Merging infrared and visible images of artworks with minimum color alteration

What is it about?

We present a new method for the analysis of visible/Infrared multispectral sets producing chromatically faithful false-color images, which maintain a good readability of the information contained in the non-visible Infrared band. Examples of the application of this technique are given on the multispectral images acquired on the Pietà of Santa Croce of Agnolo Bronzino (1569, Florence) and on the analysis and visualization of the multispectral data obtained on Etruscan mural paintings (Tomb of the Monkey, Siena, Italy, V century B.C.). By imaging spectroscopy, the reflectance spectrum for each pixel of a pictorial artifact image is made available, along with a wealth of information on painting constituents such as pigments, binding media, and varnishes. False-Color rendering leverages infrared and visible information so as to allow for a rough identification of the pigments and an enhanced visualization of compositional painted changes. The different False-Color approaches, however, always sacrifice the real color rendition and often produce images not easily interpreted by non-specialists. A simultaneous visualization of some hidden details and a chromatically faithful color rendering can be extremely useful for art historians, conservators, and restorers. To this end, we propose a new approach for merging the infrared and visible information, yet preserving at best the chromatic similarity with the visible image. This can let the non-specialist appreciate otherwise invisible details in a work of art, yet leaving its overall appearance unchanged. Even cultural heritage professionals such as art historians and restorers would appreciate the possibility of studying invisible details of a painting without the need to analyze standard false-color images.

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Why is it important?

The fidelity of the chromatic appearance of the resulting images, coupled to the effective visualization of the information contained in the Infrared band, opens interesting perspectives for the use of this method to visualize the results of multispectral analysis in Cultural Heritage diffusion, research, and diagnostics.