KOORUI S2741LM

Introduction

KOORUI are a brand you may be less familiar with. Part of HKC Corporation Ltd, they are looking to expand their monitor range into more markets this year, with launches planned across their HKC, KOORUI and ANTGAMER brands. We’ve recently published an article to introduce you to these 3 brands, highlighting some of their core displays and some exciting upcoming models we know about, as well as telling you about their global expansion plans. For now, we’ve got one of their flagship KOORUI brand models with us for review.

The S2741LM is a 27″ sized screen with an IPS-type panel and a 3840 x 2160 “4K” resolution. It features an impressive 1,152-zone Mini LED backlight, offering high-end HDR capabilities for the LCD market, including certification under the VESA DisplayHDR 1400 tier. The 4K panel offers a decent 160Hz refresh rate as well, with the monitor supporting a dual-mode function that offers a boost to 320Hz when dropping to a lower 1080p resolution, useful for certain faster gaming situations where you might want to prioritise speed over image detail.

It’s also got a decent range of modern features including a USB type-C connection with 90W power delivery, KVM switch function and PiP/PbP support for handling multiple inputs. We’ve reviewed several Mini LED monitors in recent months and it’s good to see another brand choice available, at a competitive price point as well. Let’s see how it performs in our testing.

Key Specs

• 27″ flat format IPS-type LCD panel (AU Optronics M270QAN07.6)
• 3840 x 2160 “4K” native resolution
• 160Hz native refresh rate
• Dual-mode function for 320Hz at 1080p
• 1,152-zone Mini LED backlight
• VESA DisplayHDR 1400 tier certification with >1400 nits peak brightness (HDR)
• Wide colour gamut covering 99% sRGB, 99% Adobe RGB, 98% DCI-P3
• Video connectivity: 1x DisplayPort 1.4 (with DSC), 2x HDMI 2.1, 1x USB type-C (with 90W power delivery)
• Other connectivity: 2x USB-A data ports, 1x headphone jack
• Special features: KVM switch, PiP/PbP support
• Fully adjustable stand with tilt, height, swivel and rotate functions

Design and Features

The screen comes in a black and dark grey design with a 3 side “borderless” panel. There is a very thin black plastic edge around the sides and top, but with a black panel border there is a total edge thickness of ~8.5mm. The bottom edge has a standard bezel which measures ~16mm thick and is finished in a matte black plastic, with a KOORUI logo in the middle but no other writing or buttons visible.

The rear of the screen is encased in a smooth matte black plastic and there’s a circular RGB lighting feature in the centre around where the stand attaches. The stand has a quick release mechanism and can be removed in favour of VESA 100 x 100mm mounting if you’d prefer. A detachable plastic section hides some of the cables and connections.

There’s a full range of ergonomic adjustments offered from the stand with tilt, height, swivel and rotate. They are all smooth and easy to use and the stand adjustments felt of decent quality, offering a stable base for the screen with only a little wobble when you move it around.

There’s a good range of connectivity options available here as well with 1x DisplayPort 1.4 (with DSC), 2x HDMI 2.1 and 1x USB type-C (with DP Alt mode, data and 90W power delivery). There’s also 2x USB-A data ports and a headphone jack on the back of the screen. It would have perhaps been nice to see some easy-access ports on the side of the screen.

A KVM switch function is available to support multiple connected systems from a single keyboard and mouse, and a range of PiP and PbP modes are available for supporting multiple video inputs on the screen. That’s got pretty much everything you would expect or want from a modern monitor for connectivity which is good.

OSD menu

The on-screen menu is controlled through a joystick toggle on the bottom edge of the screen. This provides quite and intuitive access around the menu, although it’s not always easy to find where this is on the bottom of the screen when you’re first using the screen. There’s a separate single button which switches the dual-mode function as well.

One minor annoyance for our testing was that there’s no settings in the menu to control the position or timeout for the menu itself, which is a bit of a pain when measuring different modes. Having to start from the beginning each time you open the menu was also a bit annoying and there’s limited customisation of the quick access options too. Probably not something that’s going to bother most normal users though unless you’re having to delve in to the menu regularly.

OSD Menu
Joystick toggle controller
Quick and snappy
Intuitive to use
User updatable firmware
Software application

There doesn’t appear to be any firmware updates provided for the screen on their website, but we know that these are supported as we carried out an update for this review which was provided by KOORUI.

Testing Methodology Explained (SDR)

Performance is measured and evaluated with a high degree of accuracy using a range of testing devices and software. The results are carefully selected to provide the most useful and relevant information that can help evaluate the display while filtering out the wide range of information and figures that will be unnecessary. For measurement, we use a UPRtek MK550T spectroradiometer which is particularly accurate for colour gamut and colour spectrum measurements. We also use an X-rite i1 Pro 2 Spectrophotometer and a X-rite i1 Display Pro Plus colorimeter for various measurements. Several other software packages are incorporated including Portrait Displays’ Calman color calibration software – available from Portrait.com.

