The modification for the straightening procedure by curvilinear symmetry axis for multi-contour figures in binary raster images

The paper proposes the modification for the straightening procedure by curvilinear symmetry axis for multi-contour figures in binary raster images. This modification considers an external contour and internal contours of an analyzed figure when it is divided into parts for subsequent straightening. Each part of figure corresponds to its own fragment of curvilinear symmetry axis, which is a set of articulated segments. A mask is created for each part, containing points of the external contour and internal contours included in the mask. Each point of any contour from a created mask is transformed (rotated and shifted) relative to the corresponding fragment of curvilinear symmetry axis. To display the transformed contours, their hierarchy, a tree structure, is taken into account. The color of contour painting over changes alternately by the nesting level of the contour in the hierarchy tree. Experimental results of the proposed modification demonstrate the possibility of creating straightened figures with a different number of internal contours of different shapes and different nesting levels. A comparison of areas of transformed shapes relative to the original ones showed a decrease the number of distortions during straightening. The proposed method eliminates the restriction using the greedy algorithm to find curvilinear symmetry only for objects without internal contours.

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