直线轮廓检测是计算机视觉领域中的一个基本问题。在靶场光测图像分析中，通过提取导弹、火箭等目标的直线轮廓，可以得到目标的三维姿态参量。提出了一种基于梯度方向直方图的直线轮廓提取新方法。梯度方向直方图被定义为具有相同梯度方向的图像点的梯度幅值之和。利用梯度方向直方图可以很方便地确定图像上边缘方向，根据此方向可在图像上搜索直线边缘的位置。由于同时利用了梯度的幅值和方向信息，所以该方法能自动地提取直线边缘而无需阈值。通过在实际图像中提取直线边缘，证明了该方法的有效性。

A new boundary detection algorithm which makes use of both the magnitude and direction of gradient is presented. The algorithm first calculates the histogram of gradient's direction,which is defined as the sum of the magnitude of gradient of the pixels whose direction of gradient are similar. Based on the histogram the main or wanted direction of edge can be easily distinguished. Then the positions of the boundaries are found by searching through the whole image according to the main direction. Unlike traditional boundary detection algorithms,which use only the strength of the edge and need complex operations,the new algorithm requires no threshold and works automatically. The proposed approach is tested by a variety of images with encouraging results.