes would be made at the graphics card level. We left the  LaCie software to calibrate to "max" brightness which would just retain the luminance of whatever brightness we'd set the screen to, and would not in any way try and alter the luminance at the graphics card level, which can reduce contrast ratio. These adjustments before profiling the screen would help preserve tonal values and limit banding issues. After this we let the software carry out the LUT adjustments and create an ICC profile.

Average gamma was now corrected to 2.2 average with a 0% deviance, correcting the minor 5% deviance we'd seen out of the box in this gamma mode 2.4. The white point had now been corrected to 6480k, which corrected the 6% deviance we'd seen out of the box. Luminance had been improved thanks to the adjustment to the brightness control and was now being measured at 118 cd/m². This left us a black depth of 0.137 cd/m² and maintained a fairly decent static contrast ratio (for a TN Film panel) of 859:1. Colour accuracy of the resulting profile was excellent, with dE average of 0.5 and maximum of 1.2. LaCie would consider colour fidelity to be very good overall. Testing the screen with various colour gradients showed smooth transitions with only some slight gradation in darker tones. No banding had been introduced which was pleasing. You can use our settings and try our calibrated ICC profile if you wish, which are available in our ICC profile database. Keep in mind that results will vary from one screen to another and from one computer / graphics card to another.

Calibration Performance Comparisons

The comparisons made in this section try to give you a better view of how each screen performs, particularly out of the box which is what is going to matter to most consumers. When comparing the default factory settings for each monitor it is important to take into account several measurement areas - gamma, white point and colour accuracy. There's no point having a low dE colour accuracy figure if the gamma curve is way off for instance. A good factory calibration requires all 3 to be well set up. We have deliberately not included luminance in this comparison since this is normally far too high by default on every screen. However, that is very easily controlled through the brightness setting (on most screens) and should not impact the other areas being measured anyway. It is easy enough to obtain a suitable luminance for your working conditions and individual preferences, but a reliable factory setup in gamma, white point and colour accuracy is important and not as easy to change accurately without a calibration tool.

From these comparisons we can also compare the calibrated colour accuracy, black depth and contrast ratio. After a calibration the gamma, white point and luminance should all be at their desired targets.

Default setup of the screen out of the box was moderate, with a gamma curve that was slightly too low (2.0 average, 10% deviance from our target) and a slightly too cool white point (6121k, 6% out). The screen is aimed at gaming and so this low gamma and cooler white point are not uncommon, and often desirable for gaming uses anyway. It's very common for the TN Film gaming screens to be set up out of the box with a lower gamma, and you can see this if you look at the Acer Predator XG270HU (1.8), Asus MG248Q (1.9) and BenQ XL2730Z (1.9) for example. Thankfully a few simple OSD changes can deliver a setup more suitable for day to day use so we don't need to penalise the screen here for its gaming gamma curve at default settings.

The display was pretty good when it came to static contrast ratio for a TN Film panel, at 859:1 after calibration. This was a tad lower than some other high end gaming TN Film screens like the competing AOC AGON AG251FZ (931:1) and other displays like the Asus MG248Q (1005:1) and BenQ XL2730Z (917:1) for instance. Of course none of these TN Film panels can compete with VA panel types which can reach over 2000:1 easily, and commonly up to 3000:1 (e.g. Acer Predator Z35) or even near 5000:1 (Eizo Foris FG2421).

Viewing Angles

Above: Viewing angles shown from front and side, and  from above and below. Click for larger image

Viewing angles of the screen were as you might expect from a TN Film panel. Unfortunately this panel technology is inherently poor in this field, and so viewing angles are more restrictive than other competing technologies like IPS and VA variants. Although the manufacturer will quote a viewing angle of 170 / 160 (a classic indication that a TN Film panel is being used by the way if in doubt), in practice there are some obvious contrast and colour tone shifts horizontally, and especially vertically.

As you move your head from side to side in a horizontal plane, there is a contrast shift and the image becomes more pale and introduces a yellow hue. As you move to a wider angle the image can become more washed out as well and a slight pink hue is introduced. Vertically the fields of view are more restrictive still. From above the image becomes pale and washed out, while from below there is a characteristic TN Film darkening of the image. Unfortunately vertically the viewing angles will introduce noticeable shifts in the contrast and colour tone of the image which mean that for any colour critical work it is not really very well suited. TN Film panels have long suffered from these restrictive viewing angles due to the nature of their pixel structure. They are still fine for a single user for general use and certainly the TN Film panels offer their advantages when it comes to pixel response times and refresh rate for gaming. If however, you were hoping to do any colour critical or photography work you may find these shifts in the appearance of the image difficult. An IPS-type panel would probably be a wiser choice if you were looking for a screen with much wider viewing angles but having said that you are probably mainly interested in gaming if you are considering this screen. Remember, this screen is specifically designed for gaming, and so you will have to live with some of the sacrifices of TN Film to get the kind of gaming performance and features offered here. There are some high refresh rate gaming IPS panels available now in larger sizes as well which can offer better viewing angles than TN Film models, although they are normally priced higher and have some other characteristic differences, and so TN Film models like this still have their place for many users.

