Conventional double random phase encoding (DRPE) encrypts plaintext to white noise-like ciphertext which may attract attention of eavesdroppers, and recent research reported that DRPE is vulnerable to various attacks. Here we propose a security enhanced optical encryption system that can hide the existence of secret information by watermarking. The plaintext is encrypted using iterative fractional Fourier transform with random phase key, and ciphertext is randomly permuted with permutation key before watermarking. Cryptanalysis shows that linearity of the security system has been broken and the permutation key prevent the attacker from accessing the ciphertext in various attacks. A series of simulations have shown the effectiveness of this system and the security strength is enhanced for invisibility, nonlinearity and resistance against attacks.

Security enhanced optical encryption system by random phase key and permutation key

Automatic and rapid whole-body 3D shape measurement has attracted extensive attention in recent years and been widely used in many fields. Rapid 3D reconstruction, automatic 3D registration, and dedicated system layout are critical factors to enable an excellent 3D measurement system. In this paper, we present an automatic and rapid whole- body 3D measurement system that is based on multinode 3D sensors using speckle projection. A rapid algorithm for searching homologous point pairs is suggested, which takes advantage of the optimized projective rectification and simplified subpixel matching techniques, leading to an improved time efficiency of 3D reconstruction. Meanwhile, a low-cost automatic system with a flexible setup and an improved calibration strategy are proposed, where system parameters of each node sensor can be simultaneously estimated with the assistance of a cubic and a planar target. Furthermore, an automatic range data registration strategy by employing two aided cameras is investigated. Experiment results show that the presented approach can realize automatic whole-body 3D shape measurement with high efficiency and accuracy.

Automatic and rapid whole-body 3D shape measurement based on multinode 3D sensing and speckle projection

The present invention is applicable to the technical field of three-dimensional imaging. Provided are a three-dimensional imaging method and system for a human body and a method for simultaneously calibrating multiple control base stations. Under the condition that effective fields of view of all distributed sensors do not spatially overlap, the structural parameters and the global matching parameters of all the sensors are calibrated. By using a corresponding point searching method that combines phase shift with random structured light, the image collection time for obtaining single-viewpoint depth data is shortened. By using the thought of time multiplexing, the whole data collection time of the system is compressed, and the design of distributed computing enhances the computing capability of the whole system and increases the speed for data acquisition. According to the calibrated global matching parameters of all the different sensors, the depth data of the different sensors is matched automatically. The system can be debugged and expanded conveniently, the automation degree is high, and the three-dimensional scanning process is easy to implement.

Three-dimensional imaging method and system for human body

Field measurement of large aviation components is important in many fields of study. In this paper, a global data registration method based on the dynamic coded points is proposed. The system used in this method contains the local and global control binocular measurement systems. The local binocular measurement system measures the data of each subdomain as the local measurement data by scanning. The dynamic coded points, which are encoded based on time parameter as their encoded values, are projected to the measured object’s surface using a projector. Two sets of systems acquire the dynamic coded points to calculate their encoded values and match them automatically. These systems calculate the transformation relations between the local coordinate system and the global control coordinate system, so the local measurement data coordinates are integrated into the global control coordinate system through the transformation relations, achieving the global data registration. Experimental results in the laboratory show that the process of matching of dynamic coded points is accurate and has high robustness, and the global registration method based on the coded points proposed by this paper can eliminate the accumulated error, reaching the precision of 0.0150%. Field experimental results show that the registration method proposed in this paper satisfies the measurement requirements of large-scale aviation components.

Global Data Registration Technology Based on Dynamic Coded Points

We propose a registration algorithm based on neighborhood similarity for 3D point clouds collected by optical measurement and without prior information. The algorithm first applies the improved minimum spanning tree (Prim algorithm) to classify the point cloud in order to obtain the topology information of the data. Specifically, vectors among root nodes and child nodes are processed, and the points on nodes are classified into different levels according to their scanning angle to simplify data and preserve the most representative points. Then, through the perspective conversion between 2D and 3D and according to the corresponding point set obtained by previous classification, the fast normalized cross-correlation (a 2D matching criterion) is applied to determine the relationship between initial characteristic points. Finally, distance constraints remove the errors between point pairs and allow calculating the registration parameters. Experimental results show that the algorithm has high registration accuracy and is suitable for point cloud data obtained by laser and structured light acquisition.

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彭翔 Peng Xiang

Papers

A Method for Global Registration of Range Data Combined with Markers

3D Auto-Inspection for Large Thin-Wall Object

Phase-Aided Three-Dimensional Imaging and Metrology

Three-Dimensional Imaging Based on Combination Fringe and Pseudorandom Pattern Projection

Known-Plaintext Attack on Optical Cryptosystem Based on Projection-Onto-Constraint-Sets Algorithm and a 4f Correlator