Extract Curves a simplistic GTK Ruby-based appliaction which can convert the raster image file result of a geometric-trace-producing process's interaction with the characteristic of motion of another (interesting) process into a list of rectangular coordinates (in raster image's system) representing the inferred characteristic of motion of the midline of an image blob. Blob recognition is done by color: * by maximum pixel neighbor-to-neighbor difference * by maximum difference from blob's average color * by maximum difference from a pixel neighborhood's average color (using RGB or HSV). Use other software to pre-process (e.g. enhance contrast, or even reduce to gray scale), but Extract Curves's skeletonization is done based on the hypothesis of a recognized image blob, as opposed to a collection of pixels. Output is human-readable (tab-separated).