Above: View of an all black screen from the side. Click for larger version

On a black image there is a slight pale grey tint introduced to the image when viewed from a wide angle. This isn't too severe and shouldn't present any real problems in practice. Certainly not the obvious white glow you get from most modern IPS-type panels in similar situations and fairly standard for a TN Film panel. Very similar to what we have seen from other recent gaming TN Film screens like the AOC AGON AG251FZ, Asus MG248Q, Asus ROG Swift PG278Q and BenQ XL2730Z. The glow you see from most modern IPS panels can put off some users. So on the one hand, those IPS models have much better general viewing angles than the TN Film models, but they do show more glow which some people find an issue.

Panel Uniformity

We wanted to test here how uniform the brightness was across the screen, as well as identify any leakage from the backlight in dark lighting conditions. Measurements of the luminance were taken at 36 points across the panel on a pure white background. The measurements for luminance were taken using BasICColor's calibration software package, combined with an X-rite i1 Display Pro colorimeter with a central point on the screen calibrated to 120 cd/m². The below uniformity diagram shows the difference, as a percentage, between the measurement recorded at each point on the screen, as compared with the central reference point.

It is worth noting that panel uniformity can vary from one screen to another, and can depend on manufacturing lines, screen transport and other local factors. This is only a guide of the uniformity of the sample screen we have for review.
 

Uniformity of Luminance

The luminance uniformity of the screen was pretty good overall. The screen showed a dip in luminance towards the left hand edge, where in the worst case it dropped to 97 cd/m² (-24% deviance). 80% of the screen was within a 10% deviance from the centrally calibrated point which was decent.

Backlight Leakage

Above: All black screen in a darkened room. Click for larger version

We also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. The camera showed there was no real backlight bleed evident, but a little clouding along the lower right hand edge of the screen. Nothing that should be noticeable in day to day use.

Note: if you want to test your own screen for backlight bleed and uniformity problems at any point you need to ensure you have suitable testing conditions. Set the monitor to a sensible day to day brightness level, preferably as close to 120 cd/m² as you can get it (our tests are once the screen is calibrated to this luminance). Don't just take a photo at the default brightness which is almost always far too high and not a realistic usage condition. You need to take the photo from about 1.5 - 2m back to avoid capturing viewing angle characteristics, especially on IPS-type panels where off-angle glow can come in to play easily. Photos should be taken in a darkened room at a shutter speed which captures what you see reliably and doesn't over-expose the image. A shutter speed of 1/8 second will probably be suitable for this.

General and Office Applications

With a 1920 x 1080 resolution, the desktop real estate  of the PG258Q feels a step down compared with all the high resolution panels we've tested, and the 27" 2560 x 1440 models we are used to using day to day. You do lose a large amount of desktop space, and although side by side split screen working is possible, it's not as easy due to the more limited resolution and space. With a 0.2825mm pixel pitch, text is comfortable and easy to read natively, providing a sharp and crisp image. It is not as sharp as the 1440p panels we've become accustomed to, or of course any ultra HD/4K resolutions where scaling is used, but it is perfectly adequate. For this size screen, 1920 x 1080 is about your limit of sensible resolution without needing to use operating system scaling options.

The moderate AG coating of the TN Film panel could be considered a bit grainy, especially on white office backgrounds to a lot of people. It's not as clear as modern IPS coatings or any semi-glossy solution. Still, it's not as grainy as old IPS panels and is on par with other TN Film matrices we've tested. Perhaps the main issue with this panel technology though is the restrictive viewing angles, making contrast and colour tone shifts a bit of a problem when it comes to colour critical work. They are the same here as other TN Film panels, being restrictive especially vertically. The screen is fine when viewed head on though really for office and text work, but for colour critical work or photo editing etc you'd be better off with an IPS-type panel. The default setup of the screen was a little restrictive for normal uses, as the gamma is set up more for gaming, but thankfully this was very easy to adjust without a calibration tool via a simple change in the OSD menu. That provided a good default setup then for day to day office work, once you've turned the brightness setting down a long way. There are 4 blue light filter modes offered in the menu if you want to add further eye care protection and might be worth experimenting with for prolonged office use or text reading.

