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Scanning photos: what resolution is best?

Updated 6-30-19. Helping people with their memoirs or personal histories and organizations with their histories, I am often asked at what resolution to scan photographs to get digital files good enough to print in a book. The photos on Facebook are not high enough in resolution for a quality print or for a book. Photo archivist Brina Bolanz (Restored Stories) ("Preserving family photos one memory at a time") offered a concise answer and gave me permission to share it, below.

To begin with, scanning is different from photocopying! You need a good scanner that produces a digital file of good enough quality for use in printed books or videos. Invest in a dedicated flat-bed scanner, which will give you superior images.(A machine that only scans will produce far better scans than a multi-function machine that prints, scans, and copies.) Prices for dedicated scanners start at a reasonable $100.

As a rule of thumb, says Brina, scan at 300 dpi (dots per inch) to be able to reproduce a photo the SAME size as the original. That is, if you have an 8x10 photo and want to be able to print it as an 8x10, scan at 300 dpi. BUT if you have a 5x7 photo and you want to print it as an 8x10, you must scan at a higher resolution (more dpi). A larger low-resolution photo can always be printed smaller, which will bump up the resolution, perhaps enough for printing (240 dpi is considered the lowest recommended dpi for photo reproduction of good quality).

Brina recommends a nifty online site, A Few Scanning Tips (www.scantips.com/calc.html) for calculating how to scan a photo. She says, "It's set up in a slightly confusing way, since you can calculate a few
different things, but it's great once you get the hang of it." On the left side, you enter the size of photo you want to produce (the "output"); on the right side, you enter the size of the original photo, the one you plan to scan. The calculator will then tell you to set your scanner at X dpi. Jacci Howard Bear explains the difference between dots per inch (dpi) and pixels per inch (ppi) in Measuring Resolution Inch by Inch: SPI, PPI, DPI, LPI Demystified on About.com.

Any more suggestions from photo archivists and designers? Personal historians who do video?

What is a personal historian? A person who helps others tell and preserve their life story or family story (usually illustrated with photos). Personal historians hang stories, images, and voices on the family tree. Some work in print, some in video, some audio (plus transcripts). And some of us also help organizations tell their stories.

Someone asked: If I print a photo that Photoshop tells me is 72 dpi, it looks fine on my home printer (black and white laser), and also on an ink-jet printer. But will it look okay if I scan it for a book?

Marion Johnson, who designs books under the firm name Memory Works), writes: "A photo that is 72 dpi can be successfully converted to 300 dpi (the required resolution for printing books) only if it has an adequate pixel resolution to begin with. For instance, when a photo that has pixel dimensions of 3136 x 2352 and is 72 dpi is converted to 300 dpi in Photoshop, it ends up being 10.5” wide x 7.5” tall. You just need to make sure you uncheck the “Resample Image” box in the Image Size box of Photoshop. However, if the original pixel size of the photo is much smaller, at 300 dpi you’ll end up with an image that’s much too small to use. (You can check out the photo by pulling it into Photoshop and clicking on the Image Size box.)

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