Yoshinori Akao

Development of goniophotometric imaging system for recording reflectance spectra of 3D objects

In recent years, it is required to develop a system for 3D capture of archives in museums and galleries. In visualizing of 3D object, it is important to reproduce both color and glossiness accurately. Our final goal is to construct digital archival systems in museum and internet or virtual museum via World Wide Web. To achieve our goal, we have developed gonio-photometric imaging system by using high accurate multi-spectral camera and 3D digitizer. In this paper, gonio-photometric imaging method is introduced for recording 3D object. 5-bands images of the object are taken under 7 different illuminants angles. The 5-band image sequences are then analyzed on the basis of both dichromatic reflection model and Phong model to extract gonio-photometric property of the object. The images of the 3D object under illuminants with arbitrary spectral radiant distribution, illuminating angles, and visual points are rendered by using OpenGL with the 3D shape and gonio-photometric property.

Discrimination of inkjet-printed counterfeits by spur marks and feature extraction by spatial frequency analysis

In this paper, discrimination method for inkjet printed counterfeits and feature extraction method of spur marks are proposed. Spur marks are tool marks formed on a printout by paper conveyance gears of inkjet printers, and inkjet printers are classified into some groups by type of spurs and their arrangement. Spur marks were visualized and clearly distinguished from background by infrared oblique lighting and gradient image processing. As the characteristic values of spur marks, the pitch and mutual distance were introduced. By radon transform of spur mark images, direction of spur mark lines and the mutual distance were estimated. Spatial frequency components of spur marks were analyzed by two-dimensional fast Fourier transform to estimate the pitch. The pitch and mutual distance were extracted almost automatically. Proposed methods were applied to samples printed by a color inkjet printer. Measurement results were compared with those obtained by conventional method using x-y stage, and the accuracy was proved. By detecting existence of spur marks on printouts, discrimination of inkjet printed material was achieved. This technique will be applicable to model and manufacturer identification of printers, and significant not only for counterfeit detection but also in the field of forensic document examination.

Examination of spur marks found on inkjet-printed documents.

In this paper, we propose the examination of spur mark evidence on inkjet-printed documents. Spur marks are tool marks created by the spur gears in the paper conveyance system of many inkjet printers. The relationship between printouts and printers were investigated by comparing the spur marks found on printed documents with reference spur marks sampled from known printers. The comparison was based on two characteristics of spur marks: pitch and mutual distance. These characteristics extracted the geometric features of spur marks and provided information on the type of spur gears and their location in the paper conveyance system. The spur marks on a printout matched the reference spur marks within three percent of the measured values. Spur marks were considered to be effective class characteristics to identify certain brands of inkjet printers since spur gears are used in many types of these machines.

Feasibility Study of Visualizing Diversity of Japanese Hiragana Handwritings by Multidimensional Scaling of Earth Mover's Distance toward Assisting Forensic Experts in Writer Verification

In this paper, we demonstrated a mapping procedure to visualize the diversity of overall handwriting shapes of five Japanese Hiragana characters for the purpose of assisting forensic examiners in the process of writer verification. Multidimensional scaling was applied to Earth Movers Distance (EMD) data calculated between 60 different writers in order to visualize each writers feature in population. EMD flow was calculated between k-means cluster centroids, which are representative points of kernel density distribution of handwritten stroke of each writer within six trials. Experimental results showed that the relative relation of overall handwritten shapes of each writer was successfully visualized as the locus in multidimensional space. The state of distribution such as the density in multidimensional space is considered to provide effective information to forensic examiners in evaluating the rarity of handwritten features observed in questioned document.

Efficient gonio-imaging of optically variable devices by compound-eye image-capturing system.

In this paper, we propose a method for efficient gonio-imaging of optically variable devices (OVDs), which are applied as a counterfeit deterrence for valuable documents. A compound-eye image-capturing system composed by a microlens array, a signal separator, and an image sensor was used to capture directionally distributed light from OVDs after being collimated by a convex lens. Multiple images corresponding to different observation angles were obtained in the individual eyes of the system, simultaneously and independently. A demonstration involving a holographic grating provided 100 gonio images that exhibited sensitive color changes of the diffracted light according to the observation angle.

Wide-field time-resolved luminescence imaging and spectroscopy to decipher obliterated documents in forensic science

Abstract. We applied a wide-field time-resolved luminescence (TRL) method with a pulsed laser and a gated intensified charge coupled device (ICCD) for deciphering obliterated documents for use in forensic science. The TRL method can nondestructively measure the dynamics of luminescence, including fluorescence and phosphorescence lifetimes, which prove to be useful parameters for image detection. First, we measured the TRL spectra of four brands of black porous-tip pen inks on paper to estimate their luminescence lifetimes. Next, we acquired the TRL images of 12 obliterated documents at various delay times and gate times of the ICCD. The obliterated contents were revealed in the TRL images because of the difference in the luminescence lifetimes of the inks. This method requires no pretreatment, is nondestructive, and has the advantage of wide-field imaging, which makes it is easy to control the gate timing. This demonstration proves that TRL imaging and spectroscopy are powerful tools for forensic document examination.

Improvement of inkjet printer spur gear teeth number estimation by fixing the order in maximum entropy spectral analysis

In this paper, we estimated the number of inkjet printer spur gear teeth from shorter pitch data strings than previous study by fixing the order in maximum entropy method (MEM). The purpose of this study is to improve the efficiency of inkjet printer model identification based on spur mark comparison method (SCM) in the field of forensic document analysis. Experiments were performed using two spur gears in different color inkjet printer models. The eight kinds of pitch data length whose length ranges from three to 10 rotations of spur gear was provided for analysis. The experimental results showed that proper teeth number was estimated from shorter pitch data string compared with the strategies based on minimum AIC estimate in our previous study. The estimation was successful from the short data length nearly equal to the condition of nyquist frequency. The proposed method was considered to improve the accuracy of printer model identification based on SCM.

Estimation of Inkjet Printer Spur Gear Teeth Number from Pitch Data String of Limited Length

In this paper, we investigate the feasibility of estimating the number of inkjet printer spur gear teeth from pitch data strings of limited length by maximum entropy spectral analysis. The purpose of this study is to improve the efficiency of inkjet printer model identification based on spur mark comparison in the field of forensic document analysis. Experiments were performed using two spur gears in different color inkjet printer models, and eight different lengths of pitch data strings--ranging from three to 10 times the number of spur gear teeth. The result for a data string longer than five times the number of teeth showed a proper estimation within a deviation of one tooth. However, the estimation failed for shorter data strings because the order in maximum entropy analysis was determined inappropriately. The presented results provide information on the number of spur gear teeth from shorter data strings than in a previous study.

Differentiation of black writing ink on paper using luminescence lifetime by time-resolved luminescence spectroscopy

The time-resolved luminescence spectra and the lifetimes of eighteen black writing inks were measured to differentiate pen ink on altered documents. The spectra and lifetimes depended on the samples. About half of the samples only exhibited short-lived luminescence components on the nanosecond time scale. On the other hand, the other samples exhibited short- and long-lived components on the microsecond time scale. The samples could be classified into fifteen groups based on the luminescence spectra and dynamics. Therefore, luminescence lifetime can be used for the differentiation of writing inks, and luminescence lifetime imaging can be applied for the examination of altered documents.