Slide Scanning Work Flow

I mentioned in my previous post that I’m scanning my father’s old slides. The slides are almost all Kodachromes, spanning the period from the mid 1950s to the 1970s. The eventual goal is to have a set of scans that I can disseminate to family members at a reasonable resolution, without, hopefully, it becoming my life’s work. The slides are in a variety of states: some are well exposed, well processed, and have no color casts, some are underexposed, a set are overexposed, and some have visible color casts. All of them, I’ve found, are filthy, and many are covered with fungus.  What I didn’t realize was that I’d signed up for a restoration project.

Before Scanning

Before loading the slides into the scanner, I clean off each one. First I blow off each slide with “canned air”, then I use a special lint-free, non-abrasive fiber pad called a “Pec-Pad” to wipe down each slide with a special cleaning agent called “PEC-12”. It’s non-water based; it smells like it contains some organic solvent. I’ve been tempted to rinse the slides in water, but photographic emulsions get very soft when wet, and I’m afraid I’d ruin them. I have no expendable samples I can test on.

The Scan

As I stated in my previous post, I’m using VueScan to scan the slides. I use the scanner color profile I generated with the IT8 calibration slide, and set white balance to “neutral”. Since I’m post-processing them, I start off with 64 bit TIFF files. I decided to scan at 3600 DPI; this gives a scan that’s roughly 3100px X 4600px; I figure this will be good enough for any foreseeable enlargement I might want, yet still not quite as large as the full 7200 DPI. VueScan requires these scans to be set to “mirror”; I set the rotation as needed. I then generate a preview image, and make adjustments to it. My goal is to get the color as close as I can, and to get a tonal range that doesn’t leave the highlights burned out or the shadows too dark.

When I first started, my intention was to scan the whole carousel, then switch to Photoshop and take care of dirt. When I started rescanning in VueScan, I changed my M/O—now I scan, and either correct immediately, or scan the four slides in the holder before moving onto the next slides.

Post Scan

After scanning, I load the scan into Photoshop. The very first step is to duplicate the background (original) layer; this is in case I mess up something badly and need to get back to the original state of the scan.

The next step is tonal and color adjustment, usually accomplished via a Curves adjustment layer. Adjustment layers are essentially electronic filters laying over the image; they can be turned off or on, or modified at will. The Curves adjustment is so called because it enables you to adjust the curve of a graph of the picture’s lightness to darkness. It allows you to adjust the distribution of light or dark values overall, or by color; with a Curves adjustment you can lighten shadows, get rid of a color cast, or correct issues where one part of the tonal range needs one correction, but another part needs a different correction. For example, one of the slides I was just working with needed a little more red overall, but the shadows were too red. I adjusted the toe of the red channel’s curve, to make the shadows less red, but then increased the amount of red in the mid-tones.

Sometimes I’ll also add a Vibrance or contrast adjustment to make the picture pop a little more. I also take care of red eye at this stage.

Dirt Reduction Strategies

After that, comes the hard part—getting rid of all the schmutz on the slides. These slides haven’t always been handled well; at one point they were kept in the cellar, and I suspect they have fingerprints and other symptoms of kid handling as well. The scanner does have infrared dust reduction, and it does reduce the amount of dirt, but it’s not enough. Dust reduction can also be too aggressive, and get rid of detail.

The worst slides are the ones that have fungus on them. I can cope with the normal dots and blips from dust and lint, but a lot of these slides actually have fungal growth, which shows up as fine lines all over the picture, usually the lighter parts of the picture. It’s very hard to get rid of totally, since there’s so much of it. Sometimes the fungus has eaten into a couple of the emulsion layers, leaving bluish spots.

In general, my goal is to clean up the picture as much as I can, without obliterating detail or leaving too many artifacts of my own. I recognize that I can’t totally eliminate dirt. Theses are the tools I use:

The Spot Healing Brush

Photoshop’s Spot Healing Brush is usually the first tool I try, especially in areas with a lot of detail, or widely separated spots of dust. Designed for retouching faces, it’s content aware and uses the surrounding pixels to smooth out blemishes. When it works, it works great. Sometimes, though, it picks up the wrong content to use as a source, and creates blotches of its own.

The Spot Healing Brush doesn’t do well fixing blemishes that run parallel to a line; I’ve found it better to stroke the brush perpendicular to edges rather than along them.

