PaleoSketch: Accurate Primitive Sketch Recognition and Beautification

Brandon Paulson and Tracy Hammond

Summary

Paulson and Hammond present PaleoSketch, a sketch recognition approach that is able to recognize and distinguish basic shape primitives within a free-hand sketch. The algorithm begins with a pre-recognition stage where curvature and speed graphs for each stroke are computed. Also, the normalized distance between direction extremes and the direction change ratio are calculated to help in differentiate polyline shapes from curved shapes. A number of test are run on a stroke to determine what type of primitive the stroke represents. The tests are for line, polyline, ellipse, circle, arc, curve, spiral, helix, and complex shapes. Without a comparable error metric across the test, PaleoSketch uses a hierarchy to determine which shape is the best fit. The hierarchy is based on the minimum number of corners (or line segments) a particular shape is expected to have. The authors reported recognition accuracies above 98%.

Discussion

PaleoSketch is accurate and useful for a wide variety of applications. The biggest issue with this research is the use of a hierarchy. Developing a comparable error metric for the various test seems like a critical piece of future work. Currently, adding a new primitive means restructuring of the hierarchy. With an error metric, no hierarchy is needed, and new tests can be added easily as long as error metric can be computed for them.