We measure the screen at default settings (with all ICC profiles deactivated and factory settings used), and any other modes that are of interest such as sRGB emulation presets. We then calibrate and profile the screen before re-measuring the calibrated state.

The results presented can be interpreted as follows:

• Gamma – we aim for 2.2 gamma which is the default for computer monitors in SDR mode. Testing of some modes might be based on a different gamma but we will state that in the commentary if applicable. A graph is provided tracking the 2.2 gamma across different grey shades and ideally the grey line representing the monitor measurements should be horizontal and flat at the 2.2 level, marked by the yellow line. Depending on where the gamma is too low or too high, it can have an impact on the image in certain ways. You can see our gamma explanation graph to help understand that more. Beneath the gamma graph we include the average overall gamma achieved along with the average for dark shades (0 black to 50 grey) and for lighter shades (50 grey to 100 white).
  
  
• RGB Balance and colour temperature – the RGB balance graph shows the relative balance between red, green and blue primaries at each grey shade, from 0 (black) to 100 (white). Ideally all 3 lines should be flat at the 100% level which would represent a balanced 6500K average colour temperature for all grey shades. This is the target colour temperature for desktop monitors, popular colour spaces like sRGB and ‘Display DCI-P3’ and is also the temperature of daylight. It is the most common colour temperature for displays, also sometimes referred to as D65. Where the RGB lines deviate from this 100% flat level the image may become too warm or cool, or show a tint towards a certain colour visually. Beneath this RGB balance graph we provide the average correlated colour temperature for all grey shades measured, along with its percentage deviance from the 6500K target. We also provide the white point colour temperature and its deviance from 6500K, as this is particularly important when viewing lots of white background and office content.
  
  
• Greyscale dE – this graph tracks the accuracy of each greyscale shade measured from 0 (black) to 100 (white). The accuracy of each grey shade will be impacted by the colour temperature and gamma of the display. The lower the dE the better, with differences of <1 being imperceptible (marked by the green line on the graph), and differences between 1 and 3 being small (below the yellow line). Anything over dE 3 needs correcting and causes more obvious differences in appearance relative to what should be shown. In the table beneath the graph we provide the average dE across all grey shades, as well as the white point dE (important when considering using the screen for lots of white background and office content), and the max greyscale dE as well.
  
  
• Luminance, black depth and contrast ratio (static) – measuring the brightness, black depth and resulting contrast ratio of the mode being tested, whether that is at default settings or later after calibration and profiling. We aim for 120 cd/m² luminance which is the recommended luminance for LCD/OLED desktop monitors in normal lighting conditions. Black depth should be as low as possible, and contrast ratio should be as high as possible.
  
  
• Shadow detail – this is evaluated with the screen configured to a 200 nits white luminance for consistency between different monitors, and viewed in a dimly lit room. This first 16 greyscale shades are measured using our UPRTek MK550T spectro device (0.002 nits lower limit) for shades near-black, and the results are plotted on a graph relative to a target gamma curve (usually 2.2 gamma). Where the measurement line crosses the 0.01 nits point on the Y-axis is typically the visual threshold for where we would start to be able to detect luminance compared with black (0.00 nits). We combine these objective measurements with visual tests using a grey shade test pattern to determine the first visible shade, and then rank the shadow detail performance accordingly.
  
  
• Gamut coverage – we provide measurements of the screens colour gamut relative to various reference spaces including sRGB, DCI-P3, Adobe RGB and Rec.2020. Coverage is shown in absolute numbers as well as relative, which helps identify where the coverage extends beyond a given reference space. A CIE-1976 chromaticity diagram (which provides improved accuracy compared with older CIE-1931 methods) is included which provides a visual representation of the monitors colour gamut coverage triangle as compared with sRGB, and if appropriate also relative to a wide gamut reference space such as DCI-P3. The reference triangle will be marked on the CIE diagram as well.
  
  
• dE colour accuracy – a wide range of colours are tested and the colour accuracy dE measured. We compare these produced colours to the sRGB reference space, and if applicable when measuring a wide gamut screen we also provide the accuracy relative to a specific wide gamut reference such as DCI-P3. An average dE and maximum dE is provided along with an overall screen rating. The lower the dE the better, with differences of <1 being imperceptible (marked by the green area on the graph), and differences between 1 and 3 being small (yellow areas). Anything over dE 3 needs correcting and causes more obvious differences in appearance relative to what should be shown. dE 2000 is used for improved accuracy and providing a better representation of what you would see as a user, compared with older dE methods like dE 1994, as it takes into account the human eye’s perceptual sensitivity to different colours. 

