Cooler Master GM27-CF
Introduction
Cooler Master is a brand you might be familiar with in the PC market. They are a computer hardware manufacturer based in Taiwan who have been around since 1992 and are most well known for making PC cases, power supplies and cooling solutions. They are now set to end the PC monitor market, just like manufacturers such as Gigabyte did last year. We are always pleased to see new players appear in this market with new and interesting screen options. Cooler Master’s first venture in to the monitor market is with two displays aimed at gaming – the 34″ ultrawide GM34-CW and the 27″ GM27-CF. We have been sent both by Cooler Master so will be testing and reviewing both new models, starting here with the 27″ GM27-CF.
The GM27-CF is 27″ in size and features a curved 1500R VA technology panel. It has a 1920 x 1080 Full HD resolution with a focus on gaming performance and speed. There is a quoted 3ms G2G response time spec along with a 200Hz maximum refresh rate, supported through an overclocking feature. The screen supports adaptive-sync and so supports variable refresh rates (VRR) from both AMD and NVIDIA systems.
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Specifications and Features
The following table gives detailed information about the specs of the screen as advertised:
The GM27-CF offers a good range of modern connectivity with 1x DisplayPort 1.2, 1x HDMI 1.4 and 1 x HDMI 2.0 offered for video connections. These are located on the back of the screen along with a headphone output. Unlike many screens there are no USB ports on this model. For PC connectivity the DisplayPort is the most common option, with HDMI being available then for connecting external games consoles or Blu-ray players potentially. The screen has an external power supply and the screen also comes packaged with the power cable and brick that you need.
Below is a summary of the features and connections of the screen.
Design and Ergonomics
The GM27-CF comes in a black and dark grey design, with matte plastics used for the bezel and rear enclosure. There is a thin 5mm black plastic edge to the screen along the sides and top, and then an additional 6mm black panel border before the image starts (total edge = 11mm). Along the bottom edge is a thicker 17mm bezel and then an additional 3mm black panel border.
The back of the screen is encased in a matte black plastic for a fairly simple and smooth design. The stand connects in to the middle with a quick release mechanism and is a sturdy metal design. It has a dark silver aluminium arm and foot, which is again in the shape of the Cooler Master logo. You have to screw the stand together in a couple of places before it is attached to the screen but that’s simple enough. The back of the screen also features a simple LED lighting feature which glows purple when turned on. You can also set this to flicker in the OSD menu or turn it off altogether, but there are no other colours or settings available.
The stand is pretty strong and sturdy with its metal design. There is a reasonably thin overall profile to the screen, and you can see the subtle screen curvature in the image above.
The stand offers a fairly decent range of ergonomic adjustments with tilt, height and swivel provided. Tilt is smooth and very easy to move although it doesn’t tilt backwards very much so depending on your viewing position the screen itself it can feel a bit upright. We would have liked a bit more flexibility to tilt it backwards. Height adjustment is smooth and easy as well. At the lowest setting the bottom edge of the screen is ~55mm from the top of the desk, and at maximum extension it is ~165mm, giving a total 110mm adjustment range as advertised. Side to side swivel is smooth although a little stiff, so sometimes you end up moving the whole screen at once. There’s no rotation function offered on this screen as it’s impractical on a curved format display. There is a bit of wobble to the screen when you move it around as the stand attachment on the back is quite small.
A summary of the ergonomic adjustments are shown below:
The materials were of a reasonable standard and the build quality felt ok. There was no audible noise from the screen, even when conducting specific tests which can often identify buzzing issues. The whole screen remained cool even during prolonged use.
The OSD is controlled entirely through 4 pressable buttons on the bottom right edge of the screen. There is also a power on/off button located next to them. The menu is split in to 9 sections down the left hand side, with available options then shown in the middle and right hand columns. There’s plenty of settings to play around with in the menu which gives a good amount of configuration control. Navigation was mostly ok, although we did find ourselves accidentally switching the screen off a couple of times instead of exiting out of a section.
Panel and Backlighting
Backlight dimming at calibrated brightness setting (no PWM)
Above: backlight operation showing constant Direct Current voltage instead of PWM. Measured at calibrated brightness level
Brightness and Contrast
This section tests the full range of luminance (the brightness of the screen) possible from the backlight, while changing the monitors brightness setting in the OSD menu. This allows us to measure the maximum and minimum adjustment ranges, as well as identify the recommended setting to reach a target of 120 cd/m2 for comfortable day to day use in normal lighting conditions. Some users have specific requirements for a very bright display, while others like a much darker display for night time viewing or in low ambient light conditions. At each brightness level we also measure the contrast ratio produced by the screen when comparing a small white sample vs. a black sample (not unrealistic full screen white vs. full screen black tests). The contrast ratio should remain stable across the adjustment range so we also check that.