The range of brightness adjustment of the screen was very good, with the ability to offer a luminance between 488 and 116 cd/m². However, the adjustment potential at the lower end was limited and that means that it might be hard to use the screen in darker room conditions where there is a lower ambient light. That's certainly a limitation of the backlight adjustment on the PG258Q here. A setting of 1% in the OSD brightness control should return you a luminance close to 120 cd/m² out of the box. On a more positive note, the brightness regulation is controlled without the need for the use of the now infamous Pulse-Width Modulation (PWM), and so those who suffer from eye fatigue or headaches associated with flickering backlights need not worry. There was no audible noise or buzzing from the screen, even when specifically looking for it using test images with a large amount of text at once. The screen also remains cool even during prolonged use.

There are a couple of extra features on this screen for office environments, even though it's primarily a gaming screen. There are 2x USB 3.0 ports although both are on the back of the screen so not easy access like on some other displays. There's also a headphone connection but no integrated speakers. There is no ambient light sensor, card reader, motion sensor or anything else provided which can sometimes be useful in office environments. There was a good range of ergonomic adjustments available from the stand allowing you to obtain a comfortable position for a wide variety of angles although some were quite stiff to operate. The VESA mounting support may also be useful to some people as well.

 
Responsiveness and Gaming

The ROG Swift PG258Q is firmly a gamers screen, with key features including the native 240Hz refresh rate, 1ms G2G response time and support for NVIDIA G-sync and ULMB. You will need to keep in mind the demands on your system and graphics card to power a screen like this, as there's quite a drain on resources to run at 240Hz! The resolution is 'only' 1920 x 1080 so that is at least a bit easier than if this was a 1440p or 4k resolution screen. For systems which can't manage the 240Hz reliably or frequently, G-sync is supported for variable refresh rate control, helping to eliminate tearing and stuttering and operating in a nice wide range from 30 to 240Hz. Asus have provided a wide range of additional extras for gaming that we will talk about in a moment.

The ROG Swift PG258Q is rated by Asus as having a 1ms G2G response time which indicate the panel uses overdrive / response time compensation (RTC) technology to boost pixel transitions across grey to grey changes. The part being used is the AU Optronics Q250HTA00 TN Film technology panel. Have a read about response time in our specs section if you need additional information about this measurement. As a reminder, this is only the second native 240Hz refresh rate panel of any size and type we have seen having recently reviewed the equivalent AOC model, the AGON AG251FZ.

We will first test the screen using our thorough response time testing method. This uses an oscilloscope and photosensor to measure the pixel response times across a series of different transitions, in the full range from 0 (black) to 255 (white). This will give us a realistic view of how the monitor performs in real life, as opposed to being reliant only on a manufacturers spec. We can work out the response times for changing between many different shades, calculate the maximum, minimum and average grey to grey (G2G) response times, and provide an evaluation of any overshoot present on the monitor.

We use an ETC M526 oscilloscope for these measurements along with a custom photosensor device. Have a read of our response time measurement article for a full explanation of the testing methodology and reported data.
 

Overdrive Setting

The 'OD' overdrive control is available via the 'image' section of the OSD menu as shown above. We will test all three modes to see which is optimal first of all. For now we have taken these measurements at the maximum 240Hz refresh rate, but we will look at the implications of the refresh rate in a moment once we've established the behaviour of the response times under this setting.

In the 'off' setting the response times were mixed, with some around the advertised 1ms G2G figure, but many being much slower up around 9 - 13ms. This gave us an average figure of 7.1ms and while there was no overshoot as you would expect with overdrive turned off, but the response times were slower than we would like from a TN Film panel. Turning the OD setting up to 'normal' brought about decent and noticeable improvements, with an average response time now measured at 2.9ms. Some moderate overshoot started to appear in a couple of transitions here, but this mode was certainly faster and more fluid than the 'off' setting. If you push the OD setting up to the maximum 'extreme' level then there's no real improvements to response times overall but the overshoot becomes far more noticeable and pronounced. Stick with the 'normal' mode.
 

