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A Measure of Q-convexity for Shape Analysis

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Abstract

In this paper, we study three basic novel measures of convexity for shape analysis. The convexity considered here is the so-called Q-convexity, that is, convexity by quadrants. The measures are based on the geometrical properties of Q-convex shapes and have the following features: (1) their values range from 0 to 1; (2) their values equal 1 if and only if the binary image is Q-convex; and (3) they are invariant by translation, reflection, and rotation by 90 degrees. We design a new algorithm for the computation of the measures whose time complexity is linear in the size of the binary image representation. We investigate the properties of our measures by solving object ranking problems and give an illustrative example of how these convexity descriptors can be utilized in classification problems.

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Notes

  1. The different conventions used to indexing an item in the matrix representation starting from the top left corner and a point in the Cartesian coordinate system starting from the bottom left corner result in the discrepancy in the indexing.

  2. This number provides the condition of termination of the algorithm (see Fig. 9)

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Acknowledgements

The authors thank P.L. Rosin for providing the datasets used in [23].

We wish to thank the anonymous reviewers for their comments that greatly improved the paper.

The research was carried out during the visit of P. Balázs at the University of Siena. The authors gratefully acknowledge INdAM support for this visit through the “visiting professors” project. S. Brunetti is also member of Gruppo Nazionale per il Calcolo Scientifico – Istituto Nazionale di Alta Matematica.

Funding

This research was supported by the project “Integrated program for training new generation of scientists in the fields of computer science,” no. EFOP-3.6.3-VEKOP- 16-2017-00002. This research was supported by grant TUDFO/47138-1/2019-ITM of the Ministry for Innovation and Technology, Hungary.

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Correspondence to Sara Brunetti.

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Balázs, P., Brunetti, S. A Measure of Q-convexity for Shape Analysis. J Math Imaging Vis 62, 1121–1135 (2020). https://doi.org/10.1007/s10851-020-00962-9

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