IMAGE PROCESSING
THE acquisition of 3-D information out of 2-D images is one of the most important issues in computer vision. Techniques executing this task are often referred to as shape-from-x, where x is a visual cue such as shading, texture, contour, focus, stereo, and motion [1]. Blurring phenomena due to defocusing
are among the important cues for depth recovery. Shape-from focus is a method where a sequence of images is taken while changing the focus setting in small steps. One image of such a sequence, further on referred to as focus series, contains a focused region of the imaged object as well as an unfocused background. By determining the focus setting, that locally optimizes image focus, 3-D information about the imaged object is retrieved [2]. If the object is moving and cannot be expected to remain in a certain position during the capturing time, an alternative method for 3-D measurement is holography, where part of the 3-D information about the recorded object is stored by superimposing the back-scattered light coherently with a reference wave. Through this, the amplitude and the phase information of the scattered light field are stored as an interference pattern, for example in an analogue photosensitive material. This kind of acquisition of 3-D data has the tremendous advantage of storing the high-resolved information in an extremely short amount of time, namely in the duration of the recording laser pulse (35 ns for the setup described here). However, the only way to get access to the stored information is reconstructing the hologram.
Fig. 1. Optical reconstruction of the hologram and digitalization of a set of
2-D projections at different axial positions.
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