融合简单线性迭代聚类的高光谱混合像元分解策略
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国家自然科学基金青年基金项目(41201356)


Hyperspectral mixed pixel decomposition policy merging simple linear iterative clustering
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    摘要:

    高光谱图像中的混合像元问题广泛存在,混合像元的分解效率一直是遥感应用研究的难点和热点。目前成熟的端元提取算法有纯像元指数(pure pixel index, PPI)、内部最大体积法(N-FINDR)、顶点成分分析(vertex component analysis, VCA)、顺序最大角凸锥(sequential maximum angle convex cone, SMACC)、交替最大体积法(alternating volume maximization, AVMAX)、最小体积封闭单形体(minimum volume enclosing simplex, MVES)等,这些算法从图像所有像元中提取纯光谱,具有提取速度慢、精度不高的缺点。为此,该文引入了一种融合简单线性迭代聚类(simple linear iterative clustering, SLIC)超像元分割的高光谱混合像元分解算法。超像元分割技术能够将具有相似特征的相邻像元组成图像块,并保留进一步进行图像处理的有效信息,从而大幅减少参与端元提取的像元数量,为解决上述问题提供了有效的途径。通过试验对比了降维方式(主成分分析和最大噪声分数)、RGB对应关系(6种)、色彩空间RGB(red, green, blue)和LAB(lightness-A-B)、数据格式(JPG, BIN)和算法参数K对高光谱图像超像元分割结果的影响,并进一步分析了SLIC 超像元分割结果对2 种典型端元提取算法(AVMAX、MVES)产生的不同效果。试验结果表明,随着K值的增大,混合像元分解的时间逐渐增加,均方根误差(root mean square error, RMSE)持平或减少,而JPG(有损压缩)数据格式的时间始终比BIN(无损压缩)数据格式的要短。SLIC+MVES的RMSE略高于MVES的RMSE,低于AVMAX的RMSE,但时间远小于MVES。当K足够大的时候,SLIC+MVES的效果就近似MVES的效果了。在大部分情况下,最大噪声分数的降维效果优于主成分分析。以最大噪声分数作为降维方法、以JPG作为数据格式、以LAB作为色彩空间对混合像元分解结果较为有利。另外,SLIC的参数K的取值在5~10之间较为合适。该研究中的SLIC超像元分割算法简单易行,并且提高了混合像元分解的效率,具备很好的实用价值。

    Abstract:

    Abstract: The decomposition efficiency of mixed pixels is an important subject in the research of remote sensing application. Current mature extraction algorithms of the endmember are pure pixel index (PPI), N-FINDR, vertex component analysis (VCA), sequential maximum angle convex cone (SMACC), alternating volume maximization (AVMAX), minimum volume enclosing simplex (MVES), etc. Extracting pure spectra from all pixels of an image by those algorithms has relatively slow processing and low accuracy. Therefore, in this paper, we introduced an integration of simple linear iterative clustering (SLIC) super pixel segmentation of hyperspectral mixed pixel decomposition algorithm. The number of pixels in a hyperspectral image was one of the main reasons that affected pixel unmixing (especially endmember extraction). Super pixel segmentation techniques can compose adjacent pixels with similar characteristics into image blocks, and retain useful information for further image processing, thus significantly reducing the number of pixels involved in endmember extraction and solving the problems of low processing and low accuracy in an effective way. In this paper, endmember extraction method was modified. We used Simple Linear Iterative Clustering (SLIC) algorithm to segment hyperspectral image pixels into super pixel sets, and conducted experimental comparisons on impact of different dimension reduction methods such as principal components analysis (PCA), minimum noise fraction (MNF), correspondence between different RGB (six kinds), different color spaces (RGB, LAB), different data formats(JPG, BIN)and different algorithms' parameters K on hyperspectral image super pixel segmentation results. Furthermore, the impact of SLIC super pixel segmentation results on two typical endmember extraction algorithms was analyzed. The results showed that, with the increase of K value, the decomposition of mixed pixels gradually increased. The reason for such change was that as the K value increased, the number of pixels increased, and the size of the image was reduced and was close to a normal pixel. The JPG (lossy compression) data format of time was shorter than BIN (lossless compression) data format because a lossy compression can reduce the image size occupied in memory or disk space. The root-mean-square error (RMSE) of SLIC+MVES was slightly higher than that of MVES, and lower than that of AVMAX, with the time much less than actual MVES. In other words, relative to MVES, SLIC+MVES greatly increased processing speed, at the expense of a small amount of sacrifice in accuracy. AVMAX consumed little time itself because it did not need to solve linear programming problems repeatedly. So after adding super pixel segmentation, the time shortened for AVMAX was not significant, but the time for SLIC computing had increased. When increasing K, the computation time increased gradually, and the RMSE was flat or deceasing. When K was large enough, the results of SLIC+MVES was approximate to that of MVES. The difference in the RGB color space and Lab color space was not obvious. SLIC algorithm used Lab color space because it did not rely on the advantages of the device, but also had its own advantages, i.e., a wide color gamut. In most cases, dimensionality reduction by MNF was better than that of PCA. As to the MNF dimensionality reduction method, the data in JPG format, with Lab color space were more favorable for unmixing results. In addition, the value of SLIC parameters from 5 to10 was more appropriate. The SLIC super pixel segmentation algorithm was simple and improved the efficiency of unmixing, with a great practical value.

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张飞飞,孙 旭,薛良勇,高连如,刘长星.融合简单线性迭代聚类的高光谱混合像元分解策略[J].农业工程学报,2015,31(17):199-206. DOI:10.11975/j. issn.1002-6819.2015.17.026

Zhang Feifei, Sun Xu, Xue Liangyong, Gao Lianru, Liu Changxing. Hyperspectral mixed pixel decomposition policy merging simple linear iterative clustering[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE),2015,31(17):199-206. DOI:10.11975/j. issn.1002-6819.2015.17.026

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  • 收稿日期:2015-04-20
  • 最后修改日期:2015-07-21
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  • 在线发布日期: 2015-09-01
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