Screen size: physical vs. usable
Perhaps the most important output device for every comptuter is its screen. For the majority of people, whether using laptops or desktops, screen size is referring to the physical size – usually the nominal diagonal of the panel in inches. Pixel count, aspect ratio and the pixel density – or PPI (pixels per inch) that derives out of those, are often completely missed. Big mistake: in reality, PPI is the real resolution metric:
resolution: a measure of the sharpness of an image or of the fineness with which a device (as a video display, printer, or scanner) can produce or record such an image usually expressed as the total number or density of pixels in the image <a resolution of 1200 dots per inch>
The last few years, more and more people opt for and suggest their friends getting a 27″ monitor, and if you happen to see one from afar, you have to be impressed – 27″ surely is large!
Well…think again. The majority of the 27″ panels that are relatively affordable, are 1080p. That means that as far as pixel count goes, those are identical with your average 22″-24″ screen, but in reality the bigger screen means smaller PPI: that is, less resolution, as the same amount of pixels is called to cover a larger area.
In this table you can see really quick the available real estate as far as pixels go for the most popular resolutions. Of course most of the 4:3 and 5:4 monitors are obsolete now as nearly all the LCDs sold for the last 5 years are 16:9 or 16:10.
Assuming that the 1080p is the industry standard for displays, in the last column you can see the ratio of usable space the various monitor panels provide. Note, that there is no mentioning of a diagonal or any metric of physical size. It is irrelevant. The physical size of the pixel matrix can be set to whatever the manufacturer wants them to be. We can have minuscule pixel sizes in smartphones, to ultra small in the rMBP, too (relatively) huge in a 40~60″ 1080p panel. Of course the pixel count does account for the amount of information a panel is able to display at a given time, but as far as sharpness and image clarity goes, it doesn’t matter, as long as your viewing distance is right.
But how do we determine the optimal viewing distance?