For example, more pixels means larger image files. Not only are larger files harder to store, they are also harder to edit, e-mail, and post on a Web site. Lower resolutions such as 640 x 480 are perfect for Web publishing, e-mail attachments, small prints, or images in documents and presentations. For these uses, higher resolutions just increase file sizes without significantly improving the images. This is partly because inexpensive mass-produced prints from slides or negatives at large sizes are downright awful.
Digital prints shine by comparison.
Resolution determines the size of the image. The optical resolution of a camera or scanner is an absolute number because an image sensor's pixels or photoelements are physical devices that can be counted. To improve resolution in certain limited respects, the optical resolution can be increased using software. This process, called interpolated resolution, adds pixels to the image to increase the total number of pixels. To do so, software evaluates those pixels surrounding each new pixel to determine what its color should be.