Patent Publication Number: US-8983141-B2

Title: Geophysical data texture segmentation using double-windowed clustering analysis

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 61/453,809, filed Mar. 17, 2011, entitled GEOPHYSICAL DATA TEXTURE SEGMENTATION USING DOUBLE-WINDOWED CLUSTERING ANALYSIS, the entirety of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of geophysical prospecting and, more particularly, to identification of geobodies in volumes of geophysical data such as seismic data. Specifically, the invention is a method for texture segmentation using double-windowed clustering analysis. 
     BACKGROUND OF THE INVENTION 
     Texture segmentation is a widely studied area of research in signal/image processing, which aims to divide a time-series or spatial dataset into sub-regions that have high internal homogeneity but differ significantly from each other. The seismic analysis community has also produced some methods that can segment seismic data automatically to facilitate faster analysis. However, most of these methods are based on designing “texture attributes”, or derived properties of the signal, i.e. the data, that can highlight different textures a priori. Other methods begin with small homogeneous regions that are then sequentially merged according to some pre-defined similarity criterion. Still other approaches use libraries of templates or training data for segmentation. Some examples of existing approaches are shown in the following list:
     1. S. Todorovic and N. Ahuja, “Texel-based Texture Segmentation”, Proc. IEEE Int&#39;l. Conf. Computer Vision (ICCV), Kyoto, Japan, 2009   2. M. Donoser and H. Bischof, “Using covariance matrices for unsupervised texture segmentation”,  ICPR,  2008   3. M. Galun, E. Sharon, R. Basri and A. Brandt, “Texture segmentation by multiscale aggregation of filter responses and shape elements”,  ICCV, pp.  716-723, 2003   4. R. M. Haralick, “Statistical and structural approaches to texture”,  Proc. Of the IEEE  67(5), pp. 786-804 (1979)   5. J. H. Hays, M. Leordeanu, A. A. Efros and Y. Liu, “Discovering texture regularity as a higher-order correspondence problem”,  ECCV  2, pp. 522-535, 2006   6. T. Hofmann, J. Puzicha, J. M. Buhmann and R. Friedrich, “Unsupervised texture segmentation in a deterministic annealing framework”,  IEEE TPAMI  20, pp. 803-818, 1998   7. B. Julesz, “Textons, the elements of texture perception and their interactions”,  Nature  290, pp. 91-97, 1981   8. T. Leung and J. Malik, “Representing and recognizing the visual appearance of materials using three-dimensional textons”,  IJCV  43(2), pp. 29-44, 2001   9. W. C. Lin and Y. Liu, “A lattice-based MRF model for dynamic near-regular texture tracking”,  IEEE Trans. Pattern Anal. Mach. Intell.  29(5), pp. 777-792, 2007   10. J. Malik, S. Belongie, T. Leung and J. Shi, “Contour and texture analysis for image segmentation”,  Int. J. Comput. Vision  43(1), pp. 7-27, 2001   11. B. Schachter and N. Ahuja, “Random pattern generation processes”,  CGIP  10(2), 95-114, 1979   12. M. Varma and A. Zisserman, “A statistical approach to texture classification from single images”,  IJCV  62(1-2), pp. 61-81, 2005   13. H. Voorhees and T. Poggio, “Computing texture boundaries from images”,  Nature  333, pp. 364-367, 1988   14. S. C. Zhu, C. E. Guo, Y. Wang and Z. Wu, “What are textons?”,  IJCV  62(1-2), pp. 121-143, 2005   15. M. Fernandez Limia, A. Mavilio Nunez, M. Tejera Fernandez, “Texture Segmentation of a 3D Seismic Section with Wavelet Transform and Gabor Filters”,  ICPR  3, pg. 3358, 15 th  Int&#39;l. Conf. on Pattern Recognition, 2000   16. Brian West and Steve May, “Method for Seismic Facies Interpretation Using Textural Analysis and Neural Networks,” U.S. Pat. No. 6,560,540.   

