Several kinds of resolution can affect bitmap quality: screen resolution, image resolution, and pixel resolution. You should understand the differences between all three when working with bitmap images.
Screen resolution is the maximum image area of the computer screen, expressed in horizontal and vertical pixels, for a particular video mode. The standard video mode for the Multimedia PC is 640 pixels by 480 pixels. You'll have to consider screen resolution when establishing a target image size for a scanned photograph.
Image resolution is the size of the digitized image expressed in horizontal and vertical pixels. The image resolution can differ substantially from the screen resolution. For example, say you display a 320-by-240 pixel image on a 640-by-480 pixel display. In this case, the image size is one-half the screen resolution, so the digitized image only fills one-half of the screen. When the image size and screen resolution are identical, the image fills the screen. When the image size is larger than the screen resolution, the screen can display only a portion of the image—requiring the display software to support scrolling to see other portions of the image.
Pixel resolution can become a factor when you move images between different graphic display modes or computer hardware. Pixel resolution refers to the ratio of a pixel's width to its height (also known as the pixel's aspect ratio). This can cause unexpected distortions in an image that's transferred between machines with different pixel resolutions. For example, if you capture an image on a device that uses rectangular pixels with an aspect ratio of 1:2, and later display it on a device that uses square pixels with an aspect ratio of 1:1, the image will be distorted. Fortunately, pixel resolution inconsistencies don't occur frequently as most displays use square pixels with an aspect ratio of 1:1. Also, most capture devices let you adjust the pixel aspect ratio for your system.