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New approach to study the damage due to environmental fluctuations of textile objects by image processing with IDS cameras.
Preventive conservation plays an important role in the preservation of works of art and property culture. In order to preserve their authentic state as long as possible, it is essential to slow down aging processes and to evaluate the factors of alteration of materials. For this, it is necessary to apprehend and understand the object in its entirety. The methods of the sciences of cultural heritage to understanding the behavior of materials are important parameters that require a interdisciplinary approach. Textiles are among the most fragile artistic and cultural assets. At During their manufacture and handling, their presentation and conservation, they are often exposed to influences that can have adverse effects on their material. The start-up French S-MA-C-H has been looking at the Bayeux tapestry as part of a research project and has developed, with the help of IDS cameras, a system that provides valuable information for a conservation and presentation of this fragile and exceptional object. The expertise of the curators- combined with state-of-the-art technology, allows for the early detection of the factors to minimize or, in the best of cases, to exclude them completely.
The system was designed for an in-depth study of the mechanical behavior of the tapestry of Bayeux. This study was commissioned and financed by the Direction régionale des affaires culturelles de Normandy. " We brought our expertise in mechanical engineering by closely monitoring the deformations and stresses of the entire tapestry. In addition to the control, we helped to the development of conservation solutions. This involved ranking and assessing the level of risk to the tapestry and its sensitivity to the ambient climate "explains Cécilia Gauvin, co-founder and director of S-MA-. C-H. A multidisciplinary team of textile conservators and conservation consultants as well as curators of heritage has depicted the reaction of the object to variations corresponding environmental issues. " The project addressed two key questions: What are the optimal parameters for presentation on inclined supports and how does the tapestry react to its microclimate? "
In order to answer these questions, the tapestry was monitored by temperature sensors and The heart and the brain are also equipped with force sensors to detect the force of gravity. The heart and the brain of the system: a full-field 2D non-contact digital image correlation (DIC), composed of a IDS camera as well as an in-house developed software for digital image correlation.
" Digital image correlation is an image processing method that allows the analysis of movements and deformations of objects. To do this, high resolution images of the surface of of the object are taken and then analyzed using software algorithms to detect changes in shape, position or size of the object "Patrick Schick, Product Marketing Manager at IDS, explains. At the In the search for the camera model adapted to the system, it is mainly parameters such as the interface, the sensor and the price-performance ratio that were decisive. " The analysis of the tapestry requires Very high resolution shooting with low image noise to capture the smallest details ". The camera USB 3 uEye CP used meets these requirements with the IMX183 rolling shutter CMOS sensor of the STARVIS series from Sony, particularly sensitive to light. This one ensures a quality of image technology ("back side illumination"), even under the most difficult lighting conditions. difficult. " The camera is therefore ideal for demanding image evaluations such as this control, which, for for conservation reasons, takes place in low light conditions. The USB3 Vision camera records high-resolution images at very low frequencies over an extended period of time "adds Patrick Schick. For the research project, for example, the control system ran around the clock for one month, with only one shot per hour.
" The Python interface of the IDS peak API allowed us to quickly and easily develop a software to set up the camera and capture images " Cécilia Gauvin, co-founder and director of S-MA-C-H explains. The images are then processed by DEFTAC3D, a software specially developed by French Institute Prime for digital image correlation. This results in measurement data on the entire surface of the object, based on thousands of 2D or 3D coordinates at very high resolution. The displacement of the pixels during the analysis period is interpreted as a deformation due to a load or a mechanical stress on the object. On the basis of the results full field deformation maps as well as deformation maps are established.
Full field deformation maps illustrate the displacements of a material over its entire surface. They show if and how the tapestry has deformed globally. The deformation maps, as for They give information on local deformations within a material. They indicate to of S-MA-CH if the tapestry has been deformed in certain places and provide information on how it was done. The full field deformation maps are processed at the same time as the knowledge of environmental variations in order to understand the hygromechanical behavior of the Bayeux tapestry. The hygromechanical behavior refers here to the interaction between humidity and the mechanical properties of the textile. This can be influenced by various factors, including the type of yarn used to make the fabric and the type of weaving or embroidery technique used to make the tapestry, which contributes to the complexity of the study.
In order to integrate scientific data into the decision-making process, tests were conducted both on copies and on the tapestry itself. On the copies, the full-field deformation maps have been combined with the stress results obtained from the load cell measurements and the climate (temperature and humidity). The results allow us to draw conclusions on the regulation necessary climate to achieve optimal conservation of the object. The data collected by the sensors and the camera system were documented in real time to analyze long-term trends. The information provided ensures that the conditions of the Bayeux Museum are within the optimal limits to avoid damaging the fragile works of art or historical objects on display, such as the Bayeux tapestry.
Perspectives
The market for the protection and conservation of cultural heritage is slowly opening up to structural diagnosis. " Our goal is to develop corresponding systems for conservators in a plug-and-play system "explains Cécilia Gauvin. In addition, the French startup would like to monitor the structural damage of paintings in museum galleries and historical monuments with the help of vision systems. This approach, which transcends disciplines, allows assess the condition of the exhibits thoroughly enough to take appropriate action conservatory measures that are necessary. " Our knowledge in mechanical engineering, combined with the processing of of industrial image, open up new approaches, broaden the field of action and bring out new innovative solutions. "
An elaboration of the conservation conditions for the handling, storage or presentation of objects, based on these interdisciplinary research results, offers protection against other damage. Historical and modern textile art products can thus be preserved in the best possible way for the future. The image processing components make a valuable contribution in this respect.
Some figures on tapestry
68 meters long
52 cm high
9 strips of woven fabric
4 seams
10 colors of wool yarns
58 individual scenes
623 people
202 horses
55 dogs
505 other animals
27 buildings
41 ships and boats
49 trees
The Bayeux tapestry is a work of embroidery made in the second half of the 11th century on a band of fabric of about 52 centimeters high. The conquest of England, represented in images and in text on 68 meters in 58 scenes, is considered one of the most important pictorial monuments the high Middle Ages because of the abundance of detailed individual representations, the the well thought iconography and the quality of the craft. Despite its name, the Bayeux tapestry is not It is not really a tapestry, but rather a narrative embroidery. It is composed of images and inscriptions, and consists of nine interconnected fabric strips. Camera GigE uEye CP - exceptional speed, exceptional reliability, exceptional sensors
Interface: USB 3 Vision
Model: U3-3800CP-C-HQ
Sensor type: CMOS
Manufacturer: Sony-
Frame rate: 19.5 frames per second
Resolution (h x v): 5536 x 3692
Shutter: Global Shutter
Resolution: 20.44 MPixel
Dimensions: 29 x 29 x 29 mm
Weight : 49 g
Connector: USB 3.0 Micro-B, screwable
Applications: industrial image processing, surface inspection, measuring techniques, techniques medical, biotechnology and life sciences quality assurance, among others