Graphics card settings were left at default with no ICC profile or calibration active. Tests were made using an X-rite i1 Display Pro Plus colorimeter. It should be noted that we used the BasICColor calibration software here to record these measurements, and so luminance at default settings may vary a little from the LaCie Blue Eye Pro report you will see in other sections of the review.
At the full brightness setting in the OSD the maximum luminance reached a high 371 cd/m2 which was a fair bit higher than the 300 cd/m2 max brightness spec from the manufacturer. There was a decent 324 cd/m2 adjustment range in total, so at the minimum setting you could reach down to a luminance of 47 cd/m2. This should afford you a low luminance option for working in darkened room conditions with low ambient light. A setting of ~18 in the OSD menu is suggested to return you a luminance as close to 120 cd/m2 as possible at default settings.
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. The average contrast ratio of the screen was measured at 3541:1 which was excellent thanks to the VA technology panel.
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 Plus 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 – confirms 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. Usually shown as a comparison against the common sRGB space
- Colour space coverage volumes – we also measure using a piece of software called ChromaPure the colour space (gamut) volumes produced by the backlight in comparison to the sRGB, DCI-P3 and Rec.2020 colour spaces. sRGB is the most commonly used colour space so it is important to have a decent coverage from the screen here. If the colour space is >100% sRGB then the screen can produce a wider colour gamut, often reaching further in to the wider gamut DCI-P3 (commonly used for HDR) and Rec.2020 reference spaces.
- 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 (static) – we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present
- dE average / maximum – we aim for 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:
Make sure that in the OSD and in your graphics card control panel the display is set to a full RGB mode, and not limited. We found that for some reason our NVIDIA control panel had defaulted to limited mode which massively impacts contrast ratio and performance. Out of the box the screen was set in the ‘warm’ colour temp preset mode and with a very bright 90% brightness which was uncomfortable to use for long periods. You will want to turn that down as with most screens. The colour balance felt pretty good out of the box and you could tell that the screen was using a wide gamut backlight, as the colours looks vivid and bright, especially greens and reds. The image did look a bit washed out though suggesting the gamma was too high. 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) extends a considerable way beyond the sRGB reference space (orange triangle), mostly in green and red shades. We measured using ChromaPure software a 120.6% sRGB gamut volume coverage which corresponds to 88.9% of the DCI-P3 reference and 63.8% of the Rec.2020 reference. This is a little under the specified 125% sRGB / 90% DCI-P3 although close enough. There is no sRGB emulation mode available on this screen unfortunately, so no way to reduce the colour gamut if you wanted to specifically work with smaller standard gamut content. The wider gamut here with more vivid and saturated colours is nice for gaming which is the screen’s primary target usage, but keep in mind the limitation if you are wanting to do any colour critical work with sRGB content.
Default gamma was recorded at a very high 2.8 average with a large 27% deviance from the target. This was with the screen set at the 2.2 gamma mode in the OSD. Thankfully there are some other gamma modes available in the OSD and we found a simple change to mode 2.0 delivered us a gamma far closer to our target and improved the image quality all round significantly. You can see we improved the default setup a lot by some simple optimal OSD settings in the next section. A factory calibration could have helped ensure a more reliable setup out of the box of course, although often gaming screens are set up in this way.
Luminance at the default high 90% brightness level was recorded at 331 cd/m2 which is a far too high for prolonged general use, you will need to turn that down. The black depth was 0.09 cd/m2 at this default brightness setting, giving us an excellent 3750:1 contrast ratio which is an obvious strength of this panel, and thanks to the use of VA technology. Colour accuracy measurements should be ignored here really as they are comparing the produced wider gamut display colours against an sRGB reference which will always lead to errors, not to mention the very high gamma that’s messing those up further. There was no sign of any colour banding when testing gradients which was good news, and only small amounts of gradation in darker tones evident.
Optimal Settings Pre-Calibration
We also measured the screen after adjusting only the OSD controls, to obtain the optimal setup without a full calibration, and without the use of an ICC correction profile. This represents what could be achieved through just simple changes to the monitor itself, and also what you could expect when working with content outside of an ICC profile managed workflow. The early stages of our calibration software helped identity these optimal OSD settings.
For this section we switched to the ‘User’ colour temp mode, which would allow us access to the RGB controls and therefore the ability to correct the white point which was now more closely met. We also changed to gamma mode 2.0 which as you can see delivered a gamma curve much closer to our 2.2 target (1% overall deviance average). The brightness adjustment also allowed us to reach a much more comfortable level. The contrast ratio was still excellent although had dropped a bit through the RGB and gamma corrections.
