On-line segmentation of freehand sketches by knowledge-based nonlinear thresholding operations

Ivan Jordanov, Shengfeng Qin, David Wright

Research output: Contribution to journalArticlepeer-review


This paper describes an on-line procedure for segmenting freehand sketches into 2D primitives and smooth curves by knowledge-based nonlinear thresholding operations. Drawing position, direction, speed and acceleration information is used for establishing fuzzy knowledge and inferring user's intention. The procedure can be divided into three stages: (1) obtaining corner points based on the fuzzy knowledge and adaptive thresholds, which includes detecting “obtuse” and “acute” corner points; (2) finding smooth join points, during which stage we use both curve linearity and curvature; and (3) classifying the sketches into the corresponding curves according to curve linearity and changes of curve convexity. The method is illustrated and tested with a number of sketches.
Original languageEnglish
Pages (from-to)1885-1893
Number of pages9
JournalPattern Recognition
Issue number10
Publication statusPublished - 1 Oct 2001


  • heurestic knowledge
  • on-line sketches
  • curve segmentation and classification
  • conceptual design


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