目前国内一次性输液针手瓣装配基本上采用手工装配，因而存在许多弊端。为此，结合输液针的特点，对多种描述方法做了分析，提出了用Hu矩不变量来描述输液针图像，并用逆光拍摄方法来获取各个角度输液针针尖图像，从而获取了完整的轮廓信息，其二值化后的图像避免了矩值灰度级计算的不稳定性。实验结果表明，随着输液针角度的增加，其图像的矩不变量在有规律地发生着变化；用Hu矩不变量来描述输液针图像特征是可行有效的。

Hand petal of intravenous needles for single use is assembled by hand in most enterprises in China, but there are many shortcomings. In this paper, an image description method of identifying intravenous needles images by Hu moment invariants is studied. Images of intravenous needles of different angles are obtained by means of backlighting, which is able to acquire the intact and available information of outline of intravenous needles. The experiment proves that with the increase of angle, the moment invariants of the images are changed by the rules. Hu moment invariants are feasible and effective to describe the images of intravenous needles for single use.