A new global balancing algorithm has been developed which takes a group of sub-images from a Hamamatsu Infra-red camera and adjusts their lightness levels to compensate for variations due to camera drifts. This is used in the Conservation Department at the National Gallery London to assemble infra-red reflectogram mosaics of paintings from the collection, particularly those from the early German and Netherlandish schools.
Infra-red reflectograms show the preparatory drawings beneath the final paint layers and can allow conservators and art historians to determine whether these drawings were made with a pen or brush and can identify changes in the composition as the work evolved. The presence or absence of a drawing can also indicate whether a composition was original or a copy of an existing work.
The image below left is a reflectogram mosaic of Jan Van Eyck's: "A Man in a Turban", (NG 222), which has been made without balancing. The image on the right was produced with balancing:
Links to: vips/ip, VASARI lab