When discussing PC monitor resolution everybody refers to 72 ppi resolution. How comes? Most modern monitors have from 640 by 480 pixel to 1200 by 800 pixels and larger desktop areas. So, resolution should be different for those various monitor settings. Also, what is the correlation between monitor resolution and monitor dot pitch? Can anybody provide the source for a good article that explains the differences between ppi and dpi. It seems that some authors don't understand this issue thus creating more confusion with their articles.

-- Bork Mulnik (neslonik@aol.com), March 03, 2000

Answers

It sounds like a tall order, but try this and see if it helps:

PPI - Pixels Per Inch, is simply how many pixels can be expressed in a linear inch. Pixels are considered to have the ability to be displayed with almost any color or brightness level. In the real world the number of colors depends on how many bits are used to represent each pixel. With 24bits you get nearly 16.8 million possible combinations of color and brightness.

DPI - Dots Per Inch, is similar, but used mostly by printer manufacturers. In the case of most printers each dot is only one of up to about 6 separate colors depending on the printer model. The dots are printed next to each other to blend (or dither) together so that the human eye perceives the properly shaded pixel. To be fair, a 1440 DPI printer actually prints considerably less pixels per inch since it takes several printer dots to form each pixel.

Monitor resolution: 72DPI thats the standard setting. It really should be PPI.

Dot pitch: Is the decimal fraction of a millimeter that is found between the center of one pixel and the next on a monitor. For instance .28 dot pitch means the monitor is capable of showing a separate pixel .28mm from the center of the preceeding and following ones. I think most newer monitors of .28 dot pitch are actually capable of more like 90 DPI, but 72 seems to be the standard rule. At least that seems to be what I've found.

Resolution: merely how many dots, pixels, whatever you're talking-a bouts there are per inch. Often stated as # x #, like 1280x1024, when talking about 2D objects or representations.

Correlation between monitor resolution and dot pitch? Well, it seems there isn't a lot really, though some programs "assume" 72 DPI when they report sizes in inches, if that helps? Naturally, a monitor would have to have a tight enough dot pitch to display a certain resolution on a certain size tube.

If I goofed somewhere, someone please jump in and set it right.

-- Gerald M. Payne (gmp@francomm.com), March 04, 2000.

I'll just add that 72 ppi (or dpi) is just a 'typical' monitor setting. Of course, the actual number will depend on your particular computer. Sometimes it is useful to tell your operating system the correct value, so that programs that show rulers can show them at the correct size.

-- Alan Gibson (Alan@snibgo.com), March 05, 2000.