A basic article on resolution shows how to find the monitor with the optimal pixel density (ppi).
There are some misunderstandings about resolution. Furthermore, although higher resolutions are always desirable, they also come at a price and sometimes cause problems in practice that were not even expected before the purchase. In the end, dissolution is not an end in itself. The cost-benefit ratio must be right.
With our basic article, we, therefore, want to explain what resolution actually is, shed light on the jungle of marketing terms and show how you can estimate the cost-benefit ratio for yourself even before the purchase.
In the second part, we give our subjective assessment of common combinations of display size, display format and resolution with regard to sharpness and suitability in the sense of a purchase consultation.
Resolution – what is it?
The term resolution has been around much longer than computers. Nevertheless, most people today associate it with a megapixel number. This is the total number of pixels in a raster graphic. A raster graphic, in turn, describes an image in digital and thus in computer-readable form. To do this, the image is divided into individual pixels, which are arranged in rows and columns in a grid pattern and to which a colour is assigned in each case.
The megapixel number on its own does not say much. If a format specification such as 16:9 is added, we at least know what the screen looks like and can also describe the resolution as 2560 x 1440 (QHD) or 3840 x 2160 (UHD, 4K). However, we still do not know how fine or coarse the representation (resolution) actually is. Only when an indication of the real size of the displayed area is added, it becomes clear how large the individual pixels actually are and how coarse or fine they describe reality.
Because in analogue reality there are no pixels and no resolution limits. If we keep enlarging an object under the microscope, pixels will not appear at some point. Depending on the performance of the microscope, the magnification increases, but also the appearance of new, ever finer details.
With digital images, however, it is only a question of magnification until the pixel grid becomes visible. Resolution is, therefore, a measure of the accuracy of the representation of reality. In this respect, the digital resolution cannot actually be high enough to approach reality.
Digital image files are usually represented by digital display devices as square pixels, which are also arranged in rows and columns. Some projectors also use diamond-shaped pixels, but this should not play a role here. The number of pixels that a display can display simultaneously (native resolution) is independent of the amount of data in the displayed image file – it depends on both.
Current SLR cameras with full-frame sensor already deliver images with 45 megapixels or more. Even smartphones have long been equipped with 12-megapixel sensors. For example, an iPhone already delivers 6s (4032 x 3024 pixels in 4:3 format) – significantly more pixels than you can display simultaneously on a UHD 4K display (3840 x 2160 pixels).
So far, it is more the display devices that represent a bottleneck. The issue of resolution becomes problematic at the latest when the screen resolution of the display device is too small in relation to the display size so that the screen becomes visible to the naked eye.
But even before that, the digital raster has a negative impact. With lines running exactly horizontally or vertically, the resolution does not yet play such a large role, but the problem becomes clearly visible with lines running at an angle. Due to the square pixels, these cannot be displayed correctly, resulting in staircase-shaped digital artifacts.
The figure below shows how these artifacts disappear with increasing resolution – from left to right.
Graphics from left to right: Improved edge sharpness through higher resolutions
From left to right: Improving edge sharpness through higher resolutions (Graphic: Website EIZO)
There are some smoothing algorithms in operating systems and applications, such as ClearType, that try to smooth these staircase effects by inserting additional grey pixels. This smoothing works quite well but also causes a certain amount of blurring due to inaccuracy or double contours. At the “K” on the far left, you can see this well.
Higher resolutions not only improve the richness of detail and sharpness in the image, but also the colour representation. This is particularly evident in colour gradients and is easy to understand. Where on a Full HD screen a certain area is represented by exactly 1 pixel with an (ultimately averaged) colour value, 4 pixels are available on a 4K display, which can also have different colour values.
The higher the resolution, the sharper and more brilliant the image appears, since the inaccuracy caused by the square pixels is no longer visible.
The term HD rather comes from the TV area, means the resolution 1280 x 720 (also called 720p) and was actually only a transitional solution to the “sharpener than the reality full HD” with 1920 x 1080 pixels (also called 1080p). Since no customer today can be lured into the “I am not stupid” market with “sharper than reality”, UHD-4K (3840 x 2160 pixels) was needed.
