Scan Resolutions and Photo Preservation and Sharing

A common question among families and historical society volunteers is what resolution should be used for scanning photos and documents for archiving and sharing.

As you might expect, the simplest answer is that it depends. It primarily depends upon the size of the original to be scanned and the anticipated size of prints that may be made.

When considering digital scan and print resolution, our primary interest is pixels per inch (ppi) that we capture in the scan and then have available to spread over a selected print size. Generally, we will want to capture more pixel resolution as the size of the original decreases and/or the size of the intended print increases. At LocalArchiver.com, there are several articles on scanning and printing that are intended to clarify how these activities relate.

The human eye is pressed to discern print quality differences at greater than 300 ppi and quality images can be printed at resolutions well below this. In the LocalArchiver.com article on printing, I compare the minimum resolution requirements for several major online printers. This is informative as these resolutions have been found to be satisfactory to a vast majority of their customers.

If you are scanning a 4 x 6 print so that you can then print several additional 4 x 6 prints to distribute to family, a scan at 300 ppi should be plenty of resolution. This is the case as 300 ppi is described as professional print quality. If you believe that you may someday desire to print an enlargement, you may wish to capture more pixels in your scan, perhaps 600 ppi. This would allow you to spread captured pixels on a print size that is twice the size of the original and still maintain a print resolution of 300 ppi.

In articles at LocalArchiver.com, the relationships between pixel capture by scanning and printing pixel needs are developed further. In general, LocalArchiver.com recommends that families and historical societies routinely scan at 600 ppi to maintain flexibility with images into the future while not generating excessively large image files. It is also recommended that the jpeg format at high quality / low compression be the digital file format of choice.

Many local photo labs are acquiring equipment to bulk scan prints. However, many are restricting their scans to 300 ppi and then save the image files at less than high quality compression. This is the case since higher resolution scans require more operator and equipment time, and more compression / lower quality files save storage space on the lab's equipment.

Professional services focused entirely on scanning will typically offer a choice of resolutions and will provide high quality files of the images. ScanDigital is such a service, and is a good choice for a family or historical society that is seeking consistent high quality scanning. Clearly there is an opportunity to take advantage of quantity discounts with such a service. However, there is no requirement to have an entire collection scanned at the same time, and giving such a service a try may represent a first and important step toward better preserving your photos and opening many additional opportunities to share your images once in digital format.