These optimal settings helped the screen look a lot better than out of the box, especially correcting the gamma and brightness. Further calibration and profiling below will help improve things even further in the next section.
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 Plus colorimeter was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.
The OSD settings were adjusted as shown in the table above, as guided during the calibration process and measurements. 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.
The default gamma curve of 2.8 had been improved to 2.2 average, correcting the very large 28% deviance we’d seen out of the box and leaving a minor 1% error. The white point was also now improved to 6502k which was great news, although out of the box there had been minimal deviance there. The brightness control adjustment had reduced the luminance to a comfortable level now and contrast ratio remained excellent thanks to the VA panel. Colour accuracy of the resulting profile was very good, with dE average of 0.5 and maximum of 1.4. LaCie would consider colour fidelity to be very good overall. Gradients remained mostly smooth with a small amount of banding introduced in darker tones.
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.
Setup 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. We have divided the table up by panel technology as well to make it easier to compare similar models. 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 some (gamma especially) are 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 poor, mainly because the gamma was far too high at an average of 2.8. That impacted many other aspects of the image. Thankfully this was simple to correct by changing to the 2.0 gamma mode, which brought about some noticeable improvements to the setup. This is the main thing that needs changing, as otherwise you have a good white point and certainly a very strong contrast ratio. This contrast far surpasses what is possible from IPS and TN Film panels and is a strength of the VA technology used here.
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Viewing Angles
Viewing angles of the screen were good overall, and a little better than some other modern VA panels we’ve tested. From a moderately wide side angle the image would become washed out and pale in appearance as you can see, getting more pronounced the wider that angle was. Vertically the washout was a little more noticeable but not terrible.
The GM27-CF has a Samsung VA panel and this had a bit better viewing angles than recent models featuring AU Optronics AMVA panels like the Asus ROG Swift PG35VQ and Asus ROG Strix XG438Q for instance, with a little less colour and gamma shift. The GM27-CF was quite comparable to the Samsung C27RG50, Samsung C49RG90 and Lenovo Legion Y44w-10 we tested recently for instance, which also feature Samsung VA panels. It appears that the viewing angles of Samsung VA panels are a little better than competing AU Optronics VA equivalents in general.
Users should also be aware that the panel exhibits the off-centre contrast shift which is inherent to the VA pixel structure. When viewing a very dark grey font for example on a black background, the font almost disappears when viewed head on, but gets lighter as you move slightly to the side. This is an extreme case of course as this is a very dark grey tone we are testing with. Lighter greys and other colours will appear a little darker from head on than they will from a side angle, but you may well find you lose some detail as a result. This can be particularly problematic in dark images and where grey tone is important. It is this issue that has led to many graphics professionals and colour enthusiasts choosing IPS panels instead, and the manufacturers have been quick to incorporate this alternative panel technology in their screens. We would like to make a point that for many people this won’t be an issue at all, and many may not even notice it. Remember, many people are perfectly happy with their TN Film panels and other VA based screens. Just something to be wary of if you are affected by this issue or are doing colour critical work.
On a black image from a side view there is very little glow from the panel, and the deep blacks and strong contrast ratio are still evident. You don’t get the same pale/white glow that IPS-type panels exhibit (example recently tested Asus TUF Gaming VG27AQ with IPS-type panel) which is a big plus for this panel technology, especially if you want to use the screen for night time gaming or movies in a darker room. There are some uniformity problems on this sample when viewed in this way, which is something we’d seen on other recent VA panels too including the very expensive ROG Swift PG35VQ. You can see some areas of backlight glow and blotchiness on this kind of test particularly at the top. Again these results were pretty similar to the recently tested Samsung C27RG50, Samsung C49RG90 and Lenovo Legion Y44w-10 which feature Samsung VA panels as well.
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 35 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
Luminance uniformity of the screen was moderate on our sample, with 60% of the screen within a 10% deviance of the centrally calibrated area. The bottom edge was a little darker than the upper areas of the screen where brightness dropped down to 99 cd/m2 in the most extreme example (-21%).
Backlight Leakage
We also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. There was a little bit of leakage from the top and bottom edges, with the most noticeable area being the bottom left hand corner. Overall though this was pretty minimal, and you had nice deep blacks thanks to the high contrast ratio VA panel.