The monitors also feature QHD resolution (2560 x 1440 pixels). This stands for Quad-HD – the fourfold HD resolution that has never played a role in monitors anyway. Instead, the comparison with Full HD would be more honest: QHD offers a resolution gain of 33 percent in comparison.
This also leads us directly to the next misunderstanding, which is often fired by the manufacturers’ marketing and is therefore widespread. 4K resolution is not four times higher than Full HD resolution. Only the amount of pixels is four times as high. However, the image consists of height times width, and the resolution is measured accordingly in horizontal and vertical line pairs. It has only doubled compared to Full HD (1080p x 2 = 2160p).
Here, buyers are misled, especially with camera sensors. The jump from an 8 to a 12-megapixel smartphone camera in the next generation sounds quite impressive at first glance – after all 1.5 times. However, the actual gain in resolution is only half, i.e. 25 %. This is just above the perception threshold. But only if the additional pixels can actually record additional information. And this is usually no longer fully the case with the tiny smartphone sensors. The real gain in resolution is therefore much smaller.
The photo on the left shows the photo of an iPhone 6s under optimal light conditions with ISO 25 in full screen. At first glance, the shot looks quite reasonable and rich in detail. When zooming into the 100% view, however, it becomes clear that the pixel grid of the camera sensor is no longer able to adequately capture the existing details. Instead of single grass.
The purely quantitative number of pixels in the input material does not say anything about the quality of the pixels. To take full advantage of high-resolution displays, both the resolution and the quality of the input material must grow accordingly. However, as long as the resolution of the input material can at least match the resolution of the output display, one can at least say that even a photo with suboptimal image quality does not look worse on a 4K display than on a Full HD display.
But the next resolution leap in the displays is already in the starting blocks with 8K (UHD-2). Here the resolution is doubled again compared to 4K in height and width (7680 x 4320). The number of pixels is four times as large.
The photos of a 36-megapixel DSLR such as the Nikon D810 (7360 x 4912) are just enough for this without image cropping (the height is decisive, not the width). In the next chapter, the marketing term “retina” leads us to the question of the meaning of this upward spiral in the resolutions.
Why still higher resolutions?
So it’s all just marketing rubbish or does it make sense somehow? That depends…
First, the display size, because we were just talking about resolutions again and ignored the important relation to the real size of the display. This information is usually summarized in the specification ppi – i.e. pixels per inch. It describes how many pixels in the display diagonals fit in a row on 1 inch (2.54 cm).
Due to the trend towards ever-larger TVs and monitors, the resolution must therefore also be increased in order to compensate for this. On the desk, 24-inch monitors with full HD resolution are still the most widespread. That’s only 93 ppi. Today, a modern daily newspaper achieves 150 dpi, 300 dpi is usually used for photo printing, and 300 dpi or more is also used for fine art printing.
A 24-inch screen would require a resolution of 6275 x 3530 pixels for 300 ppi. UHD-4K is not enough here either. Unless there are intermediate stages, 8K (7680 x 4320 pixels) – mind you on a small 24-inch monitor. If the screen is to become larger – or even a TV – 8K is no longer sufficient. With a glance at their wallets, some technology enthusiasts who are perhaps thinking about purchasing an expensive 4K beamer may find their stomachs queasy. For a 90-inch diagonal screen (2 meters wide) we would need 23 523 x 13 237 pixels for a 300ppi resolution.
So, if “shepherd as reality” doesn’t exist and we can approach reality digitally at best, do we have to wait until the ppi specifications for the devices run against infinity before we should buy a new monitor/TV/projector?
I don’t think so. The terms “useful” resolution and “dead” resolution also exist in connection with (analog) optical instruments. A resolution is only useful if it is adapted to the resolution of the human eye. Anything beyond that no longer provides any additional benefit.
For the technical description of the resolution, the relation of display size to resolution is sufficient. To answer the question of meaningfulness, however, the viewing distance in connection with the resolving power of the human eye is still decisive.
