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.

Planning a Digital Study

Fran Adams

Once a collector turns to exhibiting, the requirement to increase one’s philatelic knowledge expands exponentially, typically as a result of the need to display that knowledge to further an award level. Accumulating reference material is not the goal of the exercise. The references must be organized, indexed and readily available to support your information needs.

Accessibility of information is the most important element and electronic media is one way to make your knowledge requirements quickly available. Digital references can be invaluable information organization tools, especially if they’re portable and cross platform. Once assembled, digital information can also be published for public consumption in the forms of printed matter, slide shows, digital philatelic studies (DPS) or references, distributed on compact disc or through the World Wide Web.

Building a DPS or digital reference requires planning, organization, a logical structure and personal effort. Hopefully, this series of articles will benefit interested readers as they contain steps I’ve found valuable in producing such electronic philatelic presentations and references.

Defining the Project Scope

In 1999, I began with the idea that an electronic philatelic exhibit would be valuable if I could integrate additional information. Thereafter, imagining how comprehensive it could be and what types of data it might include produced a goal of a full-bodied reference machine. As with most labors of love, my visions were greater than my expertise. I was forced to confront unforeseen obstacles but continued as this was something I really felt would be both interesting and useful.

That early digital exhibit has since grown into the proportions originally envisioned and become a digital philatelic reference (Bone and Stone) rather than a 16 page digital exhibit with a bit of support material. I’ve since promised myself that for future projects, I would be more thoughtful in regard to my personal ambitions.

You may be thinking the challenge of building a digital reference is too great a task.If that’s true – you’ve successfully constructed a self-defeating wall – start with individual tasks to achieve the end goal. You’ll be surprised how fast a simple thing grows in the world of digital philately.

Perhaps you also believe you’re unable to do this alone. There are plenty of other collectors interested in sharing information and expertise. Find someone with similar interests whom you admire and would like to work with. Ask if they might be willing to join forces and produce a joint work. If there’s more than only one person, that’s fine. Joint projects can mesh the knowledge and talents of many individuals into a greater whole. (Finally, a use for those techie guys…)

The Nuts and Bolts

The how-to is variable depending on your goal. The items you’ll need are:

Hardware —

1. Computer, and
2. Printer, and
3. Access to a Scanner or Digital Camera, and
4. Supplies — ink, labels, CDs.

Software — Microsoft, Adobe or others

1. Word Processing software (MS Word), or
2. Presentation software (MS PowerPoint), or
3. Page Layout software (Adobe InDesign), and
4. Graphics software (Adobe Photoshop Elements).

Other Essentials —

1. Time — each of us has some,
2. Information and Knowledge — of the subject area, and
3. Philatelic Material — your collection and other images.

All but one of these items is straightforward; most people have misgivings about the second – software. You believe you need to be an expert user of PowerPoint or whatever software you have, right? Wrong.

Doing a Google search for a “free PowerPoint tutorial,” I found a large number of quick lessons that were graphical and free. I’ve used both free and paid (Lynda.com) online graphic tutorials and they do help. Other resources are the local adult education classes, or, if you’re really having trouble and need an in-house expert, ask the grandkids!

Most high-end programs come with online tutorials. The XXX for Dummies series (Wiley Publishing, Inc.) and Visual Quickstart Guides (Peachpit Press) books are also excellent resources.) Another consideration is publication production costs. If you burn a CD for distribution and add a plastic case with a printed label, a single finished CD is less than $3 for materials, including label, printer ink, and electricity.

I’d like to encourage all collectors and exhibitors to share their knowledge by building digital philatelic studies, electronic exhibits, and/or reference documents.

Use the software you are most comfortable with as familiarity, aside from being a main concern, allows you to concentrate on the content. Each method has its benefits and practicalities and learning about the areas you’re not familiar also brings great satisfaction.

DPS Critique – Mega-Event 2007

Bob Odenweller, David Herendeen and Fran Adams

The following is a general letter provided as feedback to the participants of the 2007 DPS Competition.

“The jury for Digital Philatelic Studies (DPS) entered in the 2007 Mega-Event in New York reviewed each submission using the Mega-Event DPS definition as a basis. The jury suggests exhibitors review the following points, in addition to their evaluation sheets, to assist in further developing their entries.

A DPS is NOT a scan of a regular stamp exhibit and is intended to be much more. A DPS is more closely related to an article or research paper than an exhibit.

In an article, the first paragraph establishes the article’s goal and the rest of the article provides further details.

The goal of the DPS must be stated up front and the rest of the DPS must support and illustrate that goal.

A DPS differs from a physical philatelic exhibit in that it is not restricted to a limited space and the content is not limited simply to philatelic material with descriptive captions. A DPS should include more. In addition to story line text, enhanced graphics, references and explanations of terms are expected as supportive information to elaborate on the goal and the philatelic material shown.

A common mistake is to present material like a bulleted slide show. Bullet points can’t convey stories, they’re triggers for you to speak to. When giving a slide show, you have speaker notes used to tell your story to an audience. All that background information is not on the slide you show. The idea is to include “some” of that story line text in your DPS as you’re not present to tell the story.

Don’t be afraid to do things differently, but make sure viewers can read your work. Centering text under an item as a caption is fine. However, would you read a novel with page after page of centered text?

Many facets of a study demand showing details of stamps, etc. Enlarge those details and flaunt your errors and varieties. Ensure that the viewer will be able to visibly recognize what you’ve taken the time to describe. When doing so, give each enlargement its time in the sun. Don’t cram everything on a single page. Making enlargements appear at the reader’s request rather than forcing all viewers to see all details provides the viewer with interactivity and gets them involved with your study.

Take credit for personal research, but give others their due and cite your sources. Showing your research and knowledge is simple – include a bibliography at the end of the DPS. Have a synopsis? Link it in. Did you write the definitive article on the subject? Great; link it in.

A method of tying all this information together must be employed or it’s just a bunch of “electronic stuff.” A single file or a file with links to external files is the best method and a navigation system is required. Using the ‘enter’ and ‘backspace’ keys is fine (please do not disable this function), but employing links to move between sections or pages is better. To help viewers navigate through your study, a description of control mechanisms should appear early in your presentation.

A Table of Contents is a great addition. Link the entries to the main sections within the study. Do you use abbreviations and jargon? How about a page at the end with an explanation of terms, or use of a tool-tip that defines a word when the cursor goes over it? Simply try to help your viewer as much as you can.

Keep in mind what you appreciate in others’ writing. Have someone else review your DPS as a “sanity” check. A non-philatelist can often be most helpful.

Lastly, keep it simple as fancy effects are very disruptive to a viewer and are not required. Many have said this before: “Because you can doesn’t mean you should.”

Respectfully submitted,