Numismatic and History Discussions > Coin Photography, Conservation and Storage

Article of Interest/Imaging of Coins

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Carla, welcome to  Forum. Your system is very interesting and useful.  Many of the members are not just coin collectors, some are associated with museums or other professional groups, so there is a very wide range of skills and abilities. Please feel free to stop in and add to this area.


That is impressive.  Here are two view of a denarius using the Java PTM viewer, first at the default setting, then set to "effects: specular."  (I have not resized them, and I have kept the edges of the Java viewer software, but this is just an image so it won't work here!)  This is shown here as a JPEG, which is a lossy format, but you can see how it enhances the detail of the surface even of the 18% grey card it is set on.  And in each of these, you can see the coin lit from many different angles by moving the mouse around.  This is a great tool for studying objects like the Antikythera machine, but I still think it's overkill for the average coin collection.

But a simplified technique is on its way ..

In a separate discussion, I envisaged a robot arm that moved a light around while programmed photos were taken.  This is existing technology.  This could be completely automated, with settings for different sizes and types of object.  I have no idea what the route taken by Carla and her colleagues is, but I can see that if there is enough demand, such a service might become available.  But I also suspect it would be for academics, and not necessarily cheap.

Such an enhancement might be useful for coins like this cast "follis" of Constantine VII and Romanus I from Cherson.  The reverse shows a cross on two steps, with a pellet on either side, and I can see it quite clearly with the light at the right angle, but hardly at all in this photo!  And there will certainly be coins of special interest for which this will be a wonderful tool.

I'm dredging up an old thread, having searched this discussion board for any reference to Reflectance Transformation Imaging, or RTI. It's also known as Polynomial Texture Mapping, or PTM. 

I ran across an interesting website while researching medieval coins of Cyprus, CMCHC, Cypriot Medieval Coins History and Culture, where The Cyprus Institute and the Bank of Cyprus Cultural Foundation have used RTI and published their coin collection online.  The technique uses computational photography and a specialized lighting arrangement.  Sounds interesting!

I currently use High Dynamic Range (HDR), but focus-stacking is beyond me, so something as advanced as RTI is unlikely to work its way into my repertoire. 

To paraphrase their description:

A custom-build RTI dome consists of a hemispherical domical device with thirty-six embedded lights. A coin is placed at the base of the dome and a camera points down through a hole at the top. Thirty-six photographic images are taken, each with a single light shining on the coin, creating thirty six images with different light angles. Then, the RTI algorithm synthesizes the data from these images to create a single image that can be examined on a RTI viewer. The viewer allows the user to move the light angle. 

I can see how useful RTI can be to read some of the torturous Medieval legends. 

I'd welcome knowing if this technique has been used in other collections, and where the technology may have changed in the intervening years.


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