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Study of Reducing Laser Speckle Noise by Utilizing a Phase-Only Spatial Light Modulator in Laser Projection System
No full text在雷射投影的光學成像系統中由於雷射的高度同調性，使得在螢幕端會產生建設性及破壞性干涉的亮暗交雜的光強分佈，這就是“光斑 (speckle)現象”，然而光斑現象被認為是在影響影像品質的雜訊，因此減弱或消除光斑的影響便成了在雷射投影光學系統上的主要目標之一，在本論文中我們改良已經發表的常見的雷射投影系統，可達到簡化系統架構、抑制光斑現象與提高影像品質，並且在整個系統中加入特殊設計的數位全像片(computer generated hologram, CGH)，使得本質的光斑(intrinsic speckle)被抑制，我們並以此系統探討降低光斑的方法及將其量測出來。 本論文中我們將介紹雷射投影顯示的概述，之後介紹光斑的現象、原理以及整理抑制光斑的方法，其分為極化分集、波長分集、角度分集與其他元件設計四大類別，在我們所研究的抑制光斑方法中以光斑對比 (speckle contrast, SC) 作為我們判別光斑嚴重程度的重要參數和相關係數 (correlation coefficient) 來輔助優化數位全像片的設計。 在我們的系統中，以反射式液晶空間光調變器取代常見抑制光斑的方法中的移(轉)動式擴散片。藉由使用遞迴傅立葉演算法 (iterative Fourier transform algorithm, IFTA) 設計出數位全像片，其可以將雷射光束整形 (beam shaping) 成方形，使雷射光能完整照明在幻燈片上以增進投影效率，同時也利用相位調變的技術來取代移(轉)動的擴散片，如此一來可以避免機械式的轉動或者移動，而且也能以相位調變來降低光斑對比，也透過分析數位全像片間的相關係數了解到光斑對比值在實驗與理論上差距的主因。然而以這個系統為基準下再探討光束整型後的光，利用相位補償的方式設計另一種數位全像片我們稱為，相位補償數位全像片，使光斑對比可以藉由設計相位接近全建設性干涉而達到光斑對比下降而且均勻度上昇。 在本論文中也以組合式全彩的方式分析在我們的系統中使用全彩光源，經過我們的抑制光斑的設計後，分析光斑對比去討論。未來可以使用實際全彩光源來探討分析此雷射投影系統的光斑抑制效果，也可以將數位全像片連續播放與設計相位補償數位全像片做結合來探討光斑抑制情形。A speckle distribution is a mixed bright and dark intensity distribution with some constructive and destructive interference which is caused by the high coherence of laser light. It is of practical significance because it introduces noise in Laser Projection Display Systems (LPDS), which damages the image quality. Therefore, speckle suppression is one of the main goals in LDPS. In this dissertation, the general LPDS is optimized to simplify the system, suppress the speckle on the illumination part of the LDPS and improve the image quality by more uniform illumination. A Computer Generated Hologram (CGH) specially designed to reduce the intrinsic speckle from the uniformly illuminated part of the LPDS is added to the system. We discuss the speckle suppression method we design and measure it in the optimized LPDS. In this dissertation, we will introduce the laser projection display, the speckle phenomenon, the speckle principle, and speckle suppression methods. We separate speckle suppression methods into four parts: polarization diversity, wavelength diversity, angular diversity, and other element designs. The Speckle Contrast (SC) and Correlation Coefficient (CC) are important parameters that can determine the degree of speckle. We design our CGH by analyzing the SC and CC. In our LPDS, we utilize the reflective spatial light modulator (SLM) to replace the moving diffuser, which is a common speckle suppression method. We use the Iterative Fourier Transform Algorithm (IFTA) to design a CGH which can shape the beam for improving the projection efficiency and modulate the phase to replace the moving diffuser. In this way we can avoid mechanical rotation or vibration and reduce the SC by phase modulation on the illumination part of the LPDS. Moreover, we realize that the main reason for the difference in SC between experiment and theory after analyzing the CC between the front and back CGHs is sequential time. Based on this system, we designed another CGH by phase compensation that we call “compensation CGH”. It can approach full constructive interference to