Refresh Rate and G-sync

The PG258Q supports a refresh rate of up to 240Hz natively, and as we've discussed earlier this is one of the first panels supporting such a high refresh rate on the market. You can quickly and easily select this refresh rate in Windows as shown above, although we did find we had to use the provided DisplayPort cable rather than our regular day to day cable, so perhaps it is a little fussy on the cabling choice. Just stick with the one provided in the box and you will be fine. When enabled, and from a compatible system, G-sync is also available which operates in a range between 30 and 240Hz. There are improvements in perceived motion clarity as you increase the refresh rate, and the 240Hz certainly feels more fluid and faster than 120 / 144Hz. The improvement is not as noticeable as when you move from 60 to 120/144Hz for the first time, but the ability to deliver even higher frame rates from 144 - 240Hz is certainly welcome. From an NVIDIA test system we found stable performance without any frames being dropped at all refresh rates from 60Hz to 240Hz which was good news.

Refresh Rate Impact, Overdrive Mode = Normal

We stuck to the 'normal' overdrive setting for now and we wanted to test the response times at a range of refresh rates to see if that influences the pixel transitions. It's quite common for the overdrive impulse to be dynamically controlled across a wide refresh rate range like this. The overshoot can also be impacted we have seen in the past.

As you can see from these measurements the actual pixel transition times vary a little as you increase the refresh rate. at 60Hz the overdrive impulse seemed to be a little more modest, resulting in a 4.9ms G2G response time and no overshoot being measured. If you increase the refresh rate up to 144Hz, the response times are improved a little to help ensure the pixel transitions can keep up with the frame rate demands. At 144Hz, the response times need to be reliably under 6.94ms average to avoid additional smearing and blurring being introduced, and so the boost in the overdrive impulse helps achieve that nicely. The response times are pushed a little more by the time you reach 240Hz where they need to be <4.16ms and again this is largely achieved. Only moderate levels of overshoot start to appear at these higher refresh rates as well which was pleasing. This 'normal' OD mode is capable of handling the full refresh rate range nicely, so you can stick with this for all your refresh rate settings, including when G-sync is dynamically controlling it for you.

Detailed Response Time Measurements
Refresh Rate = 240Hz, Overdrive = Normal

We stuck with the optimal 'normal' response time setting at the maximum 240Hz refresh rate. The average G2G response time was measured at 3.4ms which was very good and represented very fast pixel transition times from this new TN Film panel. Some transitions reached basically as low as the advertised 1ms G2G as well. There were a few transitions which were a little slower than the required 4.16ms figure to maintain a 240Hz frame rate but overall the response times were very good here.

If we evaluate the Response Time Compensation (RTC) overshoot then the results show very little overshoot overall, with only a couple of transitions really showing anything at all, and even then at only moderate levels. In this normal OD mode the overshoot was minimal which was excellent news and actually very rare for a fast TN Film panel. They typically have higher levels of overshoot than seen here so Asus have done a nice job keeping it under control.

Display Comparisons

The above comparison table and graph shows you the lowest, average and highest G2G response time measurement for each screen we have tested with our oscilloscope system. There is also a colour coded mark next to each screen in the table to indicate the RTC overshoot error, as the response time figure alone doesn't tell the whole story.

As a reminder, these figures are at 240Hz refresh rate and with overdrive set to 'normal'. The response time performance of the PG258Q was very impressive overall, with some of the fastest TN Film response times we've seen, while still keeping overshoot at a low level. A few other models such as the AOC AGON AG251FZ reached a little lower at 2.6ms G2G but with moderately high levels of overshoot then apparent. We would rather have the slightly "slower" (3.4ms G2G isn't slow!) response times here to be honest with lower overshoot, so we were impressed with the PG258Q's performance. The G-sync module did a nice job of dynamically controlling the response times across a wide refresh rate range as well, making it easy to stick with one OD setting and have excellent performance across the range.
 

Ultra Low Motion Blur (ULMB)

The PG258Q also features an integrated Blur Reduction Backlight system, dubbed "Ultra Low Motion Blur" (ULMB) by NVIDIA. This is linked to the G-sync module and is provided on most G-sync enabled screens that have a native high refresh rate. We have already seen a lot of positive improvements in perceived motion blur from such systems in the past. Our in depth article from June 2013 (updated 17 March 2015) looked at this in a lot more detail, and tested some of the original LightBoost "hacks" to achieve a strobed backlight and blur reduction benefits. Since then we've seen a quite a lot of monitors integrate a strobed backlight with simple user control from the menu and with better implementation than LightBoost methods.

