Restored Kodak Ektachrome photographs of the paintings in their original state from 1963 serve as a reference. These transparencies which have also faded over the last 50 years are scanned using narrow bandwidth light sources ensuring that the recorded optical densities are proportional to the photographic dye concentrations. The original color of the Ektachromes is then digitally reconstructed using a chemical fading model based on these dye concentrations. Further digital processing is required to compensate for the overemphasis of red in the Ektachrome film and the uneven illumination of the paintings when photographed.
With a camera-projector system we calculate the geometric mapping and the radiometric compensation. The geometric mapping yields the coordinate transformations between the projector, the camera, and the digital target image. Subsequently, the color mixing matrix and nonlinear projector response are calculated. With all parameters of the system known, we can calculate the compensation image pixel by pixel and project it with the correct registration onto the faded canvas.
This novel restoration technique uses colored light from a digital projector to compensate for color alteration. To our knowledge this approach has not been used for the restoration of paintings before. It recreates the original color appearance without physically changing the paint surface and is therefore completely reversible. In fact, one can easily compare the unrestored and color corrected object by switching the projector on or off. Microfading tests insure that the paintings will not continue to fade as a result of this treatment. As a result, Mark Rothko’s Harvard Murals can be viewed and experienced as in 1962.