Sunday, January 02, 2022

rNumis digital library expands

rNumis.com has been steadily adding digital auction catalogs for several years. As of January 2, they have a database of 4565 catalogs, 1579 of which include links to digital versions of the catalog.

The site also includes a proof-of-concept provenance research tool for Greek coins of Italy and Sicily. There is no full-text search but the coins of each Greek city can be filtered by weight and metal. Best: if a coin has multiple auction apperances, such as this Akragas tetradrachm, the full auction chain is displayed.

As always, the site contines to offer numismatic literature for sale.

This site is an important resource to numismatic researchers. Merely by curating links to online coin catalogs on file sharing sites such as issuu.com and research library archives such as HEIDI the site saves time by making it easy to learn if a particular catalog is online.

Even when I own a physical copy of a catalog, I find it easier to use digitized ones. My physical libary is mostly either mis-filed or in boxes in my attic! Digital copies save a very dusty trip.

The provenance tool is an interesting start. I have not used it much. The tool includes photos and metadata about 4926 ancient Greek coins of Italy and Sicily, scraped from public-domain auction catalogs. The concept is similar to the the important but sadly obscure photo-file of the American Numismatic Society. The ANS effort, which took decades of work, covers 268,000 coins. rNumis currently has only 2% of that scope. Yet that is 2% is online and growing.

I have been building a library of numismatic auction catalogs covering my areas of interest for many years. Due to limited shelf space I don't acquire catalogs that are already online in acsearch.info. At this point rNumis is good enough that I will no longer be buying catalogs if rNumis can reveal a digital copy.

I encourage numismatic researchers to check out the site. The operator is friendly and seems to be open to suggestions. Don't miss the catalog sale section for enlarging your own literature collection.

Tuesday, November 02, 2021

Ancient coin NFTs

D.F. Grotjohann, who has a VCoins store until about 2010, is now selling ancient coin NFTs at https://opensea.io/DFGrotjohann.

He has 13 ancient coins listed as well as two samurai cartoons. One of the coins is a nice looking Alexander Octodrachm. The price is 3.5. The currency of that price is Ethereum, which works out to US$15,532.

The buyer receives the ancient coin in addition to the digital rights.

Press release on einnews.com here.

Monday, October 11, 2021

Currency Counterfeiting in Peru

National Geographic gives a detailed look at how currency counterfeiting is done in the underworld of Lima, Peru. Mariana van Zeller interviews a convicted printer, visits a currently operating printer and as well as a finisher. A money mule explains how to sneaks cash into the US.

You can watch the complete 47 minute episode on NationalGeographic.com or on Hulu.

Monday, August 09, 2021

Miracle headache cure

Here are two auction sales. (Not eBay.)

The upper coin sold for about $300+fees. The lower coin sold for about $600+fees. I do not have access to the coins, I merely stumbled across the photos online.

My first impression was that I was looking at two different coins. At least one of the coins is a modern cast forgery.

Several people suggested that it was more likely that both pictures show the same coin, before and after a 'repair'.

I am curious what my readers think. In the comments, tell me if you think these are one or two coins, genuine or fake, repaired or not. I can tell you that the reported weights are within 0.3%.

Tuesday, June 29, 2021

Pandemic in NYC

I haven't posted in a while.  Here is a photo of me in NYC during a height of the pandemic.

La Moneda restaurant, Jerome south of 175th st


Friday, November 13, 2020

Harlan J Berk catalogs 168-213 online

Most Harlan Berk catalogs for Buy or Bid sales 168 to the present and Gemini VI through XIV are available on issuu.com. These are the catalogs issued in the last 11 years. I haven't been able to find the earlier ones online. This item isn't news -- they have been there for a while -- but it took me a while to find them this morning.

Monday, August 10, 2020

Notes on 'New Developments in the Computer-Aided Die Study'

What can artificial intelligence and image processing tell us about coins? Zachary Taylor of the American Numismatic Society gave a walkthrough in April of 'CADS'.

