遥感相机自动检焦技术研究

将基于图像处理的自动检焦技术应用于线阵CCD推扫成像的空间遥感相机中。图像法检焦的关键在于对焦评价函数的选取。通常对焦评价函数是在摄影目标不变的情况下得出的,而推扫成像的线阵CCD相机在任意时刻所拍摄的景物都是不同的,这就给对焦评价函数的选取增加了难度。用功率谱的方法对任意景物在空间频域进行分析表明,功率谱对于自然景物具有一定的不变性。由此建立了基于功率谱的对焦评价函数,采用小波去噪与亮度归一化相结合的图像预处理技术有效地去除了图像噪声和亮度变化对对焦精度的影响。通过对功率谱评价函数进行加权处理,提高了对焦评价函数曲线的灵敏度。仿真实验表明了所构造的对焦评价函数是可行的。

Study on automatic focusing technique for remote sensing camera

Digital image processing is applied to measure the defocus of linear scan CCD with push broom for space remote-sensing camera.The selection of focus measure is the key to the auto-focusing by digital image processing.Most of the functions derived generally base on the same scene.As for the camera working in linear CCD sweep imaging mode,the scenes shot are different at any time.Different scenes are analyzed in the power spectrum spatial frequency domain,it can be shown that the power spectrum of most natural scenes is of invariability.The focus measure based on power spectrum is developed.The image pre-processing techniques based on wavelet denoise and normalization of image brightness are proposed to weak the influence of image noise and brightness variation.The acuity of the focus measure is improved effectively by weighting the focus measure based on power spectrum.The simulations show the feasibility of the proposed focus measure.