A NASA satellite algorithm is now resurrecting faded rock art from antiquity

Decorrelation stretch — an image-enhancement method developed at NASA’s Jet Propulsion Laboratory to squeeze more detail out of satellite data — has become a standard tool for reading ancient art that has faded past the point of visibility. Rather than simply boosting contrast, the technique remaps an image’s colors into an expanded range, exposing subtle differences the eye can’t catch. JPL’s Ronald Alley documented the algorithm in a 1996 paper while working on scientific requirements for the ASTER imager (still operating on the Terra satellite), refining an earlier JPL approach built on the Karhunen–Loève Transform and speeding it up by replacing lossy intermediate steps with matrix multiplication.