Three-dimensional attenuation map reconstruction using geometrical models and free-form deformations

We address the issue of using deformable models to reconstruct an unknown attenuation map of the torso from a set of transmission scans. We assume the three-dimensional (3-D) distribution of attenuation coefficients to be piecewise uniform. We represent the unknown distribution by a set of closed surfaces defining regions having the same attenuating properties. The methods of reconstruction published so far tend to directly deform the surfaces, the parameters being the surface elements. Rather than deforming the surfaces, we explore the possibility of deforming the space in which the geometrical primitives are contained. We focus on the use of free-form deformations (FFD's) to describe the continuous transformation of space used to match a set of transmission measurements. We illustrate this approach by reconstructing realistically simulated transmission scans of the torso with various noise levels and compare the results to standard reconstruction methods.     

Registration of image sets using silhouette consistency

A new algorithm is described for estimating the change in orientation and position of an object in two sets of images. The images within each set are calibrated but the exact geometrical relationship between the two sets of views is unknown. Variations in the two-dimensional silhouette of a fixed and rigid three-dimensional object, as the viewpoint is changed, are analysed to estimate the relative position and orientation of the object in the two different image sets. The main advantage of this method is that no explicit point, or line, correspondences need be identified; the only requirement is for reliable segmentation of the object from the background. It is shown that an incorrect estimate of the relative object pose gives rise to silhouettes which are inconsistent in that they violate a certain geometrical constraint. The extent to which the images are consistent is quantified using a certain consistency metric. Standard minimisation techniques are then used to obtain accurate estimates for both rotational and translational parameters. Results are presented for the registration of synthetic images, with added noise, and for the registration of real image data. For small test objects the relative orientation estimates are consistent to within ±6 degrees and the relative translation estimates to ±1.8 mm     

Sufficient conditions for stability of multidimensional discrete systems

A number of simple conditions equal to the number of monomials in the denominator polynomial of the transfer function of a discrete multidimensional system, are each shown to be sufficient for the multidimensional part of the stability test for such causal systems.     

Sufficient conditions for instability of multidimensional discrete systems

Some new simple sufficient conditions were presented for the multidimensional part of the stability test of discrete multidimensional causal systems. However, it is shown in this letter that these conditions also violate the one-dimensional part of the stability test. Hence, they are sufficient conditions for instability of the system.     

Laser-beam attenuation measurement using acousto-optic modulator

A laser-beam attenuation-measurement method using the first-order diffraction from an acousto-optic modulator is newly developed. The attenuation is determined from the voltage of the 30 MHz driving signal of the modulator. A value of attenuation of more than 50 dB can be measured at 633 nm.     

Adaptive image denoising using scale and space consistency

This paper proposes a new method for image denoising with edge preservation, based on image multiresolution decomposition by a redundant wavelet transform. In our approach, edges are implicitly located and preserved in the wavelet domain, whilst image noise is filtered out. At each resolution level, the image edges are estimated by gradient magnitudes (obtained from the wavelet coefficients), which are modeled probabilistically, and a shrinkage function is assembled based on the model obtained. Joint use of space and scale consistency is applied for better preservation of edges. The shrinkage functions are combined to preserve edges that appear simultaneously at several resolutions, and geometric constraints are applied to preserve edges that are not isolated. The proposed technique produces a filtered version of the original image, where homogeneous regions appear separated by well-defined edges. Possible applications include image presegmentation, and image denoising.     

Analysis of SAW attenuation measurement using acoustic microscopy

Effect of acoustic loss in solids on depths of dips in V(z) curves obtained by reflection acoustic microscopy was calculated. The results were in good agreement with the observed V(z) curves of steels. The applicability and limitations of measuring attenuation of surface acoustic waves from V(z) curves are discussed.     

Stabilising discrete polynomials using spectral factorisation

A simple technique for stabilising discrete polynomials is presented. The technique does not require the roots of the polynomial to be computed but instead uses the familiar spectral factorisation method. If the polynomial has unstable roots, they are automatically reflected back inside the unit circle. Stable polynomials remain unaffected.<>     

Radiation models using discrete radiator ensembles

In recent literature radiation emitted or reflected from a body or surface has been modeled as equivalent radiation from a collection of individual discrete radiators. This model has application to the analysis of forward and backscatter from rough surfaces, clutter and chaff models for radar, and cavity emissions at optical frequencies. In this paper we investigate radiation using a generalization of the above radiator ensemble. We allow some degree of coupling to exist between individual radiators, and we assume each radiator emits random energy bursts as a Poisson process. Analysis is confined to power spectral densities and first-order statistics of the resulting scalar radiation fieid. The results indicate that the pulsed radiator model can account for many properties of radiation. A by-product of the analysis is a filter model for dispersive channels, applicable to radar design problems. Theoretical results are compared with previously reported experimental results wherever possible. Some consideration is given to a relativistic interpretation of the radiator ensemble.     

Stereo matching using colour consistency and hierarchical stochastic diffusion

A stereo matching algorithm is proposed using colour consistency and hierarchical stochastic diffusion. The colour consistency is introduced to the prior Markov random field (MRF) model to consider both the smoothness and the discontinuity of the disparity field. The energy function derived from the MRF model is minimised in the hierarchical stochastic diffusion, which first propagates the probability distribution of the reliable disparity field into the neighbourhood. Experimental results show good disparity maps compared with other propagation based methods.     

Non-uniformly sampled mosaic construction using resolution map

A new type of mosaic is suggested: a non-uniformly sampled mosaic to minimise the loss of image data occurring by coordinate transformations. A resolution map is introduced in order to measure the spatially variant number of samples. By using an appropriate method of blending and interpolation, we construct a non-uniformly sampled mosaic. Simulation results show an increase in the image quality of the frames reconstructed from the non-uniformly sampled mosaic.     

