Does PPI matter or does a higher resolution almost always look better?

durrburger · November 23, 2020

I always though that PPI is the most important metric for display clarity, but everything I've seen so far indicates otherwise.

A few years ago I had a 4k 40inch TV and a 1440p 27inch monitor both hooked to my PC. At appropriate viewing distsnces the TV always looks better at the native res both on desktop and within games.

Now I have a 49 inch 4k TV and recently looked at a friend's 1080p 24 monitor which has a higher ppi technically, 91 against 89, but in terms of clarity there is no context, the TV kills it at any distance.

Does PPI only matter when the resolution is the same and display size is the only factor? Will 4k always be >1440p and 1440>1080 etc?

Glenwing · November 23, 2020

19 minutes ago, durrburger said:

I always though that PPI is the most important metric for display clarity, but everything I've seen so far indicates otherwise.

A few years ago I had a 4k 40inch TV and a 1440p 27inch monitor both hooked to my PC. At appropriate viewing distsnces the TV always looks better at the native res both on desktop and within games.

Now I have a 49 inch 4k TV and recently looked at a friend's 1080p 24 monitor which has a higher ppi technically, 91 against 89, but in terms of clarity there is no context, the TV kills it at any distance.

Does PPI only matter when the resolution is the same and display size is the only factor? Will 4k always be >1440p and 1440>1080 etc?

Pixel density isn't an absolute measure of clarity. Pixel density tells you clarity per metre of distance from you. So if you have two displays with pixel densities of 100 px/in and 200 px/in, the 100 px/in one has lower density and won't appear as sharp as the other display, if both are placed at some given distance. However, if you place them at different distances, the comparison is different.

This is because objects that are farther away from you appear smaller. Pixels are no exception to this. So if you place a display with 200 px/in at 2 metres from you, but you place the 100 px/in display at 6 metres away, the 100 px/in will look sharper than the 200 px/in display. If you triple an object's distance from you, it appears one third the size, so at 6 metres all the pixels in the display will appear to be 1/3 as large as they would at 2 metres away. So having the 100 px/in display at 6 metres is equivalent clarity to having a 300 px/in monitor at 2 metres, so it will look sharper compared to the 200 px/in display at 2 metres.

40" 4K and 27" 1440p have around the same pixel density. But if you view the TV from further away than the monitor, then the pixels will appear smaller and closer together.

durrburger · November 23, 2020

6 minutes ago, Glenwing said:

Pixel density isn't an absolute measure of clarity. Pixel density tells you clarity per metre of distance from you. So if you have two displays with pixel densities of 100 px/in and 200 px/in, the 100 px/in one has lower density and won't appear as sharp as the other display, if both are placed at some given distance. However, if you place them at different distances, the comparison is different.

This is because objects that are farther away from you appear smaller. Pixels are no exception to this. So if you place a display with 200 px/in at 2 metres from you, but you place the 100 px/in display at 6 metres away, the 100 px/in will look sharper than the 200 px/in display. If you triple an object's distance from you, it appears one third the size, so at 6 metres all the pixels in the display will appear to be 1/3 as large as they would at 2 metres away. So having the 100 px/in display at 6 metres is equivalent clarity to having a 300 px/in monitor at 2 metres, so it will look sharper compared to the 200 px/in display at 2 metres.

Thanks for elaborating! Is there a way to calculate how close do I have to sit near, for example a 32inch 1440p monitor that I plan on getting, to achieve the same clarity of my current 4k 49inch TV? I wanted to get a 1440p higher refresh screen but I got really used to large screens and having sharp text and games with little to no aliasing, so don't how how much of a difference this monitor would prove.

Glenwing · November 23, 2020

13 minutes ago, durrburger said:

Thanks for elaborating! Is there a way to calculate how close do I have to sit near, for example a 32inch 1440p monitor that I plan on getting, to achieve the same clarity of my current 4k 49inch TV? I wanted to get a 1440p higher refresh screen but I got really used to large screens and having sharp text and games with little to no aliasing, so don't how how much of a difference this monitor would prove.

Yes it's simply:

(Pixel density of old display) ÷ (Pixel density of new display)

The result is how many times farther away you need to place the new display at to look the same. For example if the result is 2, that means the new display needs to be twice as far away to look the same. If the result is 0.5, it means the new display needs to be half the distance to look the same.

Keep in mind that even if you have an object twice as large and place it twice as far away, it will never look exactly the same as an object at half the size and half the distance, because of stereo vision/depth of field effects you will still be able to tell that the object is further away so it won't feel exactly the same as a smaller but closer object, even when the math matches up.