CN107886538A - A kind of stellar camera asterism detection method and system - Google Patents
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Abstract
Description
技术领域technical field
本发明涉及一种星相机星点检测方法及系统，属于航天光学遥感技术领域，应用于高分辨率对地观测遥感相机姿态测量。The invention relates to a star point detection method and system of a star camera, belongs to the technical field of aerospace optical remote sensing, and is applied to attitude measurement of a high-resolution earth observation remote sensing camera.
背景技术Background technique
提高遥感影像的几何定位精度是高分辨率遥感应用的基础，实现高精度几何定位，首要的工作是检校和补偿高分辨率遥感相机的系统误差。星相机作为星上姿态控制系统中姿态测量精度最高的测量部件，实践中常用标校遥感相机和星相机之间的姿态关系矩阵实现系统误差的补偿，并通过遥感相机和星相机主光轴之间交联角来直观反映。Improving the geometric positioning accuracy of remote sensing images is the basis of high-resolution remote sensing applications. To achieve high-precision geometric positioning, the primary task is to calibrate and compensate the systematic errors of high-resolution remote sensing cameras. As the measurement component with the highest attitude measurement accuracy in the attitude control system on the star, the star camera is often used to calibrate the attitude relationship matrix between the remote sensing camera and the star camera to realize the compensation of the system error, and through the distance between the main optical axes of the remote sensing camera and the star camera Intuitively reflect the cross-linking angle between them.
随着遥感相机分辨率越来越高，这也对星相机的姿态测量精度提出了更高的要求。通常会采用减小星相机视场，提高光学系统灵敏度，扩大探测器像素规模的设计方式来获得较高的测量精度。扩大探测器像素规模会使像素数成倍增加，这直接影响星相机星点检测效率。工程中应用较多的星点检测方法为阈值法，通过设定背景阈值的方法将背景与目标分离开，其中固定阈值法由于阈值固定，不能很好适应温度变化、杂光带来的背景噪声变化，应用较少；而动态阈值法具有很强的灵活性，主要根据实时得到的图像数据进行阈值的计算，由于需要统计整幅图像所有像素，运算量较大，影响系统实时性。As the resolution of remote sensing cameras is getting higher and higher, this also puts forward higher requirements for the attitude measurement accuracy of star cameras. Usually, the design method of reducing the field of view of the star camera, improving the sensitivity of the optical system, and enlarging the pixel scale of the detector is adopted to obtain higher measurement accuracy. Enlarging the pixel scale of the detector will double the number of pixels, which directly affects the star point detection efficiency of the star camera. The most widely used star point detection method in engineering is the threshold method, which separates the background from the target by setting the background threshold. The fixed threshold method cannot adapt to the background noise caused by temperature changes and stray light because of the fixed threshold. The dynamic threshold method has strong flexibility, and the calculation of the threshold is mainly based on the image data obtained in real time. Since all pixels of the entire image need to be counted, the computational complexity is large, which affects the real-time performance of the system.
发明内容Contents of the invention
本发明的技术解决问题是：克服现有技术的不足，提供一种星相机星点检测方法及系统，解决固定阈值法不能很好适应环境变化、动态阈值法计算量大等问题，提高了星相机星点检测效率。The problem solved by the technology of the present invention is: to overcome the deficiencies of the prior art, to provide a star point detection method and system of a star camera, to solve the problems that the fixed threshold method cannot adapt well to environmental changes, and the calculation amount of the dynamic threshold method is large, and the star point detection method is improved. Camera star point detection efficiency.
本发明的技术方案是：Technical scheme of the present invention is:
1、一种星相机星点检测方法，其特征在于包括如下步骤：1, a star camera star point detection method is characterized in that comprising the steps:
1)在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，作为探测器暗电流基准图像；1) Continuously collect multiple frames of images within the integration time, and accumulate and process the pixels at the same position of the collected multiple frames of images as the reference image of the dark current of the detector;
2)间隔时间t后，在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，获得待补偿图像，将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差，获得目标图像；2) After the interval time t, multiple frames of images are collected continuously within the integration time, and the pixels in the same position of the collected multiple frames of images are accumulated and processed to obtain the image to be compensated, and the pixel value of each pixel in the image to be compensated is compared with the detected The pixel value of each pixel in the dark current reference image of the device is compared to obtain the target image;
3)在目标图像上选取待检测像素域，检测待检测像素域是否为星点；3) Select the pixel field to be detected on the target image, and detect whether the pixel field to be detected is a star point;
4)选取不同的待检测像素域，重复步骤3)，直至分析完目标图像所有的待检测像素域，完成星点检测。4) Select different pixel domains to be detected, and repeat step 3), until all the pixel domains to be detected in the target image are analyzed, and the star point detection is completed.
