Graf Photography - Dust on slide scans

Revised Oct 2, 2005

For those dealing with dust on DSLRS, I highly recommend a visit to this site; CopperHill Images
He offers great tutorials for cleaning your sensor. Otherwise, see advice below for dealing with dust on film scans...

Does the cleanup needed for this image look familiar?

An increasing number of photographers are embracing the tremendous advantages of the digital darkroom. The ability to make large, quality prints from slides taken right off your light table gives you the wonderful advantages of control and convenience. Ever since we began scanning our own slides, we have been dealing with the frustrating task of removing dust specs from slide scans. We hope to offer you a few tips that will help in dealing with dust!

Photographers with filmscanners can relate to this mundane, but necessary chore to be sure none of these little specs end up on your final print or images for your website. They are often removed one by one with the clone tool in Photoshop at 60-100% magnification. They stand out like a sore thumb on clean backgrounds. When scanning at 4000 dpi, you start to notice quite a few of these annoying and unwelcome additions to your image! Nikon offers a hardware dust removal system called Digital ICE, but we had to pass on that feature when we decided on the Polaroid 4000 scanner.

However, precautions can be taken that will greatly reduce your time with the familiar cloning tool. Some labs are better than others for returning your slides clean, but you will likely have some dust to deal with for each scan. First and foremost, a clean environment to work in is a must. Slides sitting on a light table waiting for your cat to walk all over them is probably a bad idea. Storage is also key. For us, each slide goes into the 20-slide archival pages after cataloging and labeling and then into a file cabinet. This at least helps prevent any further dust from accumulating on the images.

When it comes time for scanning, you will have some dust removal to do. The biggest time savings is obtained by cleaning your slides prior to the scan. We have been using 3 tools to help reduce this chore to a minimal amount of effort in post-scan cleanup:

• A Staticmaster 1" brush
• A can of compressed air (Dust-Off)
• A Milty ZeroStat Anti-static gun

The Staticmaster brush has been around for awhile, commonly used in both digital and chemical based darkrooms. It utilizes, believe it or not, a tiny piece of radioactive material called Polonium to dispel static charges on items you brush with it. No, you don't have to keep it in a lead container or worry about becoming a walking light table after using it. We have found these to be fairly effective. Generally it is best to avoid any contact with the film emulsion, so the brush is used sparingly on really dirty slides. You can find them in photographic stores or online at B&H, just do a search on the word "static."

For contact-free cleaning, we use a combination of compressed air and a neat tool called a Zerostat anti-static gun. This gadget is actually an "ion gun" that releases positive and negative ions at the surface you aim it at. It neutralizes the positively (or negatively) charged dust particles on your slide, uses no batteries and lasts for 50,000 trigger operations. These were popular amongst audiophiles in the 70s/80s to improve sound quality on statically charged vinyl records. The difficult part is finding stores that sell them, music stores don't seem to carry them anymore. The source we bought ours from is linked above on the name, or you can do a Google search on "Zerostat" to turn up other sources and info. Generally they cost around $60 US.

Once the particles are "neutralized" on each side of the slide, they lose their static adhesion and can be blown off with a few short bursts from the can of compressed air. It is much more effective than using air by itself. Compressed air cans can be found at any computer, office, or photographic supply store. To illustrate how effective this can be, take a look at the images below. The first is an enlarged portion of a slide scan without any prior cleaning. You can see all the dust spots that need to be "cloned" off. (They're hard to see in a small web image, so all the dust specs are circled.) The second enlarged image is the same slide scanned again, but after using the Zerostat gun and compressed air. Hardly any dust clean up at all, and without ever touching the sensitive film emulsion.

There are also software methods of removing dust after scanning, like the clone tool or the "Dust and Scratches" filter in Photoshop. The drawback is they can cause some softening of the image which will require re-sharpening later. This can also happen when using Digital ICE. Using the clone tool can take quite a bit of time if you have a lot of dust to clean off. So it is best to limit use of these software remedies to small portions of the slide instead of over the entire image. Another alternative using Photoshop is a sequence of steps involving the dust and scratches filter and the History functions. Like using the clone tool, you still have to go in and remove each individual spot. To use the History method, try these steps:

Using Photoshop 6.0;

1) Apply the Dust & Scratches filter to the entire image (Radius=7/Threshold=0 is a good start)

2) Go to History Palette and click on the "Create New Snapshot" icon

3) Undo the previous Dust & Scratches filter

4) Click to the left of that new snapshot in the History Palette to indicate use with the History Brush

5) Click on the History Brush in the toolbar and select "Lighten" as your brush mode

6) Use the History Brush to wisk away dust spots

This method of using the history brush can speed up the dust removal process. Since you are essentially "uncovering" a localized, filtered portion of the image (ie. with the D&S filter applied), you don't have to be as precise your brush strokes, or picky about adjacent areas like when using the clone tool. You can go in with larger brushes, or use sweeping strokes, and the result is much truer to a dust-less image.

We still prefer the pre-scan cleaning methods as they take less time and won't degrade image sharpness. As strange as it may sound to use an "ion gun" and a "radioactive" brush, both are great tools in dealing with this annoyance in the digital darkroom.

UPDATE 6/3/02: Polaroid just released some dust removal software that is getting a lot of positive reviews. You can use it as a Photoshop plug in or stand-alone. You don't even need a Polaroid scanner to use it. Here is the link. From our limited use so far, this looks to be a nice piece of software if used selectively. The results vary quite a bit depending on what the resolution of your file is and the amount of fine detail that you have.

Enlarged section of image before dust removal
(dust specs above birds head and below lower mandible)

Enlarged section of image after dust removal

Note the feather detail that remains after dust removal, as well as the film grain. However, the couple of dust specs are gone. This was highly dependent on the settings of the filter shown above.

While we will evaluate this filter's effectiveness on an image by image basis, we think Polaroid's new Dust & Scratches software is another effective tool for anyone's digital darkroom.