Brightness and Contrast

These results were with local dimming turned OFF in SDR mode.

The screen offers a very wide adjustment range for the backlight with a maximum SDR luminance measured at 654 nits which was very high, and exceeded the spec of 550 nits considerably. At the bottom end of the adjustment the screen can reach a nice low 27 nits luminance as well, which should be perfectly adequate for using the screen in darker room conditions.

The IPS-type panel delivers a typical IPS contrast ratio of ~1187:1 average, which remains consistent across the brightness adjustment range. You can find higher contrast ratios from VA-type LCD panels, and of course from OLED technology, and this is a fairly standard result in that area for an IPS-type panel and expected.

Local Dimming (SDR)

The local dimming setting is available in SDR mode as well as in HDR, meaning you can enable the Mini LED backlight to enhance your overall contrast if you want in certain situations. There’s 3 settings available – low, medium and high.

The luminance figures shown here for a 10% APL test are if you also push the brightness setting up to maximum setting, and the black depth improves only a small amount as you move up to the low and medium settings with some moderate improvements in maximum contrast observed. When you move up to the high setting, blacks look noticeably darker and you get the most significant improvements in overall possible contrast. The Mini LED backlight is capable of dimming the darker parts of the screen with a good level of control thanks to the 1,152 dimming zones and haloing was at low levels on this screen.

If we examine the brightness capability in the low and high modes a bit more (medium just sits in the middle), we can see that both modes behave similarly for low APL tests, representing small highlights in dark content where the luminance is dimmed to help reduce haloing and blooming around those small highlights. That’s a common and sensible practice on a Mini LED monitor and we’ve seen the same thing on other recent Mini LED monitors we’ve tested. All the local dimming modes can reach slightly higher maximum luminance levels for higher APL scenes than the ‘off’ mode as well, by around 75 nits or so.

We’d recommend only enabling local dimming though for gaming, multimedia and dynamic content, not for static and general usage as there’s some variation to gamma and colour temp in certain situations otherwise. Most significant is the variation for small highlights due to the blooming algorithms and again this is normal for Mini LED screens. This isn’t the kind of thing you should notice during gaming and multimedia though.

It would have been helpful to be able to set the local dimming setting to one of the menu quick access shortcuts, but unfortunately that’s not possible so you have to dig through several layers of the menu to turn it off and on when you want. Note that the local dimming control is remembered independently for HDR mode so you don’t have to turn it on each time you activate HDR thankfully.

Blooming levels seemed low from a head-on viewing position in our testing and the Mini LED backlight performed very well. From an off-angle you will see more noticeable halos and blooming due to the IPS glow inherent to this panel technology, and so it is best viewed from a head on viewing position when using local dimming and viewing darker content. VA-type panels fare better in this regard due to their higher native panel contrast ratio and less off-angle glow.

Haloing and blooming seemed to be a little less than the competing KTC M27P6 model which we tested side by side against this KOORUI model, with a slightly improved black depth and reduce blooming. Although on the flip side the KTC model pushed maximum contrast ratio a little higher in the equivalent brightness mode during SDR (when set to ‘low’ local dimming).

SDR Performance

The screen comes out of the box in the ‘standard’ scenario mode with a low brightness setting of 7, but full access to adjust the brightness, contrast, gamma and colour controls. By default there is a nice accurate gamma with an adjustment near black which improves shadow detail nicely (measured more a bit later). The greyscale was pretty good too with a minor deviance of only 2 – 4% from our target.

The screen has a very wide native gamut, extending a considerable way beyond the sRGB reference with ~138% relative coverage measured. This leads to the expected over-saturation of red and green colours especially, and results in a poor accuracy for sRGB colours. That is to be expected on any wide gamut screen and we will look at ways to more accurately work with sRGB / SDR content in a moment.

The colour space is closer to the DCI-P3 wide gamut reference, but still extends a fair bit beyond that space (~110% relative coverage), and so DCI-P3 colour accuracy is only moderate natively. There is at least good absolute coverage for the DCI-P3 and Adobe RGB colour spaces should you want to work with either, but we will need a good way to clamp the wide native colour space back closer to those targets for more accurate performance.

Colour Space Emulation Modes

The screen provides 3 different emulation modes via the ‘Scenario mode’ menu, for sRGB, DCI-P3 and Adobe RGB. When using these presets you still have access to adjust the brightness and contrast settings, which is good news as like in the default mode the brightness is turned down very low out of the box (setting = 8). You’ll be able to adjust that to suit. You lose access to the colour temp settings, RGB channels and gamma settings though which is a shame for those who might like to adjust things, and we will be at the mercy of KOORUI’s configuration here.

