Imaging Changes: Smartphone Cameras and Citizen Science Meet Heritage Conservation
Eric Doehne, Conservation Sciences, Pasadena, CA
Wensen Ma, Northwestern University, Evanston, IL
Oliver Cossairt, Northwestern University, Evanston, IL
Cultural heritage is under constant attack from the elements and entropy. The role of conservators is to manage and mitigate this change, not stop it. Imaging is a natural tool for measurement and detection as it reveals changes in context, unlike point measurements.. While point methods (i.e., FTIR, Raman) can typically provide detailed information on the current state of the materials, they are not well suited to macroscale and repeated measurements.
We propose a citizen science approach, using mobile phone cameras, to create a fine-grained, time-stamped image dataset for change detection and management. These data will serve as the inputs for measuring change and determining rates and patterns of changes caused by biodeterioration, material loss, vandalism and soiling. Plus, the data can be used to detect color changes as proxies for surface changes such as UV damage, bleaching and pollution-driven chemistry.
The methodology is particularly well-suited for built heritage – historical buildings, monuments, excavated archeological sites and any sort of large-scale cultural heritage exposed to the elements. Accurate color calibration is vital for this program and we have designed and tested calibration kiosks to be imaged alongside objects. We calibrated mobile cameras against color standards and compared results on minimum detectable color changes with known values of color and color change on built heritage from biofilms and pollution.
Crowd-sourcing will enable collection of large numbers of images over time, from remote or urban locations that would be cost-prohibitive to acquire using mounted site cameras.. Using social media, we will create an engagement loop for participants that will make it fun and easy to take images, spread the word and pull in feedback and outreach. “Then and Now” images of popular heritage sites are particularity compelling. Users will have the choice of a stand-alone app or web based, to frame and take pictures; a translucent overlay will guide users to the correct image and ascertain that all are approximately the same.
Significant computation issues at the back end need to be addressed and we report on progress. The images must be aligned, registered, color-calibrated and corrected for zoom, dolly and other artifacts of acquisition. In addition, we need to adapt existing systems for detecting, quantifying and visualizing change to the needs of heritage sites and develop the necessary ‘glue’ in terms of criteria, design and software for evaluating change. We anticipate that the final output will be multiple time-lapse movies keyed to different changes; these will be cloud based and available to conservators, site manages and the participating public.