所述待检测像素域为4*4像素域，且4*4像素域划分为第一象限像素域至第四象限像素域，以及中心像素域。The pixel domain to be detected is a 4*4 pixel domain, and the 4*4 pixel domain is divided into a first quadrant pixel domain to a fourth quadrant pixel domain, and a central pixel domain.
所述4*4像素域划分为第一象限像素域至第四象限像素域，以及中心像素域的方法为：将4*4像素域划分为四个象限，每个象限中有一个2*2的像素域，定义第一象限内的2*2像素域为第一象限像素域，定义第二象限内的2*2像素域为第二象限像素域，定义第三象限内的2*2像素域为第三象限像素域，定义第四象限内的2*2像素域为第四象限像素域，4*4像素域中心的4个像素定义为中心像素域。The 4*4 pixel field is divided into the first quadrant pixel field to the fourth quadrant pixel field, and the method of the central pixel field is: divide the 4*4 pixel field into four quadrants, and each quadrant has a 2*2 The pixel field of , define the 2*2 pixel field in the first quadrant as the first quadrant pixel field, define the 2*2 pixel field in the second quadrant as the second quadrant pixel field, and define the 2*2 pixel field in the third quadrant The domain is the third quadrant pixel domain, the 2*2 pixel domain in the fourth quadrant is defined as the fourth quadrant pixel domain, and the 4 pixels in the center of the 4*4 pixel domain are defined as the central pixel domain.
所述检测待检测像素域是否为星点的方法为：满足每个2*2像素域内的4个像素的像素值之和均小于无效像素阈值H，且中心像素域的4个像素的像素值之和大于星点灵敏度阈值h；中心像素域的4个像素至少有2个像素的像素值大于星点灵敏度阈值m，且至少满足下列条件中的一个条件：The method for detecting whether the pixel field to be detected is a star point is: the sum of the pixel values of the 4 pixels in each 2*2 pixel field is less than the invalid pixel threshold H, and the pixel values of the 4 pixels in the central pixel field The sum is greater than the star point sensitivity threshold h; the pixel value of at least 2 pixels in the 4 pixels in the central pixel domain is greater than the star point sensitivity threshold m, and at least one of the following conditions is met:
A)在所有2*2像素域中，中心像素域的像素值之和最大；A) In all 2*2 pixel domains, the sum of the pixel values of the central pixel domain is the largest;
B)第一象限像素域的像素值之和大于星点灵敏度阈值h，第三象限像素域的像素值之和大于星点灵敏度阈值h，第二象限像素域的像素值之和小于等于星点灵敏度阈值h，第四象限像素域的像素值之和小于等于星点灵敏度阈值h；B) The sum of the pixel values in the first quadrant pixel field is greater than the star point sensitivity threshold h, the sum of the pixel values in the third quadrant pixel field is greater than the star point sensitivity threshold h, and the sum of the pixel values in the second quadrant pixel field is less than or equal to the star point Sensitivity threshold h, the sum of the pixel values in the fourth quadrant pixel field is less than or equal to star point sensitivity threshold h;
C)第二象限像素域的像素值之和大于星点灵敏度阈值h，第四象限像素域的像素值之和大于星点灵敏度阈值h，第一象限像素域的像素值之和小于等于星点灵敏度阈值h，第三象限像素域的像素值之和小于等于星点灵敏度阈值h。C) The sum of the pixel values in the second quadrant pixel field is greater than the star point sensitivity threshold h, the sum of the pixel values in the fourth quadrant pixel field is greater than the star point sensitivity threshold h, and the sum of the pixel values in the first quadrant pixel field is less than or equal to the star point Sensitivity threshold h, the sum of pixel values in the third quadrant pixel domain is less than or equal to the star point sensitivity threshold h.
所述无效像素阈值H为像素饱和值的95％，星点灵敏度阈值h为星相机全遮光条件下8～12倍图像噪声；星点灵敏度阈值m为星相机全遮光条件下4～6倍图像噪声。The invalid pixel threshold H is 95% of the pixel saturation value, the star point sensitivity threshold h is 8 to 12 times the image noise under the full shading condition of the star camera; the star point sensitivity threshold m is 4 to 6 times the image noise under the full shading condition of the star camera noise.
所述间隔时间t＝1/f，其中f为星相机工作帧频。The interval time t=1/f, where f is the working frame rate of the star camera.