At a distance of 25 cm, most adults can see an object clearly and permanently. Some people can still distinguish structures at a distance of 0.15 mm. This is actually very different for each individual.
From this, Apple declared the upward spiral of smartphone displays to be over almost eight years ago with the term “retina display” on the iPhone 4 (960 x 640 pixels, 326 ppi). Apple calls the retina display screens of its own products, which have such a high dot density that the human eye should not be able to recognize individual pixels from a typical viewing distance.
The “typical viewing distance” explains why a 27-inch iMac with a 5K display (5120 x 2880 pixels) and “only” 217 ppi may also be called a retina, but not why iPhone X suddenly needs 458 ppi. Ultimately, it is a pure marketing term. Just as the typical viewing distance is different for everyone, human vision is also very different even in healthy, young people. An exact ppi limit for “good is good enough” does not exist and would have to be defined differently depending on the viewing distance.
Overview of common resolutions for monitors in comparison
| designation | Screen resolution in pixels | Dot density in ppi |
| HD | 1280×720 | 24 inches: 61 27 inches: 54 32 inches: 46 |
| Full HD | 1920×1080 | 24 inches: 92 27 inches: 82 32 inches: 69 |
| QHD, WQHD | 2560 x 1440 | 24 inches: 122 27 inches: 109 32 inches: 92 |
| 4K (UHD 1) | 3840 x 2160 | 24 inches: 184 27 inches: 163 32 inches: 138 |
| 8K (UHD 2) | 7680 x 4320 | 24 inches: 367 27 inches: 326 32 inches: 275 |
| iMac with Retina 5K display (27 “) | 5120 × 2880 | 27 inches: 217 |
| UWQHD-1440p, Ultra Wide QHD (QHD) | 3440×1440 | 34 inches: 110 |
| QHD + 1600p UW4k, Quad High Definition Plus (Ultra Wide 4K) | 3840 x 1600 | 38 inches: 111 |
How can one subjectively estimate for oneself which resolution one needs for the next monitor/TV/projector?
There can be no generally valid information about the relation of ppi to the viewing distance, but you can still easily find out for yourself when good is “good enough”.
The structure width of 0.15 mm, from which most adults should be able to see the structure from a distance of 25 cm, corresponds almost exactly to the pixel size of a 27-inch display with 4K resolution.
From this distance, the author can no longer see the complete pixel grid in the subjective self-test, but he can see staircase effects for certain letters. However, the distance of 25 cm from the eye to the display is less than you might think – the nose is almost there. From a distance of 50 cm, the author can no longer recognize the staircase effects on a normal desktop. The usual working distance at the desk should be 60 to 70 cm for most people.
For the same picture quality, a 4K TV from a distance of 2 meters should be 108 inches, a Full HD TV at least 54 inches. However, ClearType improvements are usually still active on the normal desktop, which reduce the staircase effects (at the expense of sharpness).
For the self-test, we, therefore, recommend that you create a text file with different font sizes (preferably Arial as font), output the file as a PDF and then view it in a PDF reader with 100% scaling. Before that, you should deactivate all render improvements like “Smooth text”, “Display thin lines more clearly” etc. in the settings of the PDF reader. Especially with the letter “A” and the number “4” you can see the staircase effects from close up.
Then simply increase the distance successively. If you can no longer see any staircase effects, carefully measure the distance between the eye and the display and then convert.
Example: The reader has very good eyes and a standard 24-inch monitor with full HD resolution. From 1.20 m, the staircase effects can no longer be seen, even with the best will in the world. Then a device with double resolution (4K) would be perfect for him at half the distance (60 cm). For the planned acquisition of a new 40-inch TV, on the other hand, the Full HD resolution is completely sufficient even from a distance of just 2 metres. Apart from the “must be better” effect, a 4K device should hardly bring a sharpening advantage.
The price of the higher resolution
If we keep doubling the resolution, the limit of what makes sense may have been exceeded at some point, but it can’t hurt, can it?
No, but unfortunately this still has its price, and it is increasing disproportionately. A doubling of the (perceptible) resolution means four times as many pixels. File size and thus storage space requirements also increase fourfold. The videographer, who changes from Full HD to 4K, really gets to feel it.
