Study Design: Our test data-set com

Study Design: Our test data-set comprised 5 drawings, created by us for uniformity, but carefully done to match the spirit of drawings by the artist community (Figure 10). The drawings comprise a mix of human and robotic forms, typical of layered 2D concept art (Figure 2): droid, pan and orb are inspired by Microsoft Studios’ Halo,Blizzard Entertainment’s Starcraft, Valve Corporation’s Portal, series of games respectively. We formulated our study as a set of 40 curve-type queries (8 per sketch). The number of sketches and questions was chosen so the typical time to complete the study was≈ 10 mins. The four curve-types were verbally explained to participants using illustrations (this was done on drawings that were not used as testing data). Users were then asked to imagine each sketch as a layered 3D model, possibly with multiple layers like orb in Figure 10 and then classify 8 query curves as one of the four curve types or no-type (to reduce any bias towards the set of curve types). Queried curves were unobtrusively numbered avoiding perceptual bias possible when using color or visual markings. The study was performed by 15 participants on print-outs, 10 of whom had some computer graphics background.