The other problem with the Spot Healing Brush is simply that you have to address each spot individually. For some pictures, this isn’t a problem, for others, there are so many blemishes that it takes forever to get rid of all of them. Within the past week, I’ve found than using a graphics tablet (I use a Wacom Intuos) makes things go much faster; it’s easier to control, and the pressure sensitivity of the stylus allows you to control the size of the brush.

The Clone Stamp Brush

In some cases, dirt will be positioned in such a way that the Healing Brush can’t correct the blemish effectively. In these cases, I’ll use the Clone Stamp tool to pick up a nearby piece of the picture, and stamp it over the blemish. It’s ticklish work, but eventually, you can get rid of the dirt.

The Dust and Scratches Filter

The Dust and Scratches Filter (a submenu of the Noise filter) is a very tempting tool. It promises to get rid of all the dust and scratches in the selected area. It works by detecting pixels that are very different from their neighbors, and blurring the differences away. You can control the effect by choosing the radius and difference threshold.

The problem is that it also blurs out detail, making it unsuitable for use in areas with detail. I’ve found it’s most useful for cleaning up skies, or large areas of flat or smooth color. On slides heavily infested with fungus, I find I’ve had to select small areas of the picture and run dust and scratch on each one.

Polaroid Dust and Scratches

I was talking to the folks at Hunt Photo, and they said that I should look into a piece of software called Polaroid Dust and Scratches. Apparently, when Polaroid was making scanners, they developed this software for their own scanners, but it isn’t restricted to their own hardware. It has a reputation of being very good at removing dirts from scans. It is—but there are definitely problems with it too.

The first problem is that it’s old software, and unsupported. When Polaroid wrote it, Macs ran on PowerPC CPUs. My current Mac is an Intel MacBook Pro, running OS X Mountain Lion, and it simply cannot run PowerPC software anymore (Ted pauses to glare at Apple for removing PowerPC support.) Fortunately, I still have my old PowerMac G4, and it’s a doable to move files over to it, run the filter, and then move it back. It’s a nuisance though, and the version of Photoshop I have on the old machine doesn’t support some of the options of Photoshop CS5 running on my laptop.

Still, the Polaroid software is a marvel. It really does get rid of nearly all dirt on the scan. Unlike Photoshop’s own Dust and Scratches, it doesn’t blur out dirt; it replaces it with pixels of the appropriate color. Unfortunately, it’s too good—it also removes detail. I’ve chosen to use it this way: When I first examine the scan, I decide whether I can handle the amount of dirt manually, or whether I need to run it through Polaroid. If I need to run the Polaroid software, I’ll fire up the old machine, start up file sharing on the new machine, copy over the scan, run the filter, and save the result back to the laptop, under a different name. I call this the DS version.

Back on the laptop, I open the original file, and duplicate the layer as I ordinarily would. Then I open the DS version, and copy the DS layer over to the original file, and put the DS layer on top of the copied layer. So now I have three layers—the original version, usually called background, which is my safety. Next is my copy, and finally is the DS layer. I then zoom in very closely to the picture — at least 100%, sometimes closer, and examine the picture centimeter by centimeter, toggling the DS layer. If I see detail emerging when I turn off the DS layer, I erase that part of the DS layer, letting the original copy layer show through. If I still need to get rid of dust, I make the additional edits to the copy layer. This is slow and laborious, but still faster than trying to get rid of each spot by hand.

Sometimes, the dirt seems heaviest in particular parts of the picture, while other parts are relatively clean. In these cases, I’ll only bring over the parts of the DS version that I need.

Managing the Process

The slides vary greatly in how dirty they are. Some require only minor correction or cleanup before they can be called finished; I’ve had a couple of that have turned into major restoration projects. I’ve found that if I get bogged down on one slide, it’s best to split my time—make some progress on the really dirty slide, but also do one or two of the easier slides to get a sense of overall progress.

It’s important, once I think I’m done, to check the edited layer against the original layer. There was one picture I cleaned up of my sister wearing a checked coat. Close up, the Spot Healing Brush seemed to be doing a really nice job, but once I backed out, I realized it was throwing all the checks out of phase and was really noticeable. I had to clean that one up by copying bits and pieces of the check pattern and pasting them over the affected areas.

Once I am done, I flatten the image, and save it to a special folder for all my completed pictures. It would be nice if I could save the layers, but the files are big enough as they are. It’s my intention, as the final step, to bring them into Aperture, add as much metadata as I can, and then make them available to family members.

Update, January 2014: I’ve found a faster way to deal with dust, detailed here.