Chuck Sutherland

D-Stretch is an image enhancement technique that I first learned about when I saw it applied to prehistoric pictographs. There is a plugin to the software ImageJ which will handle an image and produce a d-stretched version of it that can be found here . However, as someone who is comfortable working with digital images in Photoshop, I wondered if there was a way to replicate the effect in house. Here I present to you what I learned, and some thoughts on the process. Let's start with a photograph of the Horned Dog, a particularly well preserved red ocre pictograph in Tennessee. The photograph was shot as raw, and processed for optimal display. White balance was adjusted based on the scale present in the image. We will want to convert the image to the Lab color space to proceed (Image > Mode > Lab Color). Check your channels tab, you should see these three channels present: Lightness, A, and B. We'll be individually adjusting these channels so keep this handy....

Broadly the process of digitizing large format images with a camera can be broken down into two components: imaging, and image processing. The following steps work well for an image which would be processed as a black and white line map with the goal of eventually georeferencing the map. Imaging Mounting Mount the map on a sturdy board to keep it flat. Use clips where you are able to keep the document flat against the board. Alternatively one could lay the document behind glass, or plexiglass, though this introduces the possibility of glare. This is discussed more later. Camera settings Obviously using a camera with a high resolution (measured in megapixels) is better than using one with a low resolution. The camera will need to be mounted with with a medium focal length lens. For this exercise I used my 50mm (the crop factor on my camera puts that around 70mm). If you photograph regularly you'll be aware that every camera has a "sweet spot" f/stop which maxi...

I found myself on a long, lonely road a few weeks ago. It was River Canyon Road that crosses from Marion County to Hamilton county as it follows the course of the Tennessee River through the Tennessee River Gorge. As I drove this road, I wondered, "Is this the longest segment of road without any intersections in the state?" I have the data and tools to solve this problem. First, let's look at River Canyon Road. As I look at my data, I can see that it is broken up with several named and unnamed smaller roads that lead off from it. However, my intuition wasn't far off base. It's combined segment lengths between intersections (not spurs) is 18.93 miles. However for the purpose of this analysis, it will not appear again. Longest Road Stretches between Intersections 1) Cold Spring Rd, Monroe County - 15.12 miles 2) Game Reserve Rd, Marion County - 11.82 miles 3) Lower Pain Creek Rd, Greene County - 10.07 miles 4) Meadow Creek Rd, Cocke County - 9.52 miles ...

An elevation raster, or DEM, is a great place to start with producing your own basemaps. The DEM can be cooked into a number of other products, which when used with the DEM make pleasing maps. Other layers can be produced from elevation data, depending on how detailed it is. For this tutorial I have used a canopy layer and a TPI layer. If you've not made those yet, check the tutorials I've put together on them here: Canopy Basemap from Lidar Topographic Position Index (TPI) as an Alternative to Hypsometric Shading This tutorial assumes you have access to Photoshop, or GIMP, as well as GIS software to produce raster basemap images for processing. Here is what our basic ingredients look like. Elevation Hillshade TPI Canopy Our mixture of those results in different forms. First, let's look at basic combinations of Elevation and Hillshade. Combinations of Elevation and Hillshade Where elevation is set to 50% transparent, and atop a fully visible hillsha...