Samsung C27F591FD

Responsiveness

Input lag

Using a sensitive camera and small tool called SMTT 2.0, we compared the latency of the C27F591FD (CF591) with a range of monitors of known latency. By taking over 30 repeat readings to enhance accuracy, we measured 6.70ms (over 1/3 of a frame @60Hz) of input lag. We did not measure a significant difference in input lag at 72Hz and don’t have the means to accurately measure input lag whilst FreeSync is doing its thing. This value is influenced both by the element of input lag that you feel (signal delay) and the element that you see (pixel responsiveness). This value indicates a very low signal delay that shouldn’t impede gaming performance.

Perceived blur (pursuit photography)

In this article we explore the key concepts related to monitor responsiveness. Chief amongst these is the concept of perceived blur and how it is not only the pixel responsiveness of a monitor that contributes towards this but also the movement of your eyes as you track movement on the screen. This second factor is often the predominant cause of perceived blur, in fact. We also explore ‘pursuit photography’, a method of image capture which reflects both of these elements of perceived blur rather than just showing the influence of pixel responsiveness.

The images below are pursuit photographs taken on the UFO Motion Test for ghosting, with the test running at the default speed of 960 pixels per second. Such a speed is practical for taking such photos and highlights any issues on the test nicely. The first column shows results with the dark cyan background whilst the second column shows the medium cyan background (top and middle row of the test, respectively). All response time settings on the monitor were tested as well as a capture with the monitor running at 72Hz, which this monitor will also do comfortably as we’ll come onto later. The bottom image shows a ‘Fast 60Hz reference’, which is a Samsung S27A750D set to full brightness (forces DC dimming, without flicker) and 60Hz using its ‘Faster’ response time setting. This reference shows how things should look in this test at 60Hz where motion blur due to eye (camera) movement is the only real limiting factor.

Perceived blur with various settings

When using the ‘Normal’ setting, there is a fair degree of trailing behind the object in addition to moderate blurring of the object itself. This trailing is attributable to slower than optimal pixel responses, whereas the blurring of the object itself is down to eye (camera) movement. The trailing is more pronounced with the dark cyan background due to pixel responses being particularly slow for these transitions. Using the ‘Faster’ setting offers a marginal reduction in trailing and changes the nature of the trailing a bit. There appears to be a bit of a ‘dirty’ quality to it – this actually indicates a little bit of overshoot (inverse ghosting) due to fairly high levels of grey to grey acceleration being used. The ‘Fastest’ setting shows more extreme overshoot, with obvious colourful inverted trails behind the UFOs.

When observing the monitor under more realistic and varied testing scenerios (such as games), it becomes clear that the ‘Faster’ setting does cut down on conventional trailing quite a bit compared to the ‘Normal’ setting. And the trade-off of that – slight overshoot in places – is really the lesser of two evils. Having established that this is the optimal setting to use, we also tested the monitor at 72Hz using this setting. On these captures things really look quite similar to 60Hz. The object is perhaps a bit more compact (it appeared so when observing it directly) but the trailing remains very much the same. Essentially motion blur due to eye movement is cut down just a little from the increased refresh rate, but pixel responsiveness remains a limiting factor as is usual for VA models. Something not shown here is how the monitor actually feels when you interact with the game world – 72Hz provides a slightly more ‘connected’ feeling in that respect.

Running a custom resolution (overclocking)

The monitor will comfortably run at up to 72Hz at 1920 x 1080. If you enable FreeSync in the OSD, it will automatically default to 72Hz. If you’re running an Nvidia GPU, you can set a custom resolution to ‘overclock’ the monitor to 72Hz. Doing so does not have negative implications for the image such as changes to gamma, contrast or colour temperature nor does it cause frame skipping. If you try to set the monitor to a higher refresh rate, such as 75Hz, you are given an ‘input not support’ message. This seems to occur regardless of connection used and timings. The video below shows you how to set the monitor to 1920 x 1080 @72Hz, by creating a ‘custom resolution’ – for users who are unable to use FreeSync.

Because the monitor is designed to run at 72Hz, this is to be considered a ‘mild’ overclock that is completely within manufacturer tolerances. There is minimal risk involved and in all likelihood the monitor will last for its useful life in much the same way as if it was run at 60Hz. The general advice we give at this stage as to be aware that overclocking is something which you do at your own risk. The risk may well be very low, especially as the monitor is clearly designed to run at 72Hz, but we accept no liability should anything happen to the monitor which may or may not be due to running it at an increased refresh rate.

