Dell U2518D

Interlace pattern artifacts

On some monitors faint interlace patterns can be seen during certain transitions, particularly noticeable where light shades (muzzle flashes, explosions etc.) briefly pop up on the screen. These are sometimes referred to as ‘inversions artifacts’. Alternatively, static interlace patterns can be seen with some shades appearing as faint horizontal bands of a slightly lighter and slightly darker version of the intended shade. We did not observe any such artifacts on this monitor.

Responsiveness

Input lag

We used a small program called SMTT 2.0 alongside a sensitive camera to compare the latency of the U2518D with a range of monitors of known input lag. We took over 30 repeat readings to maximise accuracy. Using this method, we measured 5.18ms (under 1/3 of a frame) of input lag. This is influenced both by the element you see (pixel responsiveness) and that which you feel (signal delay). It indicates a very low signal delay that shouldn’t be bothersome even to sensitive users. Rather peculiarly we measured ~16ms of input lag using the ‘Game’ preset, even with Dynamic Contrast disabled. We have no way to accurately measure the input lag with ‘Smart HDR’ active on this display.

Perceived blur (pursuit photography)

In our responsiveness article, we take a look at some of the key concepts related to monitor responsiveness. Chief amongst these is the notion of ‘perceived blur’, which is contributed to not just by the pixel responses of the monitor but also the movement of your eyes as you observe motion on the screen. This second factor is generally the predominant one on modern monitors. We also introduce a technique called ‘pursuit photography’, which uses a moving rather than static camera to capture motion on a monitor in a way that reflects both eye (camera) movement and pixel responsiveness.

The images below are pursuit photographs taken using the UFO Motion Test for ghosting, with the test running at 960 pixels per second. This is a practical speed for capturing such photographs and highlights both elements of perceived blur nicely. The UFOs move across the screen from left to right at a frame rate matching the refresh rate of the display. All background shade levels (dark, medium and light) were used and both ‘Response Time’ settings on the monitor were tested. The final image shows a 60Hz reference monitor, a Dell S2417DG, which gives an idea of how things should look where pixel responsiveness isn’t really a limiting factor.

With ‘Response Time’ set to ‘Normal’ you can see that the image is soft and unfocused. The same applies to the reference screen, however. This reflects perceived blur that can be attributed to eye movement when you observe motion on the monitor. There is also a little bit of trailing behind the object for the darkest background (top), although this is not too pronounced. For the medium background (middle) and lightest background (bottom) things look rather close to the reference image, with no obvious weaknesses attributable to pixel response times. Using the ‘Fast’ setting introduces a colourful inverted trail behind the object; this is inverse ghosting (overshoot) and indicates an overly aggressive pixel overdrive impulse. It is very clear from this analysis that ‘Normal’ is the setting to use, with ‘Fast’ introducing issues that are far more noticeable than the slender benefits it might bring to some pixel transitions. Note that we will not be including a section on ‘overclocking’ in this review as the monitor skipped frames when set at all above 60Hz.

Responsiveness in games and movies

On Battlefield 1 (BF1) there was a moderate degree of perceived blur, intensifying and becoming most noticeable as the pace of action increased. This was predominantly caused by eye movement and therefore much in line with what you’d see on even the fastest 60Hz LCDs. There were some slight weaknesses beyond this, caused by slower than optimal pixel transitions, but nothing that really stood out. There was a faint powdery trail, most notably accompanying light shades with a dark background – for example when moving past a light source in a dark room. This was really quite similar to the slight trailing shown earlier on Test UFO – faint and not really distracting at all. It also had limited effect on perceived blur and if a user is sensitive enough to find this problematic then they are very unlikely to get on with any 60Hz LCD. There was no obvious overshoot, either, only slight traces here and there that even our sensitive eyes found completely undistracting.

