NASA's Decorrelation Stretch Technique Adapted for Rock Art Analysis

Origin of Decorrelation Stretch

The decorrelation stretch technique was developed in 1978 by researchers at NASA's Jet Propulsion Laboratory (JPL). Its initial purpose was to improve the interpretation of high-correlation remote sensing and satellite imagery, including images from Mars. The method is based on the Karhunen–Loève Transform, which maximizes energy compaction in statistical analysis.

Adaptation for Rock Art

In 2005, archaeologist Jon Harman encountered images of Mars processed with this NASA technique. Recognizing its potential, Harman researched the algorithm and applied it to photographs of rock art. His initial tests on rock art in Baja California, Mexico, revealed a new yellow figure, confirming the technique's usefulness for archaeological study.

How the Technique Works

Unlike simple contrast enhancement, decorrelation stretch maps original colors to a different, expanded range of colors. This process, refined by Ronald Alley at JPL in 1996, makes subtle color variations more apparent. Harman, with a background in medical imaging and mathematics, developed the Dstretch software plug-in to apply this method specifically to rock art imagery.

Impact on Archaeology

The application of decorrelation stretch allows archaeologists to uncover details in ancient rock art that are otherwise invisible to the naked eye or standard photographic methods. This provides new data for understanding historical cultures and their artistic expressions, contributing to the study of some of the world's oldest paintings.