说明：  function gmodify(pic,uv,gm,og) 功能：对发生桶形畸变的数字图像进行校正 输入：pic-要处理的图像的路径文件名 uv-在发生畸变的图像上的点的坐标 gm-在未发生畸变的图像上对应点的坐标 og- 代表对称中心，它是一个二维向量
(the function of gmodify is aimed to rectifying the digital image in which Barrel Distortion has emerged .The fact has proved that the method in function is effective.)