DStretch is a software tool for digital enhancement of rock art. It has changed the way archaeologists and rock art enthusiasts view and discover rock art. DStretch was written by Jon Harman and his website describes it as "A tool for the digital enhancement of pictographs". To be honest it is a miracle tool for uncovering pictographs that are otherwise invisible to the human eye when viewed out in the field.
DStretch can be a bit confusing at first and the documentation on the authors website is great for looking at examples of what the software can do but I found it limited in clearly explaining step-by-step instructions on how to get good results. Most people can figure out how to get some basic results and while they are really impressive I wanted to do more with it and provide a more realistic interpretation of the rock art I personally have found.
Here is a before / after example of a pictograph that was very faded and almost invisible when looking at it directly out in the field.
Pictograph with no digital enhancement
The same pictograph with DStretch enhancement applied
You can see a considerable difference in what is easily visible out in the field and what DStretch can uncover thru sophisticated color manipulation algorithms.
The focus of this tutorial is to introduce you to DStretch, how to get it installed on your computer and do some basic enhancements. The first thing you need to do is visit Jon Harman's website and email him a request for the DStretch software. Go to his website here http://www.dstretch.com
While you are waiting for Jon to reply you will need to download and install ImageJ. DStretch is only a plugin to the modular image application ImageJ. You can download and install ImageJ from the website here http://rsb.info.nih.gov/ij/index.html. ImageJ is available for most operating systems including Windows, Mac OS and Linux. I personally use Linux on my computer and is what I will be using for this tutorial.
Once you have installed ImageJ and DStretch you will need a photo of some rock art. If you don't have a photo of anything you probably should stop reading this tutorial now and go photograph something. To get a basic enhancement, open the photo in ImageJ using the File > Open menu. I will be using the image above as an example for this tutorial.
Here is the ImageJ window with our example photo opened
Next you want to run DStretch on the image. You do this by selecting the "Plugins > DStretch > DStretch Run..." menu. A new window will open with your image and the DStretch options. I like to use this option because it allows me to compare the original unmodified image with the DStretch enhanced image.
If you prefer to only have one window open that works directy with DStretch click the menu option "Plugins > DStretch > DStretch One...".
For this Getting Started example I chose the "CRGB" color option. CRGB is a good all purpose color enhancement to choose for photos that are unknown and if you just want to see if anything will show up with pigment enhancement. To see what the CRGB enhancement will do just click the CRGB button on the DStretch enhancement window (circled in red).
Here is the result from the CRGB option
You can see the default enhancement is full of wild and crazy colors. I will cover some techniques to remove the unwanted colors from the rest of the photo in the next series of tutorials.For now you should experiment with some of the other color enhancement choices and see what makes your particular pictograph photo look best. You will be surprised by what the different color algorithms produce, no two pictographs are the same!
If you want to try a new color enhancement option just click a different color enhancement type and in most cases it will reset the original colors and then apply the new color enhancement type. You can also click the "Reset" button and then click the color enhancement option you want to try if it does not reset the colors back to the original settings.
Here are two more examples of the default color enhancement options.
I encourage you to try all of the default filters and see what they produce for your particular pictograph, each photo and pictograph is different.
If you want to save your new DStretch photo, just click the Save button and it will prompt you for the name and location to save it. DStretch by default will append the color type to the original name of the file. This is very handy when you want to go back and look at what color type you used.
Links to all of my DStretch Tutorials are here:
DStretch Tutorials - Getting started
DStretch Tutorials - Modifying the Default Enhancements
DStretch Tutorials - Batch Mode
DStretch Tutorials - Removing the Wild and Crazy Colors
Please do not email me and ask me for locations of rock art, I will not reply to you.