Hexagonal sampling grid offers less storage time, less computation time, increased coding efficiency, less quantization error, equidistant property and consistent connectivity, etc., Edge detection is one of the important preprocessing steps in many of the image processing applications. Various edge detection techniques are available for images on rectangular grids such as classical operators, CLAP algorithm based edge detection, wavelet based edge detection etc. Wavelet based edge detection is found to be a better technique for specific application such as iris recognition system, 3D vertebrae shape recognition, infrared target recognition etc. These techniques are not suitable for hexagonal domain. For these we need to choose proper addressing scheme. In this paper, (i) Edge detection using masks on hexagonal grid (using spiral addressing scheme) is performed (ii) CLAP algorithm is performed on rectangular domain and hexagonal domain (using alternate pixel suppressal and half-pixel shift method) (iii) Wavelet based edge detection was performed on rectangular domain. For hexagonal domain, we need to choose proper directional wavelet. Gabor wavelet based edge detection is proposed for the hexagonal grid and we were able to get good results. For performance evaluation we are considering Mean Square Error, Peak Signal to Noise Ratio and ratio of edge pixels to size of image. For all operations, edge detection on hexagonal domain gives better results and better visual appeal of images compared to edge detection on rectangular domain.
P. Vidya, S. Veni, and Narayanankutty, K. A., “Performance Analysis of Edge Detection Methods on Hexagonal Sampling Grid”, International Journal of Electronic Engineering Research, vol. 1, pp. 313–328, 2009.