• sRGB
• DCI-P3
• Adobe RGB

sRGB

DCI-P3

Adobe RGB

The sRGB emulation mode offers good overall gamma accuracy which remains close to 2.2 average in our measurements, with the Adobe RGB mode showing a little more variation than the other two modes near black where gamma is too high, and that causes some loss of shadow detail and some black crush (more in the following section on that).

The RGB balance is also pretty good in each mode, being close to the 6500K target although a little too warm in each mode. Contrast ratio remains consistent in each mode at ~1200:1, although the default luminance is low as brightness is only set to 8% in the menu. You can change that though to suit your requirements and user environment thankfully.

• sRGB
• DCI-P3
• Adobe RGB

sRGB

DCI-P3

Adobe RGB

Each preset mode offers very good clamping of the native colour space back to the target gamut, cutting down the over-coverage you see in the native ‘standard’ mode. This results in much better colour accuracy for the target colours which is great news. Each mode is well configured and useable for working with different target colour spaces, whether that’s sRGB for general SDR content, DCI-P3 for HDR content or Adobe RGB for photography applications.

Shadow Detail

We also tested the near-black shadow detail which can sometimes be a challenge on any monitor, especially on IPS-type panels which have a weaker black depth than competing VA and OLED panel technologies. For these tests screen was configured to 200 nits white luminance, and we tested the screen in several colour space modes.

• Default and sRGB
• DCI-P3 and Adobe RGB

Default and sRGB

DCI-P3 and Adobe RGB

Shadow detail performed best in the native ‘standard’ preset mode, where there is an adjustment to the gamma curve near black to bring out more detail and help overcome the weaker IPS technology black point. The first visible greyscale shade was RGB 1 in that mode which was excellent.

Unfortunately the performance was worse in the emulation modes. In sRGB mode the luminance tracked the target gamma accurately, but because of the weaker black point of the IPS LCD panel, this means the first few shades were crushed to black, and the first visible greyscale shade was RGB 5.

This was worse in the DCI-P3 and Adobe RGB emulation modes where the luminance doesn’t really start to increase until RGB 8 or 9. That left us with poor shadow detail in those modes unfortunately. IPS panels often struggle with darker content due to their limited contrast ratio and comparatively weak black point so it’s not a major surprise, and it’s tricky unless you specifically alter the gamma near black like they have done in the standard mode. That is strictly less “accurate” if you do that, but it can help improve shadow detail so there’s a balance there to be considered by manufacturers.

‘Dark Field Bright Effect’ control

KOORUI provide a setting in the menu called ‘Dark Field Bright Effect’ which acts like a black stabilizer / shadow boost control. There’s a slider which can be increased to brighten darker content and we tested this in the sRGB mode.

Moving it up just 1 setting helped a little, and the first visible greyscale shade was now RGB 4 instead of RGB 5, with darker content being a little easier to see. The setting does raise the black point of the panel a little though, dropping the contrast ratio from ~1200:1 to ~860:1 but it’s a viable option to use for darker movies and gaming we think if you are using the sRGB mode. Any higher setting raises blacks and darker grey shades too much we think, crushing the contrast ratio, so stick with option 1 as a maximum.

Calibration

Calibration and profiling can produce some very good overall results and could be useful if you wanted to operate the screen within its native wide gamut mode, but then map the colour space back to something else like sRGB or Adobe RGB for instance for colour-aware applications (e.g. Photoshop). You would need a suitable calibration device and software for this, or you could also try our calibrated ICC profile.

The screen was profiled to 2.2 gamma, 6500K colour temp and to the sRGB colour space. The screen was left in its native wide gamut mode, but this profile will be used in colour-aware applications to map back to sRGB in this instance. Overall the calibrated results were excellent as you’d hope, and our gamma adjustments through this process also improved shadow detail very nicely.

Best Settings Guide

• On our Patreon Insider tier and above you can find our full ‘Best settings guide’ for this screen which includes all our recommended calibrated settings and ICC profile for SDR mode, as well as other best settings guidance for other configurations, modes, HDR, gaming and everything else.
• Please note that you have the option to either join our Patreon on a subscription basis, which will also open up access to other locked posts on our page; or you can purchase just the single post for these best settings as a one-off if you’d rather.
• If you only want just our standard SDR settings and calibrated profile, that is available via our ICC database (without all the other best settings guide).

General and Office

The screen is well-suited to office and general uses with a high resolution and pixel density, along with a solid feature set. Being an LCD panel, you don’t have any of the concerns you might have with OLED panels around image retention, burn in or abnormal sub-pixel layouts which is good news, and the panel uses a standard RGB stripe layout so text clarity is excellent, especially with the 4K resolution pixel density offered here (~163 PPI).

