As you prepare photos for on-screen use, remember that monitors display images using one screen pixel for every image pixel. The exception is when you're working in a photo-editing program or other application that enables you to zoom in on a picture, thereby devoting several screen pixels to each image pixel.
Most monitors can be set to a choice of displays, each of which results in a different number of screen pixels, or, in common lingo, a different monitor resolution. Standard monitor resolution settings include 640 x 480 pixels, 800 x 600 pixels, 1024 x 768 pixels, and 1280 x 1024 pixels. The first number always indicates the number of horizontal pixels.
To size a screen picture, you simply match the pixel dimensions of the photo to the amount of screen real estate that you want the picture to consume. If your photo is 800 x 600 pixels, for example, it consumes the entire screen when the monitor resolution is set to 800 x 600. Raise the monitor resolution, and the same photo no longer fills the screen.
For a clearer idea of how monitor resolution affects the size at which your photo appears on-screen, see Figures 1 and 2. Both examples show an 800 x 600-pixel digital photo as it appears on a 19-inch monitor (as a Windows desktop background, or wallpaper). In Figure 1, the monitor resolution is 800 x 600. The image fills the entire screen (although the Windows taskbar hides a portion of the image at the bottom of the frame). In Figure 2, the same picture displays at a monitor resolution of 1600 x 1200. The image now takes up one-fourth of the screen. A higher screen resolution means smaller screen pixels, so everything appears smaller - including your photo.
Unfortunately, you often don't have any way to know or control what monitor resolution will be in force when your audience views your pictures. Someone viewing your Web page in one part of the world may be working on a 21-inch monitor set at a resolution of 1280 x 1024, while another someone may be working on a 13-inch monitor set at a resolution of 640 x 480. So you just have to strike some sort of compromise.
For Web and email images, you should size your photos assuming a 640 x 480 monitor resolution - the least common denominator. If you create an image larger than 640 x 480, people who use a monitor resolution of 640 x 480 have to scroll the display back and forth to see the entire photo. Of course, if you're preparing images for a multimedia presentation and you know what monitor resolution you'll be using, work with that display in mind. For online use, also keep in mind that the Web browser or email window itself takes up some of the available screen space.
Figure 1: An 800 x 600-pixel digital photo fills the screen when the monitor resolution is set to 800 x 600.
Figure 2: At a monitor resolution of 1600 x 1200, an 800 x 600-pixel photo consumes one-quarter of the screen.
