Design And Implementation Of Space Camera With High Dynamic Range Imaging

The dynamic range is a key performance index of space camera technology. While the space camera observing a target in aerospace, the dynamic range of light intensity generally varies between 0.001 lux and 109 lux. A common way to obtain high quality images under different space work conditions is by remotely adjusting the camera's exposure parameters on the ground. However, we cannot get the desired pictures because of the low experience of operators and the delay of remote operating response. More importantly, the dynamic range of the space camera is far less than the dynamic range of the ambient light, so it is usually unable to obtain the full details of a target object by the fixed exposure parameter.Funded by NSFC key projects, this paper analyzes and designs the image processing pipeline of space camera. In this paper, a low complexity and high efficiency method of high dynamic range imaging is proposed for the application in space camera. Meanwhile, an adaptive exposure parameter selection algorithm is offered for a rapid response. Based on these research achievements, we design a high dynamic range camera and verify the above algorithms.The main work of this paper includes the following four parts. Firstly, a series of necessary image preprocessing modules are designed for the space camera on the basis of the research on ISP modules in the most existing cameras. At the same time, we study the relationship between each functional module, organize the processing sequence and design an ideal processing frame. Secondly, combined with the existing high dynamic realization methods and the characteristics of FPGA hardware implementation, a new designed method based on the maximum entropy principle is proposed considering the space environment. By adjusting the exposure parameters of any adjacent two images, the details of both bright areas and dark areas can be achieved, from which can obtain the high dynamic range image through the given algorithm. Thirdly, while producing the high dynamic range images, this paper adopts the optimization design idea and automatically compute the best two exposure times to obtain the complementary sources. One of the sources has details in the bright area and the other has details in the dark area. This adaptive exposure parameter selection algorithm can effectively solve the problem of "ghost" in the high dynamic range images, caused by some uncertain reason, such as camera jitter due to manual exposure settings. Finally, with all the theoretical accomplishments, this paper designs a high dynamic range camera based on “FPGA + DSP” architecture, which is composed of four layer hardware plates. These plates realize the image light source acquisition, digital image processing, video image compression and power supply etc.To summarize, this paper effectively solves the problem of overexposure or underexposure due to the limited dynamic range in the space camera. Compared with the current high dynamic implementation methods, this method can achieve better results with low complexity and high efficiency. And, a practical way is provided to improve the performance of the space camera.