Now you want to print a picture for her sized 5 x 7 on your inkjet printer. The first case, you want to know what the optimum scan resolution is. A printer may require 300dpi or more to accurately render an image with all its original detal. On the computer screen, 72dpi should be sufficient to produce an good image for posting on the web or sending by email attachment. Pixels are the unit used to measure the height and width of the image displayed on your computer screen or stored on a computer disk.
Dots are the unit used to measure the resolution of the printed image.
Optimum DPI Is Suppose you want to scan an original picture whose dimensions are 5 inches x 7 inches. The intended purpose for your scan always is the main fact in this decision. For example, if you wanted to archive the image, you would use the highest physical resolution available on the scanner and that fits your storage requirments. In those cases, you know what kind of output your are going to generate therefore an optimum scan resolution can be calculated so nothing is wasted. If your scan is larger than necessary, your computer or priter may not be able to handle it and crash or run inefficiently.