When your output device is a monitor instead of print, the screen size determines the size of the image. Since there are a fixed number of pixels on a screen, if you’re going to display that 800 by 600 image on a screen, then the number of pixels across the image will always be 800, but depending on the screen size, the pixels will be closer or farther apart. When working with monitors, the number of pixels from top to bottom is described as the number of lines. Using your 800 by 600 image as an example, there would be 600 pixel rows (lines) vertically when the image is displayed on that screen. When the resolution of the monitor changes, the image will still be displayed across 600 lines of the screen, but it may appear larger or smaller because the lines are closer together or farther apart.
– From Vickie Claiborne’s Video Digerati column in the April issue of PLSN
