Storage is cheap though, so I say scan as high a resolution as you want, and use my rule of thumb as the minimum guideline. That said, a small old print with lots of grain probably wouldn’t benefit by going beyond my rule of thumb, and some likely could be safely scanned at a lower resolution. That means you can basically max out a 4000dpi slide scanner and get a good result. Not all photographs are high enough quality to give you a better picture when scanned at very high resolution.Ī Kodachrome slide supposedly has enough resolution to output about 20 megapixels. Of course, it doesn’t hurt to scan more than you need, although there are diminishing returns. So if you are scanning a 4×5 print, and want to be able to print at 8×10, you need twice the DPI you’ll print at, so 600dpi. Minimum resolution (DPI) should be the number of inches of the largest side you want to print, divided by the largest side in inches of what you’re scanning, multiplied by 300. Here’s the summary:įor people reading this on a small screen where the image is hard to read, the basic rule is: I have a rule-of-thumb that I use to determine the correct DPI to scan at, and basically it has to do with figuring out the largest size you want to be able to print (printing is usually done at 300dpi) and then adjust your scanning dpi to insure you’ll have enough pixels to print. Here’s another way to look at, in a slide from my presentation:īasically, if you look at scanning photographs (or negatives/slides) you can see that scanning it at 300dpi for different sizes will give you much different size images. Note that doubling the DPI effectively quadruples the number of pixels, since the dpi increases in both vertical and horizontal directions. Doubling the DPI to 200dpi, gives you 1600×2000 pixels, or 3,200,000 pixels, or 3.2 megapixels. That’s less than a million pixels, or another to say it is it is less than a megapixel.
For example, if you had an 8×10 inch photograph, and you scanned it at 100dpi, you would have a photo that was 800×1000 pixels, or 800,000 pixels altogether. The two most common questions I get about scanning photographs are:Ģ) What file format should I save the file in?ĭPI stands for dots-per-inch, and refers to how many pixels are present in each inch of the photograph. While I can’t post the video of the presentation on my blog, I do want to share some of the information from the lecture here.
My lecture Preserving Photographs, Scanning, and Digital Backups at this weeks’ IAJGS International Conference on Jewish Genealogy was well attended with somewhere around 150-200 people.
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