Yoshimichi Ito

Frequency response of sampled-data systems

This paper develops a frequency-domain theory that provides a method to analyze and design sampled-data control systems, including their intersample behaviors. The key idea is to consider the signal space Xϑ

Exact Stability Analysis of 2-D Systems Using LMIs

= {x(t) ¦x(t) = ∑n∞ = −x xn exp (jϑt + jnωst), ∑n = −x ∥xn∥2 < ∞}, where ωs is the sampling angular frequency. It is shown that a stable sampled-data system equipped with a strictly-proper pre-filter before the sampler maps Xϑ into Xϑ (≡l2) in the steady state. That mapping is denoted by Q(jϑ) and is referred to as an ‘FR operator’. It is proved that the norm of the sampled-data system as an operator from L2 to L2 is given by maxϑ ∥Q(jϑ)∥/2//2, where 12ωs < ϑ ≤ 12ωs. A set of equations relating outputs of a closed-loop system to its inputs in the frequency domain is derived, and their solution is given in an explicit form. Based on that solution, the sensitivity FR operator Y(jϑ) and the complementary sensitivity FR operator T(jϑ) are defined for feedback control systems, and it is shown that Y(jϑ) gives the improvement of the sensitivity of the transfer characteristics from the reference to the controlled output and also represents the ability of rejecting disturbances, and that T(jϑ) represents the degree of robust stability and, at the same time, gives the effect of detection noises. It is also shown that Y(jϑ) + T(jϑ) = I, and thus a frequency-domain paradigm for the design of sampled-data control systems, which is exactly parallel to the continuous-time case, is established.

PriSurv: privacy protected video surveillance system using adaptive visual abstraction

In this note, we propose necessary and sufficient conditions for the asymptotic stability analysis of two-dimensional (2-D) systems in terms linear matrix inequalities (LMIs). By introducing a guardian map for the set of Schur stable complex matrices, we first reduce the stability analysis problems into nonsingularity analysis problems of parameter-dependent complex matrices. Then, by means of the discrete-time positive real lemma and the generalized S-procedure, we derive LMI-based conditions that enable us to analyze the asymptotic stability in an exact (i.e., nonconservative) fashion. It turns out that, by employing the generalized S-procedure, we can derive smaller size of LMIs so that the computational burden can be reduced

Corrections to "Bisection algorithm for computing the frequency response gain of sampled-data systems - infinite-dimensional congruent transformation approach"

Recently, video surveillance has received a lot of attention as a technology to realize a secure and safe community. Video surveillance is useful for crime deterrence and investigations, but may cause the invasion of privacy. In this paper, we propose a video surveillance system named PriSurv, which is characterized by visual abstraction. This system protects the privacy of objects in a video by referring to their privacy policies which are determined according to closeness between objects in the video and viewers monitoring it. A prototype of PriSurv is able to protect the privacy adaptively through visual abstraction.

Recoverable privacy protection for video content distribution

This paper derives a bisection algorithm for computing the frequency response gain of sampled-data systems with their intersample behavior taken into account. The properties of the infinite-dimensional congruent transformation (i.e., the Schur complement arguments and the Sylvester law of inertia) play a key role in the derivation. Specifically, it is highlighted that counting up the numbers of the negative eigenvalues of self-adjoint operators is quite important for the computation of the frequency response gain. This contrasts with the well-known arguments on the related issue of the sampled-data H/sub /spl infin// problem, where the key role is played by the positivity of operators and the loop-shifting technique. The effectiveness of the derived algorithm is demonstrated through a numerical example.

A discrete wavelet transform based recoverable image processing for privacy protection

This paper presents a method which attains recoverable privacy protection for video content distribution. The method is based on discrete wavelet transform (DWT), which generates scaling coefficients and wavelet coefficients. In our method, scaling coefficients, which can be regarded as a low-resolution image of an original image, are used for producing privacy-protected image. On the other hand, wavelet coefficients, which can be regarded as privacy information, are embedded into the privacy-protected image via information hiding technique. Therefore, privacy protected image can be recovered by authorized viewers if necessary. The proposed method is fully analyzed through experiments from the viewpoints of the amount of the embedded privacy information, the deterioration due to the embedding, and the computational time.

Bisection algorithm for computing the frequency response gain of sampled-data systems

This paper presents a novel scheme of a recoverable image processing for privacy protection in real-time video surveillance system. The privacy information is embedded into the video using information hiding. Thus, the original privacy information can be recoverable with secrete key if necessary. In the proposed system, the privacy information is defined as information of objects that consist of detailed data to recover the original image of objects. The scheme is based on discrete wavelet transform (DWT) which is used for generating privacy-protected low resolution image, as well as the high resolution data including privacy information. An amplitude modulo modulation based information hiding scheme is used to hide the privacy information. Experimental results have shown that the proposed system can reduce the amount of the privacy information significantly, and allows the privacy information to be revealed after being embedded in real time.

Stability analysis and H/sub /spl infin// norm computation of 2-D discrete systems using linear matrix inequalities

Presents a bisection algorithm for computing the frequency response gain of sampled-data systems composed of a continuous-time and a discrete-time system together with a sampler and a hold. Although a bisection algorithm is known in the literature, it is applicable only to those frequencies at which the frequency response gain is greater than /spl par/D/spl par/, where D, denotes the direct feed-through term in the lifted transfer function of the sampled-data system. The paper gives a new bisection algorithm that can be applied to any frequencies. The derivation given is based on the lifting technique, and the properties of the congruent transformation (the Schur complement and the Sylvester law of inertia) play a key role. To facilitate the algorithm, a bisection algorithm for computing the singular values of D is also presented with the combined use of the lifting and FR-operator techniques.

Depth-Estimation-Free condition for projective factorization and its application to 3d reconstruction

This paper presents a stability criterion and a method for computing the H/sub /spl infin// norm of 2-D discrete systems. Both methods are based on linear matrix inequalities (LMI), and hence, they are computationally tractable. In deriving these methods, finite-order Fourier series approximation of the solution for frequency-dependent LMI (FDLMI), and the properties of quadratic form representation of finite-order Fourier series play key roles. From the view point of the proposed methods, the existing LMI-based methods can be regarded as the ones which are obtained by Fourier series approximation of order zero, and thus, it is expected that the proposed methods lead to less conservative results. This is illustrated by numerical examples.

Performance Analysis of Anonymous Communication System 3-Mode Net

This paper concerns depth-estimation-free conditions for projective factorization. We first show that, using an algebraic approach, the estimation of the projective depth is avoidable if and only if the origins of all camera coordinate systems are lying on a single plane, and optical axes of the coordinate systems point the same direction that is perpendicular to the plane. Next, we generalize the result to the case where the points are possibly restricted on a plane or on a line. The result clearly reveals the trade-off between the freedom of camera motion and that of point location. We also give a least-square-based method for Euclidean reconstruction from the result of the projective reconstruction. The proposed method is evaluated through simulation from the viewpoint of computational time.