所述将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差的方法为：待补偿图像中每个像素的像素值减去探测器暗电流基准图像同一位置像素的像素值，像素差值大于等于0，则像素差值保留，像素差值小于0进行则像素差值置零。The method for making a difference between the pixel value of each pixel in the image to be compensated and the pixel value of each pixel in the detector dark current reference image is: the pixel value of each pixel in the image to be compensated minus the detector dark current reference The pixel value of the pixel at the same position of the image, if the pixel difference value is greater than or equal to 0, the pixel difference value will be kept, and if the pixel difference value is less than 0, the pixel difference value will be set to zero.
一种星相机星点检测系统包括图像采集模块、图像处理模块、星点检测模块；A star camera star point detection system includes an image acquisition module, an image processing module, and a star point detection module;
图像采集模块在积分时间内连续采集多帧图像，将采集得到的图像同一位置的像素进行累加处理，作为探测器暗电流基准图像；间隔时间t后，在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，获得待补偿图像；The image acquisition module continuously acquires multiple frames of images within the integration time, and accumulates and processes the pixels at the same position of the acquired images as the detector dark current reference image; after the interval time t, continuously acquires multiple frames of images within the integration time, and The pixels at the same position of the collected multi-frame images are accumulated and processed to obtain the image to be compensated;
图像处理模块将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差，获得目标图像；The image processing module makes a difference between the pixel value of each pixel in the image to be compensated and the pixel value of each pixel in the detector dark current reference image to obtain the target image;
星点检测模块在目标图像上选取待检测像素域，根据比较准则，检测待检测像素域是否为星点；然后获取新的待检测像素域，继续对新的待检测像素域进行星点检测，直至检测完目标图像所有的待检测像素域，完成星点检测。The star point detection module selects the pixel field to be detected on the target image, and detects whether the pixel field to be detected is a star point according to the comparison criterion; then obtains a new pixel field to be detected, and continues to perform star point detection on the new pixel field to be detected, Star point detection is completed until all to-be-detected pixel domains of the target image are detected.
所述待检测像素域为4*4像素域，且将4*4像素域划分为四个象限，每个象限中有一个2*2的像素域，定义第一象限内的2*2像素域为第一象限像素域，定义第二象限内的2*2像素域为第二象限像素域，定义第三象限内的2*2像素域为第三象限像素域，定义第四象限内的2*2像素域为第四象限像素域，4*4像素域中心的4个像素定义为中心像素域。The pixel field to be detected is a 4*4 pixel field, and the 4*4 pixel field is divided into four quadrants, each quadrant has a 2*2 pixel field, and the 2*2 pixel field in the first quadrant is defined is the first quadrant pixel field, define the 2*2 pixel field in the second quadrant as the second quadrant pixel field, define the 2*2 pixel field in the third quadrant as the third quadrant pixel field, and define the 2*2 pixel field in the fourth quadrant The *2 pixel field is the fourth quadrant pixel field, and the 4 pixels in the center of the 4*4 pixel field are defined as the central pixel field.
所述检测待检测像素域是否为星点的方法为：满足每个2*2像素域内的4个像素的像素值之和均小于无效像素阈值H，且中心像素域的4个像素的像素值之和大于星点灵敏度阈值h；中心像素域中4个像素至少有2个像素的像素值大于星点灵敏度阈值m，且至少满足下列条件中的一个条件：The method for detecting whether the pixel field to be detected is a star point is: the sum of the pixel values of the 4 pixels in each 2*2 pixel field is less than the invalid pixel threshold H, and the pixel values of the 4 pixels in the central pixel field The sum is greater than the star point sensitivity threshold h; the pixel value of at least 2 of the 4 pixels in the central pixel domain is greater than the star point sensitivity threshold m, and at least one of the following conditions is met:
D)在所有2*2像素域中，中心像素域的像素值之和最大；D) In all 2*2 pixel domains, the sum of the pixel values of the central pixel domain is the largest;
E)第一象限像素域的像素值之和大于星点灵敏度阈值h，第三象限像素域的像素值之和大于星点灵敏度阈值h，第二象限像素域的像素值之和小于等于星点灵敏度阈值h，第四象限像素域的像素值之和小于等于星点灵敏度阈值h；E) The sum of the pixel values in the first quadrant pixel field is greater than the star point sensitivity threshold h, the sum of the pixel values in the third quadrant pixel field is greater than the star point sensitivity threshold h, and the sum of the pixel values in the second quadrant pixel field is less than or equal to the star point Sensitivity threshold h, the sum of the pixel values in the fourth quadrant pixel field is less than or equal to star point sensitivity threshold h;
F)第二象限像素域的像素值之和大于星点灵敏度阈值h，第四象限像素域的像素值之和大于星点灵敏度阈值h，第一象限像素域的像素值之和小于等于星点灵敏度阈值h，第三象限像素域的像素值之和小于等于星点灵敏度阈值h。F) The sum of the pixel values in the second quadrant pixel field is greater than the star point sensitivity threshold h, the sum of the pixel values in the fourth quadrant pixel field is greater than the star point sensitivity threshold h, and the sum of the pixel values in the first quadrant pixel field is less than or equal to the star point Sensitivity threshold h, the sum of pixel values in the third quadrant pixel domain is less than or equal to the star point sensitivity threshold h.
