A Material Investigation of Color Film Technology through the Koshofer Collection

The Koshofer collection is an invaluable resource about the history of color film technology from the late nineteenth century until the 1980s, including film frames from early applied hand coloring, tinting and stencil coloring, to mimetic color processes such as Kinemacolor, Gasparcolor, and many other rare and popular color film stocks. Multispectral imaging in the visible range has been carried out to characterize the optical properties of the color processes, and an extensive microscopic examination allowed to reveal minute material features. These investigations highlight distinctive elements for the identification of some of the most significant historical color processes on film, and at the same time, offer crucial information for classical restoration techniques and for rigorous digitization strategies

Dye Purification. An Image-processing Technique for the Digital Restoration of Chromogenic Film

The majority of color film heritage shot between the 1940s and the 1980s is faded. The bleaching of dyes cannot be reversed with chemical methods. Digital technologies can provide the means to recover faded colors. Still, the result of the digital unfading depends on the amount of residual color present in the film, the quality of the image capture operation, and the efficacy of the digital image processing. This paper first discusses the strategies to best capture the residual color information in the film, and then presents a processing method that consistently improves the digital restoration of the most common type of fading: the bleaching of the cyan dye that results in the typical pinkish cast of historical photographs