High-resolution visible and infrared imaging for large paintings: a case study on Israel in Egypt by Poynter

Israel in Egypt is an oil on canvas painting by Sir Edward Poynter. In 1868 the painting was depicted in the Illustrated London News in which there are reports of changes made to the composition of the painting after its first exhibition. Visible and infrared imaging techniques have been used to determine whether additions to the initial composition can be identified from underdrawings. The painting measures 137 cm x 317.5 cm and was not able to be relocated for the study, therefore portable imaging equipment was used throughout. A Canon 700D DSLR camera was modified to allow near-infrared imaging when combined with a set of longpass filters at 720 nm, 850 nm and 950 nm. An Osiris infrared reflectography camera was also used to look further into the infrared with a sensitivity range of 900 nm - 1700 nm. To obtain high-resolution images with the modified DSLR, a 100 mm lens was used from a distance of 6 metres. In both visible and near-infrared, eight images were taken across the surface of the painting and these images were combined into high-resolution visible and near-infrared panoramas Images from the Osiris infrared camera were processed in Matlab to create a mosaic from the overview image with high-resolution regions of interest. All processed images were registered in Matlab along with the woodcut engraving of the painting shown in the Illustrated London News. An interactive web-browser viewer was created to enable display and comparison of the registered high-resolution images, allowing users to explore and zoom in to specific areas of interest across the four high-resolution images simultaneously. Conservators and art historians can utilise the resulting images combined with the image viewer to analyse the painting and potentially develop a new interpretation of the composition.