Although output resolution (ppi) has a dramatic effect on the quality of printed photos, it's a moot point for pictures displayed on-screen. A computer monitor (or other display device) cares only about the pixel dimensions, not pixels per inch, despite what you may have been told by some folks. The number of pixels does control the size at which the picture appears on the screen, however.
Like digital cameras, computer monitors (and other display devices) create everything you see on-screen out of pixels. You typically can choose from several monitor settings, each of which results in a different number of screen pixels. Standard settings include 640 x 480 pixels, 800 x 600 pixels, and 1024 x 768 pixels.
When you display a digital photo on your computer monitor, the monitor completely ignores any output resolution (ppi) setting you may have selected in your photo-editing program and simply devotes one screen pixel to every image pixel. For example, Figure 2-9 shows my 19-inch monitor as it appears when set to a screen resolution of 1024 x 768. The Pompeii photo inside the e-mail window contains 640 x 480 pixels - and therefore consumes 640 of the available 1024 horizontal screen pixels and 480 of the 768 vertical pixels.
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| Figure 2-9: You don't need many pixels to fill a computer screen. |
This fact is great news for digital photographers with low budgets, because even the most inexpensive digital camera captures enough pixels to cover a large expanse of on-screen real estate. And again, the pixel count doesn't alter the on-screen quality; all that varies is the display size of the photo. For more specifics on sizing pictures for the screen, turn to Chapter 10.
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