Pixel Density - What Is PPI Exactly?

What is PPI exactly? - Retina 5K iMAC compared to Full HD monitor

PPI (pixel per inch), alias pixel density represents the number of pixels per inch.
So 100 PPI point density is about approximately 0,25mm x 0,25mm pixels.

Why is interesting the pixel density at screens?
This number shows us from what distance can be a display enjoyable (has nice picture)
For example, we can not see pixels at a screen with 100 PPI from 1m distance.
I first saw the pixels on the edge of the letters from 11cm at a desktop like retina iMAC with 218 PPI. In my opinion this is the ideal pixel density at which higher is unnecessary.
Getting closer to a mobile (which has 386 PPI) the human eye proves to be insufficient because they no longer see as close as the pixels could be seen.

Some interesting facts from the Wikipedia: Getting older the minimum focus distance of our eyes is moving away from us :)

age (year)	minimum focus distance(cm)	age (year)	minimum focus distance(cm)
10	7,5	50	40,0
20	10,0	55	66,5
30	13,5	60	100,0
40	22,0	65	200,0
45	28,5	70	400,0

What kind of display you have?
find it out at the dpi.nu website!

I have made close-by images about some current display. 

LG 22MP55 - 22” Full HD (1920x1080)  100PPI

price-experience winning display

Retina iMAC - 27” 5K (5120x2880)  218PPI

the screen with the highest resolution available on the market

Sony Xperia Compact Z1 - 4,3” HD (1280x720)  342PPI

HD resolution on a cell phone display

Samsung Galaxy Note 3  - 5,7” Full HD (1920x1080)  386PPI

Full HD resolution on a cell phone display

I have made high resolution images about the surface of the screen (32mm x 9mm) 

You can download the original image  HERE (21.87 MB)

This image presents quite well what we are talking about. I wanted to show a display with another arrangement of pixels (Note3) as a point of interest.

Thanks for watching!
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