空间太阳望远镜在轨自动调焦的最小图像熵判据

Using the minimum entropy as a criterion for the in-orbit automatic focussing of space solar telescope

由于复杂的发射状态和动态在轨空间环境以及高达0 1″的角分辨率,所以自动调焦技术已成为太阳空间望远镜在轨图像处理中的关键技术。在分析图像离焦时的状态特性的基础上,提出了一种新的更适用于空间相机的离焦判据———最小图像熵判据。最小图像熵合焦判据更适合于低对比度的天体目标。利用计算机仿真程序演示了给定目标经系统成像的过程,计算了不同离焦状态下的图像熵。这一技术将应用于2005年发射的太阳空间望远镜中。

The automatic focusing (AF) is a key technology for the in-orbit imaging processing of space solar telescope (SST) because of the complicated launch condition, dynamic in-orbit space environment and its high angle resolution (γ=0.1'). The new minimum entropy (ME) criterion of the off-focus state is put forward based on the analysis of the definition feature of the off-focus states. The method of ME is more suitable for the space camera and the observation of the heavenly bodies of low contrast. The image of a given object formed by an optical system is shown using the emulation program, and the imaging entropy of different off-focus states is calculated. The data indicates that precision is l‰ (δ=1‰). The technology will be applied to automatic focusing of the space solar telescope in 2005.