a b s t r a c tThis paper investigates the application of Fresnel based numerical algorithms for the reconstruction of Gabor in-line holograms. We focus on the two most widely used Fresnel approximation algorithms, the direct method and the angular spectrum method. Both algorithms involve calculating a Fresnel integral, but they accomplish it in fundamentally different ways. The algorithms perform differently for different physical parameters such as distance, CCD pixel size, and so on. We investigate the constraints for the algorithms when applied to in-line Gabor digital holographic microscopy. We show why the algorithms fail in some instances and how to alter them in order to obtain useful images of the microscopic specimen. We verify the altered algorithms using an optically captured digital hologram.

This paper demonstrates a technique that could prove useful for extracting three-dimensional (3D) models from a single two-dimensional (2D) digital in-line holographic microscopy (DIHM) recording. Multiple intensity images are reconstructed at a range of depths through a transmissive or partially transmissive scene recorded by DIHM. A two step segmentation of each of these reconstructed intensity images facilitates the construction of a data set of surfaces in 3D. First an adaptive thresholding step and then a border following step are implemented. The surfaces of segmented features are rendered in 3D by applying the marching cubes algorithm to polygonize the data set. Experimental results for a real world DIHM capture of a transmissive glass sample are presented to demonstrate this segmentation and visualization process.

This study explores the effectiveness of wavelet analysis techniques on digital holograms of real-world 3D objects. Stationary and discrete wavelet transform techniques have been applied for noise reduction and compared. Noise is a common problem in image analysis and successful reduction of noise without degradation of content is difficult to achieve. These wavelet transform denoising techniques are contrasted with traditional noise reduction techniques; mean filtering, median filtering, Fourier filtering. The different approaches are compared in terms of speckle reduction, edge preservation and resolution preservation.

Digital holography is the process where an object's phase and amplitude information is retrieved from intensity images obtained using a digital camera (e.g. CCD or CMOS sensor). In-line digital holographic techniques offer full use of the recording device's sampling bandwidth, unlike off-axis holography where object information is not modulated onto carrier fringes. Reconstructed images are obscured by the linear superposition of the unwanted, out of focus, twin images. In addition to this, speckle noise degrades overall quality of the reconstructed images. The speckle effect is a phenomenon of laser sources used in digital holographic systems. Minimizing the effects due to speckle noise, removal of the twin image and using the full sampling bandwidth of the capture device aids overall reconstructed image quality. Such improvements applied to digital holography can benefit applications such as holographic microscopy where the reconstructed images are obscured with twin image information. Overcoming such problems allows greater flexibility in current image processing techniques, which can be applied to segmenting biological cells (e.g. MCF-7 and MDA-MB-231) to determine their overall cell density and viability. This could potentially be used to distinguish between apoptotic and necrotic cells in large scale mammalian cell processes, currently the system of choice, within the biopharmaceutical industry.

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