CCD图像数字定心算法的比较

Comparison of Digital Centering Algorithms Based on CCD Images

从CCD采集的数字图像中提取天体的位置和光度信息对于天文研究具有基础意义。其中,恒星星像中心像素位置的精确测量对于天体测量至关重要。针对国际上常用的三种位置测量算法:修正矩方法、Gauss拟合法和中值法,利用实测的CCD图像进行了试验研究。具体地,采用云南天文台1m望远镜观测的CCD图像同时使用这些算法进行了实际测量,根据每幅图像中测得的像素位置,对这三类定心算法进行了比较和精度分析。可视化方法被用于不同阈值的选取和设定比较。实验数据表明,无阈值的二维Gauss拟合方法是一种精度相对较高的定心算法。

One of important objectives of astronomical observations is to obtain physical information, including positions of measured stars with high accuracy from digitized CCD images. By means of CCD images taken by the lm telescope at Yunnan Observatory, research on the comparison of the accuracy among three often-used centering algorithms is carried out, including Modified Moment, Two-dimensional Gaussian Fit and Median. The positions of 70 stars whose magnitudes vary from 10.2 to 17.6 in 18 CCD images are measured in our experiments. Based on the experimental results, these algorithms are compared and discussed. A visualization, which is a distinct feature of this paper, is used to analyze and select different thresholds. Since each algorithm is programmed using several thresholds, the influence of threshold settings on precision in both x and y direction is also discussed in details. Through a comparison of the same algorithm with different thresholds to choose an optimal threshold as well as a comparison among different algorithms aimed to study the accuracy of centering algorithms, significant finding is displayed. Experimental results show that two-dimensional Gauss method with no threshold fits a stellar distribution best and therefore is a relatively high-accuracy centering method for faint stars as well as bright ones.