Different computer monitors have different pixel densities. These are often expressed in pixels per inch or dots per inch (DPI). If the computer's idea of the monitor's DPI does not match the physical DPI of the connected monitor, or if it does not compensate for differences in seating distance, text and other objects will look too large or too small. Setting DPI is a procedure to make things on a monitor look as large as intended to the viewer.
Personal computer window systems are designed for 96 DPI and a 28-inch seating distance.[1] But for a high-definition television (HDTV), typical seating distances are greater and pixel densities are lower. To compute the effective pixel density:
For example, if I'm sitting 1.8 m away from my VX32L, a "32 inch class" 720p TV made by Vizio measuring 0.8 m diagonally, the window system DPI should be set to 720 * 2.04 / 0.8 * 1.8 / 28 = 118 DPI. We can round that to 120, which is in fact the predefined setting for "large fonts" on Windows XP.
The obscurity of this formula has been cited as one of the reasons why HTPCs are for geeks. An ideal home theater PC should include a tool to ask the user for the TV's diagonal measure and seating distance and configure this automatically.
Once you have calculated the effective DPI, you need to tell the window system what DPI to assume. Most desktop environments allow this:
This gives you a starting point. Feel free to revise it up or down based on your own visual acuity.
Categories: HOWTO, Home theater PC