The ULMB feature is accessible from the 'image' section of the OSD menu. It is only available when running the screen at 100, 120 and 144Hz modes. It is not available at 200Hz or 240Hz sadly, and it is also important to note that ULMB does not work when you are using G-sync, it's one or the other. When you enable the ULMB feature a new option appears for the "ULMB Pulse Width" which allows you to control the duration of the backlight strobes. A shorter "on" period can help reduce perceived motion blur even more, but at the cost of screen brightness. You can adjust this between 100 and 10, and as you lower the setting the screen also becomes progressively darker as you reduce the "on" period of the strobe. Nice to see this included as an option within the menu for those who like to play around with the setting, much like you could do by adjusting LightBoost levels on older models using the "hack" method. There is no control to adjust the timing of the strobe to impact the strobe cross-talk it can introduce, so we will have to hope that the default timing setup is suitable. We will look at that in a moment.

Operation - 100Hz

ULMB backlight cycling, 100Hz (scale = 5ms)
pulse width setting= 100

We measured the screen using our oscilloscope when viewing a solid white image, with ULMB feature turned on and with refresh rate set at 100Hz. This is the lowest refresh rate at which you can operate the ULMB mode. As a reminder, it works at 100, 120 and 144Hz only. We left the pulse width (strobe length) setting at 100 initially. Normally the oscillograph would show a flat straight line when measuring a static white image (as no PWM is being used for backlight dimming), but here the ULMB feature is cycling the backlight off and on rapidly.

The time for each complete cycle is 10ms which shows that in this case the backlight is being cycled at the same frequency as the refresh rate, 100 times per second. The strobe is in time with the refresh rate of 100Hz.
 

Operation - 120Hz

ULMB backlight cycling, 120Hz (scale = 5ms)
pulse width setting = 100

When running the screen at a 120Hz refresh rate the behaviour is exactly the same. The only difference is that the strobe is now synced with the new refresh rate, with a new strobe every 8.33ms (120 times per second).

Operation - 144Hz

ULMB backlight cycling, 144Hz (scale = 5ms)
pulse width setting = 100

Again when set at 144Hz refresh rate the strobes are in sync again, with a new strobe every 6.94ms (144 times per second). The above is with pulse width at the default 100. We can also see what impact on the strobing it has if you lower the pulse width setting.

ULMB backlight cycling, 144Hz (scale = 5ms)
pulse width setting = 50

ULMB backlight cycling, 144Hz (scale = 5ms)
pulse width setting = 10

As you reduce the pulse width setting you are adjusting the 'on' period of the strobe, shown by the top portion of each peak. As you reduce the setting the strobe 'on' time gets progressively shorter as you can see from the above 2 graphs, the first at a setting of 50 and the second at a setting of 10 (the minimum setting available). This impacts the perceived blur somewhat, with the shorter 'on' times resulting in a clearer image. At the same time though the brightness of the image is affected and it becomes very dark, the lower you go with the setting. More on that in a moment. There will be a point where the user does not see any further benefit to their eyes of reducing the strobe length further, but you can have a play around with the setting to find your personal preference to balance perceived motion blur and brightness of the image.
 

Pulse Width Setting - Strobe Length

We measured the strobe length at a variety of the Pulse Width settings, while running at the maximum 144Hz refresh rate mode. You can adjust the setting in steps of 1 incidentally. Each complete strobe lasts a total of 6.94ms (144 strobes per second).

Pulse Width Setting - Brightness Range (144Hz)

We tested the brightness output of the screen when ULMB was turned on at 144Hz. You can independently control the brightness setting as well if you want, but we left it at the default 100 and just changed the pulse width (PW) strobe length setting to establish the brightness range when using this option. With the PW setting at 100 the maximum achievable luminance of the screen was a very good 275 cd/m². This should be plenty for most uses, but you cannot get a brighter display when using ULMB if you wanted to. This is a very strong performance from a strobe backlight though. You can achieve a slightly brighter display if you use the feature at 100 or 120Hz since the strobes are less frequent, but it's not a significant amount.

As you reduce the PW setting the luminance drops significantly, at the lowest setting probably being far too dark for any practical use. At least you can control a reasonably wide range here, so you can find a level which suits your needs. We suspect a PW setting of 100 will probably be perfectly adequate for most normal users anyway, as the ULMB mode certainly brings about positive improvements to the perceived motion blur. If you want to lower the brightness output of the screen, reducing the pulse width setting is probably a better option than simply lowering the brightness control, as it should bring about some minor blur reduction benefits as well.

Brightness Range (PW at 100, 144Hz)

We also wanted to test the brightness range when leaving PW at its default 100, and changing the brightness control of the screen instead. This leaves the strobe behaviour alone, operating as it does with PW at 100, and instead just dims the backlight. The table above confirms the range available through that control. You can achieve a slightly brighter display if you use the feature at 100 or 120Hz since the strobes are less frequent, but it's not a significant amount.

