Comparison of radiography testing and ultraviolet inspection in identifying hidden designs and defects of exquisite paintings

Art paintings are valuable cultural assets in any country that they are always threatened by dangers such as rupture, scratches, and loss of pigments. Natural disasters, irresponsible handling, exposure to light and temperature changes are all dangers factors. Various non-destructive methods such as radiography testing (RT) and ultraviolet (UV) inspection can be used to identifying detect the location of defects without any damage the paintings. The radiography testing recognized hidden patterns and deep defects and the general structure of the painting due to the penetration of X-rays to the lower surfaces. In the ultraviolet inspection, information about scratches and surface defects is obtained, depending on the type and material of paint used. Images of both methods provide excellent information to restoration experts, but problems such as blurring images of the RT and UV inspection darkening of some colors under ultraviolet light make it difficult to identify the defect regions. It is appropriate to use image processing techniques as an auxiliary tool to increase the contrast of the image. In this research, the Gabor filter has been used to increase the quality of the RT and UV images and reduce the blur of images; The Gabor filter use an automatic threshold level based on the deviation and mean pixel information of the images. Images reconstructed by the Gabor filter are efficient in identifying hidden designs and the location of defects.