Friday, April 15, 2011

Fold shadows and backlight

Haste and laziness do not reward
Yesterday, I fooled myself by trying to gain some time by making a "quick" scan of an American stock certificate. I put its front side on the scanning surface. The cover of my scanner device has been removed, which allows me to scan parts of large certificates more easily. I pressed the "scan" button on the device and thirty seconds later, the image was generated. This was the result. Poor !

Hm, not good at all. This was not the result that I expected as several shortcomings in the image can be identified (click the image to enlarge) :
  1. Shadows along the folds
  2. Hazy details and letters along the fold areas
  3. Print patterns from the backside visible through the image
  4. Faint colors

Scripophily from The Moore Telephone and Telegraph Company
This uncancelled share, printed by Goes was issued in 1914 and signed by R.J. Moore. The company's offices were located in Glasgow, Montana.

The Moore Telephone and Telegraph Company
left : embossed seal with telephone pole
right : vignette of the company's offices
More on naming your scanned detail images, see here.

Avoid daylight and flatten a folded surface
As is the case with many of them, American stocks and bonds have been folded in the past under normal usage. Even smaller certificates, like this one, often show 2 folds. Because I simply laid the certificate on the scanner without the scanner's cover on top of it, the paper's folds were strong enough to raise up a few milimeters from the glass surface. When the image was scanned from side to side, shadows along the folds were created in the process and captured in the image. The hazy lettering and details in the areas along the folds were als caused by the distance difference between the paper and the glass surface (wrong focus).

As there was no cover or any other material that could prevent the daylight from shining through the paper, two other image imperfections are seen. You can distinguish the printing on the backside and also the colors are faint, certainly not comparable to the full colors in real.

Solving the issue
My first solution was to put a white sheet of paper on top of this share and scan it again. This is the result.

The paper blocked the roomlight. You can see, the colors were perfect and the printing on the backside was hardly visible. Yet, there were still shadows visible in the areas along the two folds.

In the next step, on top of the certificate and the extra white sheet of paper, I put an auction catalogue, some extra weight, on the certificate in order to flatten it further against the glass surface. And again, I scanned the certificate. As you see below, fold shadows were gone and details and lettering were clear.

It is important, in case the cover of the scanner is removed, that you insert a white sheet of paper between the certificate and anything else, let's say a book, that is on top of it. That way you prevent any background patterns, in our case from the book, from being captured in the digital image.

Lessons learned
First, I aimed for a quick scanning operation in order to gain time but ended up with doing three scan operations. I would have gained half the time if I'd have done the job properly from the start. Well, I've had similar experiences before ..


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