超半球环形成像系统的图像恢复

在实现全景成像的光学系统中,采用圆柱面到平面投影的环形成像系统相比采用中心投影法的传统透镜系统具有边缘视场畸变小、便于图像恢复展开等优点.通过考察环形成像系统所成环形图像与矩形图像之间的映射关系,研究像面上子午弧矢方向最小分辨角的变化规律,得出了超半球环形成像系统在90°视场角处子午弧矢方向CCD采样角分辨率相同的结论,由此可把该视场角对应的圆环像作为基准来确定展开矩形图的宽度和高度.实际的图像恢复过程分为2步：首先将环形图像恢复成三维像空间中的圆柱面,然后把圆柱面展开得到恢复后的矩形全景图.图像恢复中最关键的90°视场角所对应的圆环像位置和环形图像中心点的确定可以用定标实验的方法实现,在图像恢复过程中采用三次样条插值法,得到了较好的恢复效果.

Image restoration for super hemisphere annular imaging system

In the realization of panoramic view, the annular imaging system using the flat cylinder perspective is easier to restore panoramic images compared with the ordinary ones designed by the center point perspective because of the merit of low distortion at large angle of view. The mapping relation of the annular images, generated by the annular imaging systems, and the rectangular images was investigated, and the resolution angles on the meridian and sagittal directions on the image plane were discussed. It is concluded that the resolution angles of the system at the sagittal and tangential planes are equal when the super-hemisphere annular imaging system taking photo at the 90° angle of view into a circle image. That circle image can be used as a standard to calculate the height and width of the restored image. There are two steps during the restoration period: the first is to transform the annular image back into a cylinder in three-dimensional space, and the second is to spread out the curved plane into a flat one. The keys before the restoration are to identify the circle image of the 90° angle of view and the center of the annular image. The cubic spline interpolation method was applied in the image restoration as it is the best interpolation method approaching the sinc function.