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基于FRFT的机动目标ISAR成像算法 总被引:2,自引:1,他引:1
研究目标机动性不太剧烈、散射点子回波序列多普勒变化满足一阶近似条件下的机动目标ISAR实时成像问题.提出了一种新的基于分数阶傅里叶变换(FRFT)的机动目标ISAR距离一瞬时多普勒成像算法,用FRFT代替传统的快速傅里叶变换(FFT)实现目标的方位向分辨,利用目标运动的先验信息缩小算法的搜索范围,提高运算效率.实测数据处理结果表明该算法较好地解决了机动目标成像问题.与已有的机动目标成像算法相比,该算法在保证成像质量的前提下,大大减小了运算量,可用于机动目标实时成像. 相似文献
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运用二维时域有限差分法(2D-FDTD)建立点目标雷达近场成像的全电磁场模拟模型.可以任意设定收发天线(阵)以及目标的位置,对2D点目标双/多站雷达成像进行了模拟.将在合成孔径雷达(SAR)成像算法中得到广泛应用的时域相干法(TDC)、后向投影法(BP)以及地震信号处理中的相移偏移法(PSM)应用于近场成像.对这几种成像算法进行了近场成像,对成像质量及计算量进行了比较和分析.成像结果表明,BP算法和PSM算法用于近场成像时效果是不同的,文中对效果不同的原因进行了分析. 相似文献
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多角度SAR图像能够更全面描述目标不同角度下的特征信息,对目标识别具有重要意义.实现多角度SAR成像需要解决两个问题,一是在多角度测量模式下,传统成像算法的远场条件不能满足,成像散焦严重;二是空间采样不连续使得基于傅里叶变换的成像算法产生很高的旁瓣.本文利用二维匹配滤波函数的聚焦功能实现多角度SAR成像.通过调整成像参考点位置构造二维匹配函数,然后将测量数据用匹配函数进行滤波.与传统SAR成像算法相比,本文提出的多角度SAR成像算法突破了空间采样必须均匀和连续的束缚,更具有普适性.实验结果表明本文算法不仅能够实现多角度SAR成像,提高成像分辨率,而且多角度SAR图像能够描述目标散射特征的空间变化. 相似文献
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Fractal coding has been proved useful for image compression. In fractal coding, an image is represented by a number of self-transformations (fractal code) by which an approximation of the original image can be reconstructed. The authors present a block-constrained fractal coding scheme and a nona-tree decomposition based matching strategy for content-based image retrieval. In the coding scheme, an image is partitioned into non-overlapped blocks with a size close to that of a query iconic image. The fractal code is generated for each block independently. In the similarity measure of the fractal code, an improved nona-tree decomposition scheme is adopted to avoid matching the fractal code globally in order to reduce computational complexity. The experimental results show that the authors' coding scheme and matching strategy are useful for image retrieval, and compare favourably with two other methods tested in terms of storage usage and computing time 相似文献
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目前,分形图像编码技术最主要的缺点仍然是编码时间太长.因此,如何提高分形图像编码速度成为当前分形图像编码技术的研究热点.本文从分形图像编码通用公式推导出一个不等式,利用此不等式,可以预先排除大量不可能与值域块匹配的定义域块,从而减少值域块与定义域块的匹配计算,以此达到缩短编码时间的目的.实验结果表明,在解码图像质量基本不变情况下,本文的方法所使用的编码时间比Fisher方案所需的编码时间减少了很多. 相似文献
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基于图像活动性的序列图像分形编码方法 总被引:2,自引:0,他引:2
介绍了分形的概念以及分形压缩的主要思想;阐述了传统的分形图像压缩编码的基本原理与实现方法;提出了一种基于图像活动性序列图像分形编码方法。该方法首先由相邻帧之间的预测差值来判断当前编码块的活动性,然后根据图像的活动性,对不同特性的块采用不同的分形编码策略,最后对编码后得到的迭代函数系统(IFS)码进行可变长度编码(VLC),以获得更高的压缩比。 相似文献
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《AEUE-International Journal of Electronics and Communications》2014,68(7):687-697
Based on the classical fractal video compression method, an improved object-based stereo video compression scheme with Shape-Adaptive DCT is proposed in this paper. Firstly, we use more effective macroblock partition scheme instead of classical quadtree partition scheme; thus reducing the block searching strategy. The stereo fractal video coding is proposed which matches the macroblock with two reference frames in left and right view results in increasing compression ratio and reducing bit rate when transmitting compressed stereo data. The stereo codec combines the Motion Compensation Prediction (MCP) and Disparity Compensation Prediction (DCP). Fractal coding is adopted and each object is encoded independently by a prior video segmentation alpha plane, which is defined exactly as in MPEG-4. The testing results with the nature monocular and stereo video sequences provide promising performances at low bit rate coding. We believe it will be a powerful and efficient technique for the object-based monocular and stereo video sequences coding. 相似文献
