以C-Means為色彩一致性方法之三維物體重建

Abstract

本論文主要採用立體像素模式(voxel-based)重建三維物體，整個重建過程可分為四個步驟。第一步驟為相機校正，此步驟主要目的是取得相機的內、外部參數；第二步驟為影像分割(segmentation)，主要將物體從背景中分離出來；第三步驟為建立三維模型，目標是要得到大量的三維物體表面點的座標，而在此步驟中會使用到兩種方法，分別是立體像素的可見度(voxel visibility)及色彩一致性(color consistency)，其做法是在三維世界座標中，先建立一個立方體包含有N×N×N的立體像素 (voxel)，將每一個立體像素透過相機參數投影在相機的影像平面上，再利用立體像素的可見度及色彩一致性方法重建3D物體，其中色彩一致性是本論文重點；第四步驟為顯示介面，主要利用VC++程式及OpenGL函式庫將所建立的三維物體顯示出來。 目前常用的色彩一致性方法有單一臨界值(single threshold)、長條圖(histogram) 及適應臨界值(adaptive threshold)三種方法，在此提出一種新的色彩一致性方法，主要利用 C- 平均法 (C-means)來實現色彩一致性，並與其它三種色彩一致性方法做比較。C-平均法主要利用色彩分類的方式來判斷相機所看到立體相素的顏色是否一致，由實驗結果得知，C-平均法能有效刪除不需要的立體像素且能精確得到立體像素的顏色，使得重建模型更接近實際的三維物體。

A voxel-based approach for 3D volumetric reconstruction is used in this thesis, and there are four steps in the process of a voxel-based 3D reconstruction system. In the first step, the camera is calibrated, and the purpose of camera calibration is to get the intrinsic and extrinsic parameters of the camera. Second, image segmentation is executed to extract object from background. Third, a 3D model is built, and the coordinates of a large amount of surface points of the object are determined. The third step includes two sub-steps that are voxel visibility and color consistency, and color consistency is the main issue of this thesis. Finally, a reconstructed 3D object is displayed by computer language VC++ with OpenGL libraries in the fourth step. So far, generally speaking, there are three different methods for implementing color consistency, and these three methods are single threshold method, histogram method and adaptive threshold method. A new color consistency method by using the C-means method is proposed in the thesis, and the proposed method is compared with the other three color consistency methods. According to the experimental results, the proposed method can eliminate the unnecessary voxels and determine the true colors of voxels very well.