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There are no shortage of things you can do to photos when you scan them in for archival purposes. You can set the scan resolution, the file's DPI, and you can even post process them to enhance them to be more legible or make repairs.

For archiving photos, it seems to me that it makes sense to scan them at a reasonably high quality (front and back), and then store them unadulterated. Should you want to enhance them, you can make copies of them that can be modified.

But at what quality should we scan and store them at? For example, is 600dpi good for a standard 4x6? Does it make sense to scan all photos at 1200/2400dpi instead?

The obvious problems with simply scanning all photos at 1200+ dpi are:

  • takes considerably longer for the scan to complete (and with hundreds of photos, you'll be sitting there a long time waiting for the scanner, and then waiting for the computer)
  • significantly increased storage requirements

While the resolution is higher the benefits of this seems unclear. Certainly higher resolution images will print nicely as posters for enlargement, but it seems unlikely that 11x15 or higher posters will be printed for 99% of all photos scanned.

What do professional genealogists do? What do other amateur genealogists do?

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    The Library of Congress recommends the following for personal collections: “In general, scan documents and photos (4”X6” and 5”X7”) at 300 dpi/ppi. To enlarge 4”X6” and 5”X7” photos to 8”x10” or greater, scan at 400 or 600 dpi.” Please see also the answer to Preferred file format to exchange images. Personally I stick with 600 dpi as a reasonable compromise between quality, scan time and file size. – lejonet Aug 13 '13 at 10:40
  • It is now 2018 and I have the same questions. Does the same advice apply? – Laura Jun 15 '18 at 14:59
  • Hi, @Laura, welcome to G&FH.SE! I've converted your post to a comment since it isn't an answer to the question. – Jan Murphy Jun 16 '18 at 0:05
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But at what quality should we scan and store them at? For example, is 600dpi good for a standard 4x6? Does it make sense to scan all photos at 1200/2400dpi instead?

Yes & No.

Let me explain a little. Most (not all) commercial printers are set to print at 300dpi which directly correlates to 300ppi. PPI being Pixels Per Inch & DPI being Dots (of ink) Per Inch. So, scanning in your old photos at 600ppi to print out directly as a 6x4 only means that your printer will have to downsize the pixel count before it sends it to the printer.

That being said, for archival purposes I would generally use 600ppi for the everyday snaps that you trawl through & 1200ppi or 2400ppi for any decent portraits, things that you will want to have restored one day or used for any professional printing such as Fortiter says.

When a client wants to scan in their photos themselves for me to restore, I tell them to scan in at their scanners highest rate (usually either 1200 or 2400ppi) with all software enhancements turned off in 24-bit colour.

The reason you ask for the highest ppi for restoration, is that you have 4x more information to work with at 2400ppi than you do at 600ppi. After the work is finished, you keep a master copy at the higher pixel rate, & a downscaled 300ppi version to print from.

As you say, the downside of having the larger resolution files is that it takes up a hell of a lot more disc space.

I find that the best workflow for going through a stack of photos is:

  1. Go through the whole lot and organise into groups. (Get a digital copy; Get Reprinted; Enhance/Restore; Use for publishing)
  2. Decide on a resolution for each pile. i.e. 300ppi for the digital copies and straight reprint, 2400ppi for the Enhance/restores etc...
  3. Set-up your scanner settings for one stack and work through that.
  4. Repeat with the next stack with amended scanner settings.

Hope all this helps a little.

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You have correctly identified that there are costs and benefits associated with moving to higher resolution when you digitise records. As with most other issues in life, your final decision will be a compromise.

The glib answer is that you should always scan at the lowest resolution that will yield a file suitable for everything you may wish to do with it. Of course, there will always be "new" uses that you did not anticipate.

The best rule of thumb is that there cannot be one rule that applies to every image. When you settle on a basic provision of 600 dpi and 24-bit colour (as many people do), be alert for that one striking picture of your third-great-grandparent's wedding party that will be the perfect cover image for your book (that you will write one day) and get a 2400 dpi file to be used for making the colour separations for the dust jacket.

Be realistic but also be flexible.

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