One of the perennial problems that we have come across in a variety of contexts, including CNC artwork and producing artwork for the Egg-Bot, is the difficulty of creating good-quality toolpaths– i.e., vector artwork representing halftones –when starting from image files. One of the finest solutions that we’ve ever come across is Adrian Secord’s algorithm, which uses an iterative relaxation process to optimize a weighted Voronoi diagram, mathematically producing a set of points (stipples) that can closely approach the appearance of a traditional stipple drawing.
Another important technique is TSP art, where the image is represented by a single continuous path. You can generate a path like this by connecting all of the dots in a stipple diagram. Designing a route that visits each dot exactly once (and minimizing the distance travelled) is an example of the famous Travelling Salesman Problem (or just “TSP”), and an optimal TSP path can give a surprisingly good grayscale representation of an image. From the standpoint of toolpaths (for the Egg-bot and most other CNC machines), a TSP path is even nicer than stipples, because little or no time is spent raising and lowering the tool.
StippleGen is easy-to-use software that can generate TSP and stipple drawings from input images. It saves its files as editable, Eggbot-ready Inkscape SVG files, which can in turn be opened by other vector graphics programs, or re-saved as PDF files for use in other contexts. It can also generate a TSP path from the stippled image, and either save that path as an SVG file or simply use that path as the order of plotting for the stipple diagram.
You can read an extended introduction to StippleGen at Evil Mad Scientist Laboratories. An introduction to StippleGen version 2 is also available here.
It is worth pointing out, right up front, that our software does not fill a vacuum. StippleGen is not the first, fastest, or most accurate software yet developed to produce stipples or TSP paths. Rather, it is designed to be easy to install, easy to use, and easy to modify. It is capable of producing excellent quality output with up to 10,000 points, when speed is not a primary concern.
While Adrian Secord’s own stippling software is no longer available for download, there are a few other codebases worth of note. In particular, the weighted voronoi stippler at
saliences.com has a Windows executable, and runs as a command-line utility. And there are also a number of fast TSP solvers, including Concorde, which is available with a GUI for Windows.
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