其中，无效像素阈值H为像素饱和值的95％，星点灵敏度阈值h为星相机全遮光条件下8～12倍图像噪声；星点灵敏度阈值m为星相机全遮光条件下4～6倍图像噪声。Among them, the invalid pixel threshold H is 95% of the pixel saturation value, the star point sensitivity threshold h is 8 to 12 times the image noise under the full shading condition of the star camera; the star point sensitivity threshold m is 4 to 6 times the image noise under the full shading condition of the star camera noise.
所述间隔时间t＝1/f，其中f为星相机工作帧频。The interval time t=1/f, where f is the working frame rate of the star camera.
所述将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差的方法为：待补偿图像中每个像素的像素值减去探测器暗电流基准图像同一位置像素的像素值，像素差值大于等于0，则像素差值保留，差值小于0进行则像素差值置零。The method for making a difference between the pixel value of each pixel in the image to be compensated and the pixel value of each pixel in the detector dark current reference image is: the pixel value of each pixel in the image to be compensated minus the detector dark current reference The pixel value of the pixel at the same position in the image, if the pixel difference value is greater than or equal to 0, the pixel difference value is retained, and the pixel difference value is set to zero if the difference value is less than 0.
本发明与现有技术相比的有益效果是：The beneficial effect of the present invention compared with prior art is:
1)本星点检测方法，灵敏度阈值通过实验室定标确定，非实时计算，不消耗处理器运算时间，有利于提高星点检测效率；1) In this star point detection method, the sensitivity threshold is determined by laboratory calibration, non-real-time calculation, and does not consume processor computing time, which is conducive to improving the star point detection efficiency;
2)本星点检测方法星点检测过程计算量少，仅存在加减运算和大小比较，易于硬件实现，因此识别效率高；2) The star point detection method of this star point detection process has a small amount of calculation, only addition and subtraction operations and size comparisons exist, and is easy to implement in hardware, so the recognition efficiency is high;
3)本星点检测方法采用多帧累加提高图像信噪比，补偿探测器暗电流处理过程，大大降低噪声影响，可以探测到更低星等，增加检测到的星等数目，适用工程化应用于高精度星相机研制过程，提高星相机姿态测量精度。3) This star point detection method uses multi-frame accumulation to improve the image signal-to-noise ratio, compensates the dark current processing process of the detector, greatly reduces the influence of noise, can detect lower magnitudes, and increases the number of detected magnitudes, which is suitable for engineering applications In the development process of high-precision star camera, the attitude measurement accuracy of star camera is improved.
附图说明Description of drawings
图1是本发明中涉及的星相机星点检测方法流程图；Fig. 1 is the flow chart of star point detection method of star camera involved in the present invention;
图2是多帧图像累加过程示意图；Fig. 2 is a schematic diagram of multi-frame image accumulation process;
图3是4*4像素区域示意图。Fig. 3 is a schematic diagram of a 4*4 pixel area.
具体实施方式Detailed ways
一种星相机星点检测方法及系统，如图1所示，系统模块包括：图像采集、图像处理和星点检测。A star point detection method and system of a star camera, as shown in Figure 1, the system modules include: image acquisition, image processing and star point detection.
所述图像采集模块：如图2所示，在积分时间内连续采集多帧图像，通常N取3或4帧，并进行累加处理，提高图像信噪比，获得第一幅图像F1。The image acquisition module: as shown in Figure 2, continuously collects multiple frames of images within the integration time, usually N takes 3 or 4 frames, and performs cumulative processing to improve the image signal-to-noise ratio and obtain the first image F1.