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 GM27-CF feels a pretty big 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 0.311 mm pixel pitch, text is comfortable and easy to read natively, providing a still fairly 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. We would have preferred a full 1440p resolution on a 27″ screen like this to be honest, although it is primarily aimed at gaming. With the high 200Hz refresh rate in mind, it’s probably more realistic to be powering a 1920 x 1080 resolution than 2560 x 1440 anyway for those purposes. It’s just a shame when it comes to more general office work that the resolution is pretty low.
The curved format was ok on a screen this size, although not super-necessary given it’s not an ultrawide panel. A flat format would be just as comfortable on a 27″ screen we felt. The light AG coating of the VA technology panel is certainly welcome, and avoids any unwanted graininess to the image. The wide viewing angles provided by this panel technology on both horizontal and vertical planes, helps minimize on-screen colour shift when viewed from different angles. There is the typical VA off-centre contrast shift though which might crush dark grey details on darker content when viewed head on. So it’s not as well suited to colour critical work or photo editing as an IPS technology panel. But it is on the other hand much better than a TN Film panel.
The out of the box setup was more aimed at gaming, particularly with the inaccurate gamma curve (2.8 average). After a few simple OSD tweaks it offered decent setup though for kind of uses, with only minor deviance from our targets for gamma and white point and a strong contrast ratio thanks to the VA panel. One issue for general use is that the screen does not offer any sRGB emulation mode, it will only operate with the full gamut of the backlight (in this case 120.6% sRGB). This gives you more vivid and saturated colours which can look attractive for gaming and multimedia, but could present a problem if you’re working with standard sRGB gamut content. We would have liked to see an sRGB emulation mode available for those who are doing colour critical work or photo editing and working with this smaller colour space.
The brightness range of the screen was good, with the ability to offer a luminance between 371 and 47 cd/m2. This should afford you a decent enough range for darkened room conditions and low ambient light. A setting of 18 in the OSD brightness control should return you a luminance close to 120 cd/m2 out of the box. The brightness regulation is controlled via a flicker free backlight, without the need for 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 from the screen, even when conducting specific tests which can sometimes cause issues.
Spectral distribution graph showing calibrated mode at 6500k
Spectral distribution graph showing Low Blue Light set at 50
Spectral distribution graph showing Low Blue Light set at 100
There are some low blue light filter settings available in the OSD menu as well as quick access to turn this on (at 50% level) and off via one of the control buttons. There are 4 modes available at 25, 50, 75 and 100. The colour temperature gets warmer as you increase the setting, and the blue light output is reduced as you do so. At 50% the white point was 5282k and felt pretty comfortable to use. At 100% the colour temp is now 4565k and looks too warm really, unless you are perhaps doing a lot of text work.
Unusually for a modern display there are no USB ports provided on this screen. There are no other extras like motion sensors or card readers on this screen which are sometimes useful for office-type uses. There is a reasonable range of ergonomic adjustments from the stand with tilt, height and swivel offered. There is also VESA 75mm mounting capabilities for those who want to mount the screen instead.
Responsiveness and Gaming
The screen uses overdrive technology to boost pixel transitions across grey to grey changes as with nearly all modern displays. The part being used is a Samsung LSM270HP09 SVA (VA-type) technology panel with a custom backlight. Have a read about response time in our specs section if you need additional information about this measurement.
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.
Response Times and Refresh Rate
There’s various things you need to consider when it comes to response times and gaming, particularly on a display with high refresh rate support. Gaming screens invariably give you a control for the overdrive impulse in the OSD menu which can help you tweak things, but response time performance and overshoot levels can vary depending on the active refresh rate. This behaviour is often different depending on whether the screen is a traditional G-sync screens (with hardware module) or whether it’s an adaptive-sync screen as well, and not all screens behave in the same way. We always try to test each variable in our reviews but the key considerations you need to make are:
- Performance at 60Hz – this is important if you want to use an external games console (or other device like a Blu-ray player etc) which typically run at 60Hz. Response time performance may well be different than at the higher refresh rates supported, and you may need a different overdrive setting for optimal experience.
- Performance during VRR (Variable Refresh Rate) – bearing in mind that the refresh rate will fluctuate anywhere from 1Hz up to the maximum supported by the screen (e.g. 1 – 144Hz on a 144Hz display). It’s important to understand if the response times and overshoot will vary as the refresh rate changes. There may be a need to switch between different overdrive settings in some cases, depending on your usually attained refresh rate output and graphics card capability. This can sometimes become fiddly if your refresh rates fluctuate a lot, especially between different games, so it’s always easier if you can leave a display on a single overdrive setting which is suited to the whole range. Some screens also feature “variable overdrive” which helps control the response times and overshoot depending on the active refresh rate. This is particularly apparent with traditional G-sync module screens.