Responsiveness in games and movies

On Battlefield 4 there was quite a bit of motion blur, noticeable at all paces of action (whether running about as a solider or zipping about in a vehicle). Eye movement linked to refresh rate was the main cause of this, but there was certainly an influence of slower than optimal pixel responses in places. Many pixel transitions occurred quickly enough so that there was only a little if any additional blur added to what you’d perceive on the best 60Hz or 72Hz LCDs for responsiveness. The perceived blur increased in places due to some pixel transitions being introduced that the monitor can’t perform as rapidly. This was especially noticeable where dark shades were involved in the transition, such as moving past a dark and shaded building with a fairly bright blue or grey sky in the background. The building (object) had a bit of extra trailing behind it. You could perhaps describe it as slightly smeary in its appearance, although it didn’t have the sort of extended (almost smoke-like) smeary appearance that such transitions have on slower VA models. There was a bit of overshoot in places as well, but nothing particularly eye-catching or disturbing. When moving thermal optics with white hot objects against cooler medium or darker grey backgrounds, for example, you could see a slight black tint to the trail behind the objects. And a similar trailing could be observed on the map ‘Paracel Storm’, with tree trunks set against a stormy sky having a fairly noticeable (to our eyes) semi-transparent black trail to them that did not appear as a blend of the background and object colour.

We made similar observations on Dirt Rally. It was again the case that most of the perceived blur could be attributed to eye movement, but there were some weaknesses in pixel responsiveness in places. This was most noticeable when driving at night and dark shadowy objects such as trees silhouetted the slightly brighter sky. You could see a more pronounced almost smeary trail behind the objects – but again, these were more short-lived and not as obvious as on some VA panels. There was also a bit of overshoot; something not everyone would notice and generally quite subtle rather than being something that jumps out at you.

Overall it seems that the C27F591FD (CF591) provides quite a good balance in terms of pixel responsiveness, particularly for a VA model. Most transitions are snappy enough to have limited influence on perceived blur, whilst the acceleration is not so excessive as to introduce obvious widespread overshoot. There are definitely imperfections and some slower than optimal pixel transitions, but as far as VA models goes this is one of the better ones for gaming performance. We also tested our Blu-ray film title for responsiveness and didn’t come across any obvious limitations there. The ~24fps at which the films run was really the key limiting factor, not anything that was impeded by the monitor itself.

FreeSync – the technology and activating it

AMD FreeSync is a variable refresh rate technology supported by certain AMD GPUs (such as these and future models), which makes use of VESA Adaptive-Sync. This is a capability integrated into some DP 1.2a and HDMI 1.4a port controllers, such as those found on the Samsung C27F591FD (CF591). As with Nvidia G-SYNC, this allows the GPU to communicate with the monitor to let it know what frame rate the content is currently running at. The monitor is then able to dynamically adjust its refresh rate to match this, where possible. Doing so eliminates the stuttering (VSync on) or tearing and juddering (VSync off) that occurs where the frame rate and refresh rate are misaligned. Although it isn’t something we are able to accurately measure, there is also a reduction in latency compared to running VSync enabled, in the variable refresh rate environment (i.e. frame rate below refresh rate limit of monitor).

Unlike with G-SYNC, a separate ‘G-SYNC board’ or similar is not required and instead the existing scaling and monitor electronics are used. This reduces cost to both the manufacturer and is an easier option for manufacturers to implement with their designs – hence why the number of ‘FreeSync’ (compatible) displays dwarfs the number supporting G-SYNC. As noted above the CF591 supports Adaptive-Sync and therefore AMD FreeSync via both HDMI 1.4a and DP 1.2a. Our test system uses a Club3D Radeon R9 290 royalAce, which is compatible with the technology. AMD’s recent drivers include Radeon Software Crimson, which makes activation of the technology very simple. So simple, in fact, that it should be automatically enabled when you first plug the display in. To check this, open ‘AMD Radeon Settings’ and click ‘Display’. You should then ensure that the first slider, ‘AMD FreeSync’, is set to ‘On’. If you hover over this, it will also report the variable refresh rate display supported by the display. Note that the image below is for a different monitor and is just used here for reference.

