Compact handheld digital holographic microscopy system development

Development of a commercial prototype of reflection handheld digital holographic microscope system is presented in this paper. The concept is based on lensless magnification using diverging wave geometry and the miniaturized optical design which provides a compact packaged system. The optical geometry design provides the same curvature of object and reference waves and thus phase aberration is automatically compensated. The basic methodology of the system is developed and it further explored for 3D imaging, static deflection and vibration measurements applications. Based on the developed methodology an user-friendly software is developed suitable for industrial shop floor environment. The applications of the system are presented for 3D imaging, static deflection measurement and vibration analysis of MEMS samples. The developed system is well suitable for the testing of MEMS and Microsystems samples, with full-field and real-time features, for static and dynamic inspection and characterization and to monitor micro-fabrication process.Accepted versio

Nose tip detection on three‐dimensional faces using pose‐invariant differential surface features

Three‐dimensional (3D) facial data offer the potential to overcome the difficulties caused by the variation of head pose and illumination in 2D face recognition. In 3D face recognition, localisation of nose tip is essential to face normalisation, face registration and pose correction etc. Most of the existing methods of nose tip detection on 3D face deal mainly with frontal or near‐frontal poses or are rotation sensitive. Many of them are training‐based or model‐based. In this study, a novel method of nose tip detection is proposed. Using pose‐invariant differential surface features – high‐order and low‐order curvatures, it can detect nose tip on 3D faces under various poses automatically and accurately. Moreover, it does not require training and does not depend on any particular model. Experimental results on GavabDB verify the robustness and accuracy of the proposed method

Optical image hiding under framework of computational ghost imaging based on an expansion strategy

A novel optical image hiding scheme based on an expansion strategy is presented under the framework of computational ghost imaging. The image to be hidden is concealed into an expanded interim with the same size as the host image. This is implemented by rearranging the measured intensities of the original object after the process of ghost imaging. An initial Hadamard matrix is used to generate additional matrices by shifting it circularly along the column direction, so that enough 2D patterns are engendered to retrieve phase-only profiles for imaging. Next, the frequency coefficients of the host image are modified with that of the expanded interim by controlling a small weighting factor. After an inverse transform, the host image carrying the hidden information can be obtained with high imperceptibility. Security is assured by considering optical parameters, such as wavelength and axial distance, as secret keys due to their high sensitivity to tiny change. Importantly, differing from other computational ghost imaging based schemes, many phase-only profiles are used to collect the measured intensities to enhance the resistance against noise and occlusion attacks. The simulated experiments illustrate the feasibility and effectiveness of the proposed scheme.Published versio

An optical watermarking scheme with two-layer framework based on computational ghost imaging

A two-layer watermarking scheme based on computational ghost imaging and singular value decomposition is proposed. In the first layer, the original watermark is encoded into a significantly small number of measured intensities in the process of computational ghost imaging to constitute a new watermark. In the second layer, the significant blocks chosen from the host image based on spatial frequency are combined to the reference image, which is used to embed the new watermark by using the singular value decomposition. Differing from other watermarking schemes, the information of original watermark can be verified without clear visualization via calculating the nonlinear correlation map between the original one and the reconstructed one. Besides optical parameters such as wavelength and propagation distance, a series of phase-only masks are used as security keys, which can enlarge the key space and enhance the level of security. The results illustrate the feasibility and effectiveness about the proposed watermarking mechanism, which provides an effective alternative for the related work

Local Scour around Tandem Double Piers under an Ice Cover

Compared to the scour around a single pier, the local scour process around tandem double piers is much more complicated. Based on laboratory experiments in a flume, we conducted the scour process around tandem double piers under an ice-covered flow condition. The results showed that when the pier spacing ratio L/D = 2 (where L = the pier spacing distance, and D = the pier diameter), the rear pier (the downstream one) will intensify the horseshoe vortex process behind the front pier, and the scour depth around the front pier will increase by about 10%. As the pier spacing ratio L/D increases, the scour depth around the front pier will gradually decrease. When the pier spacing ratio L/D = 5, sediment scoured around the front pier begins to deposit between these two piers. To initiate a deposition dune between piers, the pier spacing distance under an ice-covered condition is about 20% more than that under an open flow condition. The results also showed that the existence of the rear pier will lead to an increase in the length of the scour hole but a decrease in the depth of the scour hole around the front pier. The local scour around the front pier interacts with the local scour of the rear pier. The maximum scour depth of the scour hole around the rear pier increases first, then decreases and increases again afterward. When the pier spacing ratio L/D = 9, the scour depth around the rear pier is the least. With an increase in the pier spacing ratio, the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases. When the pier spacing ratio L/D is more than 17, the scour around the front pier has hardly any influence on that around the rear pier. The scour depth around the rear pier is about 90% of that around the front pier

