At a 2005 conference devoted to rock art, archaeologist Jon Harman found something that inspired him unexpectedly: pictures of Mars. He first saw one image showing the planet’s well-known rusty-red surface, then another, produced through a process devised at NASA, which rendered the Martian terrain as a vivid mosaic of red, green, and yellow hues, bringing out surprising detail. The technique instantly struck him as useful for studying some of the world’s oldest paintings.
The NASA Technique
A technique known as decorrelation stretch was created by scientists at NASA’s Jet Propulsion Laboratory (JPL) in 1978 for the purpose of improving how people read high-correlation remote sensing and satellite images. Instead of merely increasing the contrast between colors, this method changes the original colors into a new, wider range of colors, which makes small differences easier to see.
A statistical theorem that maximizes energy compaction, packing most of a signal’s information into fewer components, underlies the method. In 1978, Jim Soha, who supervised a digital image processing group at JPL, suggested using the theorem for enhancing color in digital imagery.
Alley’s 1996 Refinement
In 1996, Ronald Alley, a member of Soha’s team at JPL, improved the method to increase its speed and precision. That paper was the one Harman encountered when he first started looking into adopting the technique for his own rock art research.
Alley explained that someone needed to prepare an explanation of the item so that users could understand what it was.
Harman’s First Test
Harman holds a PhD in mathematics from Berkeley and brings background in medical imaging to the project. He believed he could work it out on his own. “I Googled it and found a NASA paper that explained how to do the algorithm,” he stated in a press release.
He tested the technique on his own photographs of rock art from Baja California, Mexico, and the outcome was instant: a previously unseen yellow figure suddenly appeared in one picture. “That convinced me of the usefulness,” he said.
Building Dstretch
Harman developed the Dstretch software plug-in after studying Alley’s paper, a tool that improves digital imagery. He has since retired in Pacifica, California.
Harman adapted the technique for rock art. He explained, “I started playing around and found that by changing the color space I was working in, I could get good results in different images.”
Custom Color Spaces
The Dstretch plug-in comes with its own set of color spaces, which have been found helpful when working with Harman’s photographs of rock art. A color space is a system for representing colors using numbers, like the RGB color space (red-green-blue), which is widely used on display devices.
Discoveries in Egypt
Dstretch has helped archaeologists uncover pictures of bats and pigs within the ancient Egyptian cemetery at Beni Hassan, bringing to light animals that seldom appear in ancient Egyptian artwork.
Graffiti in Canada
A horse and rider pictograph has been found at Writing-on-Stone Provincial Park in Alberta, Canada. Researchers believe it may have functioned as a kind of calling card left by a Crow warrior to taunt his Blackfoot enemies. The image, revealed by Dstretch, shows what some consider an early form of graffiti tagging.
Findings in Norway
The add-on program found roughly 15 new, previously unrecorded people at the Årsand 1 site in western Norway, and added new information to 28 more already documented individuals there.
| Application | Location | Result |
|---|---|---|
| Harman’s first test | Baja California, Mexico | New yellow figure revealed |
| Beni Hassan cemetery | Egypt | Images of bats and pigs found |
| Writing-on-Stone Provincial Park | Alberta, Canada | Horse and rider pictograph revealed |
| Årsand 1 site | Western Norway | 15 new figures, new details in 28 others |
Why It Fascinates
Harman explained that he is drawn to ancient paintings because no one really understands why people made them, at least in many cases, and added that the symbols are quite strange.
What had been present all along but concealed from view has now been revealed by the tool. No explanation accompanies that revelation.
Source: gizmodo.com