Algorithm 3: Lung Extraction Algorithm

input: A test 3D CT image.     output: Final 3D lung segmentation. 1st Order Density Estimation: Estimate the marginal density function for lung ($p_l\left(h\right)$) and marginal density function for chest ($p_c\left(h\right)$). Initial Segmentation/Labeling: Use Bayes classifier to delineate the initial lung region by using the marginal estimated densities. Estimation of Gibbs Potentials: Applying Equation (11) on the initial segmentation to estimate the Gibbs potentials. Refine Segmentation: Use iterative conditional mode (ICM) algorithm [45] to find the map that maximize the likelihood of joint MGRF model shown in Equation (13).