As you might imagine, a large part of recording rock art involves the use of photography. And among the tools used by those recording and analyzing images both in the field and in the lab is software that digitally enhances photographs to make the rock art clearer or even to reveal elements that are no longer visible to the naked eye due to erosion and weathering.
The software of choice is increasingly a small plugin for a freely available Java-based image processing application called ImageJ. The plugin is DStretch, developed by Jon Harman. To run the plugin, you simply drop the .zip file into the “plugins” folder of ImageJ and it’s done.
Drag an image you wish to enhance into the ImagJ application, start the DStretch plugin, then select one of the enhancement options, like “LAB” or “LDS.” Or select the Cycle button to cycle through each. Once a particular decorrelation algorithm shows the image you like, click the “Save” button to save a sample.
The image below shows an example of DStretch being applied to an image I took of the Halo Shelter in the Lower Pecos Canyonlands last year. Note how the different pigments change contrast and in one enhancement the spalling of the shelter wall is clear. All this is vital to the researcher creating an illustration from the photographs.
Two of the things I love about DStretch used with ImageJ are the cost and the ability to replicate results. ImageJ is public domain, yet very powerful; DStretch is free for use unless you’re a professional and then the suggested donation is $50. This is all several hundred dollars cheaper than the industry leader for photo enhancement, Photoshop. And minus the intense learning curve. The algorithms Harmon has built into DStretch are button pushes, rather than the infinite combinations and permutations of Photoshop slider bars.
Once the images are enhanced, I typically use The Gimp for further editing. In fact, I created the .GIF animation above through Gimp by opening each of the DStretch file saves at once as separate levels then resizing and saving as an animation.