Carla Simonetti

Superposed strokes analysis by conoscopic holography as an aid for a handwriting expert

For legal purposes there is a requirement for the validation of signatures and handwritten documents. A helpful method in this respect is the so-called superposed strokes analysis, based on the observation of some characteristics in the writing, such as some letters and their dynamics. This paper introduces a promising new technique for superposed strokes analysis based on conoscopic holography. Through a non-contact 3D measure a 3D profile is created of the superposed strokes that allows the writing dynamics to be determined, such as, for example, if a stroke was drawn clockwise or counterclockwise. We propose a 3D analysis by an opto-electronic system, in order to improve the graphology analysis for off-line signature verification.

Fragile digital watermarking by synthetic holograms

In this article is presented an application of synthetic hologram as fragile watermarking. The proposed technique is a frequency domain watermarking, based on computer generated hologram. Our technique, named Fragile Synthetic Holographic Watermarking (F-SHW), is suitable for ID Cart image authentication. In this paper, the F-SHW is applied to Color Images as well as to Gray Scale ones. The proposed schema is based on the knowledge of original mark from the Authentication Entity, for applying Image Correlation between this and the extracted one. Due to the application the mark is encrypted using a private key (symmetric schema).

Banknote security using a biometric-like technique: a hylemetric approach

Banknote security is an issue that has led in the last decades to insert, inside the banknote itself, a very high number of controlling methods with the aim of verifying possible tampering attempts. In order to distinguish the false banknotes, sophisticated means (i.e. watermark, feel of the paper, raised print, metallic threads, quality of the printing, holograms, ultraviolet features, micro-lettering, etc) are often used. The purpose of this paper is to show a new approach and related method to protect banknotes and to verify their originality, based on the idea of hylemetry (methodology conceptually similar to biometry) applied to banknotes. Specifically, the hylemetric feature used in this paper is the random distribution pattern of the metallic security fibers set into the paper pulp. The outcome of the proposed solution is to identify an original banknote using a binary sequence derived from the banknote itself.

Designing of diffractive optical element for the generation of uniform arrays of beams

A diffractive optical elements (DOEs), permits to change a wave front by means of diffraction. The proposed method has the advantage of not requiring complex computation and programming. In particular the designed process is made without computer iterative methods. The DOE, implemented by the proposed algorithm, consists of cells of equal size. Each cell is subdivided into appropriate parts. The average phase of these parts is related to the phase of the complex amplitude. The DOE phase can be easily computed according to simple formulas. In the paper designing phases and numerical simulation are reported. In particular the effect of the DOE structure quantization is considered.

Designing of binary diffractive optical elements for beams performing

At present, the progress in optics is associated with wide use of diffractive optical elements (DOEs) generated by means of computer resources. DOEs are optical elements, which modify the wave field by diffraction. They allow the conversion of the incident wave into a transmitted wave which, after free-space propagation, has a desired distribution of its amplitude. If the wave fields and their propagation are represented as digital data, computer generated DOEs carrying out complex optical tasks can be calculated. Their potentialities are dependent by fabrication technique used, which must ensure the maximum of diffraction efficiency and of the signal-to-noise ratio in the generated optical signal. It is well known that, generally speaking, they are not quite tractable in analytical terms. For this reason, specialized numerical algorithms have been devised for designing such elements. In this paper we present a DOE design method, which not use computer iterative methods. Starting from the knowledge of the expression of the propagated field on image plane, we use simple formulas to obtain the entire information necessary to characterize the desired DOE. The DOE designed with the proposed method can equate an arbitrary complex amplitude transmission T(r) and has higher imaging accuracy than other DOEs. Even if it is possible studying any level combination, the aim of this paper is to summarize the results of simulation experiments which were carried out only to test the binary level diffractive optical elements (DOEs). In particular, starting from an incident Gaussian Beam, it is proposed a binary phase DOE which allows obtaining a flat emerging field, in a well-defined region after the DOE.

IR Fringe Projection for 3D Face Recognition

Facial recognitions of people can be used for the identification of individuals, or can serve as verification e.g. for access controls. The process requires that the facial data is captured and then compared with stored reference data. Different from traditional methods which use 2D images to recognize human faces, this article shows a known shape extraction methodology applied to the extraction of 3D human faces conjugated with a non conventional optical system able to work in “invisible” way. The proposed method is experimentally simple, and it has a low‐cost set‐up.

Image authentication by means of fragile CGH watermarking

In this paper we propose a fragile marking system based on Computer Generated Hologram coding techniques, which is able to detect malicious tampering while tolerating some incidental distortions. A fragile watermark is a mark that is readily altered or destroyed when the host image is modified through a linear or nonlinear transformation. A fragile watermark monitors the integrity of the content of the image but not its numerical representation. Therefore the watermark is designed so that the integrity is proven if the content of the image has not been tampered. Since digital images can be altered or manipulated with ease, the ability to detect changes to digital images is very important for many applications such as news reporting, medical archiving, or legal usages. The proposed technique could be applied to Color Images as well as to Gray Scale ones. Using Computer Generated Hologram watermarking, the embedded mark could be easily recovered by means of a Fourier Transform. Due to this fact host image can be tampered and watermarked with the same holographic pattern. To avoid this possibility we have introduced an encryption method using a asymmetric Cryptography. The proposed schema is based on the knowledge of original mark from the Authentication

Measurement of mass diffusion coefficients by digital moiré

In order to measure small diffusion coefficients of miscible fluids, in this paper we propose an improved version of digital projection moiré. The system uses a simple and flexible fringe generator realized by means of a video projector with a modification of projection optic. The fringe patterns are projected on the bottom of a ground glass plate. The phase object (diffusion cell) is placed in front of the ground glass (in other words, in front of the fringe pattern), which is imaged by a digital video camera. Grating patterns, during the evolution of diffusion phenomena, are captured by a CCD camera and stored in a computer at different times. With the aid of signal demodulating techniques, the images are processed to obtain the diffusion coefficients. The theoretical aspects of the method are presented and the relationship between the fringe shift and the diffusion coefficient is derived. Furthermore, we report some experiments conducted for demonstrating the usefulness of the system.