Defect Detection on Hardwood Logs Using Laser Scanning
Keywords:Computer vision, defect detection, robust estimation method, scanning log laser
AbstractTo improve the sawyer's ability to process hardwood logs and stems, and thereby generate a higher valued product, automated detection methods of external defects have been developed and successfully tested on a large collection of real log samples. Since external defects provide hints about internal log characteristics, the location, type, and severity of external defects are the primary indicators of overall hardwood log quality and value. Using a high-resolution laser log scanner supplied by Perceptron, 162 red oak and yellow-poplar logs were scanned and digitally photographed. By means of 2-D circles fitted using a robust estimation method, a residual image is extracted from the laser scan data. Other robust fitting methods, such as ellipse and cylinder fitting, also are examined and their performance is evaluated. Our investigation reveals that the residuals, which are defined as the radial distances between the data points and the fitted curves or surfaces, provide valuable information about defects exhibiting height differentiation from the log surface. In other words, the log "skins" in the residual images show most bark texture features and surface characteristics of the original log or stem. Based on the contour levels estimated from a residual image, the developed methods allow us to detect most severe defects using a combination of simple shape definition rules with the height map. Less significant, yet severe defects are pinpointed using a shape profile.
Bhandarkar, S. M., T. D. Faust, and M. Tang. 1999. CATALOG: A system for detection and rendering of internal log defects using computer tomography. Machine Vision and Applications.11:171-190. Springer-Verlag Berlin, Germany.nGander, W., G. H Golub, and R. Strebel. 1994. Fitting of circles and ellipses—least squares solution. Tech. Rep. 217, Insitiut fur Eisenschaftliches Rechnen, ETH Zurich. Available via anonymous ftp from ftp://ftp.inf.ethz.ch/doc/tech-reports/2xx'>ftp://ftp.inf.ethz.ch/doc/tech-reports/2xxnGuddanti, S., and S. J. Chang. 1998. Replicating sawmill sawing with TOPSAW using CT images of a full length hardwood log. Forest Prod. J.48(1):72-75.nHampel, F. R., E. M. Ronchetti, P. J. Rousseeuw, and W. A. Stahel. 1986. Robust statistics: The approach based on influence functions. John Wiley, New York, NY.nHaralick, R. M., and L. Shapiro. 1992. Computer and robot vision. Vol. 2. Addison-Wesley Longman Publ. Co. Inc., Boston, MA.nLeedan, Y., and P. Meer. 2000. Heteroscedastic regression in computer vision: Problems with bilinear constraint. Int. J. Computer Vision.37:127-150.nLi, P., A. L. Abbott, and D. L. Schmoldt. 1996. Automated analysis of CT images for the inspection of hardwood logs. Proc. Int. Conf. on Neural Networks, Washington, D.C. Volume 3:1744-1749.nMarr, D, and H. K. Nishihara. 1975. Spatial disposition of axes in a generalized cylinder representation of objects that do not encompass the viewer. Memo No 341, Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA.nMili, L., M. G. Cheniae, N. S. Vichare, and P. J. Rousseeuw. 1996. Robust state estimation based on projection statistics. IEEE Trans. on Power Systems. Vol. 11. No. 2.nPerceptron, Forest Products Division. 1999. Url: http://www.usnr.com/perceptron/products.htm'>http://www.usnr.com/perceptron/products.htmnRousseeuw, P. J., and B. C. Van Zomerman. 1991. Robust distances: Simulations and cutoff values. W. Stahel and S. Weisberg, Directions in robust statistics and diagnostics, Part II, 195-203. Springer-Verlag, Berlin, Germany.nSamson, M. 1993. Method for assessing the effect of knots in the conversion of logs into structural lumber. Wood Fiber Sci.25(3):298-304.nSchmoldt, D. L. 1996. CT imaging, data reduction, and visualization of hardwood logs. In D. Meyer, ed. Proc. 1996 Hardwood Res. Symp. National Hardwood Lumber Association, Memphis, TN.nSteele, P. H., T. E. G. Harless, F. Wagner, L. Kumar, and F. W. Taylor. 1994. Increased lumber value from optimum orientation of internal defects with respect to sawing pattern in hardwood sawlogs. Forest Prod. J.44(3): 69-72.nThomas, E., L. Thomas, L. Mili, R. Ehrich, A. L. Abbott, and C. A. Shaffer. 2003. Primary detection of hardwood log defects using laser surface scanning. IS&T/SPIE's Electronic Imaging 2003, 20-24 January 2003, Santa Clara, CA. Vol. 5011:39-49.nThomas, L., L. Mili, C. A. Shaffer, and E. Thomas. 2004. Defect detection on hardwood logs using high resolution three-dimensional laser scan data, IEEE ICIP 2004, Singapore, October 24-27, 2004:243-246.nTian, X., and G. E. Murphy. 1997. Detection of trimmed and occluded branches of harvested tree stems using texture analysis. Int. J. For. Eng. Vol. 8, No. 2.nWagner, F. G., F. W. Taylor, D. S. Ladd, C. W. McMillin, and F. L. Roder. 1989. Ultrafast CT scanning of an oak log for internal defects. Forest Prod. J.39(11/12):62-64.nZhu, D., R. Conners, F. Lamb, and P. Araman. 1991. A computer vision system for locating and identifying internal log defects using CT imagery. Proc. 4th Int. Conf. on Scanning Tech. in the Wood Ind., Miller Freeman Publishing, Inc., San Francisco, CA:1-13.n
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