We made similar observations on Dirt Rally, with the perceived blur we observed whilst racing around very similar to what is observed on even the fastest 60Hz LCDs. For example the Dell S2716DG set to 60Hz, sitting next to this monitor. When racing at night we could see some of the powdery trailing noted on BF1 and Test UFO, as there were strongly contrasting pixel transitions with very bright objects moving against much darker backgrounds. Even here the effect on overall perceived blur was slight and the trailing itself was not what we’d describe as eye-catching. Equally subtle was the overshoot, which was as good as non-existent and never eye-catching even to users as sensitive to this as ourselves. The monitor was also free from obvious weaknesses when testing our Blu-ray test titles. These are restricted in their fluidity by the ~24fps at which they run, but there were no weaknesses associated with pixel responsiveness (trailing or inverse ghosting).

We also tested our Blu-ray movie test titles, which did not highlight any weaknesses in pixel responsiveness. The fluidity was limited by the low frame rate at which the films run (~24fps), but was not impeded by pixel responsiveness; there was no trailing or overshoot related to imperfections in that department.

HDR (High Dynamic Range)

HDR (High Dynamic Range) as it applies to monitors describes the ability to distinctly display very deep dark shades and very bright light shades simultaneously. It is also a requirement to display a huge variety of shades in between, from weakly saturated to very heavily saturated shades. Ideally the monitor will have hundreds (if not more) dimming zones on the backlight, or alternatively have a per-pixel light source (OLED technology, for example). This would give the monitor an exceptional contrast ratio and allow it to simultaneously display good deep dark content and very bright light content. It also helps if the monitor can pump out a very high luminance, to help the brightest elements of the image really stand out in a brilliant way. Having a wide colour gamut (Rec. 2020 being the ultimate goal as described in our backlighting article) and a high level of precision of 10-bits per subpixel or more is also desirable for proper HDR handling.

On paper, the U2518D ticks none of these boxes whatsoever. The backlight is not split into hundreds of dimming zones, its contrast is entirely typical for an IPS-type panel (~1000:1), its peak luminance is decent but not outstanding (<400 cd/m²) and it offers a bit of extension beyond sRGB for its colour gamut but no support for any wider colour spaces. The monitor does ‘support HDR’, though, in as much as it has a dedicated mode called ‘Smart HDR’ that can be activated when using HDMI 2.0. This uses an HDR signal and allows the monitor to respond to HDR10 content; HDR10 being the ‘standard’ (a term we use loosely) associated with HDR for PC usage at the moment. Our test system uses an Nvidia GTX 1070, which supports HDMI 2.0 and hence supports HDR on monitors such as this. Our AMD GPU (Radeon 290) has an older revision of HDMI and therefore couldn’t be used for any testing of this feature.

As soon as we hooked up the monitor by HDMI 2.0 and enabled the ‘Smart HDR’ feature, we were greeted by a blank screen. The monitor lost signal – not a promising start. To get around this rather pertinent issue, we had to keep the monitor hooked up via HDMI 2.0 but also connect it up using DisplayPort. This allowed us to get a signal (via DP) whilst the PC still saw a monitor connected to the system via HDMI 2.0 – it treats this as a separate display, which is useful for diagnostic purposes. The issue was that Windows 10, with the ‘Creator’s update’, has a feature called ‘HDR and advanced colour’. This is found in ‘Display settings’ (right click the desktop) and is enabled by default when an HDR-capable display is connected, such as the Dell with its ‘Smart HDR’ feature on. This feature is highlighted in the image below. Note that when you have the display connected by DP and HDMI 2.0 simultaneously, you will only see the ‘HDR and advanced colour’ toggle for the HDMI 2.0 input which should be assigned as (screen) ‘2’. Click ‘2’ and turn this feature off – you can then disconnect the DP or switch to HDMI 2.0 and the screen should display a signal.