     Other examples are compiled and discussed in the survey article by Jean-Pascal Aribot entitled Texture Segmentation that may be downloaded at http://www.mics.ch/SumIntU03/JPAribot.pdf. 
     The present invention is a method that does not require any training data, attributes or pre-defined similarity measures designed to distinguish textures. Instead, it extracts statistical distributions of user-defined windows on the data, and clusters the distributions according to a standard similarity metric between probability distributions, including similarity metrics commonly used in the literature. This lack of pre-defined criteria, combined with the sensitivity of the method, which enables significantly better and more robust results than alternatives, make the present inventive method particularly advantageous for datasets that do not have a well known pre-defined structure, which is often the case for complex datasets such as seismic data. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the invention is a computer-implemented method for performing texture segmentation of one or more volumes of geophysical data, comprising using local statistical distributions of data values, said distributions computed using two moving windows of user-selected size and shape, one being a pattern window and the other a sampling window larger than the pattern window, wherein the pattern window moves about within the sampling window to generate the local statistical distribution for the sampling window&#39;s location, and then selecting a distance measure of similarity followed by partitioning the geophysical data into clusters on a basis of application of the distance measure of similarity to the local statistical distributions for pairs of locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fees. 
       The present invention and its advantages will be better understood by referring to the following detailed description and the attached drawings in which: 
         FIG. 1  is a flowchart showing basic steps in one embodiment of the present invention of method; 
         FIG. 2  is a time-series example with multiple texture segments; 
         FIG. 3  is a 2-dimensional image with multiple textures; 
         FIG. 4  is a schematic diagram illustrating the pattern window and the sampling window as used in the present invention&#39;s definition of texture; 
         FIGS. 5A-5B  illustrate agglomerative clustering ( 5 A) and a typical tradeoff curve and selection of optimal number of clusters ( 5 B); 
         FIG. 6  is a schematic diagram of new distance function for probability distributions and showing its relation to the K-L Divergence distance function; 
         FIGS. 7A-7D  show four examples where the distances could differ substantially between the K-L measure and the measure of the present invention, and the K-L distance could be misleading; 
         FIG. 8  illustrates texture segmentation of 1-D signal using the present inventive method with pattern window size w=20, sampling window size W=100, using a K-means clustering algorithm that provides a hierarchy of segmentations capturing varying degrees of internal structure within the textures; 
         FIG. 9  illustrates texture segmentation of a 150×150 2-D texture image using the present inventive method, with a 5×5 pattern window and 10×10 sampling window; 
         FIG. 10  shows an application of the present automatic texture segmentation method to the seismic cross-section with anticline unconformity shown on the left of the figure, with a possible interpretation of some important segments shown on the right; and 
         FIG. 11  shows two more seismic data test examples: segmenting a salt dome (top of figure) and dipping layers of clinoform (bottom of figure). 
     
    
    
     The invention will be described in connection with example embodiments. However, to the extent that the following detailed description is specific to a particular embodiment or a particular use of the invention, this is intended to be illustrative only, and is not to be construed as limiting the scope of the invention. On the contrary, it is intended to cover all alternatives, modifications and equivalents that may be included within the scope of the invention, as defined by the appended claims. Persons skilled in the technical field will readily recognize that in practical applications of the present inventive method, it is performed on a computer programmed in accordance with the teachings herein. Indeed, the method was developed with automated use in mind, which is one of its advantages. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Texture segmentation (see the references listed in the “Background” section), in one of its many equivalent forms, is a long studied topic in many fields of research involving spatial or time-series data analysis, including but not limited to computer vision, signal processing (telecommunications by wireless/data or optical networks, image processing (e.g., terrestrial, satellite, radar, medical, or robotic), time-series analysis (stock or financial data) and many others. The basic task consists of breaking up a sequence of data values such as in a time-series, or a spatial configuration of values such as in an image, into regions which are internally statistically homogeneous, with clear and quantifiable differences across regions, as shown in  FIGS. 2 and 3 . 
     The distinct regions in these figures can then be considered distinct textures, a term that is widely understood by illustration, but without a clear mathematical definition so far either in the theoretical or practice-oriented literature. While there is a lot of literature based on the concept of “textons”, which are elementary texture patterns that can compose repeating image patterns, it is not clear how textons can be defined to be robust or comprehensive. In this document, an alternative intuitive definition of texture is proposed that naturally enables the segmentation (separation) of such datasets into the distinct regions that are obvious to the human observer. With this introduction, the new concept of texture and how it may be used for segmentation follows next. 
     Definition of Texture as Window Statistics 
     Consider the following general definition of a multi-dimensional dataset: At each point x i εR N : i=1, . . . K in N-dimensional space, a vector v i εR M : i=1, . . . K, is given. For example, a 256×256 RGB-color image has N=2, M=3, K=256×256=65536. In another example, time series data of an industrial process unit with 50 measurement points that produce a single reading each in one minute intervals for an hour would have N=1, M=50, K=60. 
     Next, define two nested windows of user-defined size and shape on such a dataset. The smaller window, known as the Pattern Window is contained within the larger Sampling Window as shown symbolically in  FIG. 4 . 
     For example, in  FIG. 4 , the wx×wy pattern window moves within the WX×WY sampling window. The window can move from one position to an adjacent position where it will partly overlap its previous position. For now, assume the data to be a 2-D grayscale image (not shown). The “texture” at the center of the sampling window will then be defined by the wx*wy dimensional joint distribution of the pattern window over the sampling window. Consider the simplest case where the distribution is represented by a multi-dimensional Gaussian. At each location x′,y′, define a pattern vector V(x′,y′) obtained by concatenating all values within the pattern window as a linear vector. The mean and covariance of the distribution at x,y may then be computed as the mean and covariance of (WX−wx)*(WY−wy) pattern vectors contained in the sampling window centered at x,y, assuming that the pattern window stays inside the sampling window for all positions. 
     Note that the above definition thus characterizes texture at a spatial scale characterized by the pattern window, with statistical estimation determined by the sampling window. The set of distributions obtained by scaling the two windows can then be viewed as textures at each location at those scales. It is also straight-forward to extend this method to data in any number of dimensions, with any number of independent attributes at each point in that space, i.e. xεR N , y(x)εR M . In this case, with a cuboidal window of size vector w={w k , k=1, . . . N}, the pattern vector V(x) would be the concatenation of all the y&#39;s in the window, and would hence have dimension given by 
               dim   ⁡     (     V   ⁡     (   x   )       )       =     M   ⁢           ⁢       ∏     k   =   1     N     ⁢       w   k     .               
This clearly implies the explosion of the dimensionality of the algorithm, and computational limitations will rule out use of very large window sizes, unless significant parallel computing can be brought to bear. This can be accomplished by the use of Summed Area Tables (SATs), which are standard data structures used in image processing and other spatial data applications like radar, hyper-spectral imaging etc. See, for example, the online reference: Hensley, J., Scheuermann, T., Coombe, G., Singh, M. and Lastra, A. (2005), Fast Summed-Area Table Generation and its Applications,  Computer Graphics Forum  24, pp. 547-555.
 