- Performance at fixed refresh rates including maximum – this is important for those who have a powerful enough system to consistently output a frame rate to meet the max refresh rate capability of the screen. They may want to run at max refresh rate without VRR active, or even is VRR is active they may know they will be consistently at the upper end of the range. Many gaming screens show their optimal response time performance at the maximum refresh rate. Knowing the performance at high fixed refresh rates may also be applicable if you want to use any added blur reduction backlight which typically operate at a fixed refresh rate.
- Whether the response times can keep up with the frame rate – you will also want to consider whether the response times of the panel can consistently keep up with the frame rate. For instance a 144Hz screen sends a new frame to the display every 6.94ms, so the pixel response times need to ideally be consistently and reliably under this threshold. If they are too slow, it can lead to added blurring in practice and sometimes make the higher refresh rates unusable in real life. We consider this in our analysis.
We carried out some initial response time measurements and visual tests in each of the overdrive settings, and at a range of refresh rates. The overdrive control is available in the OSD menu via the ‘Response Time Override’ option. There are 4 levels available – Off, Normal, Fast and Fastest. Oddly they are in a weird order in the menu here.
Increasing Refresh Rate
We quickly established that using even the maximum ‘Fastest’ mode was fine on this screen. It didn’t introduce any obvious halos or overshoot artefacts in motion tests and offered some improvements in motion clarity and blurring compared with the lower modes. We tested the response times at a range of refresh rates from 60Hz up to the maximum native 165Hz. You can see that the screen actually uses variable overdrive here which is good news, a feature normally reserved for Native G-sync hardware screens and rarely used on adaptive-sync displays as it is quite hard to get working and configured. The response times therefore improved as the refresh rate was increased, helping them to keep up better with the higher frame rate demand which was good news. There was very little measured overshoot in any of these modes here, although it increased a little as refresh rate (and overdrive impulse) was increased. We will do some further measurements in a moment to show a fuller view.
The response times overall were very good for a VA panel, with 5.1ms G2G measured at 165Hz for instance if we ignore the usual problematic slow black > grey transitions that plague most VA panels and are shown along the top row of the tables above. While other transitions were sped up nicely to support the higher refresh rates, these black > grey transitions were still an issue as with most VA panels and leads to some black smearing on moving content, particularly on darker backgrounds. The higher refresh rates did improve the motion clarity significantly though compared with 60Hz, as these higher refresh rates have a direct impact on how the human eye perceives motion on LCD displays.
Overclocked 200Hz Refresh Rate
You don’t have to do anything on the screen to enable the 200Hz overclocked mode, it should just be available within your graphics card control panel. This pushes the native 165Hz panel a little more beyond its default. We found this to work mostly fine, although we did experience on occasion enabling it where we lost picture, and as always with these overclocked modes the results may vary from system to system. From our response time measurements you can see that for this overclocked refresh rate range the variable overdrive seems to stop, and the response times were now a bit slower than they had been at 165Hz. Perhaps this was deliberate to prevent overshoot becoming too high, or perhaps it was difficult on the out-of-standard panel specifications.
The extra frame rate can help with motion clarity but we found in practice that the slower response times led to increased smearing and blurring and offset that improvement you got in frame rate. We felt on balance that the 165Hz mode was optimal. They both looked visually quite similar with the slight edge going to 165Hz overall. That offered better response times and will also be a lesser drain on your system resources to run, allowing you to instead focus on pushing details and settings in your games. The 200Hz mode worked here, but didn’t really offer any benefits.
Above are some pursuit camera photos of the screen running at 165Hz and the overclocked 200Hz mode. This is designed to capture the motion blur as you would perceive it with the naked eye in real terms. You can see fairly clearly the black smearing caused by the particularly slow black > grey VA pixel transitions. This is most noticeable on darker backgrounds at the top where the black colour is changing to a dark shade. It is less of an issue on paler backgrounds though and lighter content as those response times are a bit better. Some VA panels will show more black smearing on those medium shades too, but it was fairly low here on the GM27-CF.
The middle row demonstrates quite nicely what we’ve said about 165Hz vs. 200Hz. The overall motion clarity and sharpness of the moving image felt quite similar, but you can see the colours smear a little bit more at 200Hz as the response times are less able to keep up with the frame rate. You get a bit more yellow smearing behind the cabin of the UFO and the black smearing also increases a little on the red body of the UFO because the slow black > grey response times are even less capable of keeping up than they were at 165Hz.