With a 4K resolution packed in to a 27” screen size you get a super-sharp and clear image, better than common 1440p resolutions that are available at this size. You’ll need to use OS scaling to avoid tiny text and icons, but at 150% you get the same desktop area as a 1440p monitor, just with a much higher pixel density for a very sharp and clear image, 125% scaling would give you some further desktop space as long as it doesn’t look too small for you.

This model has a standard light anti-glare coating as with other modern IPS LCD panels, which provides good glare and reflection handling with minimal visible grain.

The IPS panel provides the usual wide viewing angles and stable image you’d expect from this technology, although a pale IPS glow is visible when viewed from an angle like you’d see on most IPS panels, so for darker content this screen is definitely best viewed from a head on position.

	Features	Notes
USB type-C connectivity (DP Alt mode)
USB type-C power delivery		90W
Daisy chaining support
KVM switch
PiP and PbP support
USB data ports		2x USB-A
Easy access USB data ports
Integrated speakers
Audio output / headphone out
Mic input
Integrated webcam
Ambient light sensor
Motion sensor
Stand adjustments		Tilt, height, swivel, rotate
VESA mount support		100 x 100mm
Integrated power supply		External brick used
Tripod socket
Firmware updates
Fan-less design

There’s a very good range of connections with 1x DisplayPort 1.4, 2x HDMI 2.1 connections and 1x USB type-C which offers DP Alt mode, data and 90W power delivery; very useful for single cable connectivity from laptops and other devices. There’s also 2x USB-A data ports and a headphone connection, but note that there’s no speakers on this model. With USB-C present, the screen also has a KVM switch function, and there’s also support for PiP or PbP modes if you’re inputting multiple video sources.

Backlight dimming

Flicker
Flicker free verified
PWM / flicker frequency	n/a

We also confirmed the screen operates with a flicker free backlight, free from any PWM dimming which is great news, which includes when local dimming is enabled from the menu.

Blue light

Blue light output
Blue peak wavelength	449 nm
Blue light portion	28.97%
Low blue light modes available
Low blue light mode temp	n/a

The spectral distribution of the backlight at a calibrated ~6500K white point is shown above. Note that there are no specific ‘low blue light’ modes available on this screen, and no specific preset modes designed for reading/text work. The closest thing would be the ‘warm’ colour temp mode but that is only marginally warmer at ~6300K so isn’t of much value.

HDR

When it comes to HDR support, the Mini LED backlight featured here significantly improves brightness and contrast in HDR usage, compared with typical LCD monitors. The backlight is split in to 1,152 local dimming zones behind the panel, with each zone capable of being dimmed and brightened independently. That’s a big step up from normal LCD monitors which typically have a very limited number of dimming zones along the edges of the screen, often something like 8 or 16, or in many cases none at all. With LCD monitor local dimming, basically the more zones the better in terms of offering greater control over the image, reducing the presence of halos or blooms around bright objects, and increasing the brightness and contrast as much as possible.

An OLED panel takes this a step further with per-pixel level dimming which is excellent, but Mini LED monitors can reach much brighter in HDR where needed, and the 1,152 zones like that available here is a high number for an LCD panel of this size.

The screen has been certified under the VESA DisplayHDR 1400 tier, meaning a peak brightness of over 1400 nits and a wide colour gamut, covering >98% DCI-P3 according to the specs.

HDR modes and settings

This screen has only 2 HDR preset modes available to choose between – ‘GameMode’ and ‘Movie’. For some reason the screen seems to default to a very low brightness level of 8% when you first enable HDR, or at least it did during our testing, and so you will want to increase that to 100% in the menu for maximum brightness performance in HDR mode. The brightness setting is remembered independently between SDR and HDR modes though which is good news so set it at 100 in HDR, and then whatever you find appropriate and comfortable in SDR.

Luminance and contrast

We tried both HDR modes but found the GameMode to offer the better performance, especially in darker scenes as the Movie mode causes more significant black crush. In GameMode the first visible greyscale shade was RGB 7, while in Movie mode it was RGB 17! Although this was with local dimming on ‘high’ which is preferrable for HDR mode as it gives the highest contrast and best blacks as you can see from the results above. This is obvious in real-world content as well, with a deeper, more impressive black when using the high mode.

If you were to lower the local dimming setting, shadow detail in both modes does improve, but you lose overall contrast and the blacks aren’t nearly as deep. Anyway, GameMode with local dimming on high were optimal we felt for HDR. This is also nice and simple should you want to use local dimming in SDR mode, which is also optimal on high. Note that you do not have access to the ‘Dark Field Bright Effect’ (aka black equalizer) in HDR mode so that cannot be used to make any further tweaks.