     Next it is shown how the above definitions can be used to perform texture segmentation. 
     Texture Segmentation Algorithm 
     In one embodiment of the present invention, a texture segmentation algorithm may be constructed as described in this section. For a given set of window shapes and sizes, compute the distributions p x,y (V) of the pattern vectors at each location x,y, using a 2-D data set as an example. This may be considered to be a single two-dimensional distribution, a joint distribution of the pattern window using all its samples within the sampling window. In the Gaussian case this reduces to computing the mean vector and covariance matrix of V at each location. (See PCT Publication No. WO2010/056424). While this looks computationally very daunting, we will discuss a relatively efficient method later that can exploit the high level of redundancy in the computations using the data structure referred to above, i.e. Summed Area Tables (“SATs”). 
     We then perform a clustering of similar distributions using any standard clustering algorithm, such as K-means. See, for example, http://www-users.cs.umn.edu/˜kumar/dmbook/ch8.pdf. For greater robustness, and to obtain a better handle over the number of clusters, we may also implement a connectivity-based clustering algorithm, that provides a trade-off curve of the number of clusters vs. clustering quality. Such an algorithm is based on a well-known procedure called “agglomerative clustering”, but it maintains clustering metrics that can provide the trade-off curve. See U.S. Patent Publication No. 2010/0121851. Agglomerative clustering and the trade-off curve are illustrated in  FIGS. 5A-5B , respectively, where in  FIG. 5A  clustering is indicated by lines connecting the dots. In  FIG. 5B , the irregular curve shows the clustering results. The smooth curve is a concave minor, i.e. a concave lower bound to the irregular curve. The straight line connects the curve endpoints. The tangent to the smooth curve is moved along the curve until the slope matches that of the straight line. This is one way to determine the optimum trade-off, shown in the drawing as (n*,d*). 
     Note on the Distance Function Between Distributions 
     An important ingredient in this process is the distance/similarity metric, which determines which textures are similar based on their distributions p(V) and q(V), i.e. one x,y location having a distribution p(V) and a second x′,y′ location having a distribution q(V). A standard metric used in similar situations is the well known Kullback-Leibler Divergence (K-L) defined as 
               D     p   ,   q     KL     =     ∫       ⅆ     Vp   ⁡     (   V   )         ⁢       log   ⁡     (       p   ⁡     (   V   )         q   ⁡     (   V   )         )       .               
See M. Bocquest, C. A. Fires, L. Wu, Beyond Gaussian statistical modeling in geophysical data assimilation (http://idl.ul.pt/carlospires/nongaussianity_review-24032010.pdf, pp. 1-51). For multi-dimensional Gaussians, this takes the form
 