Variable Refresh Rates (VRR)
The screen supports VESA Adaptive-sync and so can support variable refresh rates from both AMD FreeSync and NVIDIA G-sync systems. The VRR range supported is between 48 and 200Hz maximum. The screen has not currently been certified by NVIDIA under the ‘G-sync Compatible’ scheme. It does fall under AMD’s new FreeSync certifications though, to the ‘Premium’ level in fact. This includes support for Low Framerate Compensation (LFC).
The support for G-sync and FreeSync will be very useful given the significant system demands of running a screen at 1920 x 1080 resolution and up to 200Hz refresh rate. It was of course very good to see it included here. You might also want to read our newly updated article about Variable Refresh Rates here for more information.
Detailed Response Times
To achieve the optimal performance from the GM27-CF we would recommend sticking with the ‘Fastest’ response time setting. This looked a bit clearer and sharper than the lower modes, and didn’t introduce anything too noticeable in the way of overshoot or halos. While the screen will happily run at 200Hz we did feel that 165Hz was probably the optimal mode here, as the response times were a bit better, it looked visually slightly better and will also be less of a drain on your system resources allowing you to focus on game settings and detail instead. It was great to see the use of variable overdrive for refresh rates up to 165Hz as well, helping to optimise performance and keep up with the increasing frame rates. This also meant you could stick with a single setting for all refresh rates and for VRR, making it much easier than many other adaptive-sync screens. The higher refresh rates supported by the screen really do help improve motion clarity and reduce perceived blur, making the screen far better for gaming than 60Hz-only models.
Recommended Settings
| Optimal Refresh Rate | 165Hz |
| Optimal Overdrive Setting (for above) | Fastest |
| Optimal Overdrive Setting for 60Hz | Fastest |
| Optimal Overdrive Setting for VRR | Fastest |
Detailed Measurements at 165Hz, Overdrive = Fastest
We carried out some further response time measurements at 165Hz. We measured an average 7.3ms G2G response time in this mode which was good overall for a VA panel, and that includes the few particularly slow black > grey transitions along the top row that are nearly always a problem for VA panels. If we were to ignore those problem transitions then the average response time would be 4.7ms G2G which was impressive and very good for a VA technology screen. The best case even reached down to 1.4ms G2G which was excellent, albeit introducing some moderate to high overshoot in doing so.
There were moderate levels of overshoot measured at this Fastest mode, although there were few obvious overshoot artefacts in practice. You might see a bit of overshoot in some cases, but we felt this mode was still useable. That bit of overshoot is the trade-off here for some pretty decent response times in general. In fact 76.7% of them were fast enough to keep up with the 165Hz refresh rate which was pleasing (83.3% with a 1ms leeway included), meaning there was not much additional response time smearing caused by their inability to keep up with the frame rate. The few problem black > grey pixel transitions meant that you got the fairly typical VA technology “black smearing” on moving content, particularly on darker backgrounds. This was at a modest level (60% in our rating, explained a bit more below).
Detailed Measurements at 165Hz, Overdrive = Fast
For reference we also took further measurements at 165Hz but with the overdrive mode set to the more modest “fast” level. This eliminated pretty much all the overshoot measured in the “fastest” mode, but the response times were not as fast. There was a 9.6ms G2G average, 7.0ms if we ignored the particularly slow black > grey transitions and this meant it was less capable at keeping up with the high refresh rate. We felt the “fastest” mode was optimal on this display.
Refresh Rate Compliance
In a new section for our reviews we look at the response time behaviour across the range of supported refresh rates and consider whether they are sufficient to keep up with the frame rate demands of the screen. The grey line on the graph shows the refresh rate threshold, that being the average G2G response time that the panel needs to be able to achieve to keep up properly with the refresh rate and frame rate. For instance at a 60Hz refresh rate the response times need to be consistently and reliably under 16.67ms, while at 144Hz refresh rate the response times ideally need to be under 6.94ms to keep up with the frame rate demands. If they are not then this can lead to some additional smearing and blurring on moving content as the pixels can’t keep up. For these tests we will plot the average G2G figure at a range of measured refresh rates, while operating at the optimal overdrive control.
The table to the right then explains whether that overdrive control needs to be adjusted by the user depending on the refresh rate (not ideal), or whether adaptive overdrive is utilised to keep things simple. Ideally you’d want to be able to stick with a single mode for all refresh rates especially when you consider how these will vary during VRR. We also include a measurement of the % of the overall response time measurements that were within the refresh rate, as well as a slightly more lenient measurement of how many were within the refresh rate window within a 1ms leeway.
