Here is a great question from a #Cazillion on DPI. In my video I explain how it works and why DPI/PPI really don't matter when exporting your images.
To: Gregory Cazillo
Hey Greg, I am new to printing and I am having a problem regarding resolution/printing. Some of my pics say x and y resolution 72 dpi and a pic taken minutes later will say 300 dpi.(I am getting this from the exif info in flickr). Also, at this time i have only edited in iphoto.
1. How do I set my resolution for the best possible quality?
2. How does dpi relate to printing size and quality?
3. How/Can I print large prints ex. 20x30 with my D90
Thanks for all your help....
Definitions from Wikipedia:
PPI: Pixels per inch (PPI) or pixel density is a measurement of the resolution of devices in various contexts; typically computer displays, image scanners, and digital camera image sensors.
DPI: DPI is used to describe the resolution number of dots per inch in a digital print and the printing resolution of a hard copy print dot gain; the increase in the size of the halftone dots during printing. This is caused by the spreading of ink on the surface of the media.