Is this Rembrandt a real one?
About a year ago, I told you about how computer scientists from Dartmouth college were investigating digital images. But they're also interested in old paintings authentication, as reports Wired Magazine in The Rembrandt Code. Mathematicians are using high-resolution digital cameras and computers to examine old paintings and evaluate their authenticity. Even the New York's Metropolitan Museum of Art is asking them to discover which of the 42 paintings it owns and that were once believed to be Rembrandts are really authentic.
Let's start with some quotes from the Wired article about mathematician Dan Rockmore, who's been asked for help by the Met.
"The fact that you can put everything on the computer means that everything is numbers," Rockmore says. "As soon as everything is numbers, it makes perfect sense to ask mathematical questions about what the numbers represent." If he's right -- if computers can distinguish between artists more accurately than connoisseurs can -- the art world is in for some high-stakes corrections. Rockmore's scientific approach will boost the value of some collections by millions of dollars -- while devastating others that are tainted by imitations and fakes.
Rockmore's method is summarized in a sidebar to the main article, "Is This Rembrandt Real?."
Here are the four steps of the authentication process: digitize the artwork; use a software to convert the image to grayscale and segment it into squares; use another piece of software to search for patterns indicating the artist's style; and finally plot points on a 3D grid and compare them to points produced by other paintings.
Now, it's time to look at a real example. Below is a photograph of Dartmouth researchers -- with Dan Rockmore in the middle -- looking at 'Madonna with Child' by Pietro di Cristoforo Vannucci (Perugino) (1446-1523), a painting belonging to Dartmouth's Hood Museum of Art (Credit: Joseph Mehling, for Dartmouth college).
You'll find more details about this picture in a Dartmouth news release from November 2004, "Researchers develop digital technique for art authentication."
For more information, let's switch now to this technical paper, "A Digital Technique for Art Authentication" (PDF format, 9 pages, 1.55 MB).
On the image below, extracted from this document, you can see the six faces present in 'Madonna with Child' by Perugino. How many hands contributed to this painting?
Here is the answer.
As with many of the great Renaissance paintings, it is likely that Perugino only painted a portion of this work -- apprentices did the rest. To this end, we wondered if we could uncover statistical differences amongst the faces of the individual characters.
The painting was photographed using a large-format camera (8x10 inch negative) and drum-scanned to yield a color 16,852 x 18,204 pixel image [before being] converted to grayscale.
The six facial regions were then localized and partitioned into 144 regions which were subjected to different statistical methods to discover some patterns. And here is what the researchers found.
This clustering pattern suggests the presence of at least four distinct hands, and is consistent with the views of some art historians.
And here is their conclusion.
We have presented a computational tool for digitally authenticating or classifying works of art. This technique looks for consistencies or inconsistencies in the first- and higher-order wavelet statistics collected from drawings or paintings (or portions thereof). We showed preliminary results from our analysis of thirteen drawings either by, or in the style of, Pieter Bruegel the Elder as well as a painting by Perugino. We expect these techniques, in collaboration with existing physical authentication, to play an important role in the field of art forensics.
So will computers replace art historians? Not so fast, as reminds us Wired.
Rockmore's system worked well enough for the Bruegel drawings, says Walter Liedtke [,from the Met.] But drawings are simpler than paintings. Rembrandts sometimes have eight to 10 layers of paint, some conservation, some slight editing by later artists, and many other factors that could confound the analysis, he cautions.
As you can guess, Rockmore disagrees and comes with an analogy of his own. For him, analyzing paintings and drawings is like comparing chess and checkers. And for him, computer programs have already beaten men in chess tournaments. So will art historians be the next victims of computers? Time will tell.
Sources: Bijal P. Trivedi, for Wired Magazine, Issue 13.12, December 2005; and various web sites
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