用射影不变性纠正鱼眼镜头畸变

计算机视觉通常采用针孔摄像机模型，但对于存在较大畸变的鱼眼镜头或广角镜头，必须首先纠正镜头畸变才能应用针孔模型。为了从同时存在透视变形和鱼眼畸变的图像中纠正鱼眼畸变，采用了以下射影不变性：空间中直线的投影为直线；平行直线束的投影平行或相交于一点；直线段投影的交比不变。首先，用待纠正的鱼眼镜头对一幅等间隔正交网格图成像，提取网格结点作为控制点，然后用射影不变性求解畸变模型，达到纠正畸变的目的。该算法巧妙地运用三次方程的Cardan解法。大大提高了速度。结果表明，运用该方法纠正鱼眼镜头畸变速度快、精度高。

A Correction Method of Fish-eye Lens Distortion Using Projective Invariability

Many algorithms in computer vision usually use pin hole camera model. Since fish eye lens have large distortion,it is necessary to correct it first. In order to correct lens distortion from an image which is caused by both the lens distortion and projective transform, three projective invariants should be used. Stratight line should be straight after projection. Parallelline should be intersect at one point or still parallel. Cross ratio should be constant after projection. During the correction, firstly, capture an equal space orthogonal grid image by the fish lens and then use the projective invariant to find out a polynomial distortion model. In order to speed up the algorithm, the Cardan method is used to solve the cubic equation, result show hat the new distortion correction method is fast and accurate.