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Author Topic: Article of Interest/Imaging of Coins  (Read 2434 times)

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Offline museumguy

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Article of Interest/Imaging of Coins
« on: November 16, 2007, 09:09:26 am »
Hi All,

Discovered (sort of by accident) this interesting article on coin imaging.  Its long and a bit technical for my small brain but there appears to be a lot of interesting stuff regarding new methods of viewing coins (focus on ancients) using Reflection Transformation Imaging - sort of a virtual look at coins.  Check it out.  I've got to spend some more time with it myself.

Steve

http://www.c-h-i.org/events/VAST2005_final.pdf

Offline Gilgamesh

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Re: Article of Interest/Imaging of Coins
« Reply #1 on: November 22, 2007, 06:35:21 pm »
 ;D Thanks for the link. I'm about to start trying this.
Every day I know less and less about more and more. Soon I expect to know nothing about everything.

Offline moonmoth

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Re: Article of Interest/Imaging of Coins
« Reply #2 on: November 24, 2007, 04:28:34 pm »
Well, it is interesting, but you need a lot of resource to do it.  Their original subject, a cuneiform tablet, required 400 separate photographs.  Luckily, the paper describes a method for coins that only requires 48 photographs per coin.

You also need a purpose-built stage, special software to integrate the photographs, and special software to view the result.

You would have to be really serious about remotely studying a coin to do this.
"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."

Offline bruce61813

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Re: Article of Interest/Imaging of Coins
« Reply #3 on: November 26, 2007, 08:06:58 pm »
If you look up "photogrammetry" you will find there is software that is capable of doing this type of work. It has been around for over 20 years, and started with special calibrated cameras. then progressed into the digital world as equipment became better. Look at this site: http://www.photomodeler.com/index.htm.

 there used o be a simple program available that allowed to to photograph and object, then by marking reference points, the computer would use the 2D images to create a 3D picture, they could be rotated, turned or twisted in any direction.  the total detail was only limited by the number of pictures us used. for a normal item, say a child's block, 6 pictures worked, one of each face.  A vase required more , about 12 plus top and bottom. The more the easier it was for the computer to reconstruct the image. the 'operator' did have to supply 'key' point markers for alignment purposes. I think the software is still on the web somewhere. If I also remember correctly, the 'output' included the controls for viewing.

Bruce
too many coins - too little time!!

cdschroer

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Re: Article of Interest/Imaging of Coins
« Reply #4 on: November 27, 2007, 08:48:54 pm »

I'm one of the authors of this paper, and ran across your posts.  I thought folks might be interested in our website where you can see more coin examples that use the technique and can be interactively viewed with different lighting.

http://www.c-h-i.org/examples/ptm/ptm.html is the index page, and there is a coin gallery available. You need a Java enabled browser to look at them.  The demos are low resolution due to web constraints, but we shoot at a much higher resolution, that allows you to zoom in and out.

You can also learn more about this technique, in a less academic format, from this article on our website:  http://www.c-h-i.org/technology/ptm/ptm.html

This technique is quite different from photogrammetry (something we also use) in that it generates 3D information  based on the reflectance properties of the surface, and stores it in a 2D format. This surface information allows you to see fine detail of the surface characteristics, more than you would get from a 3D model, and with enhancements, more than you can see on the object itself.  Also the technique works on highly reflective material, which is very difficult to capture with traditional 3D scanning and imaging techniques. The article I mention has a good explanation of what's going on for those who are interested. The technique has been used to decipher heavily worn and/or corroded inscriptions, most famously on the Greek Antikythera mechanism. http://www.hpl.hp.com/research/ptm/antikythera_mechanism/index.html

And finally, there is a new technique for capturing this type of image that we developed last year in conjunction with HP labs that doesn't require a light dome. So, it's easy to try out without investing a lot, and it's more flexible for different size objects.  We've been using it for documenting rock art.

We are a 501(c)(3) non-profit corporation, and the software we develop will be made available as open source.  We have some active projects and expect to make more stuff available during 2008.

Thanks for your interest!
Carla

Offline bruce61813

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Re: Article of Interest/Imaging of Coins
« Reply #5 on: November 27, 2007, 10:34:51 pm »
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.


Bruce
too many coins - too little time!!

Offline moonmoth

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Re: Article of Interest/Imaging of Coins
« Reply #6 on: November 28, 2007, 03:00:09 am »
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.
"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."

Offline moonmoth

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Re: Article of Interest/Imaging of Coins
« Reply #7 on: November 28, 2007, 03:04:05 am »
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.
"... A form of twisted symbolical bedsock ... the true purpose of which, as they realised at first glance, would never (alas) be revealed to mankind."

Offline Anaximander

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Reflectance Transformation Imaging (RTI) of Coins
« Reply #8 on: August 05, 2021, 12:13:04 pm »
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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