Thankfully the brightness setting when ULMB is turned on is independent to when ULMB is off, and it remembers your last setting as well (or at least it seemed to most of the time). So you can have the brightness down at 1% for normal desktop use (as per our calibration section) to achieve a comfortable brightness, and then have it at a completely different saved setting when you enable ULMB. This is great news as at 1% brightness the luminance with ULMB on is far too low. you will want to bump it up when you're using ULMB and thankfully there's a great range available and a very bright upper limit if you need it. That's rare for a strobed backlight system, and so we were impressed with the way it's been implemented on the PG258Q.

Maximum Blur Reduction Brightness - Display Comparison

For ease of reference we have also provided a comparison table below of all the blur reduction enabled displays we've tested, showing their maximum luminance before blur reduction is turned on (normal mode) and their maximum luminance with the feature enabled. This will give you an idea of the maximum brightness you can expect from each model when using their blur reduction feature, if that is important to you. A lot of people want a brighter display for gaming and sometimes the relatively low maximum luminance from blur reduction modes is a limitation.

These comparisons are with the refresh rate as high as is available for the blur reduction feature to function. For most this is at 120Hz, but some also support the feature at higher. You can achieve a slightly brighter display if you use the feature at 85 or 100Hz since the strobes are less frequent, but it's not a significant amount. That can also introduce more visible flicker in some situations.

Note: Pulse Width setting at max where applicable.
*Note 2: The Acer XB270HU was later updated to include a 120Hz mode, which will produce a slightly darker maximum luminance
 

Blur Reduction Tests

ULMB enabled, central screen area

Of course the main thing we want to test is what improvements the Blur Reduction mode offers when it comes to motion clarity and gaming. We were pleased with the results we'd seen from LightBoost backlights when we tested them, and also from the natively supported blur reduction feature on other displays including the other popular TN Film gaming models we've tested.

We were very pleased with the results here as we had been on other blur reduction displays, with an obvious and marked improvement in perceived motion blur experienced. Tracking of moving objects became much easier and the image looked sharper and clearer. We used the BlurBusters full-screen TestUFO online motion test (all ULMB supported refresh rates) as well to put the feature through its paces and were pleased with the results. The upper half of the screen was a little clearer than the bottom, and in the bottom third of the screen some strobe cross-talk became apparent. It is impossible to eliminate strobe cross-talk completely due to the way they operate, but the important thing is whereabouts on the screen this manifests itself and to what level. The central region (as pictured above) is probably the most important since that's where a lot of your gaming focus will be, where crosshairs and the likes are. We were pleased that there was minimal cross-talk here in the central region and the image looked very good. Having the ability to alter the strobe length through the PW setting was also very useful, and you could tweak it to your preference to reduce even more of the persistence if you wanted, as long as you didn't mind sacrificing some brightness. With the high maximum brightness potential of the PG258Q when ULMB was enabled, this was at least possible to do, as you have a decent brightness range to play with.

ULMB enabled, upper, middle and lower screen area cross-talk

Another very good implementation of a strobe backlight system here, we were impressed. It's probably the best we've seen actually so far, considering the high brightness potential. We suppose the only minor quibble is the inability to operate the feature at 200 or 240Hz or in an ideal World, at the same time as using G-sync. We suspect that most systems will struggle anyway to consistently offer 200 and 240Hz refresh rates for a lot of games, so perhaps it was a deliberate decision by Asus to limit the ULMB to 144Hz maximum. There's obvious blur reducing benefits and you still get nice high frame rates anyway so it's no massive deal.

Pursuit Camera Tests

We've already tested above the actual pixel response times and other aspects of the screen's gaming performance. We wanted to carry out some pursuit camera tests as well to give an even more complete idea of the performance of this screen.

Pursuit cameras are used to capture motion blur as a user might experience it on a display. They are simply cameras which follow the on-screen motion and are extremely accurate at measuring motion blur, ghosting and overdrive artefacts of moving images. Since they simulate the eye tracking motion of moving eyes, they can be useful in giving an idea of how a moving image appears to the end user. It is the blurring caused by eye tracking on continuously-displayed refreshes (sample-and-hold) that we are keen to analyse with this new approach. This is not pixel persistence caused by response times; but a different cause of display motion blur which cannot be captured using static camera tests. Low response times do have a positive impact on motion blur, and higher refresh rates also help reduce blurring to a degree. It does not matter how low response times are, or how high refresh rates are, you will still see motion blur from LCD displays under normal operation to some extent and that is what this section is designed to measure. Further technologies specifically designed to reduce perceived motion blur are required to eliminate the blur seen on these type of sample-and-hold displays which we will also look at.

