I have started to scan photos to keep them in digital form. The scanner has dpi settings, and it takes much longer to scan at 600 dpi than at 300 or 150. Does the higher dpi setting result in a higher quality scan so that in the future I could enlarge it to print as a poster, or crop it, without losing quality?
–John Lydon, Peru
Exactly, John. The dpi setting, which stands for dots per inch, controls how large your scanned photo will be, measured in pixels. Suppose your original photo is 3 inches across. If you scan it at 150 dpi, the digital version will be 3 x 150 = 240 pixels wide. If you scan it at 300 dpi, it’ll be 900 pixels wide. So the higher you set the dpi on the scanner, the more detail you’ll capture, which will enable you to make bigger prints.
Of course, there are always caveats. For example, there’s an upper limit beyond which increasing the dpi will have no effect. Your photo only has so much information in it. Scanning at 4000 dpi won’t give you additional information if the original source material is only 300 or 600 dpi to begin with; it’ll just make the digital file enormous. And many scanners can be set to resolutions far above their true optical resolution, which yields no real benefit. Check the guide that came with your scanner to see what its real resolution is, and never go beyond that value