Slide Scanning

This material is a lightly edited version of an email written in response to a person who wanted to know how to get started with slide scanning. His inventory included about 2,000 35mm slides, all of which had been carefully catalogued in an MS Word file. There are professional services that will do this, at a price, but for many people the cheapest solution is to buy a scanner and go at it.

Digitizing your slide collection is time consuming but, if done well, very much worth the effort. We have scanned and catalogued about 4,000 of our department’s slides and found that these once dusty images have taken on new life as digital copies. We hope to secure funds to have the rest of our collection (in the many tens of thousands) scanned.

I presume that you have reasonably up-to-date hardware–no more than about two years old–with enough RAM to run your operating system and imaging software (as a rough guide, shoot for double the recommended amount for your O/S). I presume, as well, that you do not yet own a copy of Adobe Photoshop or Elements. You should seriously consider purchasing a copy of this software both for its image-editing and modest cataloguing capabilities. A good alternative (perhaps a better one, if your catalog is less than 5,000 slides) is Adobe Lightroom, which combines cataloguing and image-editing in a single package. If you don’t feel you need editing software (ie, if your slides haven’t lost their color and aren’t plagued with dust spots, etc.), you can get a dedicated image-management program, such as one of those described here.

In any case, the first question you need to answer for yourself is how you expect to use these images in the future. Are they simply a reference collection for the originals? Will they only ever be viewed on-screen or do you intend to print them out or use them in publications? Will they be part of your legacy as a photographer (especially important as the original slides degrade)?

Basic Equipment (moderate-resolution flatbed)

If you are sure that your goals for these images are modest, then scanning them as jpegs, at a moderate resolution, on a flat-bed scanner with a slide adapter is just fine. Those that can be had very cheaply–around $100–will only scan at lower resolutions, up to 1600 dpi or so. If all you want to do is make Powerpoint presentations and you don’t expect to need to crop your images, this might be fine.

Better Equipment (high-resolution flatbed or slide scanner)

There are plenty of consumer flatbed scanners that can do a much better job and achieve quite high resolutions–look for major imaging brands like Canon and Epson. A recent Epson flatbed, the V700, can scan prints as well as slides at up to 6400dpi and automatically separates multiple images into individual scans. It runs for about $500. Lower-resolution flatbeds will cost less than half that, though I would not bother with anything with an advertised resolution of less than 2000dpi. A dedicated slide scanner will cost at least $500 and will add the ability, with a feeder attachment, to scan larger batches of slides unattended but of course will be worthless when it comes to scanning anything else.

A Word or Two about Resolution

If you do decide on a flatbed scanner, it’s worth getting the highest resolution you can afford, to give you the greatest flexibility in how you use your images down the road. You probably know that publishers require 300dpi files at full size for illustrations meant for print. In the low-cost example above, a 1600dpi scan of a 1″x1.5″ slide would produce, at most, a 1600×2400 pixel image, good enough for publication up to 5″x8″. I would shoot for a minimum of 2000 dpi so that you could get a 2000×3000 pixel image out of your slides (incidentally, equivalent to the resolution supplied by a 6MP digital camera), good enough for a c. 6.5″ x 10″ print.

As you get closer to 4,000 dpi (the maximum resolution of many dedicated slide scanners), you approach the limits of your originals and start scanning film grain. If you were using perfect technique and pro-quality film when you shot the original slide, you could theoretically get a good c. 13″x20″ print enlargement from a 4000 dpi slide scans. That resolution, at 4000 pixels by 6000, is about what you would get from a 24MP digital camera, the top of the DSLR range in 2008. This is almost certainly overkill for most slides.

I suspect (though I haven’t tested this and would be happy to be shown wrong) that for most of us, the right balance between capturing all the detail in the original and keeping file sizes manageable is somewhere between 2,000 and 3,000 dpi for 35mm slides.

File Format Choices

As to file format, jpegs are indeed fine and used by many professional photographers for their modest file size. There is a tradeoff, however, in that they are not an archival format. A jpeg is degraded with use, as the file itself is uncompressed and recompressed each time it is opened and closed. Smaller file sizes mean higher compression rates and greater degradation. With high compression, images begin to lose detail pretty quickly. In time, they become completely unusable and can’t even be opened.

THE stable, archival image format is a tiff. Tiffs will last as long as the device they are stored on–no matter how many times you open or manipulate them–but are uncompressed and therefore quite large. Your 2000 dpi slide scan will be about 3-4MB as a low-compression jpeg but 15MB as a tiff. In addition, art and architectural publishers do not accept jpegs for publication–only tiffs. Of course, jpegs are lean and mean and can be easily opened in the Windows file browser and readily imported into Powerpoint, posted on the web, etc. For this reason, we maintain two digital copies of each slide we scan–a tiff for the archives and for publication and a jpeg for quick reference and screen presentations. I encourage you to do the same, as digital storage is cheap (especially compared to archival slide storage).

Digital Storage

You will need, no matter what you do, to plan for storage. If you only maintain jpegs, 2,000 4-megabyte files is 8 gigabytes’ worth of material but if you keep jpegs and tiffs, that number will be quadrupled, to 32GB. At higher resolutions, these numbers go up quickly. And, as you (presumably) start shooting with a digital camera, this will be only the beginning. Before you know it, a terabyte (1,000 gigabytes) doesn’t look that huge. The principal storage medium for all this material should be close at hand–ideally an external RAID hard drive that can be taken away and migrated to new computers as you upgrade (a RAID setup describes multiple hard drives that can be configured to back each other up, should one disk ever fail). You will want a backup, as well, preferably on another hard drive but DVDs are another alternative (though you will need to plan to move the DVDs onto new ones in 5 years or so because the disks themselves degrade). These expenses are not large but neither are they free. If you have access to regularly backed-up, network storage space, by all means use it. Drives DO fail, CDs and DVDs DO become unreadable, etc.

Cataloguing

Digital cataloguing is where the real benefits in scanning come–in the ability to sort and resort your material by building type, site, date, architect, or whatever else you feel is important. It IS possible, and a very good idea, to import your existing list of images from MS Word into a spreadsheet, like Excel, as long as you have been consistent with how you separate fields (i.e., with commas or carriage returns). If not, you’ll have to do it the hard way, via cut-and-paste. From there, you could bring the data into a database or into one of many image-management programs. Whatever you do, embed your caption information into the image itself, via the IPTC metadata fields. This way, if you change programs, or give your files to someone else, all of the descriptive information stays with the image.

Oh, and don’t forget to clean your slides before you scan them. You can automate color-correction through Photoshop but you have to clean up dust one speck at a time (the “Magic Healing Brush” is great for this purpose but doing it on a whole collection is a fast route to carpal-tunnel syndrome).

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