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.