Note that there are two ‘FreeSync’ settings on the Samsung, found in the ‘System’ section of the OSD; ‘Standard Engine’ and ‘Ultimate Engine’. The ‘Standard Engine’ offers support for a variable refresh rate range of 58 – 72Hz, whereas ‘Ultimate Engine’ supports 48 – 72Hz. There didn’t seem to be any drawbacks to using the latter option and the broader refresh rate range it supports, so we suggest users simply stick with that. Outside of this range, the GPU respects your selection of ‘VSync on’ or ‘VSync off’ in the graphics driver. With ‘VSync on’ the frame rate will not be allowed to rise above 72fps, with VSync activating automatically at this point and imposing the usual latency penalty when it does so. With ‘VSync off’ the frame rate is free to rise above 72fps (72Hz refresh rate ceiling of the monitor). This will deactivate FreeSync and cause tearing and juddering which some users would find bothersome.

VSync is configured in the ‘Gaming’ section of ‘Radeon Settings’, where it is referred to as ‘Wait for Vertical Refresh’. This can either be set globally under ‘Global Settings’, or alternatively for each game title on its own. The default is ‘Off, unless application specifies’ which means that VSync is only active if you enable it within the game itself, if such an option exists (it usually does). It might not be called ‘VSync’ but may be referred to as ‘sync every frame’ or something like that. Most users will probably want to enable VSync when using FreeSync to ensure that they don’t get any tearing. One of the final two options in the list, shown in the image below, would therefore be preferable.

There are a couple of final points to note. Firstly, the application must be running in fullscreen mode, not a window (borderless or otherwise). Secondly, this monitor does not provide any obvious indication that FreeSync is actually active such as an LED light or on-screen notification. You will simply have to assume that it is working – provided you’ve activated the setting in the OSD and Radeon Settings, then it certainly should be. And finally, FreeSync can only remove stuttering or juddering from frame and refresh rate mismatches and can’t compensate for other issues caused by network latency, lack of memory and suchlike.

FreeSync – the experience

Usually when we test FreeSync it is on monitors with a higher refresh rate and/or higher resolution, which provides to be potentially rather demanding. It is not too difficult to achieve a consistent 72fps (to match 72Hz) at the 1920 x 1080 resolution using a moderately powerful GPU and fairly sensible in-game settings. There are still some dips that can be expected here and there, though, especially on more demanding titles. It also allows you to crank up the detail settings a bit if you have the headroom to do so – and you don’t need to worry about those slight dips below 72fps that you might experience. Note that sensitivity to tearing and stuttering varies, so some users won’t find the difference as striking as others. It’s very subjective, so note that the observations below are just our observations as seasoned reviewers with a keen eye for this sort of thing.

The first title we decided to test was Tom Clancy’s The Division, which is a fairly graphically demanding title depending on the settings used. We used fairly modest settings, with which the frame rate tended to fluctuate between around 60 – 72fps. With FreeSync disabled there was (to us) obvious stuttering or tearing, making the experience quite jarring and disrupting the ‘flow’ of gameplay. With FreeSync enabled, the refresh rate was matched to the frame rate and such unwanted aspects were eliminated. There were times where the action intensified such that the frame rate dropped further. You could definitely feel and see the effects of this (i.e. increased motion blur, decreased connected feel) so the lower frame rates alone were quite jarring in a way. There were times when the frame rate even dipped momentarily below the 48fps (48Hz) floor of operation for the monitor, leading to tearing or stuttering as you’d see on any monitor.

We also tested GTA V (Grand Theft Auto 5), which again has the potential to strain a poor little Radeon 290 even at the Full HD resolution. Using fairly high settings, the frame rate tended to hover somewhere around 65 – 72fps, but not always reaching 72fps. Even these small drops from what would be the static refresh rate of the monitor cause bothersome tearing, juddering or stuttering without FreeSync. With the technology enabled everything had that sort of ‘frame rate at refresh rate’ flow to it, without any such interruptions. Occasionally the frame rate dropped lower than this, sometimes closer to 50fps. The experience here was certainly much nicer than without FreeSync enabled, but the decrease in frame rate could still be felt. The level of motion blur was increased and interactions with the game world felt a bit more sluggish.

The curve

Samsung are marketing curved screens quite heavily at the moment – indeed it’s something that began with some of their ‘E’ series models last year. They’re keen to point out that having a concave curve to the screen is more natural and comfortable on the eyes. That’s because the edges of the screen are brought closer to the eyes (i.e. distance from centre to edges of screen decreased). We’ve reviewed the S27E590C, for example, which had a gentle 4000R curve. This proved to be so subtle that it barely changed the experience at all – it didn’t really add much or take much away from the experience. Such a gentle curve was the norm for their curved 24 – 27” ‘E’ series models.

