def v_cycle_3d(n, k, delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement, depth=0): r"""Multi-resolution Gauss-Seidel solver using V-type cycles Multi-resolution Gauss-Seidel solver: solves the linear system by first filtering (GS-iterate) the current level, then solves for the residual at a coarser resolution and finally refines the solution at the current resolution. This scheme corresponds to the V-cycle proposed by Bruhn and Weickert[1]. [1] Andres Bruhn and Joachim Weickert, "Towards ultimate motion estimation: combining highest accuracy with real-time performance", 10th IEEE International Conference on Computer Vision, 2005. ICCV 2005. Parameters ---------- n : int number of levels of the multi-resolution algorithm (it will be called recursively until level n == 0) k : int the number of iterations at each multi-resolution level delta_field : array, shape (S, R, C) the difference between the static and moving image (the 'derivative w.r.t. time' in the optical flow model) sigma_sq_field : array, shape (S, R, C) the variance of the gray level value at each voxel, according to the EM model (for SSD, it is 1 for all voxels). Inf and 0 values are processed specially to support infinite and zero variance. gradient_field : array, shape (S, R, C, 3) the gradient of the moving image target : array, shape (S, R, C, 3) right-hand side of the linear system to be solved in the Weickert's multi-resolution algorithm lambda_param : float smoothness parameter, the larger its value the smoother the displacement field displacement : array, shape (S, R, C, 3) the displacement field to start the optimization from Returns ------- energy : the energy of the EM (or SSD if sigmafield[...]==1) metric at this iteration """ # pre-smoothing for i in range(k): ssd.iterate_residual_displacement_field_ssd_3d(delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement) if n == 0: energy = ssd.compute_energy_ssd_3d(delta_field) return energy # solve at coarser grid residual = ssd.compute_residual_displacement_field_ssd_3d( delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement, None) sub_residual = np.array(vfu.downsample_displacement_field_3d(residual)) del residual subsigma_sq_field = None if sigma_sq_field is not None: subsigma_sq_field = vfu.downsample_scalar_field_3d(sigma_sq_field) subdelta_field = vfu.downsample_scalar_field_3d(delta_field) subgradient_field = np.array( vfu.downsample_displacement_field_3d(gradient_field)) shape = np.array(displacement.shape).astype(np.int32) sub_displacement = np.zeros(shape=((shape[0] + 1) // 2, (shape[1] + 1) // 2, (shape[2] + 1) // 2, 3), dtype=floating) sublambda_param = lambda_param * 0.25 v_cycle_3d(n - 1, k, subdelta_field, subsigma_sq_field, subgradient_field, sub_residual, sublambda_param, sub_displacement, depth + 1) del subdelta_field del subsigma_sq_field del subgradient_field del sub_residual displacement += vfu.resample_displacement_field_3d(sub_displacement, 0.5 * np.ones(3), shape) del sub_displacement # post-smoothing for i in range(k): ssd.iterate_residual_displacement_field_ssd_3d(delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement) energy = ssd.compute_energy_ssd_3d(delta_field) return energy
def v_cycle_3d(n, k, delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement, depth=0): r"""Multi-resolution Gauss-Seidel solver using V-type cycles Multi-resolution Gauss-Seidel solver: solves the linear system by first filtering (GS-iterate) the current level, then solves for the residual at a coarser resolution and finally refines the solution at the current resolution. This scheme corresponds to the V-cycle proposed by Bruhn and Weickert[1]. [1] Andres Bruhn and Joachim Weickert, "Towards ultimate motion estimation: combining highest accuracy with real-time performance", 10th IEEE International Conference on Computer Vision, 2005. ICCV 2005. Parameters ---------- n : int number of levels of the multi-resolution algorithm (it will be called recursively until level n == 0) k : int the number of iterations at each multi-resolution level delta_field : array, shape (S, R, C) the difference between the static and moving image (the 'derivative w.r.t. time' in the optical flow model) sigma_sq_field : array, shape (S, R, C) the variance of the gray level value at each voxel, according to the EM model (for SSD, it is 1 for all voxels). Inf and 0 values are processed specially to support infinite and zero variance. gradient_field : array, shape (S, R, C, 3) the gradient of the moving image target : array, shape (S, R, C, 3) right-hand side of the linear system to be solved in the Weickert's multi-resolution algorithm lambda_param : float smoothness parameter, the larger its value the smoother the displacement field displacement : array, shape (S, R, C, 3) the displacement field to start the optimization from Returns ------- energy : the energy of the EM (or SSD if sigmafield[...]==1) metric at this iteration """ # pre-smoothing for i in range(k): ssd.iterate_residual_displacement_field_ssd_3d(delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement) if n == 0: energy = ssd.compute_energy_ssd_3d(delta_field) return energy # solve at coarser grid residual = ssd.compute_residual_displacement_field_ssd_3d(delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement, None) sub_residual = np.array(vfu.downsample_displacement_field_3d(residual)) del residual subsigma_sq_field = None if sigma_sq_field is not None: subsigma_sq_field = vfu.downsample_scalar_field_3d(sigma_sq_field) subdelta_field = vfu.downsample_scalar_field_3d(delta_field) subgradient_field = np.array( vfu.downsample_displacement_field_3d(gradient_field)) shape = np.array(displacement.shape).astype(np.int32) sub_displacement = np.zeros( shape=((shape[0]+1)//2, (shape[1]+1)//2, (shape[2]+1)//2, 3), dtype=floating) sublambda_param = lambda_param*0.25 v_cycle_3d(n-1, k, subdelta_field, subsigma_sq_field, subgradient_field, sub_residual, sublambda_param, sub_displacement, depth+1) del subdelta_field del subsigma_sq_field del subgradient_field del sub_residual displacement += vfu.resample_displacement_field_3d(sub_displacement, 0.5 * np.ones(3), shape) del sub_displacement # post-smoothing for i in range(k): ssd.iterate_residual_displacement_field_ssd_3d(delta_field, sigma_sq_field, gradient_field, target, lambda_param, displacement) energy = ssd.compute_energy_ssd_3d(delta_field) return energy