慢速行車時的主要交通事故在於車體結構與後照鏡角度造成的盲點區域，導致駕駛無法判斷與車輛周圍障礙物的距離所造成車體與人員的碰撞。為了讓駕駛能以俯瞰的方式看清車輛周遭情況，避免因為盲點區域所造成的交通事故，提高在停車、狹路行車、或低速會車時的安全性，本研究提出一套可調整影像接合與亮度的全周俯瞰監視系統。整個系統包含兩大部分：一是全周俯瞰監視用於輔助駕駛觀察車輛周遭的狀況；二是人工影像接合調整提高全周俯瞰畫面的正確性。 全周俯瞰監視系統共分為二個程序分別是離線程序和線上程序。在離線程序中我們在車輛四周架設四台廣角相機，計算每部相機的內部參數，校正扭曲現象，補償暗角現象。並在車輛四周拍攝大型校正板，透過特徵點的對應關係求得四周俯瞰影像的對位關係，將四相機影像透過平面投影轉換轉為俯瞰影像後融合成一張全周俯瞰影像。線上程序則是根據上述校正好的關係，即時內插出全周俯瞰影像，並根據計算出的亮度參考分佈調整整張影像的亮度均勻性。 全周俯瞰畫面的對位如果不夠正確，四相機影像的結合處會有明顯的落差。目前市面上有些廠商的全周俯瞰系統有提供人工影像接合調整的功能，但是只提供2D影像的上下左右位移和一個維度的旋轉，在調整影像接合的限制較多。我們提出一個人工影像接合系統提供視覺化的界面，可以讓使用者調整相機外部參數三軸方向的3D旋轉、位移，相機內部參數的焦距、影像中心點，及扭曲參數等調整選擇；讓使用者可根據畫面修改內外部參數及扭曲參數，最後根據更新過的參數修正原有的校正關係。 我們全周俯瞰監視系統在經過人工拼接調整後可以產生對位準確影像重疊區無落差的全周俯瞰影像；可在影像的解析度為720×480的情況下，於Intel Core™2 Duo 2.83GHz及3.00GB RAM的個人電腦上執行達到每秒 20 張的展示速度。 ;A lot of traffic accidents are caused by driver′s couldn’t see the area around the vehicles. To reduce the accidents caused by collision with surrounding obstacles, we mount four wide-angle cameras at the front, rear, and both sides of the vehicle to capture consecutive images; then we present a real-time adjustable image registration and brightness for surrounding top-view monitoring system. In offline steps of surrounding top-view monitoring system, we first calibrate camera intrinsic parameters, distortion of lens, and vignetting effects of four wide-angle cameras. Then we calibrate the geometric relationships (extrinsic parameters) of four cameras using a proposed multi-camera calibration method. Third, we calculate the feathering weights of pixels on overlapped image areas to produce a seamless surrounding top-view image. At last, we build look-up tables for the mapping between the captured images and the surrounding synthesized image to speed up the processing. In online procedure, the proposed system interpolates and generates the surrounding synthesized image by those look-up tables directly, and adjust image brightness automatically. In image registration steps, we provide a graphical user interface for user, This interface can provide roration and shift of three-axis direction, and adjustment options for intrinsic parameters and distortion parameters. After user adjusted image registration, we will build new look-up tables ,use it in online prcdedure. In our experiment, the frame rate of real-time adjustable image registration and brightness for surrounding top-view monitoring system is 20 frames per second.
