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May
2001

On the Trail of Dust

One of the biggest enemies of effective scanning and photographic retouching is dust. Dust on the scanner, dust on the original, dust in the digital camera all conspire to leave those ubiquitous little white dots and squiggles all over your scanned image. You can easily spend hours working on a photo-composite or retouch project and feel that it is perfect, but when you output the image to a high-resolution printer you are bedeviled by those little spots. We will never be able to completely get rid of dust. High-end graphics shops have tried, using clean rooms, ionizing the air, employing anti-static brushes and compressed air with varying amounts of success, but most of us cannot afford such extreme measures. This month, we talk about simple things we can do to alleviate this graphic arts menace.
The first and simplest thing is to try and keep your workstation clean. Computer stores sell those little cans of compressed air (usually for blowing out your keyboard), they are great for blowing some dust off your scanner surface and the originals you will be scanning. On flatbed scans, dust will appear white; but on transparency scans from a film scanner, dust will be black. Swiffer-type cloths also work well for wiping down your computer equipment. It will be a constant struggle since we all know how much dust computers attract, but keeping a clean area for your scanning will save you time in the long run. On a flatbed scanner, be sure to clean the glass using a streak-free cleaner, but be careful not to get the spray inside the scanner.
There are two types of flatbed scanners with regard to dust: open and closed. Most older flatbed scanners are of the open variety. They had vents in the body to cool the interior of the scanner. Unfortunately this also allowed dust to get inside the scanner, onto the underside of the glass, the light source or the CCD element. Occasionally with older scanners it may be necessary to disassemble the scanner (carefully) and dust out the interior. Dust on the CCD manifests itself as a fine line running down the length of the scan. Newer, closed scanners run cooler so they do not need to be ventilated in the same way. This is a good thing to look for when purchasing a scanner.
Upon making a scan, no matter how fastidious you are, there will be some dust spots on the image (fig 1). After sharpening the image (in Photoshop select Sharpen: Unsharp Mask from the Filter menu), you will see more dust spots. It is important to view the image at 100% (in Photoshop select View: Actual Pixels or double click the Zoom tool). This will allow you to see all the spots that need to be removed.

Fig. 1

There are two basic ways to remove spots, the Dust & Scratches filter or the Clone or Rubberstamp tool. The Dust & Scratches filter (select Noise: Dust & Scratches from the Filter menu) does an effective job of removing spots at the expense of image sharpness (fig 2).

Fig. 2

A high radius amount will eliminate larger dust spots, but will also smooth out the actual detail of the photo and can make somewhat of a watercolor look (fig 3). The Cloning tool is much slower but more precise. It is important to choose a source point similar enough to make the spotted area blend well.

Fig. 3

Since viewing the image at 100% often makes it much larger than the size of your monitor, start cloning at the top-left corner of the image and work in a tiling manner. Use the page down key or the scroll bar to move down one screen and retouch out any spots. Once you hit the bottom move the scroll bar right and work on the next column going up until you have covered the entire image.
A combination of the two tools is often the best; you can use the filter at a low radius for the small stuff and then go in manually with the cloning tool to take out the bigger chunks. It is also possible to mask off simple background areas where a high radius Dust & Scratches filter would not be noticeable and then do the subject with the Clone tool. Used in combination, these tools can save you a lot of time.
You cannot stop dust from getting into your images, but you can create your own digital version of perfection. It is important to carefully look over every scan before you print it. No image should go out all spotty.
Paul Vaughn is a freelance graphic artist and web designer. Mr. Vaughn has fought the scourge of dust on innumerous occasions, he can be contacted at paulv@mac.com.
 

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