立體影像分析的相機参數探討

ROI Parameters for Stereo Imaging

林雍泰(Yung-Tai Lin) ； 古文豪(Wen-Hao Ku) ； 張珩(Heng Chang)

《華岡工程學報》 14期 (2000/06) Pp. 71-85

https://doi.org/10.29987/CCUHKJE.200006.0006

摘要

影像分析是藉由照相機拍景物成像，由影像中物體的相對大小、位置、亮度明暗、等資訊，分析物像與實際狀況之關係。而其中距離或深度的探討就是構成立體的主要因素。所謂立體影像是使用兩個以上的相機，將該組相機放置於兩個幾何上相關的位置體，對同一景物各取一個影像，藉由分析這兩張影像上之物像，以計算出實際物體與相機之距離。立體影像處理的關鍵在於物像對應點的匹配過程，若在立體影像上包含許多個複雜或相似物體的話，則配對過程中將產生困難問題，在物像上會出現有許多相似或難以分辨的特徵。
本專題在探討若已知兩影像中的相對應匹配特徵，改變相機取像過程對實際物體的空間位置辨別能力的影響。量測立體影像表面的系統有很多種，通常則是採取類似人類雙眼的三角架構法來做求取深度的計算。首先假設空間中有一條特徵曲線，在取得兩匹配影像後，將所得到左右兩影像的平面座標值，代入三角架構法中求得立體曲線座標值及深度，並將立體座標值作圖，觀察出立體投影至平面的影像，再將左右兩像平面幾何特徵的XY座標，與原空間曲線圖對照，探討相機取像參數（焦距、角度、兩成像平面之距離）對影像辨別誤差的影響。

並列摘要

The first image processing procedure of a vision system is the image acquisition stage. Only after the image is properly acquired, various methods of image processing can be applied to the image to perform many industrial tasks. However, if the image is not acquired satisfactorily, the intended task may not be able to achieve even with the state of the art image enhancement techniques.
The study focuses on the stereo image acquisition system with two CCD or Vidicon tube TV cameras in order to digitize a two-dimensional image. Two 2D images are taken by cameras and compared to obtain the depth information (depth map) of the subject under study. A setup of using these two cameras in stereo imaging consists of establishing:
• Two cameras with their optical axes intersected with an angle θ are separated by a distance d.
• The line connecting the camera lens centers is called the baseline.
• The baseline must be perpendicular to the line of sight of the cameras.
• The x-axis of the three-dimensional world coordinate system is parallel to the baseline.
• The origin O of this system is midway between the lens centers.
The setup parameters, i.e. angle θ and distance d, together with the lens focal distance ƒ are investigated in the study to attain the acquired image quality. The result shows that the wider camera separation distance d increases the difficulties in correlating two images. However, the image disparity is improved with a wide camera separation distance. The camera angle θ may deform the corresponding images and can increase the difficulties in the image correlation and the disparity calculations.
Nevertheless, within a suitable selection range, the camera angle θ may facilitate the image attribute extraction in a specific application. In order to acquire a quality stereo image satisfactorily, the camera setup parameters should be carefully considered.

並列關鍵字

Stereo Image ； Parameter analysis