TDI-CCD全景航空相机快速自动检调焦方法

为了提高航空相机的实时侦察能力,提出了一种针对时间延迟电荷耦合器件(TDI-CCD)全景航空相机的快速自动检调焦方法。在检焦过程中,焦平面上的靶标图案经相机自身光学系统成像在TDI-CCD上,同时调焦反射镜沿光学系统主光轴在镜头后截距给定范围内连续快速移动,利用TDI-CCD的全帧转移工作模式,对经光学系统调制后的靶标图案进行高速采集,结合精密调焦驱动结构对采集到的图像进行高空间分辨率的定位。采用梯度算子、拉普拉斯算子、傅立叶变换、小波变换等7种聚焦评价函数对采集的调制靶标图案进行了比较分析,给出了各种算法的检焦精度。实验结果表明,本方法的检焦时间小于1s,采用小波变换作为评价函数的检焦重复性精度优于9.6μm,满足成像系统对离焦量允许值的要求。

A fast auto-focusing technique for the TDI-CCD panoramic aerial camera

For improving the aerial camera’s real-time reconnaissance capability,a fast auto-focusing technique is proposed for the time delay and integration change coupled device(TDI CCD) panoramic aerial camera specially.During the focusing procedure,the target located at the image plane is imaged upon the TDI CCD.Simultaneously,the focusing mirror is moved in continuous mode within the given back-focus correction range,and the TDI CCD operates in the full-frame transfer mode.Therefore,the modulated patterns of the target are captured in the time domain with high resolution,meanwhile they are also positioned in the space domain with high resolution.Adopting the focus measures,such as image gradient,Laplacian transform,Fourier transform and wavelet transform,the focusing accuracies are analyzed.Finally,the experimental results demonstrate that the proposed focusing technique consumes less than is during the focusing process,and its focusing accuracy is higher than 9.6 μm using the wavelet focus measure,then the requirement of the amount of the tolerant defocus is satisfied.