Estimation of angular difference between tomographic projections taken at unknown directions in 3D

This paper deals with the estimation of angular difference between two tomographic projections belonging to a set of projections taken at unknown directions. The proposed method extends our former work from 2D to 3D. The method is potential for many applications such as projection refinement or projection classification, which are important in the process of tomographic reconstruction. Unlike to common line based angular estimation, the proposed method does not need reference projections. Our method relies on the selection of projection neighbors with local adaptive thresholds, the calculus of the angular difference for neighboring projections by using properties of moments. The accuracy and the robustness of our method are shown on a test database including 50 3D gray-level images at different resolutions and with different levels of noise.