Unfortunately, the fact that this integrated HDR feature on Windows itself doesn’t work means that applications that rely on this will also not work with HDR. That includes some movie software, YouTube videos and even some games. When launching Hitman with the ‘Smart HDR’ feature of the monitor enabled, the display instantly lost signal. Curiously this occurred even when the ‘HDR’ feature wasn’t enabled in the game options, which can be configured before the game itself is actually loaded. Other applications use their own separate HDR implementation and do ‘work’ with the monitor – insofar as the monitor doesn’t lose signal. Mass Effect Andromeda, for example, has an HDR10 setting that ‘worked’ with the monitor. We’ll let the images do the talking on this one, at least initially. It is impossible to convey exactly what the monitor is displaying in a photo or video – the camera, image editing software and your own PC including monitor influence what you see there. However; just bear in mind that the top image shows how things looked with HDR disabled (i.e. SDR – Standard Dynamic Range) and the bottom with HDR enabled.

Faded, lacklustre, lifeless, dull. This might sound like a shampoo commercial, but they’re all adjectives that describe the image with HDR enabled on this title. It looked almost as if the gamma was set to an extremely low value, perhaps the equivalent of ‘1.4’ or below. But the shade handling was quite bizarre, as there were some deep shades that had very good depth to them; although, from what we could perceive, no better than the deepest shades with HDR disabled. There was also a lot of crushing together of dark shades, with subtle details being lost – this was quite apparent when considering some of the dark hair or certain characters, for example. We are aware that other users have reported similar things when observing the PC version of Andromeda in HDR on different HDR-capable displays. So we aren’t necessarily blaming Dell’s implementation for this. However; add together the loss of signal in other titles and the fact that relatively few PC games actually support HDR at the moment, we weren’t prepared to waste more of our time testing this feature. At the time of review we didn’t have access to an HDR-capable GPU from AMD or an HDR-ready games console. Really, though, it is quite clear that if this is the sort of HDR experience Nvidia GPU users are provided with then it’s hardly a feature to get excited about on the U2518D.

The 2560 x 1440 (WQHD) experience on a 25” screen

With its 2560 x 1440 (WQHD) resolution and 25” screen, the Dell U2518D has a pixel density of 117.49 PPI (Pixels Per Inch). This is slightly higher than the 108.79 PPI of the more common 27” WQHD models. We specifically compare the two screen sizes and the 25” WQHD experience in our review of the AOC Q2577PWQ, this section specifically. We would advise users to take a quick read of that and view some of the images which demonstrate the differences. Essentially the difference is not profound – you’re talking about an 8% high pixel density – but that is still a difference nonetheless. It makes text and UI elements just a touch smaller than on the 27” WQHD models, although we can comfortably interact with such elements and read such text on models with significantly higher pixel densities than this. So, depending on eye sight and viewing distance, it’s not something to worry about. The image below show the desktop and some of the productivity capabilities of the monitor.

There was a slight but in our view not particularly noteworthy boost in text and image clarity when comparing to a 27” WQHD model. The amount of ‘real-estate’ (i.e. useful work space on the desktop) is certainly of great benefit compared to the 1920 x 1080 (Full HD) resolution that is more typical on models of this size. This slight edge in clarity over 27” WQHD models was also evident but not particularly striking when gaming – the difference between that and gaming on a Full HD model of this sort of size was quite profound, however. The clarity as you observe even fairly small and slender objects in the distance and the texture and particle details (provided the game uses decent textures here in the first place) was quite pleasing really. In this respect things weren’t at the level that you’d see on a 32” or smaller ‘4K’ UHD (3840 x 2160) model, but we feel the balance between GPU performance requirements to sustain a decent frame rate and image quality is quite sound at this resolution and screen size. The images below show the monitor running some games; they in no way represent how things actually look first-hand on the monitor and are just there to help fire up your imagination.

Interpolation and upscaling

For users that don’t wish to use the 2560 x 1440 resolution, perhaps because their system doesn’t run a game well at this resolution or they’re using a games console that doesn’t support it, they may need to fall back to a lower resolution. When the monitor is set to a lower resolution, such as 1920 x 1080 (Full HD or ‘1080p’), the monitor can use an interpolation process. This integrated scaling capability translates that Full HD signal onto all 2560 x 1440 pixels of the screen. For best results, you should ensure the monitor is handling this rather than the GPU, if you’re a PC user. For AMD GPU users this is automatically handled by the monitor when gaming, by default. Nvidia users should open the Nvidia Control Panel and navigate to ‘Display – Adjust desktop size and position’. They should ensure that ‘No Scaling’ is selected and ‘Perform scaling on:’ is set to ‘Display’ as shown below.