More powerful hardware is also required to cope with the amount of data. The gamer immediately thinks of the graphics card, which, however, only offers acceleration in a few areas in the EBV. Here, above all, the CPU is required and more memory is needed.
And the price is not only monetary. Even when money doesn’t matter and the PC is state of the art, Lightroom users know how to sing a song about the painfully long waiting times when rendering previews and exporting images. Of course, this doesn’t get any better when you jump onto a 4K monitor. Larger previews must be rendered, and more pixels must be loaded and calculated simultaneously in the development module.
After all, version 7.2 of Lightroom Classic CC has changed a lot in terms of performance. Even though Adobe is selling us a long overdue fix as a new feature, it is still a step in the right direction.
In Photoshop, however, we did not notice any performance difference between working with Full HD, QHD or 4K monitors in the test. Here it is primarily the resolution of the processed file and the colour depth (8 bpc vs. 16 bpc) that can increase the processing time.
Another price will be paid by others. Whether smartphone or desktop applications, for the software developers it means a not insignificant effort to adapt their applications – especially the icons and the text scaling – to the higher resolutions.
Switching to a monitor with 4K resolution can therefore also bring unpleasant surprises for the user. Older applications, which do not really need an update, suddenly show scaling problems.
Also with the OS, you may not get along with the previous scaling setting of 100 % (i.e. no scaling). Example: If you switch from Full HD to 4K resolution with a 24-inches, the icons on the desktop occupy only a quarter of the previous area. Now twice as many icons fit in the bottom of the taskbar, but they also get fiddly small.
At the latest, the tiny font in the file explorer forces you to increase the scaling in the OS. At 200%, the desktop then looks exactly the same as under Full HD – only much sharper. However, the prerequisite is that all icons have already been adapted for higher resolutions. Otherwise, they now look quite pixelated.
Apart from this, scaling has gradually improved under Windows 10 (version 1709 at the time of testing), but problems still occur time and again, especially when using several monitors with different sizes and resolutions.
Those who travel a lot with mobile devices will also feel the price of the battery life. The power consumption is higher at least currently with higher-resolution displays so that otherwise identical devices with Full HD resolution usually last considerably longer instead of 4K resolution.
Different resolutions for multi-monitor systems
Ideally, a multi-monitor system should use a corresponding number of the same devices from the same manufacturer. Manufacturers such as EIZO, LG and Dell also offer additional software to synchronize the OSD settings for all devices in one go.
Not everyone has the money for this ad hoc, and anyone who buys a new QHD-27-inches may also want to continue using their existing 24-inch full HD monitor. Of course, it is generally recommended to match brightness and colour temperature as closely as possible – preferably with calibration.
As long as you can use the same scaling setting for both devices in the OS, this works very well. But if the scaling settings are different, at least moving the windows from one monitor to the other is not as smooth as you are used to. It can also become annoying if not all devices are constantly switched on or wake up from standby in different ways. Then, if necessary, all window arrangements will be jumbled and certain applications will be partially scaled incorrectly.
For example, the two figures below show how moving a window from the right screen (QHD resolution, OS scaling at 100%) to the left B
In our experience, the final recommendations show which monitors/resolution combinations are compatible with each other and which are less compatible.
With the mosaic-like decomposition into a digital grid, we can inevitably only approach the analog reality – the higher the resolution, the better. How high the resolution really is, however, can only be assessed meaningfully in connection with the display size. From a technical point of view, the ppi specification provides information about this.
If you switch from a full HD monitor with 92 ppi to a 4K device with 184 ppi, the difference is immediately obvious. Texts, in particular, appear much smoother and sharper. At the same time, the accuracy and thus the balance of the colour representation is improved by higher resolutions.
Conversely, however, high resolutions also have their price, which is increasing disproportionately. Therefore, the desire for more dissolution should not be ignored.
This depends on the one hand on the viewing distance and on the other hand on individual vision. In order to take full advantage of the high resolution of the display, we also need input material, which in turn can keep up with the resolution and quality.