     
       
         
           
             
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     In particular, the example distributions in  FIGS. 7A-7D  show four circumstances under which the K-L divergence can be misleading, while the present formulation provides a more reliable similarity measure. 
     Again, for the Gaussian case, this new distance measure of the present invention can be obtained as follows: 
     
       
         
           
             
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     To summarize, basic steps in one embodiment of the present inventive method that assumes Gaussian statistics are shown in the flowchart of  FIG. 1 . 
     At step  11 , the user considers a multidimensional geophysical data set, and selects a segmentation algorithm that utilizes the double-windowed texture definition of the present invention, i.e. local statistical distributions computed using two moving windows of user-selected size and shape: (1) a pattern window (2) a sampling window larger than the pattern window. At step  12 , for each sampling window contained within the data, the statistical distribution (e.g. mean and covariance matrix in simplest case of Gaussian approximation) of all pattern windows contained within the sampling window is computed. At step  13 , distances or dissimilarity measures between pairs of distributions are determined (optionally only within a restricted neighborhood). At step  14 , distributions are clustered based on distances/dissimilarities. (In the field of data mining, the terms distance, similarity, and dissimilarity can be used interchangeably and in combination, often as modifiers of measure.) At step  15 , spatially contiguous clusters are identified as texture segments. 
     For more detail on steps  12 - 14 , consider a 2-D data set and at each location x,y, consider the sample window centered there. Each discrete cell within the sample window will have a data value associated with it. Next, construct a pattern vector for each possible location of the pattern window within that sample window by concatenating the data values contained in that pattern window into a w x ×w y  component vector. The distribution of the pattern vectors within the sample window is then computed. For example, this may be done by computing the mean vector and the covariance matrix. Then, this process may be repeated for all other x,y locations represented by the data set. Whether two such locations should be clustered together is determined by applying some similarity/distance measure to their respective pattern vector distributions. 
     In all the examples below, the various possible choices are restricted to (a) square windows of small/moderate size (b) Multi-variate Gaussian distributions (c) a simple weighted Euclidean distance metric as an approximation to the K-L divergence or its enhancement discussed earlier (d) K-means clustering. These choices are not intended to limit the scope of the invention and were made primarily for simplicity and computational tractability, as only a simple serial MATLAB implementation on a Dell  630  laptop were used. In a more commercial application, the present inventive method might be implemented, for example, on a GPU cluster, with a menu of choices of window sizes, distance metrics and clustering algorithms. We begin with the simple 1-D signal containing 3 distinct textures. 
     Test Examples of the Present Inventive Method 
     The first examples, i.e. those shown in  FIG. 8 , use the simple 1-D signal  81  containing three distinct textures as shown in  FIG. 8  (0 to approximately 350, 350-650, and 650-1000). This could be an example of any signal, such as seismic amplitude, plotted vs. time, or location in a single direction. The clustering algorithm (K-means in this case) provides a hierarchy of segmentations (four are shown in  FIG. 8 ) capturing varying degrees of internal structure within the textures. The clusters are differentiated by color in the original colored displays. It may be noted that the segmentation results mostly match what humans would likely provide from visual inspection, which confirms the reasonableness of the automated results. 
     A synthetic 2-D example is shown in  FIG. 9 , where segmentation of a 150×150 texture image was performed with the present inventive method, using a 5×5 pattern window and 10×10 sampling window. Five levels of segmentation are shown, i.e. number of clusters=2, 3, 4, 5, and 10. 
     Finally,  FIGS. 10 and 11  show example applications of the present invention method to seismic data. In  FIG. 10 , the automatic texture segmentation of the present inventive method is applied to an anticline uniformity in a seismic cross-section, and a possible interpretation of some important segments is shown on the right of the figure. The anticline uniformity is captured in segment  101  and segment  102  is a possible hydrocarbon migration path.  FIG. 11  shows more seismic data test examples: segmenting salt dome (top of figure) and dipping layers of clinoform (bottom of figure). 
     All or part of  FIGS. 8-11  were originally in color, but may be shown herewith as black-and-white reproductions depending upon patent law restrictions on use of color. 
     The foregoing patent application is directed to particular embodiments of the present invention for the purpose of illustrating it. It will be apparent, however, to one skilled in the art, that many modifications and variations to the embodiments described herein are possible. All such modifications and variations are intended to be within the scope of the present invention, as defined in the appended claims.