Scanning pictues at what dpi?

August 17, 2006 12:37 PM

I've decided to collect and scan all my family's photographs.

It's going to be a big project. The picture quality varies. Right now, I just want to get them all scanned, digital, and backed up. What dpi should I be scanning at? I don't want to go through all that work and then realize I've made a mistake.

I've tried to research it and have come up with 300dpi. Is that a good number, balancing quality and image size?

posted by gtr to Technology (13 answers total)

Are you scanning prints or film?

Assuming you're scanning prints, scan at 600dpi. You will recreate (print) them at 240 or 300dpi, and if you need to restore them, the more info you have the better.
posted by jedrek at 12:52 PM on August 17, 2006

It depends on what you want to do with them later. If you want to print the files again later, 300 dpi is OK. If they are just going to be web-only, you could probably go down to 72 dpi. How many photos are there? 1000 or 1000000?
posted by mattbucher at 12:52 PM on August 17, 2006

If you are backing them up for storage or using them for printing copies, 300dpi should be more than fine and will provide a clean and crisp print.
posted by RoseovSharon at 12:55 PM on August 17, 2006

300 dpi yields 1200 x 1800 pixels for a 4x6" print, which I think is about the maximum conceivable amount of detail from a typical amateur photo. I'd go with 600 dpi for any professional work. Image size shouldn't be a big deal since media is so cheap... I'd be more concerned with time penalties with scanning higher dpis.

I would go with compressed TIFF for archival purposes. JPEG is more universal but has lossiness, GIF doesn't have enough colors, and PNG has a big bloat factor.

And FWIW, naming the photos might be a big concern. I'd number them by book, page, and photo, such as e005c.tif or some such. There may be a reason why photos were grouped together, so keeping the original sequencing could be a help years from now, unless you have a better reason.
posted by rolypolyman at 12:58 PM on August 17, 2006

I would reccommend at least 600dpi. Try it and see if the file sizes are too large, but I don't think they will be. For one thing, most old photos are small, so I think you will want as much resolution as possible. And while 300dpi is the standard for print-quality photos, in my experience with consumer scanners I suspect they greatly exaggerate their dpi settings. Maybe it is just my scanner, but I am not as satisfied with the results when I scan at 300dpi. Also, old photos can be digitally restored if they are damaged or faded. The more pixels the better for this.
posted by daser at 1:12 PM on August 17, 2006

Our photo numbering scheme when we scanned was year-person-person-person.. (from left to right), with added hints when there were duplicate names. We found it easier to add info into filenames when we scanned, rather than try to add it later, but maybe with archive software you can do better with tags.
posted by anadem at 1:19 PM on August 17, 2006

Whatever DPI you use, don't exceed the actual optical resolution of the scanner. Many of them will claim outrageous capabilities, but just like with digital cameras there's some kind of "interpolated scaling" going on that you definitely don't want. Find out the true native DPI of the scanner and don't go any higher than that.
posted by Rhomboid at 1:54 PM on August 17, 2006

For format, I'd try a Photoshop PDF at full res with internal zip compression. I started using them for personal projects (stuff I'm not having professionally printed) and they are substantially smaller than an LZW'd tiff.
posted by nathan_teske at 2:02 PM on August 17, 2006

>I don't want to go through all that work and then realize I've made a mistake.

Well, you'll never slap your forehead and say "damn, I wish I had used a lower resolution!", will you?

I say 600.

If that's too big for your intended storage, just buy more storage. Disk space is cheap and gets cheaper every day.

But good point from Rhomboid about the scanner. There's no point scanning at 600 if it's really just 300 with a guess at the pixels in between. If your scanner isn't really doing 600 ... can you guess the answer? Buy another scanner!
posted by AmbroseChapel at 5:39 PM on August 17, 2006

Response by poster: (they're prints by the way)

Thanks everyone. I have no probem going with 600. Better safe than sorry. 600 it is.
posted by gtr at 5:45 PM on August 17, 2006

Has anyone used an automated sheet feed scanner for this? They are getting fairly cheap, and it would be tempting for a huge pile of pictures.
posted by LarryC at 6:57 PM on August 17, 2006

You might get something out of this photo-scanning thread I started last year when I considered starting a similar project.
(I'm still waiting for some technology to emerge to make this less sucky.)
posted by Tubes at 9:36 AM on August 18, 2006

Some rules of thumb, mostly but not entirely covered above:

1) Scan at at least twice your target output resolution *as scaled*. Consumer inkjets tend to print 133 to 150 equivalent linescreen, in my experience (though newer ones can simulate 200), you need at least 2 dpi per ls of output *if you're not enlarging*.

(I feel I should clarify: that's the minimum resolution that will look decent reproduced on that kind of inkjet, though newer models will make good use of higher resolutions. Remember too that you might want to have some printed on a minilab printer to actual photo paper, this will, clearly, require even higher resolution. And, if you're saving as JPG (I'd recommend PNG), make sure your JPG quality setting is up as high as possible.)
2) You can always scale down, but you can't scale up.

3) Always save the raw scans before you edit (which, if you're using Picasa, you will anyway. If you haven't looked at Picasa, check it out. I'm Mr. I Want All The Knobs, and I still like it a lot.)

4) Don't, as noted, exceed the *real* resolution of the scanner; you'll only be wasting space.

4) Remember that doubling the dpi *quadruples* the pixel count, so don't over-scan gratuitously.

5) You might want to consider scanning *very small* originals (slides and wallets) at 1200dpi, or even higher -- you should almost certainly scan slids at your scanners maximum optical resolution -- and preferably with a backlight adapter, if your scanner has one.

6) Don't use an auto feeder. Even if you have thousands of pictures to scan. They're not images, they're history. Once you've got them scanned, make half a dozen DVD-R (and DVD+R) duplicates (preferably in pairs) and scatter them around, properly labeled.

Make sure the archival copies have both the raw and retouched images as well...
posted by baylink at 9:55 AM on August 18, 2006