Iterative focus detection in hologram tomography

Abstract

Hologram tomography is a two-step method for three-dimensional topometry of extended objects. The first step consists of the hologram recording with a single laser pulse of 35 ns duration and storage in a photosensitive material. In the second step the hologram is optically reconstructed and digitized, which leads to a set of two-dimensional projections at different axial positions. A maximization of a focus measure has to be performed to extract the surface position out of the projections. Unlike with well-established methods, where the comparison of sharpness values is done parallel to the optical axis, we propose an iterative solution to perform the maximization along the direction of image formation, which is evaluated for each surface point individually. This leads to a better reproducibility of the surface in the off-axis regions.

Simultaneous depth determination of multiple objects by focus analysis in digital holography

“…Although the paper describes the method as digital holography, this is digital holography in the original sense of scanning a hologram developed from an exposure on a plate or film. Thelen demonstrated a method for measuring object surface shape from focus analysis in conventional holography by recording optical reconstruction images by CCD then analyzing the slices by computer [5]. This method also requires the labor of developing the hologram, as well as optical setup for reconstruction.…”

Improvements in Shape-From-Focus for Holographic Reconstructions With Regard to Focus Operators, Neighborhood-Size, and Height Value Interpolation

“…10 shows a facial model gained with the presented adaptive algorithm and Gaussian fitting without any postprocessing (a), with isotropic smoothing (b) and with anisotropic diffusion of normals. 5 While small features are almost obliterated in (b) they are nearly as pronounced in (c) as in the raw data. The generation of continuous surface data through the Gaussian fit or Gaussian interpolation is obligatory for the appliance of the anisotropic diffusion of normals.…”

Holographic topometry for a dense visualization of soft tissue for facial reconstruction

“…Finding the maximal focus measure along the z-axis leads to the desired axial surface coordinate [2]. Using this shape-from-focus approach, a depth value is generated for each point (x,y), resulting in a height map of the complete face [43]. The focus measure F xy (z) is determined through the image stack.…”