Abstract: To solve the problem of large trajectories extracted by improved dense trajectory（IDT） algorithm, a trajectory filtering method is proposed. Firstly, the interest points are densely sampled, and the next frame position of each interest point is calculated with the help of optical flow image to form the trajectories. Then, the maximum value normalization and binarization of the optical flow image for each frame are carried out to obtain the optical flow binarization image, which reflects whether the movement of the point is relatively significant. The validity of each point on the trajectory is counted by optical flow binarization image to judge whether the trajectory meets the effective condition, and the trajectory that does not meet the condition is filtered out and the purified trajectory is obtained. In order to verify the effectiveness of the algorithm, KTH and UCF sports, commonly used data sets in the field of behavior recognition, are used to verify the algorithm. Experimental results show that the algorithm can reduce the number of trajectories while ensuring the accuracy, and the computation is small compared with other algorithms.

Key words: action recognition, improved dense trajectory（iDT）, grayscale optical flow image, optical flow binarization, trajectory filter

摘要： 针对改进的密集轨迹算法（improved dense trajectories，iDT）提取的轨迹数量较为庞大的问题，提出了一种轨迹滤除方法。密集采样兴趣点，利用光流图计算每个兴趣点下一帧的位置进而组成轨迹，对每帧光流图进行最大值归一化以及二值化，得到光流二值化图，以此反映该点的运动是否相对显著。利用光流二值化图统计轨迹上各点的有效性从而判断轨迹是否满足有效条件，并将不满足条件的轨迹滤除，得到提纯的轨迹。为了验证算法的有效性，使用了行为识别领域的常用数据集KTH和UCF sports对算法进行验证，实验结果表明，该算法能在保证准确率的同时减少轨迹数量，并且计算量较小。

关键词: 行为识别, 改进密集轨迹算法（iDT）, 光流灰度图, 光流二值化, 轨迹滤除