Restoration of faded color images using digital technology has become widely accepted as a very effective and practical method. Restoration can be done if the bleach matrix is known, but usually it is not known. We applied two methods based on subjective judgment to restore old faded color prints. The first method uses a conversion matrix with matrix coefficients that are determined using a known color or desirable color. The second method restores the image by trial and error by judging the resulting image. For the first method, it is important to use many colors to calculate the matrix coefficients. For the second method, it is better to adjust the range of the three color signal first. Both methods give acceptable results. The second method is easier and faster than the first method, but first method has the possibility of giving better results because it can compensate fading that occurs when the fading of one color dye layer is effected by the density of other color dye layers. This type of fading happens in the case of light fading.
Yujiro Ando, Aran Hansuebsai, Kanmanus Khantong, "Digital Restoration of Faded Color Images by Subjective Method" in Journal of Imaging Science and Technology, 1997, pp 259 - 265, https://doi.org/10.2352/J.ImagingSci.Technol.1997.41.3.art00012