Thinkpads Forum

It is known that LCDs display best at their native resolution--this is the physical resolution for the LCD. This also gives us a native pixels per inch. For example, a t61p with a 15.4" screen and 1680 x 1050 resolution has 128.645 pixels per inch (ppi).

In Windows one can also adjust the dpi (dots per inch). This is set at 96 dpi, 120 dpi and 150 dpi for smaller, medium and larger setings. One can also choose a custom dpi.

What is the connection between ppi and dpi? Should one set the dpi to the ppi for best display or is it not an issue? What about fractional ppi?

Thanks

Good question. I'd like to know, too, since I'm contemplating upgrading my 15.4" T60 to WSXGA reoltion.

The PPI describes the size of three subpixels (or one pixel). This determines how fine-grained the diplay is and basically how small a "dot" can appear.
But in the world of software what does a resolution of 200x200 really mean in cm or inches? The piece of software does not necessaily know the PPI of the monitor. We know that there must be 200x200 dots, but we don't know how large any of the dots needs to be.
In monitors each "dot" is representable by one pixel, and has a finite size. Setting the DPI equal to the PPI means showing fonts at the size that the developer of the software intended. It's a way to obtain equal font sizes at any display regardless of PPI as long as DPI = PPI. Setting the DPI too low means that it uses fewer dots per inch, so not a good idea with a high-ppi monitor. Setting the DPI too high means huge fonts etc. on a low PPI screen.

In my opinion, it's not really important. What's more important is that it's comfortable to read. A high PPI LCD is easier on the eyes no matter what, if you can increase PPI. This is due to the fact that the "screen door" effect becomes less and less visible. (again, IMO)

Microsoft explains what they mean by "96 DPI", "120 DPI" etc. on this page: http://support.microsoft.com/kb/820286

Thanks for trying but I am still confused.

Here's another attempt.

ppi is determined by the native resolution of the LCD--can assume it is fixed since it is accepted that display is best at native resolution.

Let us also fix the font size at 10 pts.

Is there an optimum dpi for a given font size and ppi (leaving aside subjective factors) at which the display is best? When I say "best" I mean in the same sense that LCD display is best at native resolution.

If there is an optimum, what determines this?

Does font smoothing, like Clear Type, play a role in this?

The following link may be of some help.
http://www.microsoft.com/typography/Wha ... rType.mspx