Elucidating Reflectograms by superimposing Infra-red and Colour Images

David Saunders and John Cupitt
Technical Bulletin Volume 16, 1995

Abstract

Infrared reflectography gives better penetration of paint than infrared photography, but it can be difficult to relate a reflectogram to the painted image, since the latter does not show up clearly on the reflectogram. A method is described for combining portions of composite images of infrared reflectograms and colour images of the same painting, when both have been obtained with the VASARI image acquisition and processing system.

Distinguishing features known as tie-points are selected, which can be recognized in each image, for example craquelure and areas of loss, and the images are manipulated to bring them into coincidence in the final image. This manipulation is necessary since the infrared reflectograms have poor geometric properties, because they are collected by an infrared vidicon. It is a slow process to tie together images from large areas of a painting, and smaller areas can be selected to show interesting features. Examples of the results are printed in colour.

Keywords 

craquelure, infrared reflectography, paint

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To cite this article we suggest using

Saunders, D., Cupitt, J. 'Elucidating Reflectograms by superimposing Infra-red and Colour Images'. National Gallery Technical Bulletin Vol 16, pp 61–65.
http://www.nationalgallery.org.uk/technical-bulletin/saunders_cupitt1995

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