Information encryption based on the customized data container under the framework of computational ghost imaging

In this paper, a novel information encryption scheme has been proposed based on the customized data container, where the primary information can be recovered completely from the ciphertext encrypted with computational ghost imaging. From two aspects, the proposed scheme solves the serious issues caused by the inherent linearity and mechanism of computational ghost imaging. First, the primary information to be encrypted is transformed into the bits of information, which is used to control the formation of the customized data container. Then, the exclusive-OR (XOR) operation is performed on it with a randomly generated data container, and the XOR encoding result is scrambled based on the random sequence engendered with the logistic map so that the linearity of the cryptosystem is destroyed. Second, instead of using random phase-only masks, a number of phase masks retrieved from 2D patterns derived from the rows of the designed Hadamard matrix are used to record the measured intensities. The redundancy between these phase masks is low, which can reduce the number of the required phase-only masks greatly. Meanwhile, the conditions of the logistic map are considered as the secret keys, which can enhance the security level greatly due to their high sensitivity to tiny variation. The validity and feasibility of the proposed method have been demonstrated with a set of numerical simulations.Published versio

Local Scour around Tandem Double Piers under an Ice Cover

Compared to the scour around a single pier, the local scour process around tandem double piers is much more complicated. Based on laboratory experiments in a flume, we conducted the scour process around tandem double piers under an ice-covered flow condition. The results showed that when the pier spacing ratio L/D = 2 (where L = the pier spacing distance, and D = the pier diameter), the rear pier (the downstream one) will intensify the horseshoe vortex process behind the front pier, and the scour depth around the front pier will increase by about 10%. As the pier spacing ratio L/D increases, the scour depth around the front pier will gradually decrease. When the pier spacing ratio L/D = 5, sediment scoured around the front pier begins to deposit between these two piers. To initiate a deposition dune between piers, the pier spacing distance under an ice-covered condition is about 20% more than that under an open flow condition. The results also showed that the existence of the rear pier will lead to an increase in the length of the scour hole but a decrease in the depth of the scour hole around the front pier. The local scour around the front pier interacts with the local scour of the rear pier. The maximum scour depth of the scour hole around the rear pier increases first, then decreases and increases again afterward. When the pier spacing ratio L/D = 9, the scour depth around the rear pier is the least. With an increase in the pier spacing ratio, the influence of the local scour around the front pier on the local scour around the rear pier gradually decreases. When the pier spacing ratio L/D is more than 17, the scour around the front pier has hardly any influence on that around the rear pier. The scour depth around the rear pier is about 90% of that around the front pier

Optical image encryption via high-quality computational ghost imaging using iterative phase retrieval

A novel computational ghost imaging scheme based on specially designed phase-only masks, which can be efficiently applied to encrypt an original image into a series of measured intensities, is proposed in this paper. First, a Hadamard matrix with a certain order is generated, where the number of elements in each row is equal to the size of the original image to be encrypted. Each row of the matrix is rearranged into the corresponding 2D pattern. Then, each pattern is encoded into the phase-only masks by making use of an iterative phase retrieval algorithm. These specially designed masks can be wholly or partially used in the process of computational ghost imaging to reconstruct the original information with high quality. When a significantly small number of phase-only masks are used to record the measured intensities in a single-pixel bucket detector, the information can be authenticated without clear visualization by calculating the nonlinear correlation map between the original image and its reconstruction. The results illustrate the feasibility and effectiveness of the proposed computational ghost imaging mechanism, which will provide an effective alternative for enriching the related research on the computational ghost imaging technique.Published versio

Fringe pattern denoising based on deep learning

In this paper, deep learning as a novel algorithm is proposed to reduce the noise of the fringe patterns. Usually, the training samples are acquired through experimental acquisition, but these data can be easily obtained by simulations in the proposed algorithm. Thus, the time cost used for the whole training process is greatly reduced. The performance of the proposed algorithm has been demonstrated through the analysis on the simulated and real fringe patterns. It is obvious that the proposed algorithm has a faster calculation speed compared with existing denoising algorithm, and recovers the fringe patterns with high quality. Most importantly, the proposed algorithm may provide a solution to other denoising problems in the field of optics, such as hologram and speckle denoising