I was intrigued by the ideas of calibrating feature extraction by sizing a circle and throwing away everything outside the circle. I hadn’t thought of it myself — the die study I am attempting is on a series where the die is larger than the coins. It seems like an ingenious hack given how feature extraction works. Taylor also suggested that the images should be cleaned up — I think he mentioned removing backgrounds — but if the software removes everything except the center there is no need to remove backgrounds at all.

Greek coins, and many Roman coins, suffer from dies that degrade faster near the edges than the center. Only using the middle of the coin may help to keep degrading dies "together" in the tree (dendrogram) view later.

Taylor next showed setting the “blur radius” until the image looks “cartoonish”. He called the CADS kind of blurring “median blur”. This seems like a good idea. I suspect it could be done automatically with a small bit of work rather than requiring a human operator. Taylor said this was to remove circulation wear. I suspect this also makes the analysis more resistant to photographic and lighting concerns.

The next thing is what he calls “feature detection”. CADS uses OpenCV, which has been under development for a couple of decades. Taylor says using feature detection came from Huapeng Su’s earlier ANS CADS prototype. A 'feature' is just a contrast pattern of light and color, not something a human would call a 'feature' like a helmet decoration or nose shape. OpenCV tutorials suggest features represent “corners” — small regions on the image where the contrast changes a lot, and changes differently from nearby regions.

The coins CADS has been tested on seemed to be all VF-XF condition. I will be curious to see how it does with coins with a wider range of conditions. I was wondering if the blur could be different for each coin, with less blur being applied to lower grade coins.

The next step is calculating the “distance metric” between all coins. I suspect the computational complexity is N^2 to the number of coin images. He described this as “brute force Hamming method”, with the “20 best matches condensed into 1”, “agglomerative nesting” with “no risk of overfitting”. Taylor said CADS uses Oriented FAST and Rotated BRIEF (not SIFT). I am not a computer vision guy and only know the meaning of some of those terms … but OpenCV provides a library for all of these things: https://docs.opencv.org/master/d1/d89/tutorial_py_orb.html . Taylor’s work seems to be choosing to use that library and tuning the parameters rather than implementing a distance calculation from scratch.

Taylor said the algorithm to compute the distance metric takes “a few hours” for 3000 owls and he showed it taking less than a minute for about 100 Paphos tests. This also suggests the performance is N^2.

The next piece is the dendrogram graph, which looks nice. (It might just be the dendrogram feature of the Javascript library D3 https://www.d3-graph-gallery.com/dendrogram ?)

Taylor described the dendrogram sub-trees as representing dies if tuned correctly. I suspect his algorithm will also group coins from the same die by “die state”.

The “card view” letting the user quickly flip between all the children at a point in the dendrogram looked good. I suspect the card view would be greatly improved if the images were rotated and scaled so that the matched features of all coins on the card line up as close as possible.

After Taylor's demo, Alan Stahl showed Princeton’s work on the topic. He had previously shown this work at the New York Numismatic Club. Princeton’s approach has at least two key differences.

Stahl’s team used a complex physical technique to get the 3D height of the object. It is a great technique but it may not get traction because of the difficulty performing it and getting access to the coins. Yet it is worth pointing out that the CADS approach has only been tested on (over?)-cleaned silver coins. Bronze coins and coins with a lot of toning may not work directly with CADS — photographs of plaster casts may needed to get good results from CADS if patina variations overwhelm “feature detection”. If that is true then the Princeton approach not look so difficult compared to CADS for those series.

Stahl was concerned about the file size of his images. I suspect he could just use the calculated “height” as a greyscale pixel values and store his images as black-and-white JPEGs. That would reduce the image size to normal and I suspect it would let him use Taylor’s workflow directly.

Princeton had humans annotate manually some interesting points on the coins. This is labor intensive! Yet manual annotation might have some merit being used in conjunction with the Taylor approach. It might be that the CADS approach has a hard time “connecting” worn coins, partly reworked dies, or lighting techniques. Perhaps after CADS has reduced the 3000 obverses to a hundred “dies” the Princeton approach of manually marking points could be used on CADS-identified dies to find further matches that CADS missed.

I was disappointed that after all of these years the ANS and Mr. Taylor only managed to look at two series of ancient coin types. Taylor said this isn’t a problem because the “learning” is unsupervised.