The interpolation process gives a moderate degree of softening, but this is less pronounced than we’ve seen on quite a few models. When running 1920 x 1080 and comparing to a screen that runs this natively and is of similar size, it is quite apparent that things don’t look quite as sharp. Some finer texture detail is lost, edges appear softer etc. It doesn’t appear blurry in the same way that some monitors do when they use interpolation and indeed the game world does not appear as if it’s viewed through a soft-focus lens. If you view the monitor from further back (the exact distance depends on eyesight and your own visual sensitivities) the softening becomes less noticeable. So if you sit back a bit and want to use the monitor with a games console, for example, we feel it will do a perfectly adequate job and appear largely similar to a native Full HD display when running at 1920 x 1080. As is usual, if you keep the monitor at 2560 x 1440 and are viewing lower resolution content (such as a movie), then it is the GPU or movie software that handles the scaling rather than the monitor. This gives a slight softening when compared to running the content on a native Full HD display, although this is not something most users should find bothersome.

Conclusion

It isn’t the first time we’ve used a 25” model with WQHD (2560 x 1440) resolution, but using the U2518D reaffirmed much of what we experienced previously. The overall experience is not massively different to on the more common 27” WQHD models, although the slight edge in pixel density is something we quite like. The overall appearance of the monitor was much as we’ve come to expect from a modern UltraSharp model; sleek and professional looking, without any aesthetic gimmicks. The included stand is quite robust and offers good ergonomic flexibility, whilst the slim bezels on all four sides make the monitor a good candidate for multi-display setups in both portrait and landscape. The OSD provided decent functionality, although we can’t say we were too fond of the buttons themselves. They proved quite uncomfortable on the fingers.

Once switched on the monitor provided a solid performance in several areas as well. First and foremost, it proved to be calibrated very nicely out of the factory. It provided a vivid but accurate image, with good sRGB coverage and an agreeable and very light matte screen surface that kept graininess at bay and helped the image look relatively clear and vibrant. Easily accessible and effective ‘Low Blue Light’ settings were also included. The contrast performance was largely as we would expect from an IPS-type panel, with static contrast generally close to the specified 1000:1 and a bit of ‘IPS glow’ to contend with. This glow was actually a bit less extensive than what you might expect from an IPS-type model of this size, however.

In terms of responsiveness the model provided a good experience as well, within the confines of the 60Hz refresh rate. The vast majority of pixel transitions were fast enough for an optimal 60Hz experience, with your eye movement being the predominant cause of perceived blur. There was a little bit of trailing in places on top of that, but anybody sensitive enough to find that bothersome would find 60Hz LCDs too limiting anyway. Input lag was also rather low, although curiously seemed to change slightly on some of the image presets, notably being slightly higher in the ‘Game’ mode compared to ‘Standard’. So from what we’ve mentioned so far, there is plenty to like about the monitor and plenty of boxes ticked. One of the real headline features of this model also turned out to be the most disappointing, though; HDR. The range of ‘HDR’ content available to PC users isn’t exactly fantastic, but even then we were unable to access a lot of this due to the ‘Smart HDR’ mode not seeming to activate correctly most of the time. Where it did ‘work’ and the monitor actually retained its signal, we can’t say the results were at all impressive. At launch at least, it is clear that a premium is being put on this model due to its HDR functionality. We would expect the price to fall in time, and perhaps the older U2515H to be discontinued (edit: this is exactly what has happened in some regions). That would make this a more attractive deal, although some users may feel the initial premium is worth paying anyway.





The bottom line; a well-rounded monitor with strong performance in a number of key areas, but HDR isn’t one of them.

 

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