Image Resolution

DPI stands for dots per inch and refers to the resolution an image is scanned at. Sometimes these numbers are given as PPI (pixels per inch) instead, but the numbers are the same in both measurement units.

Which resolution is right for you?

The following are some examples of images scanned at both 300 dpi and 600 dpi

Here is the same image, scanned at 300 dpi (left) and 600 dpi (right). Zoomed out to this size, they look pretty much the same, no discernible difference.

The differences become more clear when you zoom in. Below, both images have been zoomed in to the same spot. Again, the 300 dpi scan is on the left, the 600 dpi scan is on the right. While the 300 dpi scan is pixelated and fuzzy at this level of zoom, the 600 dpi is still sharp. There is more detail.

Here’s another example.

Below is a scan of a photograph of a couple having tea in the 1890s.

If you were interested in capturing and preserving the small details such as the tea set, or the wallpaper, or the pattern on the woman’s blouse, it would be important to scan at a higher resolution, as seen by the zoomed in examples shown below.

The 300 dpi scan on the left does not have as much detail as the 600 dpi scan on the right.

Pros and Cons