suppress the speckle and improve the uniformity on the illuminated part of the LPDS at the same time. In this dissertation, we discuss the SC to use the combined analysis of a three color laser light source for simulating the white light source in our LPDS. We can use the real white light laser to carry out experiments for realizing the variation of the SC. Moreover, we can combine the CGHs in sequential time and the compensation CGH to discuss the variation of the speckle phenomenon
Study of Speckle Phenomenon in Laser Projection Systems
No full text由於以雷射當作光源的光學成像系統中會有一個嚴重影響成像品質的“光斑 (speckle)”問題，減弱或消除光斑的影響便成了此一領域的共同目標之一，在本論文中我們以液晶空間光調變器 (spatial light modulator, SLM) 為主設計一個模擬雷射投影的雛型系統，除了大幅簡化系統架構，並可抑制光斑影響，提高影像品質，我們並以此系統探討降低光斑的方法及將其量測出來。
本論文中我們將介紹投影顯示的概述與投影系統的技術，之後介紹光斑的現象與原理，其中我們以光斑對比 (speckle contrast, SC) 來作為我們判別光斑嚴重程度的重要參數，除此之外我們也介紹一般常用來消除光斑的方法，即以移動的擴散片 (diffuser) 放置在系統中，或藉由螢幕高頻率的振動，使光強度分佈得到均勻化的效果進而降低光斑對比。
在我們的系統中，以反射式液晶空間光調變器取代一般消除光斑的方法中的擴散片。藉由使用遞迴傅立葉演算法 (iterative Fourier transform algorithm, IFTA) 設計出相位圖，此相位圖可以將雷射光束整形 (beam shaping) 成方形，使其能完整照明在幻燈片上以增進投影效率，同時也利用相位調變的技術來取代轉動的擴散片，如此一來可以避免機械式的轉動或者移動，而且也能以相位調變來降低光斑對比，故在此我們討論以這種方法為降低光斑的主要方法。
在未來的研究上，可以將設計的相位圖優化，讓它在光束整形上可以達到強度更均勻。除此之外也可將投影系統中的幻燈片替換成顯示面板 (display panel) 討論靜態與動態的差異，且討論三種雷射光混色後與單色光時在光斑現象上有何差異，使我們的系統能更接近實際使用的投影機。In the Master Thesis, we design a laser projection system. There is a serious problem which influence projection image qualities from the illumination source “Laser”, called“Speckle”. Therefore, we study speckle reduction methods and measure it in this thesis.
In introduction, we will introduce the projection displays technology and classify projection systems. After that we describe phenomena and principle of speckle. By utilize the “Speckle Contrast (SC) ”to judge how critical the speckle pattern are. Besides, we introduce the speckle reduction methods that commonly used, that is to place a moving diffuser in the system or by vibrating screen with high frequency (let human eyes cannot felt) to suppress SC by averaging the total intensity.
After that we consider the laser propagation behavior in our system. And then we use reflective spatial light modulator (SLM) to replace the diffuser which is in the general suppressing speckle method. We design the phase diagrams by (Iterative Fourier Transform Algorithm, IFTA), and they can shape laser from a circle to a square for promoting the projection efficiency by complete illumination in the filmstrip. At the same time, we use the phase modulation technology to replace rotating diffuser. Thus we can avoid mechanical rotation and high-frequency vibration, and have faster modulation speed for suppressing speckle as well. For this reason we discuss this speckle reduction method in this.
In future research, we shall optimize these phase diagrams designed for more uniform intensity and more like a square. Besides, we can change filmstrip into display panel to discuss the difference between dynamic and static states, and discuss what difference between three color mixing laser and monochrome laser for making our system closer to the actual projector
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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