Rapid extraction of 3D regions of interest from digital holograms

Selective reconstruction with data reduction is the key to efficient data analysis and high quality image reconstructions from digital holograms. This paper presents an efficient method of extracting 3D regions of interest (ROIs) of object volume directly from a hologram. The new method consists of a rapid focus detection algorithm, a summation kernel for computing a sum image onto which of a sequence of object images are projected and an image segmentation algorithm. The focus detection algorithm is based on the h norm of the object spectral components and works directly on the hologram. It estimates the depth distances at which objects can be found in-focus. The summation kernel is then employed to obtain sum images that are effectively the parallel projection of object images located within each detected range of focusing distances. The lateral support of these ROIs are then obtained by segmenting these sum images. The whole process does not require full reconstruction of the object images throughout the 3D volume. Based on a lens-less DHI camera system jointly developed at MIT and WHOI, the new 3D ROI extraction technique has been applied to plankton holograms obtained in the laboratory and on shipboard. Results from plankton holograms are demonstrated.