It’s a little tricky to plot these graphs for VA panels as if you consider the overall average response time it gets affected by the few particularly slow black > grey transitions that cause problems on this technology. To give a fairer picture here we have used the average G2G figure if those few problem transitions were ignored, but keep in mind that those are still there and cause some black smearing in moving content as on most VA panels. You can see that overall the compliance with the refresh rate was good on this panel. Variable overdrive helped ensure that response times were improved as the refresh rate increased, so that the panel could keep up with the higher frame rate demands. That’s rare to see used on an adaptive-sync screen so it was great to see it offered here. The overshoot did creep up a bit as the refresh rate increased, but never reached horrible levels we didn’t feel. This was at the ‘fastest’ overdrive setting as well, and in practice there was low levels of halos and artefacts we felt.
The only issue is that for the overclocked refresh rate range (200Hz mode) the variable overdrive seems to not be used, and instead the response times slow a little bit and result in a little bit of extra smearing on moving content because they can’t quite keep up. Overall this offsets the small improvement you get in motion clarity from the increased refresh rate sadly, so we felt 165Hz was probably optimal here. Perhaps this response time behaviour is deliberate as overshoot was getting too high, or perhaps it was only used for the native refresh range up to 165Hz so as not to cause additional problems with out-of-panel-spec overclocked refresh rates. Nevertheless overall the response times were decent on this screen and could keep up well with the high refresh rates, apart from that typical VA black smearing you will see.
Gaming Comparisons
We have provided a comparison of the display against many other gaming screens we have reviewed in a similar size range and across a range of panel technologies. This table is now split by panel technology to make life a bit easier and for quicker comparison.
The GM27-CF had decent overall response times for a VA panel, being able to keep up with the high refresh rates well, and delivering good motion clarity. There was the usual VA black smearing which was a shame, but something you generally have to live with on any VA monitor. Overshoot levels were a bit higher than other VA panels compared here, but we had pushed up to the maximum “Fastest” overdrive mode which we felt looked the best, and to be fair the moderate levels of overshoot didn’t appear too noticeable in practice. The TN Film and IPS models are faster options for gaming and don’t suffer from those slow black > grey transitions. Although you do then give up things like the much higher contrast ratio that VA tech can offer.
VA Technology Display Comparison
To try and give a more direct comparison between the different VA models we’ve tested we have produced the following new comparison table below. Each screen is set to the optimal response time setting and refresh rate from our reviews.
You can see that the GM27-CF is fairly typical in its level of black smearing at 60%, sitting somewhere in the middle of the VA models we’ve tested to date. The response times were very good though for a VA panel (ignoring the slow black > grey transitions here keep in mind) although some moderate overshoot was the trade-off to achieve that.
Additional Gaming Features
- Aspect Ratio Control – the screen offers a range of aspect ratio controls from the menu including wide screen, 4:3, 1:1 pixel mapping and an ‘auto’ mode. The default 16:9 aspect ratio of the screen should be common anyway, but this gives a good range of support for other non-native inputs.
- Preset Modes – There aren’t really any preset modes on this screen apart from one called simply “game”. This has quite a few settings locked and unavailable though so you will probably be better sticking to the standard mode and calibrating it to your liking.
- Additional features– there is a crosshair graphic option in the menu, but no other gamer-oriented features to note.
Lag
Read our detailed article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. The screens tested are split into two measurements which are based on our overall display lag tests and half the average G2G response time, as measured by our oscilloscope. The response time element, part of the lag you can see, 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 of the lag you would feel from the display. We also classify each display as follows:
Lag Classification
- Class 1) Less than 8.33ms – the equivalent to 1 frame lag of a display at 120Hz refresh rate – should be fine for gamers, even at high levels
- Class 2) A lag of 8.33 – 16.66ms – the equivalent of one to two frames at a 120Hz refresh rate – moderate lag but should be fine for many gamers. Caution advised for serious gaming
- Class 3) A lag of more than 16.66ms – the equivalent of more than 2 frames at a refresh rate of 120Hz – Some noticeable lag in daily usage, not suitable for high end gaming
The total lag measured was an impressive 4.67 ms total. The pixel response times should account for most of that display lag at around 2.35ms, and so we can say that there appears to be around 2.32ms of signal processing lag on this screen which is very low. A solid result from this display and making it suitable for fast and competitive gaming.
