Somewhere along the way in a conversation about digital images, you may have heard that you should use an output resolution of 72 ppi or 96 ppi for screen pictures — pictures you intend to set as "wallpaper" for your computer monitor. With all due respect to the person who passed along this misinformation, it simply isn't true.

Way, way back in the infancy or digital graphics and the Internet, some experts did suggest that an output of 72-96 ppi was appropriate for screen images. Those numbers were based on the fact that the standard Macintosh monitor of the day left the factory set at a default screen resolution that resulted in 72 screen pixels per inch, based on the viewable area of the monitor screen. The standard PC setting delivered 96 screen pixels per inch. So if you used your photo editor to establish an output size of , oh, say 1 inch by 1 inch, and set the output resolution to 72 ppi, it would display at exactly 1 inch by 1 inch on a Macintosh monitor. However, the 72 or 96 ppi setting didn't have anything to do with how the monitor thought about the pictures — it always just used one of its screen pixels to reproduce each image pixel.

Today, monitors come in many different sizes, and people have a choice of multiple screen resolutions. So there is no standard number of screen pixels per inch, which means that the 72/96-ppi thing is totally off base. For some reason, though, this old chiphead's tale remains a popular one, especially in Internet newsgroups that discuss digital imaging.