利用LSF实现推扫式遥感相机的自动调焦

Auto-focus using LSF in aerial push-broom remote-sensing camera

为实现推扫式遥感相机自动调焦,结合推扫成像的特点提出了利用LSF作为图像质量评价函数来指导自动调焦的方法。该方法利用了LSF和MTF的傅里叶变换关系。经过边缘检测后,搜索刀刃边缘区域,提取边缘扩散函数ESF,并通过求导得到像元尺寸级的LSF;然后利用最小二乘法作LSF的曲线拟合得出亚像元尺寸级的LSF,并且由LSF的重要参数σ得到图像质量评价值(IQE)指导推扫式遥感相机的自动调焦过程;通过实验对该方法的准确性和实时性做了验证,并给出了调焦精度的计算方法,最后利用IQE改变步距的爬山坡法实现调焦过程,提高了对焦速度及可靠性。实验结果表明:调焦精度可达到0.1倍焦深,调焦一次动作不超过0.2 s。说明该方法在实时性和准确性的方面都得到了较好的体现,为推扫式遥感相机实现自动调焦提供了可能性。

In order to realize auto-focus in aerial push-broom remote-sensing camera （APRC）, a method using LSF as image quality valuation function was proposed. The method was based on the principle that MTF is Fourier transform of LSF. Firstly, after edge detection and line detection, the knife-edge was detected. Then, from the knife-edge, the ESF was got and differentiated to obtain LSF in pixel level. LSF in 0.1 times sub-pixel level was got through curve fitting of least square method whose key parameter o- was used to get the image quality evaluation （IQE） function to realize auto-focus. The veracity and real-time ability of this method was validated in experiment and the calculation method of focus precision was advanced. At last, the climb-searching method of changing steps as IQE was used in the auto-focus process, so the focus speed and reliability was improved. The experiment shows, the focusprecision is 0.1 focus depth and the focus time for one step is no more than 0.2 s. The method meets the requirement of real-time processing and accuracy. It provides the possibility for the auto-focus in APRC.