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Online recognition of sketched arrow-connected diagrams


We introduce a new, online, stroke-based recognition system for hand-drawn diagrams which belong to a group of documents with an explicit structure obvious to humans but only loosely defined from the machine point of view. We propose a model for recognition by selection of symbol candidates, based on evaluation of relations between candidates using a set of predicates. It is suitable for simpler structures where the relations are explicitly given by symbols, arrows in the case of diagrams. Knowledge of a specific diagram domain is used—the two domains are flowcharts and finite automata. Although the individual pipeline steps are tailored for these, the system can readily be adapted for other domains. Our entire diagram recognition pipeline is outlined. Its core parts are text/non-text separation, symbol segmentation, their classification and structural analysis. Individual parts have been published by the authors previously and so are described briefly and referenced. Thorough evaluation on benchmark databases shows the accuracy of the system reaches the state of the art and is ready for practical use. The paper brings several contributions: (a) the entire system and its state-of-the-art performance; (b) the methodology exploring document structure when it is loosely defined; (c) the thorough experimental evaluation; (d) the new annotated database for online sketched flowcharts and finite automata diagrams.

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The first author was supported by the Grant Agency of the CTU under the project SGS16/085/OHK3/1T/13. The second and the third authors were supported by the Czech Science Foundation under grant no. 15-04960S. The authors thank Truyen van Phan for his help with the text/non-text separation, Daniel Martín-Albo for creating the synthesized samples for the SVM classifiers and Roger Boyle for proofreading of the paper.

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Correspondence to Martin Bresler.

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Bresler, M., Průša, D. & Hlaváč, V. Online recognition of sketched arrow-connected diagrams. IJDAR 19, 253–267 (2016).

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  • Diagram recognition
  • Online document analysis
  • Max-sum problem
  • Segmentation
  • Text/non-text separation
  • Flowcharts
  • Finite automata