Movies and Video
The following summarises the screens performance for videos and movie viewing:
| Category | Display Specs / Measurements | Comments |
| Size | 27″ widescreen | Fairly typical for a desktop monitor nowadays and smaller than TV’s by a lot |
| Aspect Ratio | 16:9 | Well suited to most common 16:9 aspect content and input devices |
| Resolution | 1920 x 1080 | Can support native 1080p content only, but not Ultra HD natively |
| HDCP | Yes v2.2 | Suitable for encrypted content |
| Connectivity | 1x DisplayPort 1.2, 1x HDMI 2.0 and 1x HDMI 1.4 | Useful additional 2x HDMI input for external Blu-ray players or games consoles |
| Cables | DisplayPort only | No HDMI cable provided in the box |
| Ergonomics | Tilt, height. swivel | Good set of adjustments suitable to positioning the screen in a variety of angles for different viewing positions. Tilt doesn’t move backwards very much and swivel is a bit stiff |
| Coating | Light Anti-glare | Provides clear image with no graininess, but avoids unwanted reflections of full glossy solutions |
| Brightness range | 47 – 371 cd/m2 | Good adjustment range offered including a fairly high max brightness and decent darkened room adjustment range. Backlight dimming is also free from PWM |
| Contrast | 3074:1 after calibration | Strong contrast ratio thanks to VA panel technology, allowing for deeper blacks and better shadow detail than competing TN Film and IPS panel options |
| Preset modes | Movie | There is a movie mode available which has a lot of locked settings, but may be useful if you want to set something a bit brighter for movie viewing for instance |
| Response times | 7.3ms G2G moderate overshoot at 165Hz 12.6ms G2G at 60Hz with low overshoot | Response times are mostly very good for a VA panel especially at the higher refresh rates. There is the typically slow black > grey VA technology transitions and some black smearing on moving content as a result, particularly darker content. At 60Hz the response times are slower but adequate, with overshoot reducing as a result |
| Viewing angles | Good | Not as wide as IPS, and fairly typical for a VA panel. Free from the pale “IPS-glow” on dark content when viewed from an angle that you see on IPS panels but do suffer from the black crush when viewed head on. May lose some detail in darker scenes as a result |
| Backlight bleed | Some bleed | Some bleed on our sample from the top and bottom edges, and some clouding in the bottom left hand corner. Nothing severe, and will vary from sample to sample |
| Audio | Headphone output and 2x 3W speakers | Basic integrated speakers on this model which might be ok for the occasional YouTube clip or mp3 and are reasonable quality. A headphone jack is also provided |
| Aspect Ratio Controls | Wide screen, 4:3, 1:1 and auto modes | The default 16:9 aspect ratio is likely to serve most needs here anyway but there’s a good range of additional options if needed |
| PiP / PbP | Both supported | Various settings and modes available |
| HDR support | Not supported | This model cannot even accept an HDR input signal |
Conclusion
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It’s always nice to welcome a new manufacturer to the monitor segment, especially one who has been around the wider PC market for a long time and are well known. Cooler Master have done a nice job with their first venture and the 27″ GM27-CF offered some solid performance for gaming. The high refresh rate was welcome as always and delivered significantly improved motion clarity compared with lower refresh rate screens. This high refresh rate was accommodated well by the panel and response times. We were pleasantly surprised to see variable overdrive being used, allowing solid response time performance and minimal noticeable overshoot all the way up to 165Hz. The overclocked 200Hz mode didn’t really offer anything extra sadly, but 165Hz should still be attractive to many gamers. The availability of adaptive sync to support VRR from both NVIDIA and AMD systems was also very good, and input lag was very low too. The choice to use a VA panel might not be to everyone’s liking, and this tech has it’s issues with response times in some cases, with the common black smearing still being present. The rest of the response times were very good though for a panel of this type. You do of course also get very high contrast ratios and good all round performance with decent colours and viewing angles too.
Away from gaming the default setup could have been better, with a high gamma being the main issue and skewing everything else as a result. Thankfully there’s a decent array of OSD settings available so this was simple enough to correct to a good level even without a calibration device. The screen is missing an sRGB emulation mode though which leaves you restricted to the native wide gamut – fine for gaming and multimedia we’re sure, but a bit limiting if you wanted to do any colour critical or photo work. The stand was also a little restrictive in its adjustments and design we felt, and while Cooler Master had included a few nice extras like PiP/PbP, integrated speakers and simple lighting on the back, they did then miss out on other common features like USB ports and more menu preset modes and gamer options which was a shame.
Overall we felt this was a very solid first screen from Cooler Master and if you’re looking for a 27″ VA gaming screen this is a good option. It is available in some regions now including from Amazon (affiliate link).
| Pros | Cons |
| High refresh rate support and adaptive sync for VRR from NVIDIA and AMD systems | Missing an sRGB emulation mode if you wanted to work with a smaller colour space |
| Good response times for a VA panel overall, including variable overdrive support | Stand is a bit limiting in functionality and design |
| High contrast ratio and common VA technology benefits | Still some common VA black smearing from some problem pixel response times |
| Check Availability and Pricing – Affiliate Links |
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| Amazon |
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