Automated thread counting algorithms, in development since 2007 by Professors Rick Johnson (Cornell University) and Don Johnson (Rice University), are poised for a profound impact on the practice of technical art history. This work is a pioneering effort in the emerging application of signal and image processing to the analysis of paintings. The approach is based on the utilization of spectral analysis of x-rays of paintings. X-rays can display the periodic intensity pattern due to the greater thickness of the lead white ground between the canvas threads. With the addition of innovative application-specific signal processing, local peaks in the spectrum of the x-ray data can reveal the numbers of threads per centimeter, i.e. a thread count, separately for (nearly) vertically and (nearly) horizontally oriented threads. Such thread counts have been used previously, but their manual acquisition proved too costly to be done thoroughly. The introduction of the capability to assemble previously unthinkable thread density and angle pattern maps of high detail across the entire surface of a painting leads to correlation-based identification of canvases sharing the same pattern in thread density variations. Such weave maps and matches can now be assembled across all of the paintings on canvas of a single artist or school, thereby significantly extending the art historian's capabilities in, for example, dating and attribution. The scale, breadth, and depth of such thread-counting projects represent a bold leap in the capabilities of technical art history. This grant supports the analysis phase of the projects of such grand scope: the thread counting and subsequent weave matching among (i) all of the paintings by Vincent van Gogh (for which data can be obtained by the end of 2010) and (ii) all of the paintings by the Delft School during the career of Johannes Vermeer (for which data can be obtained by the end of 2010). This grant places Professors Rick and Don Johnson in the center of the data fusion, data analysis and database creation activities that are scheduled to occur in Amsterdam during the spring of 2011. The archives being established of thread count reports, including weave density maps providing fingerprints for weave matching and angle maps for characterizing cusping, form a groundbreaking resource at a time when museums are just beginning to address the technological and cultural barriers to technical data sharing among museums and collaborating researchers outside the museum. This project is part of a long-term effort that aims to expand the utility of thread counting from x-rays to all suitable oil paintings on canvas, and to photos of unlined backs of old master paintings and of the raw canvas, for example, of the modern colorfield painters and of densely-woven, multi-pattern fabrics prominent in the design and decorative arts.
The claim that two paintings are on canvas from the same original roll can support conclusions on dating, authenticity, and other issues of basic importance in art historical painting analysis. Traditionally such claims begin with establishing matching average thread counts for the two paintings. Averages are typically obtained from a few manual spot counts at points scattered across the painting. Manual spot counts are taken from x-rays of paintings mounted on a lightbox and viewed through a magnifying eyepiece - a tedious procedure without the possibility of precise confirmation. The principal investigator (C. Richard Johnson, Jr., Cornell University) of this grant recognized that in some cases thread counting from x-rays of paintings on canvas is approachable as a Fourier spectral analysis problem and founded of the Thread Count Automation Project (TCAP) in 2007. Being able to compute the thread count within every square centimeter across the painting revealed a striped pattern in the local weave densities. Paintings sharing threads from the same roll will possess the same striped pattern, which converts a weave match search into a correlation problem. Matches since found with this signal processing procedure include paintings by Vincent van Gogh, Johannes Vermeer, and several other 15th to early 21st century European painters. With the travel support provide by this grant, for the first half of 2011 frequent interaction was maintained with Dutch museum curators and conservators collaborating on this pioneering effort in automated canvas examination. These opportunities for collaboration - along with the data collection and computation milestone reached in 2011 with weave maps having been produced for over half of the paintings by van Gogh and by Vermeer - resulted in the preparation and submission of journal papers in 2011that were revised and accepted for publication in 2012. These publications (primarily in the art history and conservation literature) addressed a variety of art historical issues, primarily regarding studio practice, dating, and authentication. Consequently, the weave density and angle maps produced by automated thread counting are poised to become fundamental tools in the emerging field of computational art history.
