[1] Danzl R, Helmli F, Scherer S. Focus variation-a new technology for high resolution optical 3D surface metrology. [C]//The 10th international conference of the slovenian society for non-destructive testing, September 1-3, 2009, Ljubljana, Slovenia. Ljubljana: Slovenian Society for Non-Destructive Testing, 484-491(2009).

[2] Nayar S K, Nakagawa Y. Shape from focus[J]. IEEE Transactions on Pattern Analysis and Machine Intelligence, 16, 824-831(1994).

[3] Ni J, Yuan J H, Wu Q Z. Identification for optical image definition based on edge feature[J]. Chinese Journal of Lasers, 36, 172-176(2009).

[4] Wang J Q, Zhang L G, Fu T J et al. Sharpness assessment for remote sensing image based on abstracting the edge image of skeleton[J]. Laser & Optoelectronics Progress, 52, 091002(2015).

[5] Firestone L, Cook K, Culp K et al. Comparison of autofocus methods for automated microscopy[J]. Cytometry, 12, 195-206(1991).

[6] Helmli F S, Scherer S. Adaptive shape from focus with an error estimation in light microscopy. [C]//ISPA 2001. Proceedings of the 2nd International Symposium on Image and Signal Processing and Analysis. In conjunction with 23rd International Conference on Information Technology Interfaces (IEEE, 188-193(2001).

[7] Fan T T, Yu H B. A novel shape from focus method based on 3D steerable filters for improved performance on treating textureless region[J]. Optics Communications, 410, 254-261(2018). http://adsabs.harvard.edu/abs/2018OptCo.410..254F

[8] Hariharan R, Rajagopalan A N. Shape-from-focus by tensor voting[J]. IEEE Transactions on Image Processing, 21, 3323-3328(2012). http://europepmc.org/abstract/MED/22434802

[9] Kaleem M, Mahmood M T. Combining focus measures through genetic algorithm for shape from focus. [C]//2014 International Conference on Information Science & Applications (ICISA), May 6-9, 2014, Seoul, Korea. New York: IEEE, 14431736(2014).

[10] Minhas R, Mohammed A A. Wu Q M J, et al. 3D shape from focus and depth map computation using steerable filters[M]. //Kamel M, Campilho A. International conference image analysis and recognition. Lecture notes in computer science. Berlin, Heidelberg: Springer, 5627, 573-583(2009).

[11] Minhas R, Mohammed A A. Jonathan Wu Q M. Shape from focus using fast discrete curvelet transform[J]. Pattern Recognition, 44, 839-853(2011).

[12] Hu T, Liu G D, Pu Z B. Depth from focus based on zero-phase filter[J]. Opto-Electronic Engineering, 38, 145-150(2011).

[13] Jiang Z G, Shi W H, Han D B et al. Three-dimensional microscopy image system based on depth from focus[J]. Computerized Tomography Theory and Applications, 13, 9-15(2004).

[14] Malik A S, Choi T S. Consideration of illumination effects and optimization of window size for accurate calculation of depth map for 3D shape recovery[J]. Pattern Recognition, 40, 154-170(2007). http://www.sciencedirect.com/science/article/pii/S0031320306002470

[15] Lee I H, Shim S O, Choi T S. Improving focus measurement via variable window shape on surface radiance distribution for 3D shape reconstruction[J]. Optics and Lasers in Engineering, 51, 520-526(2013). http://www.sciencedirect.com/science/article/pii/S0143816612003090

[16] Muhammad M S, Mutahira H, Choi K W et al. Calculating accurate window size for shape-from-focus. [C]//2014 International Conference on Information Science & Applications (ICISA), May 6-9, 2014, Seoul, Korea. New York: IEEE, 14431716(2014).

[17] Muhammad M, Choi T S. Sampling for shape from focus in optical microscopy[J]. IEEE Transactions on Pattern Analysis and Machine Intelligence, 34, 564-573(2012). http://dl.acm.org/citation.cfm?id=2122592

[18] Asif M, Choi T S. Shape from focus using multilayer feedforward neural networks[J]. IEEE Transactions on Image Processing, 10, 1670-1675(2001). http://www.ncbi.nlm.nih.gov/pubmed/18255509

[19] Kim H J, Mahmood M, Choi T S. An efficient neural network for shape from focus with weight passing method[J]. Applied Sciences, 8, 1648(2018).

[20] Malik A S, Nisar H, Choi T S. A Fuzzy-Neural approach for estimation of depth map using focus[J]. Applied Soft Computing, 11, 1837-1850(2011). http://www.sciencedirect.com/science/article/pii/S1568494610001316

[21] Subbarao M, Lu M C. Image sensing model and computer simulation for CCD camera systems[J]. Machine Vision and Applications, 7, 277-289(1994). http://link.springer.com/article/10.1007/BF01213418

[22] Subbarao M, Choi T S, Nikzad A et al. Focusing techniques[J]. Optical Engineering, 32, 2824-2837(1993).

[23] Pertuz S, Puig D, Garcia M A. Analysis of focus measure operators for shape-from-focus[J]. Pattern Recognition, 46, 1415-1432(2013). http://www.sciencedirect.com/science/article/pii/S0031320312004736

[24] Mutahira H, Muhammad M S, Jaffar A et al. Unorthodox approach toward microscopic shape from image focus using optical microscopy[J]. Microscopy Research and Technique, 76, 1-6(2013). http://www.ncbi.nlm.nih.gov/pubmed/23070896

[25] Subbarao M, Choi T. Accurate recovery of three-dimensional shape from image focus[J]. IEEE Transactions on Pattern Analysis and Machine Intelligence, 17, 266-274(1995). http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=368191

[26] Machine Intelligence. PAMI-[J]. Pentland A P. A new sense for depth of field. IEEE Transactions on Pattern Analysis, 9, 523-531(1987).

[27] Shim S O, Choi T S. A novel iterative shape from focus algorithm based on combinatorial optimization[J]. Pattern Recognition, 43, 3338-3347(2010). http://www.sciencedirect.com/science/article/pii/S0031320310002578