The linear relationship between the sample complex object wave and its approximated complex Fresnel field obtained using single shot parallel phase-shifting digital holograms (PPSDH) is used in compressive sensing framework and an accurate phase reconstruction is demonstrated. It is shown that the accuracy of phase reconstruction of this method is better than that of compressive sensing adapted single exposure inline holography (SEOL) method. It is derived that the measurement model of PPSDH method retains both the real and imaginary parts of the Fresnel field but with an approximation noise and the measurement model of SEOL retains only the real part exactly equal to the real part of the complex Fresnel field and its imaginary part is completely not available. Numerical simulation is performed for CS adapted PPSDH and CS adapted SEOL and it is demonstrated that the phase reconstruction is accurate for CS adapted PPSDH and can be used for single shot digital holographic reconstruction.
Digital holography can process whole object information in a generic manner. We discuss a data security application in the context of digital holography and generalize the full intensity or full phase encryption to complex information encryption. A double random phase encoding (DRPE) of the complex information in free-space propagation is performed to secure holographic data. Non-phase-shifting two-intensity measurements have been used to obtain a dc- and twin-image-free decryption of a complex object field without phase shifting errors. This method can also be used to secure digital data in a virtual optics mode using holographic principles, thus preserving the optical degrees of encoding freedom in the digital domain. We highlight the issues of whole information security using digital holographic means by carrying out simulation studies to show the proof of the concept.
The complex Fresnel field that contains three-dimensional (3-D) information about an object can be retrieved from an optically generated and electronically detected single off-axis Fresnel hologram of a 3-D object. The retrieved complex Fresnel field gives the appearance of a noise-like distribution. This is primarily due to the scattering nature of the object and the resulting speckle noise, which is a salient trait of the reconstruction process of a hologram. We describe a possible method for securing holographic information by digital encoding of the Fresnel field. A single random-phase Fourier plane encoding is carried out with an assumption that the noisy nature of the complex field may be equivalent to the primary random mask-bonded field, as in the case of conventional double random-phase Fourier plane encoding. The analogy between the decryption process and the numerical reconstruction of the hologram leads to a single-step reconstruction of the complex object field from the encrypted Fresnel field, thus saving computational power. The use of a single off-axis hologram is helpful in zero-order and twin-image free reconstruction. The algorithm is explained with experimental results to support the proof of the concept.
We propose and demonstrate a technique based on digital holography for three-dimensional (3D) object recognition. In our method, the complex wavefront of the 3D object to be recognized is recorded as a Fresnel hologram using a CCD camera. A two step numerical reconstruction process, retrieval of complex wavefront recorded on the CCD plane and propagation of wavefront to the object plane, gives a complex valued two-dimensional (2D) image, which contains information regarding the amplitude and phase of the object wavefront in a 2D plane. The encoding of 3D object information as 2D digital image enables the use of various image-processing techniques for the post processing of the data. We use a Mexican hat wavelet matched filter (WMF) to discriminate between two different objects. WMF performs wavelet transform (WT) to enhance significant features of the images and the correlation of the so obtained WT coefficients in a single step. Digital wavelet matched filtering improves the discrimination capability and results in sharper correlation peaks as compared to classical matched filtering. As compared to many of the 3D recognition techniques based on the processing of 2D perspectives, our system has lesser complexity at the implementation and operational levels.