Elasticurves: Exploiting Stroke Dynamics and Inertia for the Real-time Neatening of Sketched 2D Curves

Yannick Thiel, Karan Singh, Ravin Balakrishnan

Proc. UIST 2011 (TO APPEAR)

{ythiel, karan, ravin} [at] dgp [dot] toronto [dot] edu


Elasticurves are a novel approach to the real-time neatening of 2D sketches. They are based on the observation that users naturally slow down when drawing parts of a curve where they desire precision. Exploiting this affordance allows the system to distinguish intentional fine detail from stroke noise in a sketched curve. In order to accomplish this neatening in real-time, a lag between the stroke and the committed curve is induced, and the generated curves is incrementally created as cursor movements are made. By combining these affordances of stroke speed and lag, elasticurves can be imagined as curves drawn by a pen attached to the user's hand by a critically damped spring of zero rest-length. When a user draws quickly the elasticurve lags behind the sketched stroke, smoothing over any fine stroke detail, but quickly catches up and closely matches the stroke when the user draws slowly.

Preprint: [PDF]


A high-quality render of the paper's accompanying video can also be downloaded for offline viewing here.


Demo (Requires Java 1.5 or Java for Mac)


We evaluated our system by distributing it to 6 users and asking them to try it out and send us their creations. We did not specify which input method they should use; two used a tablet computer, one a trackpad and three a mouse. Each user was aged between 20 and 40, had a familiarity with computers and drawing ability varying from professional to completely inexperienced. Notably, the experienced users used tablets, while the inexperienced ones used a mouse or trackpad as their input device. Here is a sample of the sketches submitted, with the input shown in red and the neatened sketch shown in black.

Mouse Sketches

Tablet Sketches

Further, we evaluated elasticurves relative to existing research by compare elasticurves to three popular commercial systems: Windows7 Journal, Illustrator CS5 and Sketchbook-Pro 2010. We asked an intermediate user to trace the outline of a background image using all four techniques. After a few strokes to gain familiarity with all systems, the user traced over the image with a single stroke. The four techniques were used in turn and repeated overall 7 times. The neatest visual result of each technique using a trackpad is shown below.