1080p on 4k monitor

[food158]

This is more a hypothetical question. Say one had a 1440p or 4k monitor, that person uses the internet in 4k. However, they game in 1080p. Would simply switching the resolution ingame change the displayed resolution 1080p?

[WereCat]

Yes, but it looks worse than 1080p on a 1080p display because of the upscaling.

I don't know how on 4k but 1080p on 1440p looks quite bad. I suppose it doesn't look any better on 4k even with perfect scaling.

[food158]

1 minute ago, WereCat said:

Yes, but it looks worse than 1080p on a 1080p display because of the upscaling.

I see, thanks for answering.

[Gazelem]

I have the same question. Found a lot of differing opinions on the internet. There are two main camps.

1) Those that point out that 4k (3840x2160) is twice the horizontal and vertical resolutions of 1080p (and thus 4 times the pixels) so theoretically a 4k monitor could show 1080p with 4 pixels acting like one.

2) Those that have had issues trying to do this and say it is crap and doesn't work and you shouldn't try.

 

Some say it depends on the monitor or the upscaling it uses. I am looking at buying this LG 4k monitor because it seems like an awesome deal, but want to figure this out before I buy it.

[MegaDave91]

In theory 1080 on a native 4K should offer the same clarity as native 1080. The same can't be said for 1440 on native 4K.

[Gazelem]

I just realized the sticky titled "Display Technology FAQ/Mythbuster" at the top of this display section of the forums has a section on this topic. Still trying to absorb the info in it though and figure out if there are ways around the issues.

[Unhelpful]

Copied from the sticky:

 

"Does 1920×1080 scale perfectly on 3840×2160 (4K UHD) monitors? What exactly happens when you run a non-native resolution on a display?"

Spoiler

The notion that 1080p content viewed on a 4K UHD display will always look just as sharp as if it were a native 1080p monitor is actually a misconception, admittedly one that I also held before 4K displays were really widely available and tested. However now we know better, as actual tests have shown this to be a myth. Theoretically it can be true; 1080p is an exact fraction of 4K and so could potentially be displayed natively at fullscreen. Each pixel could be represented perfectly by a block of 4 pixels on the 4K screen, so the input image could be displayed exactly as it's received without any kind of modification required. In reality though, this is usually not how these images are handled. It will depend on the display, and most 4K monitors won't scale 1080p perfectly.

Normally, when a display is fed an image at a resolution smaller than its physical/max resolution, it has to perform a process called interpolation to upscale the image to its max resolution, which basically means it has to approximate what the image would look like if it were at that higher resolution. If you had for example a 7×7 image and you wanted to show it on a 10×10 display fullscreen, the image would have to be modified in order to be displayed. The pixels in the 7×7 image aren’t going to line up evenly with the 10×10 grid on your display:



Since each pixel on your 10×10 display can only be a single color, it’s impossible to display the image exactly like it appears above. In order to display anything you need to calculate a new 10×10 pattern that approximates the original as closely as possible:



As you can see, the approximation results in some pretty obvious blurriness, although if you stand far enough back you can still sort of make out a hint of the original pattern. Sort of. The negative effects of interpolation are especially noticeable with text:





These examples are using a very simplistic interpolation technique, overlaying the desired resolution on the image and calculating each new pixel using the “average color” that lies within each boundary. This is just to help visualize the concept of interpolation, monitors use more complex approaches to interpolation that give better, sharper approximations in most situations. Unfortunately, these approaches also affect resolutions which are exact fractions of the physical resolution.

If monitors interpolated using the simple averaging method I used above, exact fractions like 1080p on 2160p actually would display natively, since each pixel on the original image would line up exactly with every 2×2 grid on the new resolution, so every pixel would be a solid color and averaging them wouldn’t change anything. But most monitors use different interpolation methods which do affect resolutions which are exact fractions, and you can easily prove this to yourself by changing your desktop to such a resolution. If you’re using a 1920×1080 monitor, change to 960×540, if you’re on 1440p change it to 1280×720, etc. If it scales perfectly without interpolation then it should look quite blocky, especially with text, but you’ll most likely find that it looks rather fuzzy instead.

Long story short: no, most 4K monitors do not scale 1080p with simple 4:1 pixel mapping, no interpolation, despite the fact that it’s an exact fraction of 3840×2160. Most monitors will still interpolate the image. It’s certainly possible for a monitor to display such resolutions natively, but it would have to be purposely designed to not interpolate those resolutions. They won’t be displayed natively simply by virtue of being an exact fraction.

If you still don't believe me you can read professional reviews of actual 4K monitors and verify that 1080p does not scale perfectly, but is in fact interpolated.

 

  PCMonitors.info said:

It is a common misconception that running 1920 x 1080 on a ‘4K’ UHD monitor will automatically provide equivalent sharpness to a native 1920 x 1080 display. That belief is held because the UHD resolution has exactly twice as many pixels vertically and twice as many pixels horizontally as the Full HD resolution. In practice monitor interpolation processes aren’t perfect.

In the case of the Dell P2415Q, though, the interpolation process is surprisingly good. In fact we’d go as far as to say it’s excellent. If you run the monitor at 2560 x 1440 (WQHD) or 1920 x 1080 (Full HD) then you do lose a degree of sharpness compared to running that resolution on a 23.8” model that has a similar screen surface. This loss of sharpness is fairly minor, though, and is in fact one of the lowest losses of sharpness we’ve seen from an interpolation process on any monitor. On the desktop text looks a little soft but not really blurry as you’d usually observe from a normal viewing distance.

https://pcmonitors.info/reviews/dell-p2415q/

 

  PCMonitors.info said:

The image appears noticeably soft, much softer in fact than running 1920 x 1080 natively on your typical 27” Full HD LCD. Text appears to have a soft fringe and games look like they are being viewed through some sort of soft-focus lens. If you’re expecting things to look like they would on a native ‘1080p’ display, think again.

[...]

It is unfortunate to see that interpolation is handled so poorly by the monitor. It’s not entirely surprising, as we saw similar performance from the 28” ‘4K’ models. The Dell P2415Q, on the other hand, handled non-native resolutions surprisingly well.

https://pcmonitors.info/reviews/asus-pb279q/

 

 

[Gazelem]

So I guess the real question is: how do you check if a 4k monitor does a good job interpolating 1080p (or doesn't use interpolation for that resolution because it is smart) before buying the monitor?

[ArduinoBen]

Informative!  I'd pay a  lot for a display with good scaling then.....

[sgloux3470]

Windows looks like shit.  I'm not sure if it's just I need to reconfigure cleartype when changing resolution or what.

 

Games look okay for the most part.  I wouldn't use it over native resolution unless I had to though.