The Mobile Phone Shooting Method Of Starry Sky Scene

Smartphones have been quite common in our daily lives. Some high-level smartphones have already equipped with cameras which are as good or ever superior to the digital cameras in pixels. With the development of smart software and tiny hardware, people’s expectation towards the cameras of the smartphones is increasingly growing. Under this circumstance, taking photos of such special scene as starry sky, thunders and fireworks has been a new competition field for many smartphone manufacturers.Traditional method of taking photos of starry sky is based on the method of single long exposure, which has been replaced by the method of overlapping due to the constrain of battery column and thermal noise. This method adopts higher ISO, larger aperture, longer exposure time. Through overlapping together, a splendid starry sky can be formed. Therefore, taking a photo of starry sky with smartphone camera confronts with following problems:how to overcome the noise of high ISO and the motion problem under long exposure time, and how to attain a perfect overlapping picture.According to today’s mobile phone focusing strategy, this paper conducts automatic focusing by adopting the auto-focus method based on image, using Laplace operator as evaluation function, as well as applying pole searching method as the search strategy. In response to the image motion-blur problem caused by the relative motion of the camera and the starry sky scene during the process of taking photos, a new restoration algorithm is put forward for the blurred image of star’s motion. First, it employs an improved thinning algorithm to obtain the star trajectories of the sky image to extract the motion kernel of the star-motion blurred image, and then restoring the motion-blurred image based on Richardson-Lucy’s restoration algorithm. The experimental results show that the use of using refinement algorithm to get the fuzzy kernel proposed in this paper has a good restoration effect for the motion-blurred image of star’s motion with its low complexity, less time consuming and high accuracy. Under the condition of insufficient light, according to the high sensitivity noise problem introduced by high sensitivity, this paper adopts fast median filtering based on the mean acceleration to denoise the star image. The results indicate that this method not only has low time complexity, but also can remove the high sensitivity noise of the star image effectively. In order to be able to capture the star under different states (such as different brightness or twinkle changes of the star), the paper adopts the method based on feature points to conduct the image registration of the star images. Under this premise, according to the characteristics of the star point, it conducts the multi-frame fusion of the analog image of the starry sky scene by utilizing the fusion method of taking big pixel value. The method with low complexity and good effect eventually get the perfect starry sky image after multi-frame fusion.The purpose of this paper is to work out a rational solution so as to solve the problems during the process of taking photos with the camera of the smartphone. For the four problems of auto-focus, the restoration of motion-blurred image, the denoising of high ISO and the registration and fusion of image, this paper carries on the thorough research and the comparative experiments of different algorithms. The simulation starry sky scene experiment result shows that through a series of the starry sky scene algorithm processing, a clear perfect star image can be obtained.