Colour correction of archival photographs for change detection and digital restoration of paintings

Reconstructing the past appearance of paintings from archival film photographs requires reliable colour correction methods. Such photographs are often subject to exposure variability, illumination differences, film-specific colour shifts, and dye instabilities, while frequently lacking embedded colour reference targets. This makes it difficult to assess the accuracy of colour correction and to distinguish genuine material changes in artworks from film-induced distortions. This study addresses this gap by investigating how accurately analogue film photographs can be colour-corrected and how visual change can be quantified, both when reference targets are available and when they are not. For this purpose, a controlled dataset was developed by photographing two mock-up paintings under various lighting and exposure conditions. The films were digitised and paired with hyperspectral scans of the paintings, acquired both before and after the accelerated UVA ageing. Several correction strategies were evaluated, including colour chart-based calibration and methods using stable pigment regions, with root polynomial regression achieving the most consistent and accurate results in terms of the Δ E 00 colour difference relative to the hyperspectral ground truth. Additionally, a reference-free change detection method combining the SAM and RMSE spectral difference metrics was applied to highlight potential pigment colour changes directly from the film photographs, without relying on reference targets or material analysis maps. • Developed a dataset to evaluate the colour correction of film photographs of artworks. • Acquired hyperspectral ground truth captures before and after artificial ageing. • Investigated change-detection methods to identify material changes in artworks. • Root polynomial regression achieved the best results in restoring the appearance of paintings.