Nasa built it for Mars. Now, it's revealing ancient secrets hidden on Earth
A technology originally developed by Nasa to study the surface of Mars is helping archaeologists uncover hidden ancient paintings, decipher faded rock art and even examine tattoos preserved on mummified human remains.
The technique, known as decorrelation stretch, enhances subtle colour differences in digital images, making features invisible to the naked eye stand out. It has been used to discover hundreds of ancient paintings at Cambodia's Angkor Wat temple complex and study archaeological sites across the world.
At Angkor Wat, an archaeologist using the technique discovered paintings between 2010 and 2012, including images of horseback riders and a traditional musical ensemble high in the temple's central tower. Thousands of visitors pass the faded artwork every day without noticing it.
The discoveries were part of a larger collection of around 200 paintings identified across the ancient Cambodian temple complex.
The technique's journey from space exploration to archaeology began around 2005, when rock art enthusiast Jon Harman noticed how Nasa images of Mars revealed significantly more surface detail after decorrelation stretch was applied.
Harman, who also had experience in medical imaging, realised the same approach could help researchers study ancient paintings that had faded over centuries.
"I Googled it and found a Nasa paper that explained how to do the algorithm," Harman said. "I knew from my medical imaging experience that I could do it, so I did."
The original research paper was written in 1996 by Ronald Alley, an employee at Nasa's Jet Propulsion Laboratory (JPL) in Southern California.An image processing method developed at JPL – for Mars – is helping uncover ancient rock art, buildings, and even tattoos on mummified human remains on Earth.See more (literally): https://t.co/hvDTt0S0FN pic.twitter.com/lQ3sKCDobo— NASA JPL (@NASAJPL) September 24, 2026
Alley was developing applications for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), a Japanese imaging instrument aboard Nasa's Terra satellite. The technique was designed to help scientists extract additional information from satellite imagery.
Harman subsequently developed DStretch, a plug-in for ImageJ, an open-source image-processing programme created by the US National Institutes of Health.REVEALING HISTORY HIDDEN IN PLAIN SIGHT
DStretch has since become a widely used tool in archaeological research. It has helped researchers identify and clarify ancient rock art at sites in Norway, Mexico, Canada and Egypt.
Beyond paintings, the technique has also been used to identify buried remains of ancient Greek buildings and examine tattoos on mummified human remains.
Harman said he receives around 200 requests for DStretch each year. He also developed smartphone applications that replicate the technique, which have been downloaded thousands of times.
While its use in rock art research was expected, Harman said the variety of applications developed by researchers had surprised him.
The technology demonstrates how techniques created for planetary exploration can help scientists uncover details of humanity's past, bringing faded and forgotten traces of ancient civilisations back into view.- Ends
