A system for line extraction in digital ink. The digital ink represents handwritten input and is comprised of a stroke sequence. The system comprises a processor configured for: receiving the digital ink from a pen device; segmenting the strokes into a sequence of substrokes; grouping substrokes about a selected substroke into a temporally preceding group of substrokes and a temporally subsequent group of substrokes; calculating a centroid for each substroke or group of substrokes; calculating angular differences between the selected substroke and its temporally neighbouring groups of substrokes; and determining positions of extrema of the angular differences. The extrema correspond to substrokes at line breaks, thereby enabling line extraction in the stroke sequence.