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基于矢量量化的层次分形编码方法 总被引:3,自引:0,他引:3
文中提出了一种新的分形图像压缩方法,该方法将矢量量化的概念应用于分形块编码中,对图像的平缓区进行矢量量化的线性组合编码,对图像的丰富细节区用分形编码,并且在分形编码时,采取了层次处理。实验表明,与基本的分形块编码方法相比,本文提出的矢量量化层次分形编码方法在保证一定的重建图像质量下,使图像的压缩比有了明显的提高,并且大大提高了编码和解码速度。 相似文献
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A new block-based fractal image coding algorithm called Fractal Block Coding in Residue Domain (FBCRD) is proposed. In basic
Fractal Block Coding (FBC) algorithm, each block (called range block) is encoded by an affine mapping from a domain block
within the same image to itself. The decoder uses the parameters of these mappings to synthesize the reconstructed image through
an iterative procedure. FBCRD is a modification of basic FBC. In FBCRD, range blocks and domain blocks are all residue blocks
subtracted from their block means and both the parameters of affine mappings and block means are coded. This modification
leads to fewer iterations at the decoder. An optimized decoding strategy is also introduced which reduces total decoding time
by more than half of that of basic FBC. This improvement is favorable for real time implementation of fractal image compression.
Supported in Part by the Defence Preresearch Foundation, the National Science Foundation of Guangdong Prooince and the National
“Chinbing” Project 相似文献
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基于分形理论的图象编码算法可以获得比经典图象编码算法高得多的压缩比,是很有潜力的一种算法。基本的分形图象编码技术虽然有许多优点,但其细码时间长,匹配复杂,从实用考虑,还须从多方面进行改进以提高性能。本文给出一种自适应的改进算法,利用混合编码将块截短编码(BTC)与分形编码技术相结合,同时采用三级分决技术和块分类技术,使压缩比可在20~256之间随图象特点而取值,此算法在信噪比(PSNR)方面亦有所提高。 相似文献
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Image coding by block prediction of multiresolution subimages 总被引:20,自引:0,他引:20
The redundancy of the multiresolution representation has been clearly demonstrated in the case of fractal images, but it has not been fully recognized and exploited for general images. Fractal block coders have exploited the self-similarity among blocks in images. We devise an image coder in which the causal similarity among blocks of different subbands in a multiresolution decomposition of the image is exploited. In a pyramid subband decomposition, the image is decomposed into a set of subbands that are localized in scale, orientation, and space. The proposed coding scheme consists of predicting blocks in one subimage from blocks in lower resolution subbands with the same orientation. Although our prediction maps are of the same kind of those used in fractal block coders, which are based on an iterative mapping scheme, our coding technique does not impose any contractivity constraint on the block maps. This makes the decoding procedure very simple and allows a direct evaluation of the mean squared error (MSE) between the original and the reconstructed image at coding time. More importantly, we show that the subband pyramid acts as an automatic block classifier, thus making the block search simpler and the block matching more effective. These advantages are confirmed by the experimental results, which show that the performance of our scheme is superior for both visual quality and MSE to that obtainable with standard fractal block coders and also to that of other popular image coders such as JPEG. 相似文献