We used the Blurbusters.com Ghosting Motion Test which is designed to be used with pursuit camera setups. The pursuit camera method is explained at BlurBusters as well as covered in this research paper. We carried out the tests at various refresh rates, with and without Blur Reduction enabled. These UFO objects were moving horizontally at 960 pixels per second, at a frame rate matching refresh rate of the monitor.

Overdrive Setting = Normal

These tests capture the kind of blurring you would see with the naked eye when tracking moving objects across the screen. As you increase the refresh rate the perceived blurring is reduced, as refresh rate has a direct impact on motion blur. It is not eliminated entirely due to the nature of the sample-and-hold LCD display and the tracking of your eyes. No matter how fast the refresh rate and pixel response times are, you cannot eliminate the perceived motion blur without other methods like blur reduction strobing backlights, which this model does also feature.

As you can see, the perceived motion clarity improves significantly as you increase the refresh rate from 60 to 144Hz levels which is common for high refresh rate panels which operate up to this refresh rate. The moving image becomes easier to track and appears sharper. As you can see, there are then noticeable improvements in perceived motion blur as you increase up to 200Hz and 240Hz refresh rate, as the frame rate increases dramatically again. The moving image becomes clearer and easier to track and it's a decent improvement over 144Hz. It was harder to see this difference when we tested the AOC AGON AG251FZ since the overdrive control was not as consistent, but here on the Asus we felt the difference was more noticeable. You can tell from the pursuit camera tests above as well that there's an improvement in motion clarity as you go from 144 > 200 > 240Hz. From a motion clarity point of view, this makes it the fastest display we've tested to date. In practice it might be harder to notice this in gaming, as you're starting to get into the realms of diminishing returns as you get in to the 144Hz range we felt, and perhaps it isn't needed for many users. But the pursuit camera tests and our motion clarity tests showed some improvement that maybe a very keen eye will spot in their gaming.

Note: optimal overdrive settings used on each screen

We can also compare the pursuit camera tests at 60Hz and 144Hz compared with a couple of very fast and very popular gaming screens above, including the recently tested AOC equivalent to this model, their AGON AG251FZ with 240Hz. The performance is very comparable in actual perceived motion blur between all three in practice, with very little to separate them. The PG258Q has a slight edge at 144Hz as the image looks a little clearer and we also know that there are lower levels of overshoot present. As we've shown a little earlier, there are then the added benefits when increasing the refresh rate to 200 and 240Hz.

If we compare the motion clarity at 240Hz between the PG258Q and the AOC equivalent, you can see the better performance from the Asus where the moving object was clearer and sharper.

ULMB Enabled

This model also offers NVIDIA's Ultra Low Motion Blur feature. When enabled, the moving image becomes even sharper and easier to track with the eye across the screen. The strobed backlight helps reduce the remnants of perceived motion blur nicely as we've discussed earlier. There is some low strobe cross talk introduced which produces a slight ghost trial image which is typical for a strobed backlight system.

Additional Gaming Features

GamePlus hotkey - the screen features the ASUS-exclusive GamePlus hotkey for in-game enhancements so you get more out of your game. The crosshair overlay gives you four different crosshair options to suit the game you're playing. There's also an onscreen timer you can position on the left of the display so you can keep track of the elapsed gaming time; while the FPS (frames per second) counter lets you know how smooth the game is running.

Asus GameVisual Technology - basically a series of pre-set display modes to optimize visuals for different types of content. There are 6 in total although some are not specifically designed for gaming per se. This feature can be accessed through the On Screen Display (OSD) settings menu. There are preset modes for scenery, racing, cinema, RTS/RPG games, FPS games and an sRGB mode.

Aspect Ratio Control - the screen does not offer any aspect ratio control options through the OSD menu at all. This is due to a limitation of using NVIDIA's G-sync technology. As we understand it, it is locked to only one defined resolution, in this case 1920 x 1080 so it is not possible (or easy) to provide G-sync support with a scaler. This isn't really a problem for PC use since you can just control the aspect ratio through your graphics card settings. Since most content is in the native 16:9 aspect ratio it probably isn't an issue.

Lag

For the full reviews of the models compared here and the dates they were written (and when screens were approximately released to the market), please see our full reviews index.

