Technique for Manipulating Satellite Photos Now Reveals Ancient Images (2025)
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A NASA satellite photo technique reveals faded ancient rock art worldwide.
Decorrelation stretch, originally developed at NASA's Jet Propulsion Laboratory to enhance satellite imagery, heightens color contrasts to reveal subtle features. Jon Harman, a math PhD and medical imaging specialist, created the Dstretch plugin after seeing the technique applied to Mars rover images. The method uncovered 200 faded paintings at Angkor Wat, revealed hidden figures at Norway's Årsand 1 site, and discovered bat and pig depictions in an Egyptian cemetery. It also works on aerial archaeology and mummy tattoos.
The technique is based on the Karhunen-Loève Transform and was refined by JPL's Ronald Alley in a 1996 paper for the ASTER satellite imager.
What commenters are saying
Commenters were intrigued by the technique and its applications. Several shared practical how-tos: a GIMP method using LAB color space decomposition, a web demo built from the paper, and links to the Dstretch mobile apps (iOS/Android, $20) and plugin (mandatory $50 contribution).
Others noted limitations: one user who tried multispectral imaging at Angkor Wat found no results, and another integrated DCS into software without a "eureka" moment. Discussion touched on false-color composites in GIS and analogies to astrophotography and UV floral photography.