洪一平臺灣大學：資訊工程學研究所吳延年Wu, Yen-NienYen-NienWu2007-11-262018-07-052007-11-262018-07-052004http://ntur.lib.ntu.edu.tw//handle/246246/53868在進行大型會議或資訊展示時，通常會需要一個大型、高解析度的影像顯示系統。而近年來由於資訊的發達，使得這方面的需求日益增多。因此，低成本且易安裝的大型顯示系統是具有相當大的市場潛力的。本論文的目的在於利用電腦視覺、影像處理、與電腦圖學的技術來發展一套方法，採用旋轉式可變焦攝影機的輔助，建構一個由多台投影機所接合而成的無接縫大型顯示系統。為了達成這個目的將要考慮兩個議題：(1)幾何矯正與(2)色彩矯正。 在此論文中我們發展了一個基於視覺的方式(利用旋轉式可變焦相機)來達成這個目的。最近已有不少論文介紹在使用多台投影機建構一個大型顯示系統時所須考慮的各種因素。本論文中提出的方法，在幾何矯正方面更加的精確，因為我們乃利用多張在不同角度拉進鏡頭所拍攝的影像來得到更精確的控制點的座標。除此之外，本論文中提出的方法不需要事前進行相機矯正，也不需要知道投影幕的三度空間幾何關係。相對於用昂貴的光譜儀來進行色彩矯正，本論文利用一般攝影機在不同曝光值之下拍攝多張影像，再組成高動態範圍圖像來估測真實的顏色，再利用事先計算好的和色度計之間的對映關係來進行色彩矯正。經過色彩矯正後，每台投影機的色彩分析將會應對到共通的色彩呈現範園。而多台投影機之間的色彩差異就會消除。對於需要大型、高解析度的應用，如科學視算、視訊顯示牆等等，本論文提供了快速、有效的演算法來進行幾何和色彩之矯正。Over the past few years a considerable number of studies have been made on building large, high-resolution displays. The aim of this thesis is to build a seamless large-scale display system by tiling multiple projectors with the help of a pan-tilt-zoom camera. It adds to the display world by combining different techniques to create a large, high-resolution, and low-cost display system. This research takes two tasks into consideration when producing the seamless display: (1) the geometric calibration and (2) the photometric calibration. Here, I develop a vision-based approach to accomplish these tasks by utilizing a pan-tilt-zoom video camera. Compared to previous work, my method for geometric calibration is more accurate because I have a much higher resolution (because I combine several zoom-in images). And it does not require a camera calibration, nor does it require the 3D geometry estimation of the display surface. As opposed to using the spectroradiometer, an expensive device previously used for color calibration, a camera is used due to its low cost. I take advantage of high dynamic range image to estimate the real color, and with a mapping between it and the colorimeter. With photometric calibration, the color across the different projectors will become uniform. This system has great potential for many applications that require large format and high resolution display, such as scientific visualizations and visual display wall.Chapter 1 Introduction ………...…………………………………………...……… 1 1.1 Motivation ……………………………………………………………….. 1 1.2 Problem Definition and Objective .……………………………………… 3 1.3 Previous and Related Works …….……………………………………… 4 1.3.1 Large Displays …………….…….………………………………… 4 1.3.2 Projectors ……………………….………………………………… 8 1.4 System Overview ………………………………………………………. 11 1.5 Thesis Organization …………………………………………………… 13 Chapter 2 Geometric Calibration ………………..………………………………. 14 2.1 Mathematical Background ……………………………………………… 15 2.1.1 Projective Geometry ………………………………………...… 15 2.1.2 Homography ……………………………………………….…… 15 2.1.3 Co-ordinate Space ……………..……………………………….. 18 2.2 Feature Detection ………………………………………………………. 19 2.2.1 Circle as Feature ……………………………………………...… 20 2.2.2 Line as Feature ..……………………………………………..…. 21 2.2.2.1 Feature Points Detection …………………………………. 21 2.2.2.2 Feature Points Identification ……………………………. 22 2.3 Geometric Calibration Using PTZ Camera ………………………….. 23 2.3.1 Finding the Starting Position ………………………………...…24 2.3.2 Collecting Images ……………………………………………...… 25 2.3.3 Extract Control Points ……..……………………...…………...… 25 2.3.4 Calculating Homography between Camera Views and Reference Frame ……….………………………………….………………………… 26 2.3.5 Transform the Coordinate of Control Points in the Camera View into the Reference Frame ………………………...…………...…………...….. 26 2.3.6 Computing Homography between Projector and Reference Frame …..……………………………….……………………………...… 26 2.4 Keystone the Projected Image …………………………………….... 27 Chapter 3 Photometric Calibration …………………………………………... 29 3.1 Color Space ……………………………………………………….…… 29 3.1.1 Color Models …………………………….……………………... 29 3.1.2 Colorimetry ……………………..……….……………………... 31 3.1.3 Color Variation among Projectors ……….……………………... 32 3.2 High Dynamic Range Image …………...……………………………... 33 3.3 In-factory Photometric Calibration of PTZ Camera .……………….…… 34 3.4 Finding the Common Color Gamut ……………………………………... 36 3.5 Color Gamut Mapping …………………...……………………………... 39 3.6 Intensity Blending ……...………………...……………………………... 40 Chapter 4 Experiment Results ……………………….………………………… 42 4.1 System Setup ……..……….….……………………………………….… 42 4.2 Results …………….……………………………………………….…… 44 Chapter 5 Conclusion and Future Work ..………………………………….… 49 5.1 Conclusion ………………………………………………………………. 49 5.2 Future Work ..………………..………………………………………...… 51 References ……………………………..…………………………………………...... i2609185 bytesapplication/pdfen-US色彩校正視訊顯示牆高動態範圍圖像旋轉式可變焦攝影機色度計多台投影機疊合幾何校正Geometric CalibrationPan-Tilt-Zoom CameraColorimeterVisual Display WallHigh Dynamic Range ImagePhotometric CalibrationMulti-projector Tilingthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/53868/1/ntu-93-R91922022-1.pdf