The C27F591FD (CF591) brandishes a steeper curve; at 1800R. Bearing in mind a lower ‘R’ value indicates a steeper curve; this makes it ‘over twice as curved’ as the previous models. The curve certainly proved more noticeable this time around, but despite how it may appear on paper and indeed some shots (especially when taken from a non-central angle) the curve remained a relatively subtle thing. It certainly wasn’t sufficient to make the monitor feel all that different when we used it – which is good in a way, as we found it very natural and adapted to it very readily indeed. If the marketing is to be believed, then it also has the potential to enhance viewing comfort. For designers or those who work with straight lines and shapes, we could certainly see how this curve could actually prove to be a less than desirable thing. We did not notice any obvious distortion on the desktop, although if we observed the task bar or other straight lines the curvature of the screen did make for an apparent subtle bending as you might expect. This was most noticeable in Excel (second image below). Note that these images are only for illustrative purposes and tend to make things look a bit different to how they do in person, with the curve generally more noticeable in the images. The interlacing patterns on some images are moiré from the camera, not artifacts from the monitor.

We found the curve again completely natural and easy to adapt to (if adaptation was even required, which is questionable) when watching movies and playing games as well. It isn’t such a steep curve that it wraps around your face or anything, but it does envelop your view a bit more than a flatter screen would. This gave a sort of extra depth to the experience, but not in a way that dramatically impacted the overall ‘feel’ of the movie or game. It is hard to describe really – we liked the effect, but found it quite subtle really. Any strange interlacing patterns in these images (and indeed those above) are moiré from the camera rather than artifacts on the monitor itself.

Video review

The video below summarises some of the key points raised in this written review and shows the monitor in action. The video review is designed to complement the written piece and is not nearly as comprehensive.

Conclusion

It seems that last year’s curved 27” models from Samsung were testing the water, seeing how consumers react to the idea of having a curved rather than flat screen. The Samsung C27F591FD (CF591) represents an evolution of these, with a significantly steeper curve. Although the curve is more of a feature this time around, it does remain quite a subtle one. Using the monitor felt natural to us, whilst we feel the curve brought a bit of extra depth to games and movies. This was something we didn’t really feel with the older (less curved) models, as the curve was simply too subtle to notice at all.

Whether or not curved monitors are your thing (perhaps you’re quite indifferent to them), the screen itself impressed on many fronts. The image took a bit of tweaking, as it was too bright and cool-looking out of the box, but following this the richness and variety of shades displayed was very pleasing. The generous (beyond sRGB – but not ‘wide gamut’ in the traditional sense) colour gamut and light matte screen surfaces helped provide a vivid but not overblown look to the image. The VA panel helped deliver these colours in quite a ‘punchy’ way and indeed the consistency was about as good as we’ve seen from a VA model of this size.

Where shades really caught the eye was in ‘high-contrast’ situations – with the contrast performance being a known strength of VA panels such as this. In this respect things were as we expected, with strong static contrast of ~3000:1 (as specified) and a backlight that remains flicker-free at all brightness levels. This helped the monitor deliver quite deep-looking blacks and dark shades and helped lighter shades ‘pop’ out amongst them. The matte screen surface was not only light; it was also smooth – presenting light shades without the graininess associated with some matte surfaces.

Responsiveness is never the strong point of VA technology and that was certainly the case here. There was a bit of trailing from slower than optimal pixel transitions, but this was not as pronounced as we’ve seen on some VA models and generally confined to darker shades. There were also some traces of overshoot. Overall, though, we’d see this was one of the better balanced VA models we’ve come across in terms of responsiveness. This helped the monitor make use of its refresh rate, which is ‘officially’ 72Hz with FreeSync enabled and can be ‘overclocked’ to that without. The monitor worked as you would hope with FreeSync, providing an experience between 48 and 72Hz (FPS) that was free from the stuttering or tearing that comes with a static refresh rate. Input lag was also low, with the signal delay clearly being minimal and the pixel response time accounting for the vast majority of the input lag readings we took.

Overall we feel this monitor delivers one of the most engaging ‘Full HD’ experiences out there. It may not be the best choice for colour-critical work (although can be used for some if you’re a hobbyist) nor will it win any wars of responsiveness with the higher refresh rate gaming-oriented screens. But when it comes to general use and providing an engrossing gaming and movie watching experience, this model hits the spot. It certainly isn’t the cheapest of models nor does it offer the sort of ergonomic flexibility some would hope for given the price. However; we do still feel it does enough to justify this price tag.

The bottom line; a screen with a curve that is subtle but noticeable, with much more to offer beyond just that.

 

Donations are also greatly appreciated.