复杂背景下的运动人体跟踪算法研究
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摘要
运动人体的跟踪技术研究是机器视觉领域的核心课题之一,目前被广泛应用在视频编码、智能交通、智能监控、图像检索及军工等众多领域中。本文就低对比度的复杂环境下运动人体跟踪技术进行了深入的研究,着重分析在了低对比度的复杂环境下如何进行运动人体目标的识别和提取以及目标的后续跟踪,主要完成了以下几项工作:
     1.背景的快速构建与更新:复杂的场景中,尤其是对于大面积监控的场景,采取单一背景生成及维护模型,总会消耗系统大量资源用于处理无用的信息。针对这一问题,我们运用了一种分区管理的背景建模方法,对于不同的区域采用不同的方法进行建模,可以更加有效地利用系统资源。在背景生成和维护阶段,把背景区域划分成一个个大小相等的区域(类似“贴片”),并根据这些“贴片”所在区域的不同变化特征分别进行更新,可以在占用很少系统资源的同时,快速地适应环境的变化。
     2.运动目标的快速精确提取:为了在得到较为细致的运动目标形状的同时,又可以避免对场景非平稳变化的敏感性,本文运用了基于局部邻域相似度的目标检测方法,在对输入视频中像素进行分析的同时考虑周围背景的相似性,通过像素周围图像块在时域中的变化来区分背景和前景,在没有任何预处理的情况下,不仅有效地降低了噪声的干扰,并能够快速准确地提取出运动目标。
     3.低对比度下运动人体的识别:针对造成低对比度下运动人体识别困难的两个主要因素,拍摄时光线昏暗和拍摄时距离较远,引入局部直方图熵概念,提出基于局部直方图熵的人体识别算法,运用检测率和虚警率对实验数据进行评价,获取两种低对比度环境下获取人体的最佳局部直方图熵差值的阈值,通过对理论和实验数据的分析,得出基于局部直方图熵的人体识别算法在准确度上仍需提高,进而引入局部灰度熵概念,提出基于局部灰度熵的人体识别算法,运用检测率与虚警率对算法进行的评价,获取局部灰度熵差值的最佳阈值,经过对算法进行的综合评价,得出基于局部灰度熵的人体识别算法更适合于低对比度下的人体识别。
     4.运动人体追踪:由于Mean Shift算法在对运动人体进行追踪时表现出了很高的实时性,而且其对一些干扰素并不敏感,所以本文在对人体进行实时性追踪时采取基于Mean Shift的运动人体追踪算法。但是为了进一步提高基于Mean Shift算法的稳健性,本文做出了一些改进,设计了基于改进的Mean Shift运动人体追踪算法:在目标建模阶段,结合人体识别对人体区域进行定位,对区域内的人体目标进行多特征建模,选择反差大的特征子模型来对目标进行跟踪;在后续跟踪阶段,通过对目标特征和周围区域的特征进行对比,选择最优子模型,强化目标与周围环境的反差,从而实现对目标的鲁棒跟踪。同时为了提高运动人体目标跟踪的匹配精度,本文引进了广义距离进行目标匹配,实验表明该方法能有效地提高跟踪精度。
Moving people tracking is a challenging task within the field of computer vision. The use of moving people tracking is pertinent in the task of video coding, intelligent traffic, intelligent surveillance, image retrieval, military industry and so on. In this paper, we mainly do some research on this technology in complex and dim contrast environment. And more attentions are put on the moving people recognition and tracking in complex and dim contrast environment. The main content and innovation of the dissertation are as follows:
     1. Background generation and maintenance. In the complex background, especially for the large-scale scene monitoring, it will consume a lot of resources to deal the useless information. To solve this problem, the background is partitioned for different regions. The background is divided into areas of equal size (similar to "patch"), and the "patch" will update in accordance with the changes at respond regions. So it can occupy very little system resources to adapt the environmental changes quickly.
     2. Moving object detection and extraction. Background subtraction is widely used in moving object detection. Pixel-based methods are sensitive to the non-stationary change of the scenes. Region-based approaches allow only coarse detection of the moving objects. In this paper, a novel algorithm based on local neighborhood similarity is proposed. Integrate the similarity of its surrounding pixels with the background model, when a pixel needs to be judged. The performance of the proposed method was evaluated by a series of indoor and outdoor experiments. Compared with the current widely used Mixture of Gaussian, the proposed algorithm in this paper achieved the perfect results in object detection and extraction.
     3. Recognition of people under the dim contrast environment. According to the two main factors,the dim light shooting and the distance shooting, that cause the people recognition difficulty under the dim contrast environment, a concept of the local histogram entropy was introduced, and proposed an algorithm of people recognition based on local histogram entropy. And evaluated through the ratio of detection and the ratio of false-alarm of the algorithm, obtained the optimal thresholds on the differential of the local histogram entropy which could get the human body under the two conditions of low contrast. Through theory and experimental data, it is concluded that the analysis based on local histogram entropy of people recognition algorithm could still be improved in accuracy. Then a concept of the local gray entropy was introduced, and proposed an algorithm of people recognition based on local gray entropy. And evaluated through the ratio of recognition and the ratio of false-alarm of the algorithm, obtained the optimal thresholds on the differential of the local gray entropy which could get the human body under the two conditions of low contrast. While the results show that the algorithm of people recognition based on the trait of the local gray entropy can obtain the better effect than the algorithm based on the trait of the local histogram entropy under the dim contrast environment.
     4. Moving people tracking. We used the algorithm of moving people tracking based on mean-shift since this algorithm showed high real-time, and it wasn’t sensitive to some interferon. But for improving the robustness of the tracking algorithm based on mean-shift, we made some improvements. First at target modeling stage a group of modals are generated to represent the object after people recognition. The one which is great contrast to the background is employed to track. And the most discriminative modal can be chose to track in the follow-up phase in order to achieve the robust results. At last, generalized distance is employed for the purpose of improving the accuracy of target matching. Experiments demonstrate the effectiveness of the new strategy.
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