Variational Bayesian Self-Calibration of Surveillance Cameras from Pedestrians

Master보행자를 대상으로 하는 카메라 자가 보정 방법들은 복잡한 보정 도구나 설치 과정이 필요하지 않기 때문에 영상 보안 시스템에 적합하다. 이런 방법들에서는 실제 보행자의 키가 카메라의 초점 거리나 설치 높이와 같은 메트릭 정보를 얻기 위한 유일한 단서가 된다. 그러므로 대부분의 방법들은 보정 과정을 통제하여 이미 키를 알고 있는 한 사람만 대상이 되도록 하며, 따라서 이런 방법들은 저장 매체에 기록되어 있는 영상 또는 네트웍을 통해 수신되는 원격영상 등에 적용할 수 없다. 본 논문에서는 실제 환경에서 사용될 수 있도록 임의의 보행자들을 보정 대상으로 하는 베이지안 카메라 자가 보정 방법을 제안한다. 임의의 보행자를 대상으로 하는 경우 각각의 키를 알 수 없으나, 만약 매우 많은 보행자를 관측할 수 있고 감시 지역 사람들의 키에 대한 통계가 있다고 가정하면, 그 통계 정보는 보정에 사용될 수 있다. 이를 위해 제안하는 방법에서는 보행자 키의 확률 분포를 정규 분포로 모델링하고, 발-머리 호몰로지를 사용하여 보행자의 발/머리 좌표와 실제 키의 불확실성을 고려하는 확률 모델을 구성한다. 이 복잡한 확률 모델로 부터 카메라 파라미터를 구하는 것이 난해하므로, 근사적 방법인 변분 베이지안 추론을 사용하였다. 다양한 실험을 통해 제안된 방법이 노이즈에 강건하며, 비교적 간단한 발/머리 검지 방법을 사용하더라도 타 알고리즘들과 비교할만한 수준의 보정 결과를 내는 것을 확인하였고, 더 정교한 발/머리 디텍터를 사용하여 성능이 높아질 수 있음을 검증하였다. 또한 계산된 카메라 파라미터에 대한 신뢰도를 예측함으로서 베이지안 추론의 장점을 극대화될 수 있음을 보였다.Pedestrian-based camera self-calibration methods are attractive to video surveillance systems because they do not require complex calibration devices or procedures. These methods use pedestrians as calibration targets, and their actual height is the only clue to obtaining metric information on camera parameters. For this reason, most existing methods control the calibration procedure to use a single person whose height is already known. Accordingly, these methods cannot be applied to video data that is recorded on storage devices or received from the networks. In this paper, we propose a novel Bayesian approach to camera self-calibration that takes arbitrary pedestrians as the calibration targets in the real surveillance environments. When arbitrary pedestrians are used as the calibration targets, the height of each pedestrian is unknown. However, statistics on the height of pedestrians can be utilized if (1) we observe enough pedestrians and (2) we have statistics of the surveillance area. Thus, we model the height of each pedestrian as a normal distribution, and construct a probabilistic model that takes into account uncertainties in both the observed image and pedestrian height. To solve the model, we use variational Bayesian inference, an approximate inference algorithm. Experimental results show that the proposed algorithm is robust to noise and comparable to other pedestrian-based algorithms

Effect of initial Pd particle size on sintering rate of Pd-based three-way catalyst

MasterThree-way catalyst (TWC) has been widely employed as the most efficient after-treatment catalytic system for gasoline engine vehicles to simultaneously remove three major air pollutants such as carbon monoxide (CO), unburned or partially oxidized hydrocarbons (HCs) and nitrogen oxides (NOx). However, the sintering of noble metal attributable to the high exhaust gas temperature typically above 600 oC leads to the deactivation of TWC. Although the fundamental sintering behavior of the noble metals has been widely examined with respect to the time on stream, a systematic study for the effect of the initial particle size on the sintering rate and sintering kinetic parameter in the Ostwald-ripening mechanism has been hardly investigated, particularly over Pd-based TWCs. In the present study, the effect of the initial Pd particle size on the sintering rate of Pd-based TWC catalysts has been examined over both the commercial Pd catalyst obtained from the GM R&D and the lab-prepared model Pd catalyst with a wide range of the initial Pd particle size as a function of the catalyst mileage from 4k to 100k miles. The average particle size of Pd has been systematically analyzed by a variety of catalyst characterization tools including CO-chemisorption, XRD and TEM analysis. The initial Pd particle size of the 4k-stabilized commercial and lab-prepared model Pd catalyst increased with the increasing Pd loading from 10 to 400 g/ft3. The sintering rate of both catalysts strongly depended on their initial particle sizes, revealing a slower sintering rate of the Pd catalyst with a larger initial Pd particle size. After the 20k-miles equivalent aging, the average size of Pd particles over the Pd catalyst decreased as the Pd loading increased from 10 to 400 g/ft3. This sintering trend of the Pd catalyst was maintained when the catalyst mileage increased from 20k to 100k miles. Moreover, the TWC performances of the 100k commercial Pd240 and Pd80 catalysts have been compared, while maintaining an identical total amount of Pd in both reactors; the 100k Pd240 commercial catalyst exhibited a higher TWC activity than the 100k Pd80 catalyst. To further confirm the sintering trend of Pd, the effect of the initial Pd particle size on the sintering rate has also been investigated over the model Pd80 catalyst supported on the fresh γ-Al2O3 or the pre-aged γ-Al2O3. The initial particle size of the model Pd80 catalyst was controlled by pre-aging the γ-Al2O3 before impregnating Pd onto the Al2O3 support. As expected, the 4k stabilized Pd80 catalyst supported on the pre-aged γ-Al2O3 exhibited a lower TWC performance and a larger initial Pd particle size, compared to that supported on fresh γ-Al2O3. After the 100k miles-equivalent aging of the catalyst, the Pd80 catalyst supported on the pre-aged γ-Al2O3 sintered more slowly than that supported on the fresh γ-Al2O3. To identify the critical factor affecting the sintering rate of the Pd catalyst, the sintering kinetics of the Pd catalyst has been investigated on the basis of the Ostwald-ripening mechanism. The sintering equation based upon the Ostwald-ripening mechanism reasonably well predicted the alteration of the Pd particle size as a function of the aging time and the initial particle size, correctly capturing the moderation of the sintering rate of the Pd catalyst with a larger initial Pd particle size. In addition, the alteration of the sintering kinetic parameter (KI) for both the commercial and the model Pd catalysts has been successfully described by an identical sintering correlation, indicating that the sintering rate of Pd strongly depends on the initial particle size, regardless of the catalyst preparation method. Furthermore, both surface tension (γm) and the rate constant of Pd monomer detachment (Dt) have played important roles in determining the sintering kinetic parameter (KI) of the Pd catalyst. The surface tension of Pd particles calculated by using a numerical simulator (Forcite module, Material studio 7.0) exponentially decreased from 3.17 to 1.77 J/m2 with the increasing initial Pd particle size from 4.0 to 17.0 nm. The rate constant of Pd monomer detachment (Dt) was also evaluated from the sintering kinetic parameter (KI), revealing the decrease of Dt as the initial Pd particle size increased. Specifically, the rate constant of Pd monomer detachment (Dt) exponentially decreased from 3.07x1019 to 4.70x1018 m-2s-1 as the initial Pd particle size increased from 4.0 to 17.0 nm. The decrease of the rate constant of Pd monomer detachment (Dt) with a larger Pd particle might be readily elucidated by the higher activation energy (E) for detaching a Pd monomer from the Pd crystallite