We have provided a comparison above against other models we have tested to give an indication between screens. The screens tested are split into two measurements which are based on our overall display lag tests (using SMTT) and half the average G2G response time, as measured by the oscilloscope. The response time is split from the overall display lag and shown on the graph as the green bar. From there, the signal processing (red bar) can be provided as a good estimation.

The screen showed a total average display lag of only 4.60 ms as measured with SMTT 2. Taking into account half the average G2G response time at 1.7ms, we can estimate that there is only ~2.90ms of signal processing lag on this screen which is basically nothing. This is fairly typical result from a G-sync screen and there are no issues here at all for gaming. The result was the same at different refresh rates and with ULMB enabled also.

Movies and Video

The following summarises the screens performance in video applications:

• 24.5" screen size makes it a reasonable option for an all-in-one multimedia screen, but being quite a lot smaller than most modern LCD TV's of course.

• 16:9 aspect ratio is more well suited to videos than a 16:10 format screen, leaving smaller borders on DVD's and wide screen content at the top and bottom.

• 1920 x 1080 resolution can support full 1080 HD resolution content

• Digital interfaces support HDCP for any encrypted and protected content

• Decent enough range of connectivity options for movie viewing and external device connection with DisplayPort and 1x HDMI offered. Limited at the moment by the G-sync module.

• Cables provided in the box for both video connections

• Moderate AG coating provides reasonably clear images with no major graininess, and without the unwanted reflections of a glossy solution. Some graininess apparent as with other TN Film panels, but shouldn't present a problem in movies.

• Wide brightness range adjustment possible from the display, including a maximum luminance of ~488 cd/m² but a rather limited lower luminance of only 116 cd/m². This should afford you good control for different lighting conditions. Contrast ratio remains stable across that adjustment range as well and is good for a TN Film panel. Brightness regulation is controlled without the need for PWM and so is flicker free for all brightness settings

• Black depth and contrast ratio are good for a TN Film panel at 859:1 after calibration. Detail in darker scenes should not be lost as a result.

• There is a specific 'cinema' preset mode available for movies or video which is cooler than our calibrated setup. Might be useful to tweak to your liking for quick switching when you want to watch movies

• Excellent good pixel responsiveness which will handle fast moving scenes in movies without issue. You will want to stick with the 'normal' overdrive mode to avoid any overshoot issues present in the 'extreme' mode.

• Viewing angles are limited due to the use of TN Film panel technology. May cause issues with gamma and contrast shift if you change your line of sight or have several people trying to see the screen at once. Not really an ideal technology for movies as a result of this viewing angle limitation.

• Good range of ergonomic adjustments available from the stand, although quite stiff to use most of them. It still should be easy enough to obtain a comfortable position if you want to sit further away from the screen for movie viewing.

• No particularly noticeable backlight leakage, and none from the edges which is good. This type of leakage may prove an issue when watching movies where black borders are present but it is not a problem here.

• No integrated stereo speakers on this model but there is a headphone connection if needed.

• No hardware aspect ratio options at all so connection of external devices may be tricky if they operate at something other than the native 16:9 aspect ratio. Shouldn't be an issue for modern Blu-ray and DVD players as well as games consoles.

• Picture in picture (PiP) and Picture By Picture (PbP) are not available.
   

Conclusion

The ROG Swift PG258Q was a very impressive gaming screen and one of the best we've tested to date. The response times were very low and the overdrive impulse was controlled nicely across a wide refresh rate range, with only low levels of overshoot being apparent. That's quite rare for a fast TN Film screen and we were impressed. The high 144Hz range refresh rates made an obvious improvement to motion clarity over 60Hz panels as we've become accustomed to with gaming displays for several years now. But the improvements offered by 200 and 240Hz modes become apparent on this display and offered again a decent improvement in motion clarity we felt. The addition of a strobed ULMB backlight system was very welcome as well. It was probably the best ULMB implementation we've seen so far in fact with a very good maximum brightness potential. If only we could also use it at 200 and 240Hz! Lag was low as ever from a G-sync screen, and the G-sync function provided the obvious benefits of that variable refresh rate technology.

There are a couple of limitations with this screen though. Firstly it is TN Film based, and so you have to live with the limited viewing angles and gamma/colour shift inherent to the panel technology. While the screen offered a very good upper brightness potential for ULMB use, this did come at the cost of a rather limited lower adjustment range which might be problematic for those wanting to work in darker ambient lighting conditions.

All in all though, as a gaming display it was excellent and comes highly recommended if you're looking in the fast 1080p TN Film space.

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