Polygonal Approximation of Contour Shapes Using Corner Detectors

 

Hermilo Sánchez–Cruz*¹; Ernesto Bribiesca²

 

¹ Departamento de Ciencias de la Computación. Centro de Ciencias Básicas. Universidad Autónoma de Aguascalientes, Aguascalientes,México. * hsanchez@correo.uaa.mx

² Departamento de Ciencias de la Computación. Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas. Universidad Nacional Autónoma de México. D.F., México.

 

ABSTRACT

A great amount of corner detectors that appear in literature are based on using the Freeman chain code of eight directions, which is used to represent contour shapes. We propose a new method for corner detection based on a three–symbol chain code representation, which requires lower storage memory and an easy way to obtain shape corners. We compare it with five existing methods, which are well known in the literature, giving our method a better performance. Furthermore, in order to reconstruct the original shapes through polygonal approximations, we propose an error parameter to quantify the efficiency. This can be accomplished by considering the redundancy of points produced when looking for corners and when computing the difference between the original region and the approximated polygon.

Keywords: Binary objects, corner detection, pattern strings, polygonal approximation, 3OT chain code.

 

RESUMEN

Gran parte de los detectores de esquinas, que aparecen en la literatura, están basados en el uso del código de cadena de Freeman de ocho símbolos, el cual es usado para representar los contornos de las formas. En este trabajo presentamos un nuevo método para detectar esquinas basado en una representación de código de cadena de únicamente tres símbolos, lo que requiere menor consumo de almacenamiento en memoria y permite, de manera sencilla, obtener esquinas en los contornos de las formas de los objetos. Dicho método lo comparamos con cinco métodos altamente citados en la literatura, dando nuestro método un mejor desempeño. Más aún, con el propósito de reconstruir las formas originales a través de aproximaciones poligonales, hemos propuesto un parámetro de error para cuantificar la eficiencia de cada detector, el cual se logra al analizar la redundancia de puntos que aparecen al tratar de localizar las esquinas, así como de establecer una diferencia entre la región original de la forma y la debida a la aproximación poligonal.

Palabras clave: Objetos binarios, detección de esquinas, patrones de cadenas, aproximación poligonal, código 3OT.

 

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