Peak white luminance was impressive in this configuration as well, reaching up to a maximum 1955 nits, surpassing easily the 1400 nits spec in certain scenes. In low APL scenes where there are smaller bright areas, the luminance is reduced to help avoid blooming and halos which is common practice for Mini LED monitors.

You can see some peak white luminance comparisons here against other recently tested Mini LED screens, and also a modern 5^th Gen QD-OLED monitor for reference. The KOORUI monitor can reach a bit brighter than the others, especially in some bright scenes where brightness is maintained more consistently where needed. The IPS models can reach brighter than the VA Mini LED MSI model here (the MSI MAG 274QPF X30MV) in higher APL scenes where needed, although on the other hand the VA panel shows better contrast and reduced blooming compared with the IPS panels, especially from an angle.

This Mini LED monitor has the hardware capabilities to get far brighter in HDR content than any OLED monitor released so far and on this graph we’ve compared the peak white luminance against one of the latest 5^th Gen QD-OLED monitors we’ve tested for example which is the blue line.

Peak highlights in dark scenes are actually quite a lot brighter on the OLED screens, where the per-pixel level dimming avoids halos and blooming that could be a challenge on Mini LED backlights, even with a high number of dimming zones like this. On the Mini LED monitor, the brightness is toned down for low APL scenes to avoid blooming issues, but once the APL increases above about 5%, the maximum brightness capabilities of the Mini LED far exceed what’s possible from the OLED monitors, where ABL dimming is needed due to the way OLED monitors are powered and how they work.

It’s no contest in terms of the brightness capabilities of Mini LED vs OLED, although keep in mind that you would need actual content to be mastered to these very high levels for the differences to be as substantial as this in real use. In some scenes there may not be as much of a visual difference in real use, if the content isn’t calling for a higher brightness anyway. These are synthetic test patterns designed to reach super high brightness levels even at 100% APL full screen, but realistically actual HDR content won’t be mastered to these levels.

The Mini LED backlight can certainly support higher HDR brightness across a range of scenes than OLED panels can, without needing to dim as aggressively and it’s great to see this technology used in the LCD market to enhance performance, and without raising the price tag too substantially nowadays.

Local dimming

In real world usage there are pretty low levels of blooming and halos in general mixed content, even in many darker games, although in extreme situations like this Christmas lights scene for instance, the blooming becomes more noticeable as the backlight tries to accommodate small bright areas on otherwise dark backgrounds and the native contrast ratio of the IPS panel is low. Despite having a very high brightness, the contrast is also very good and blooming seems to be slightly lower than similarly spec’d screens like the KTC M27P6 for instance that we reviewed in the past.

One noticeable challenge with all IPS Mini LED screens we’ve tested before is that the blooming and halos are accentuated by the off-angle IPS glow of the underlying panel, something you don’t get on competing VA panels. As a result, the screen is definitely better from a head on viewing position for HDR and when using the local dimming setting in either HDR or SDR mode.

The below photos capture the accentuated blooming when viewing the screen from an angles (it doesn’t look like this from head on! – see the picture above for that) and also quite nicely shows the differences between this KOORUI model and the KTC equivalent, which has more noticeable and larger areas of blooming.

Like on the KTC model, but to a much lesser extent, we did notice a little flickering in both SDR and HDR mode when using the local dimming feature when the refresh rate was low at 60Hz, and you can see this on this local dimming test pattern for instance on the leading edge of the moving shapes. This was a very noticeable flicker on the KTC, it’s a lot better here but you can see a bit of it sometimes.

EOTF and greyscale

We also measured the EOTF and greyscale in a variety of scenes, above captures the performance in dark (low APL) scenes and also in bright (high APL) scenes. You can see that the EOTF tracking remains pretty consistent, with some moderate over-brightening of the EOTF. This makes darker scenes a bit brighter, although accuracy purists may have preferred a more accurate tracking.

As we’ve seen on all the other Mini LED monitors we’ve tested in recent times, the greyscale varies depending on the scene and the measurement window size. In low APL scenes it is cooler than intended, with a noticeable weighting towards blue. This improves as the scene gets brighter, levelling out the RGB balance and restoring a more natural looking greyscale and white. This seems to be normal Mini LED behaviour across the board.

HDR colours

The screen operates with the full native colour space in HDR mode, offering the same gamut coverage as we’d seen in native SDR mode. The accuracy of HDR colours was overall good, although it could have perhaps been a little better calibrated in some cases.

Gaming

The 4K resolution provides a super sharp and clear image for 4K gaming, with a high pixel density on a 27” screen like this, and combined with a 160Hz refresh rate it’s a great combination for graphically focused gaming titles and for gamers who are looking to push resolution and image detail.