Deblocking filtering method using a perceptual map

A new method of deblocking is proposed. It aims to reduce the blocking artifacts in the compressed image by analyzing their visibility. A perceptual map is obtained using some Human Visual System (HVS) characteristics. This perceptual map is used as input to a recursive filter to reduce the blocking effect. The obtained results have been compared with a very recent efficient method.     

Dynamic ID authentication scheme using chaotic map

Dynamic ID authentication protects user’s identity from being revealed by any outsider during remote login processes. In independent multi-server environments, a user might have to login different servers for accessing various resources. Password based mechanisms are commonly utilized approaches. Without using complicated modular exponentiation computation, in this paper, the author will propose a Chebyshev chaotic map based dynamic ID authentication scheme for independent multi-server environments in which no trusted relationship exists among servers. The proposed scheme does not rely on the existence of registration center and each user only has to keep one single password for accessing resources of different servers. Compared with related protocols, the proposed one has more superior functionalities and lower computational costs. Furthermore, the session key security of our scheme is formally proved in the random oracle model.     

Fingerprint recognition using model-based density map.

Utilizing more information other than minutiae is much helpful for large-scale fingerprint recognition applications. In this paper, we proposed a polynomial model to approximate the density map of fingerprints and used the model's parameters as a novel kind of feature for fingerprint representation. Thus, the density information can be utilized into the matching stage with a low additional storage cost. A decision-level fusion scheme is further used to combine the density map matching with conventional minutiae-based matching and experimental results showed a much better performance than using single minutiae-based matching.     

基于离散分数阶角变换与关联混沌映射的双图像加密算法

为了实现对两个明文进行同步安全加密,提出了联合离散多参数分数阶角变换与低维映射的双图像加密算法.基于离散余弦变换(DCT)与Zigzag扫描建立了复合系数矩阵模型,通过反离散余弦变换(IDCT)将两个明文融合成一幅图像;通过耦合Logistic映射,利用明文像素均值与外部密钥计算其初始条件值,并迭代该耦合映射,输出2个随机序列;分别对这2个随机序列进行排序,设计位置数组扰乱机制对复合明文进行置乱;将置乱密文分解为2个新分量,利用Logistic映射与初始明文分别生成混沌随机与调制相位掩码,将2个新分量融合成临时密文;基于离散分数角变换构建了新的2D多参数分数阶角变换,设计加密模型并完成图像加密.结果表明,与已有双图像加密机制相比所提算法的保密性更佳,有更好的抗明文攻击特性.     

Automated vehicle guidance using discrete reference markers

Techniques for providing steering control for an automated vehicle using discrete reference markers fixed to the road surface are investigated analytically. Either optical or magnetic approaches can be used for the sensor, which generates a measurement of the lateral offset of the vehicle path at each marker to form the basic data for steering control. Possible mechanizations of sensor and controller are outlined. Techniques for handling certain anomalous conditions, such as a missing marker, or loss of acquisition, and special maneuvers, such as u-turns and switching, are briefly discussed. A general analysis of the vehicle dynamics and the discrete control system is presented using the state variable formulation. Noise in both the sensor measurement and in the steering servo are accounted for. An optimal controller is simulated on a general purpose computer, and the resulting plots of vehicle path are presented. Parameters representing a small multipassenger tram were selected, and the simulation runs show response to an erroneous sensor measurement and acquisition following large initial path errors.     

Modified ID-based cryptosystem using discrete logarithm problem

A modified ID-based cryptosystem using the logarithm problem is presented. It eliminates the constraints of the algorithm proposed by Tsujii et al. (1987) which limits the entity number to be less than the bit number. In the authors' system, however, the entities can be extended to arbitrary number without reducing the system security. It is more suitable for practical implementation     

Image coding using dual-tree discrete wavelet transform

In this paper, we explore the application of 2-D dual-tree discrete wavelet transform (DDWT), which is a directional and redundant transform, for image coding. Three methods for sparsifying DDWT coefficients, i.e., matching pursuit, basis pursuit, and noise shaping, are compared. We found that noise shaping achieves the best nonlinear approximation efficiency with the lowest computational complexity. The interscale, intersubband, and intrasubband dependency among the DDWT coefficients are analyzed. Three subband coding methods, i.e., SPIHT, EBCOT, and TCE, are evaluated for coding DDWT coefficients. Experimental results show that TCE has the best performance. In spite of the redundancy of the transform, our DDWT _ TCE scheme outperforms JPEG2000 up to 0.70 dB at low bit rates and is comparable to JPEG2000 at high bit rates. The DDWT _TCE scheme also outperforms two other image coders that are based on directional filter banks. To further improve coding efficiency, we extend the DDWT to an anisotropic dual-tree discrete wavelet packets (ADDWP), which incorporates adaptive and anisotropic decomposition into DDWT. The ADDWP subbands are coded with TCE coder. Experimental results show that ADDWP _ TCE provides up to 1.47 dB improvement over the DDWT _TCE scheme, outperforming JPEG2000 up to 2.00 dB. Reconstructed images of our coding schemes are visually more appealing compared with DWT-based coding schemes thanks to the directionality of wavelets.     

Comments on "Sufficient conditions for stability of multidimensional discrete systems"

In this letter, we indicate that the theorem in the above-titled letter which gives (m + 7) sufficient conditions for the multidimensional part of the stability test, is derived based on an incorrect intermediate step. Then the correct proof of the theorem is given. Later it is brought to light that the m additional conditions of this theorem (the other condition is already presented in [4], [5]) violates the one-dimensional part of the stability test and that each of these m additional conditions is sufficient to test the unstability of the multidimensional discrete causal system.