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1、 水下视频图像论文：具有抗误码能力的水下视频图像高效编码方法研究【中文摘要】随着科学技术的发展与进步,海洋的探测与开发日益成为科学研究的重点。海洋探测与开发主要包括海洋环境监测、深海勘探、水下施工等作业。在深海观测作业中,目前最常用的方法是基于水下机器人(ROVs/AUVs)的视频图像观测,因为图像信息是水下机器人深海近距离观测作业的主要信息之一。但是,如何将水下机器人获取的海量视频信息实时传输到水面工作站是实现深海观测作业的障碍之一。水下机器人通过水声信道传输水下视频图像信息时,必须对视频图像信息进行压缩处理,使其适应水声信道中窄带宽、高误码率的传输特性。因此,本文根据水下视频图像与水声信道
2、传输的特点,对水下视频图像的抗误码高效压缩编码进行了研究,主要完成的研究工作包括以下两个部分:(1)水下静态图像的抗误码高效压缩编码算法。为抵抗水声信道的传输差错,提出了一种具有较高抗误码能力的水下图像高效编码算法。该算法首先根据水下图像的特点,对图像进行小波变换预处理以去除其中的视觉冗余。然后,对低频系数采用定长量化编码;对重要高频系数采用数值和位置独立编码的方案,其中对重要高频系数的数值提出了变精度定长量化编码方法,而对重要高频系数的位置采用基于位置差降的可逆变长编码算法。此外,为抵抗水声信道的传输差错,提出了合理的分割、交织策略和变长编码块相对定长信道包的存放策略。最后,对低频和高频系数
3、,分别提出了相应的差错检测和掩盖算法。实验结果表明:该算法能够抵抗低于20%的丢包差错,低于2%的随机比特差错和低于2.5%的突发差错。同时,图像编码的压缩比可以高于70:1,具有较高的压缩效率。(2)具有抗误码能力的水下视频高效压缩编码算法。该算法主要由帧内编码模块和帧间编码模块组成。在帧间模块中,利用静态图像抗误码高效压缩方法对各视频序列组中首个I帧进行编码处理,增强I帧的抗误码能力,为后面的帧重建提供较为理想的参考帧。而在帧间模块中,对帧间运动估计与运动补偿过程获得的运动估计与残差信息进行合理的分组交织编码,以有效阻止错误的扩散。对其中的残差信息进行基于位置差降的可逆编码方法进行压缩,并
4、根据其重要性程度进行不同处理,有效增强其抵抗误码的能力。解码时,提出了有效的错误检测与错误掩盖处理算法,以增强码流的抗误码性能。此外,对于场景切换、摄像机快速运动等异常情况,提出了检测与处理方法,以保证编码算法适应各种复杂的视频编码环境。实验结果表明:该方法能够抵抗低于20%的丢包差错,低于1.2%的随机比特差错和低于1.8%的突发差错。同时,视频编码的压缩比可以高于120:1。本文研究是水下机器人视频图像观测的关键技术之一,对深海探测与开发具有重要研究价值和广阔应用前景。【英文摘要】With the development of science and technology, ocean e
5、xploration and development has become the focus of scientific research. This includes tasks such as ocean environment measurement, submarine exploration, and submarine operation and so on. The widely used deep-sea observation equipment is ROVs or AUVs-based video surveying system, where optical vide
6、o imaging is one of the key techniques for underwater short distance inspection and operation. However, how to transmit massive amount of video information acquired by ROVs or AUVs to the surface station is one of the challenges for deep-sea observation. Before transmitting the massive amount of und
7、erwater video, the video information must be compressed to meet the requirement of acoustic channels, which is characterized by narrow bandwidth and high error rate. According to the characteristic of underwater video and acoustic channels, efficient and error-resilient encoding algorithms for under
8、water video images are developed in this dissertation. The main research work finished includes the following two parts:(1) Research of efficient and error-resilient underwater image encoding algorithm. Firstly, the visual redundancy of underwater images is removed by a wavelet-based preprocessing t
9、echnique according to the characteristics of underwater images. Secondly, the low frequency coefficients are quantized and encoded by a fixed length algorithm, and the values and the their corresponding positions of the important high frequency coefficients are coded separately, where the values are
10、 coded by a variable precision and fixed length algorithm, and their corresponding positions are coded by a position difference reductionbased RVLC (Reversible and Variable Length Coding) algorithm. Moreover, a packing and interleaving scheme and a placing scheme of the variable length coding blocks
11、 with respect to the fixed length acoustic channel packets are proposed to resist the transmission errors of the underwater acoustic channels. Finally, error detection and concealment algorithms for low and high frequency coefficients are presented respectively. The experimental results show that th
12、e proposed coding algorithm can resist package lost error less than 20%, random bit error less than 2%, and burst error less than 2.5%. Meanwhile, the image compression ratio can reach to 70:1, with efficient compression performance.(2) Research of efficient and error-resilient underwater video enco
13、ding algorithm. The proposed underwater video coding algorithm consists of the intra-frame coding module and the inter-frame coding module. In the intra-frame coding module, the first I frame in each video sequence group is compressed by the efficient and error-resilient underwater static image enco
14、ding algorithm mentioned above, thus providing an ideal reference frame for the reconstruction of frames remained in a video sequence group. In the inter-frame coding module, after the process of motion estimation and motion compensation, an error-resilient algorithm is developed for the obtained mo
15、tion vectors and residuals, where a packing and interleaving scheme is introduced to prevent the diffusion of channel errors. In addition, the residual coefficients are coded by the position difference reduction based RVLC algorithm, and are protected from their importance. At the decoding end, an e
16、rror detection and concealment algorithm is developed to reduce the influence of transmitting errors. Moreover, in order to allow the whole coding algorithm to adapt to various complex environments, the coding algorithm can detect and resist some abnormal situations in video sequences, such as scene switch, fast camera motion and so on. Experimental results show that the developed algorithm can resist package lost error less t