The dual-mode function provides a potentially useful option if you instead want to instead prioritise frame rates and speed, allowing you to double the refresh rate to 320Hz if you drop down to a lower 1080p resolution. That’s obviously a much lower and less detailed resolution, but on a 27” screen size it’s not terrible, and looks a fair bit better than 32” sized screens that offer this function at 1080p. There’s a shortcut button on the bottom edge of the screen to switch in to dual-mode operation, or you can access it via the main OSD menu too.

That dual-mode does not operate with pixel perfect integer scaling (I don’t think we’ve seen any dual-mode monitor offer this actually so far), but it still looks pretty decent without loads of blurring or artefacts in gaming and dynamic content.

	VRR capabilities and Certification
Variable Refresh Rate Range	48 – 160Hz (native mode) 48 – 320Hz (dual-mode)
VRR certifications

Adaptive-sync is available to support variable refresh rates up to the maximum 320Hz, although there’s no certification under any of the AMD, NVIDIA or VESA schemes at this time. Being an IPS LCD panel it is free from any visible flicker though during VRR situations in our testing which is good news.

	Other Features
Overdrive settings	Normal, Fast, Fastest
Variable overdrive support
Single overdrive mode experience
Motion blur reduction mode
Dual-mode support	320Hz @ 1080p
Local dimming support	Both SDR and HDR modes
Gaming extras	Preset modes Refresh rate counter Crosshair Optix scope Timer Shadow Boost
Emulated gaming sizes

There’s a good range of gaming features and extras available like a several gamer preset modes, shadow boost setting (via the ‘Dark field bright effect’ setting), FPS counter and so on, and there’s also a strobing blur reduction mode which we will look at in more detail shortly.

Response times

When it comes to pixel response times, there is an overdrive setting in the on-screen menu with 3 different modes to choose between – normal, fast and fastest. Here’s the results at the native 160Hz refresh rate in each mode:

There’s a small benefit in moving up from the normal to the fast mode with an improved G2G response time and better refresh rate compliance, without introducing any visible overshoot at this refresh rate. It reduces the blur in moving content slightly.

The maximum ‘fastest’ mode lowers the response times further, but introduces very high levels of overshoot which results in noticeable dark and pale halos in real-world content and motion tests as you can see from the pursuit camera photos above. That mode is to be avoided.

We settled on the ‘fast’ mode as offering the optimal performance. During VRR situations the G2G response times remain basically the same, but the overshoot level starts to creep up a bit. There’s no variable overdrive being used here, but there is still a single overdrive mode experience if you set it to ‘fast’. Even at low frame rates, the level of overshoot never becomes too obvious or problematic so that’s good news. The response times are better tuned than on the similar KTC M27P6 which had shown higher levels of overshoot in it’s optimal mode, especially in VRR at lower frame rates.

When switching to the dual-mode 320Hz there is again very little change to G2G response times if you stick with the ‘fast’ mode, but the challenge here then becomes that the transitions are not really fast enough to keep up properly with the higher frame rate. As a result, you get some noticeable additional smearing to the moving image, although that is offset by the improved motion clarity from the higher refresh rate. It’s just not as clear as it should be if response times were faster.

Moving up to the ‘fastest’ mode offers better G2G speeds and a clearer image in real content, but the overshoot starts to reach pretty high levels, and this gets worse during VRR situations as the frame rate lowers which then becomes distracting again. Perhaps if you’re gaming at a fixed 320Hz (without VRR) you would find the ‘fastest’ mode useable, but for VRR gaming we’d probably recommend sticking to the ‘fast’ mode. It’s a shame the response times weren’t a bit better to handle the dual mode 320Hz better in that configuration though. If they had been, and without any variable overdrive function, that would only have driven overshoot up for the lower refresh rates so a balance had to be found somewhere.

DIC (Dynamic Image Clarity) blur reduction

KOORUI provide a strobing blur reduction backlight mode via the DIC (Dynamic Image Clarity) setting in the menu. This only works at certain fixed refresh rates, so you have to first disable FreeSync (VRR) in the menu to have access to the DIC setting. It’s a simple on/off toggle which doesn’t send the screen black or anything when you enable it.

Motion Blur Reduction Mode
Motion Blur Reduction Backlight
Refresh rates supported	320Hz, 240Hz (dual-mode only) 160Hz, 144Hz, 120Hz
60Hz single strobe operation
Blur reduction available with G-sync/FreeSync VRR
Strobe length control
Strobe timing control
Available in SDR mode
Available in HDR mode
Lag penalty	~2ms
Brightness capability (SDR, max refresh rate supported)
Independent brightness control available
Motion blur OFF – Max brightness	654 nits
Motion blur ON – Max brightness	338 nits (native mode 160Hz) 375 nits (dual-mode 320Hz)

The DIC mode is available at various refresh rates in both SDR and HDR operation, including when using the dual-mode function at 320Hz and some other refresh rates opened up when using that mode. The only refresh rate missing really is 60Hz due to unwanted flicker which some enthusiasts may miss, but most general users won’t.

