The stray light uniformity is one of the important factors affecting the signal-to-noise ratio of the optical astronomical telescope. It will cause regional differences in the background intensity of the detector image, resulting in a decrease of the differential photometry accuracy. The source that affects stray light uniformity is the inconsistency of the brightness of the sky background, which comes from moonlight, bright star, and city lighting pollution. During CCD reduction, the effect of background uniformity cannot be eliminated by dividing the flat field.
Star deletion method is used in real-time stray light analysis. It’s very convenient to achieve a ‘clear’ background image without stars in MATLAB. A contour map of stray light distribution for each object image will be given to demonstrate the background uniformity directly. The stray light uniformity analysis method is implemented by the following steps: 1) CCD reduction, including preprocessing of an object image with bias and flat field; 2) Histogram generation, performing star subtraction automatically based on ADU value and frequency; 3) Background stray light contour map generation, stray light uniformity and other parameters calculations. This method will calculate the uniformity of image surface in real time, provide background intensity distribution, statistical data of the CCD image and suggestion on compare star selection during CCD data processing and improve the photometry accuracy.