Choosing a Scanner

Peter Aiken

Many stamp collectors and dealers are interested in creating digital images of their stamps, covers, and other philatelic material. There are many uses for these images, including computerized databases, Web pages, and on-line auction listings. The process of creating a digital image from a paper document is called scanning. The procedure is not all that difficult, but it can be a bit confusing to the newcomer. I have gathered some basic information to help you get started creating digital images of your stamps and covers.

Selecting a Scanner

If you do not already own a scanner, the information in this section will help you select one that is suited to your needs. I do not recommend specific models because it is impossible for me to keep up with the constant introduction of new units. I suggest that you use this information to determine the type of scanner you want and the specifications you need, and then go shopping.

Types of Scanners

Scanners come in a variety of configurations. The type you should consider depends on both your planned scanning needs and your budget.

• Drum scanners. This type of scanner provides the highest level of image quality. They are typically found at professional printing businesses. In a drum scanner, the original is attached to a cylindrical drum and rotated past the sensing elements. These scanners are very expensive, with capabilities that go well beyond the needs of desktop scanning.
• Flatbed scanners. This type of scanner provides a flat glass surface onto which the original is placed. The illumination and sensing elements move under the glass to scan the image. Flatbed scanners are available in a wide range of sizes, prices, and capabilities. Some flatbeds offer a transparency scanning adapter as an option.
• Single sheet scanners. This type of scanner is designed for single sheets of paper. You insert one edge of the paper in a slot and the scanner grabs it, feeds it past the sensing array, and passes it out the other side. Some single sheet scanners are even integrated into keyboards. Such scanners were originally designed for digitizing documents and images for archiving, and many models are not suitable for creating high-quality images.
• Sheet-fed scanners. These scanners take a stack of pages and scan them in sequence while you get coffee. Some even do duplex (2 sided) scans. They are very useful in some situations but not much use to the philatelist.
• Photo scanners. This type of scanner is designed to scan snapshots up to approximately 4´6 inches in size. Some are separate desktop units, others install directly into a computer much like a diskette drive.
• Hand scanners. This type of scanner requires the user to manually scan an image. Hand scanners look something like an overgrown mouse. To scan, you manually drag the unit over the original document. Handheld scanners are suitable only for small originals that are no wider than the scanner itself. In theory, most hand scanners permit you to scan a wide original in two or more passes and “stitch” the scans together into a final image. This, however, never works as well as the manufacturers claim.
• Slide scanners. This type of scanner is designed for scanning slides (transparencies) rather than opaque originals, such as photographic prints. While rarely relevant for scanning philatelic material, a dedicated slide scanner is the best choice for scanning slides. Some flatbed scanners come with transparency adapters but they do not provide top quality results, particularly with small slides such as 35mm. Slide scanners have very high resolution, typically a minimum of 2400 dpi, required for getting all the details out of your slides. Many slide scanners also have the ability to scan color negatives and to convert the negative image to a positive image.

For philatelic purposes, a flatbed scanner is undoubtedly the most versatile. You can scan anything from a single stamp to an entire stockbook or album page. A hand scanner may be a viable alternative, particularly if your budget is tight, although the prices of flatbed scanners are so low that this is rarely a real consideration. The width limitation of hand scanners does not matter so much for stamps and covers. I have also seen single sheet scanners and photo scanners used successfully for philatelic purposes, although they require that the item being scanned be sandwiched between clear plastic sheets for feeding into the scanner.

Using a Scanner to Extract Postmarks

Peter Aiken, Compulatelist

Have you ever been faced with a used stamp where you cannot quite make out the details of the postmark? Postal history collectors, who are interested in place names and dates, sometimes encounter this problem. If the postmark is smudged there’s not much you can do, but if the problem is that the postmark “blends in” with the stamp design the following two techniques may enable you to make out more details. It can be used with stamps off-paper as well as stamps still on cover.

The first procedure involves scanning the postmarked stamp and an unpostmarked copy of the same stamp, then subtracting the two images. In theory the stamp design will cancel out leaving only the image of the postmark. In actuality the technique is difficult to use and requires a steady hand, some experimentation, and lots of practice.

Here’s what to do:

1. Mount the postmarked stamp and an unpostmarked copy of the same stamp in some sort of holder.
2. It is essential that the edges of the stamp design be exactly parallel.
3. Scan the stamps using a fairly high resolution.
4. In your graphics program select an area that contains only the postmarked stamp.
5. Copy and paste this selection to a new image.

Repeat step 3, this time for the unpostmarked stamp. Be very careful to select exactly the same area, with respect to the stamp, that you did for the first stamp.

Use your graphics program’s Arithmetic command to subtract one image from the other. In Paint Shop Pro the command is Image, Arithmetic. Use either the Subtract or Difference command.

The resulting subtracted image should show very little trace of the stamp design. If the design is clearly visible it probably means either that the two stamps were not parallel during scanning or the areas selected in steps 3 and 4 did not match exactly. Go back and redo these steps if required.

If the postmark is not immediately readable in the subtracted image, you may be able to improve it by adjusting the contrast and/or brightness.

This technique is based on the two stamps being the exactly the same, except for the postmark. This is often not the case, unfortunately. For example, a used stamp may have changed size slightly with respect to a mint stamp as a result of being glued to an envelope and then soaked off.

Also, colors may fade which prevents the subtraction from completely canceling the two stamp images. This technique does not always succeed, and you should not expect perfect results the first time you try it.

The second technique was told to me by Mr. Robert W. Hisey. It works best used when the postmark is black and the stamp design has little or no black in it. It involves using your graphics program to separate the image into its 4 color components: cyan (blue), magenta (red), yellow, and black. It is described in detail in the following section.

Lifting Postmarks and Overprints

Sometimes there is not a problem reading a postmark, but rather you want to “lift” the postmark to make a clean copy of it – in other words, an image of the postmark without the stamp. This is sometimes needed for overprints, surcharges, and the like as well as for postmarks. The technique described here can also be used in some situations for reading a difficult postmark. This technique works best if the postmark or overprint is black and the rest of the stamp is colored with no black elements in the design.

1. Scan the stamp in true color mode. Here’s an example of a Canada Scott #51 with a great CDS.



2. Use your graphics program’s channel splitting command (or equivalent) to create a CMYK split. This creates four new grayscale images, each containing the color information for one of the four colors of ink (Cyan, Magenta, Yellow, and blacK) that would be used to print your original image. You need only the black channel, which contains a negative image of the black parts of the original scan.



3. Invert the image colors, using the Negative Image or Invert Colors command to replace black with white and vice versa:



4. Crop and rotate the image as desired for the final product: In this example I have also done some retouching to “fill in” missing parts of the outer ring.

Detecting Forgeries and Printing Varieties

Scanning techniques can be useful in some situations to detect forgeries and printing varieties. The principal behind this technique is that the printed design on the forgery or variety will differ from the design on a normal stamp. By scanning both stamps and subtracting one image from the other, any differences should stand out. The technique is essentially the same as described for reading difficult postmarks.