There’s a couple of user experience problems with this mode though. Firstly, the brightness control is not remembered independently between the off and on modes, so you may have to alter that each time which is annoying. Secondly, when you enable DIC it automatically moves you back to the ‘normal’ overdrive mode, so each time you use DIC you’ll need to change it back to ‘fast’ (optimal) after you’ve disabled DIC again. Both of those are pretty annoying and could maybe be addressed via a firmware updated if KOORUI looked in to it.

Brightness could reach high levels in this mode still, reaching 338 nits maximum in native mode, a little higher at 375 nits in dual-mode oddly. This put maximum brightness ahead of other Mini LED monitors we’ve tested in recent times such as the KTC equivalent (268 nits) and MSI’s two models (201 / 238 nits). This was an impressive maximum brightness for a strobing mode, if you need that extra luminance room.

DIC strobing at 320Hz (dual-mode)

The strobing is in sync with the refresh rate as intended with an on period of 0.875ms and off period of 2.25ms.

DIC strobing at 160Hz (native mode)

The strobing is in sync with the refresh rate as intended with an on period of 2.25ms and off period of 4ms.

From a motion clarity point of view there’s decent improvements in image sharpness with this mode enabled and it’s easier and clearer to track moving objects on the screen, and there were low levels of strobe cross talk and ghost images too which was pleasing. This actually remained pretty consistent across all regions of the screen which was pleasing. When combined with the 320Hz dual-mode you get noticeable improvements to motion clarity. There’s a small lag penalty of around 2ms when you enable the DIC blur reduction mode, but that’s pretty minor thankfully.

Input lag

On the subject of lag we measured this at various refresh rates and this shows the total display lag, made up partly from signal processing delay, and partly from the response times of the panel. You can see this is low at all these refresh rates, even at 60Hz which is great news. When enabling the DIC blur reduction mode there is ~2ms of additional lag added, but this is still minor.

Console support

	Console Gaming
Native panel resolution	3840 x 2160 “4K”
Maximum resolution and refresh rate supported	4K @ 120Hz
4K at 24Hz support
4K at 50Hz support
HDMI connection version	2.1
HDMI connection bandwidth	48 Gbps
HDMI-CEC auto switch
VRR (variable refresh rates)
Auto Low Latency Mode (ALLM)
HDR10 support
Dolby Vision HDR support
Motion blur reduction support
Integrated speakers
Headphone connection

Console support is good, with the panel handling 4K 120Hz content natively and support for 4K 50Hz video content too, although not for 4K 24Hz on this screen. There’s VRR support, but no HDMI-CEC function unfortunately which could have been useful when powering on a connected console, and keep in mind there’s a headphone jack for audio but no integrated speakers on this model. You can use the backlight local dimming for both SDR and HDR gaming, and the ‘DIC’ blur reduction mode is also available at 120Hz which could be useful to some gamers for improving motion clarity.

Conclusion

The KOORUI S2741LM was an impressive Mini LED monitor offering a strong feature set and some solid performance, all at a competitive price point. The Mini LED backlight performed well, offering very high brightness capabilities, improved contrast and decent blooming levels as well. Since this is an IPS panel, it’s definitely best viewed from a head on position though. The high-end backlight makes the screen very well suited to HDR content, although we’d have liked some further controls in that mode over some of the colour settings and some improved shadow detail too.

SDR accuracy was very good, and the three colour space emulation modes also provide accurate configurations and good colour clamping too. The brightness of the panel was very good in both SDR and HDR usage, and contrast ratio was typical for a modern IPS panel.

The overall gaming performance was good, with decent response times in keeping with most IPS screens, although we’d have liked to see some faster performance in the 320Hz dual-mode to more effectively keep up with the higher frame rate, without having to change settings regularly or deal with high overshoot levels. That mode is probably useful to some people for certain gaming situations, but the resolution is of course pretty low and the panel isn’t as fast as it could be when trying to keep up with the higher frame rate. Lag was very low, console support was good, and the DIC blur reduction mode improved motion clarity nicely; although the user experience with that mode was annoying with having to change brightness and response time settings all the time.

There’s a good feature set on offer as well despite the good price point, and it’s nice to see things like USB type-C, a KVM switch and PiP/PbP available. The S2741LM is available at the time of writing at a price of ~$500 USD or £400 GBP, and you can check latest pricing and availability for your region using our affiliate link below.

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