Overview of Resolution
Resolution can be confusing, so it is important to remember the main points. Don't drown in a sea of technical terms; just remember the important ideas and do a little math as needed. Here is a resolution cheat sheet, which includes all the points you should keep in mind:
Match the image size to the output size. This means that smaller images work better for e-mail and the Internet and larger images for printer output.
Always save your original photograph. When modifying a picture or resizing, rename the new image with a different name so that it does not overwrite the original file.
Enlarging an image often will produce poor quality results. In this case, shoot a photograph at a higher resolution so that it does not have to be enlarged.
Reducing the size of an image is almost always successful, so when in doubt use a higher resolution setting at the beginning.
Change resolution settings as needed in your camera and use the onscreen display to let you know the particular resolution you are currently using.
See Appendix C for a resolution table.