所述图像处理：将第一幅图像F1作为补偿探测器暗电流基准图像D。间隔时间t后，在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，获得第二幅图像F2，间隔时间t＝1/f，其中f为星相机工作帧频。将第二幅图像与第一幅图像做差进行暗电流补偿，降低暗电流影响，获得目标图像S，即S＝F2-D，对目标图像S进行反饱和处理，若像素差值大于等于0，则像素差值保留，差值小于0进行则像素差值置零。The image processing: take the first image F1 as the reference image D for compensating the dark current of the detector. After the interval time t, multiple frames of images are collected continuously within the integration time, and the pixels at the same position of the collected multiple frames of images are accumulated and processed to obtain the second image F2, the interval time t=1/f, where f is the star camera Working frame rate. Make the difference between the second image and the first image to perform dark current compensation, reduce the influence of dark current, and obtain the target image S, that is, S=F2-D, perform anti-saturation processing on the target image S, if the pixel difference is greater than or equal to 0 , the pixel difference value is retained, and the pixel difference value is set to zero if the difference value is less than 0.
所述星点检测模块：如图3所示，将4*4像素域划分为四个象限，每个象限中有一个2*2的像素域，定义第一象限内的2*2像素域为第一象限像素域S2，定义第二象限内的2*2像素域为第二象限像素域S1，定义第三象限内的2*2像素域为第三象限像素域S3，定义第四象限内的2*2像素域为第四象限像素域S4，4*4像素域中心的4个像素定义为中心像素域S0，根据比较准则，检测4*4像素域是否为星点。Described star point detection module: as shown in Figure 3, 4*4 pixel field is divided into four quadrants, has a 2*2 pixel field in each quadrant, defines the 2*2 pixel field in the first quadrant as The first quadrant pixel field S2, defines the 2*2 pixel field in the second quadrant as the second quadrant pixel field S1, defines the 2*2 pixel field in the third quadrant as the third quadrant pixel field S3, defines the fourth quadrant The 2*2 pixel field is the fourth quadrant pixel field S4, and the 4 pixels in the center of the 4*4 pixel field are defined as the central pixel field S0. According to the comparison criterion, it is detected whether the 4*4 pixel field is a star point.
检测4*4像素域为星点须满足每个2*2像素域内的4个像素的和值均小于无效像素阈值H，且中心像素域的4个像素的和值大于星点灵敏度阈值h；中心像素域中4个像素至少有2个像素的像素值大于星点灵敏度阈值m，且至少满足下列条件中的一个条件：To detect a 4*4 pixel field as a star point, the sum of the 4 pixels in each 2*2 pixel field is less than the invalid pixel threshold H, and the sum of the 4 pixels in the central pixel field is greater than the star point sensitivity threshold h; The pixel values of at least 2 of the 4 pixels in the central pixel domain are greater than the star point sensitivity threshold m, and at least one of the following conditions is met:
F)在所有2*2像素域中，中心像素域的像素和值最大；F) In all 2*2 pixel domains, the pixel sum value of the central pixel domain is the largest;
G)第一象限像素域的像素和值大于星点灵敏度阈值h，第三象限像素域的像素和值大于星点灵敏度阈值h，第二象限像素域的像素和值小于等于星点灵敏度阈值h，第四象限像素域的像素和值小于等于星点灵敏度阈值h；G) The sum of pixels in the pixel field of the first quadrant is greater than the star point sensitivity threshold h, the sum of pixels in the pixel field of the third quadrant is greater than the star point sensitivity threshold h, and the sum of pixels in the pixel field of the second quadrant is less than or equal to the star point sensitivity threshold h , the pixel sum value of the fourth quadrant pixel domain is less than or equal to the star point sensitivity threshold h;
H)第二象限像素域的像素和值大于星点灵敏度阈值h，第四象限像素域的像素和值大于星点灵敏度阈值h，第一象限像素域的像素和值小于等于星点灵敏度阈值h，第三象限像素域的像素和值小于等于星点灵敏度阈值h。H) The pixel sum value of the second quadrant pixel field is greater than the star point sensitivity threshold h, the pixel sum value of the fourth quadrant pixel field is greater than the star point sensitivity threshold value h, and the pixel sum value of the first quadrant pixel field is less than or equal to the star point sensitivity threshold value h , the sum of pixels in the third quadrant pixel domain is less than or equal to the star point sensitivity threshold h.
通常无效像素阈值H取值为像素饱和值，星点灵敏度阈值h＝12δ，星点灵敏度阈值m＝6δ，δ为遮光条件下图像噪声标准差。Usually the invalid pixel threshold H is taken as the pixel saturation value, the star point sensitivity threshold h=12δ, the star point sensitivity threshold m=6δ, and δ is the standard deviation of the image noise under the shading condition.
与已取得的4*4像素域错开一列或一行获取新的4*4像素域，重复星点检测过程，直至分析完目标图像S所有的4*4像素域，完成星点检测。Obtain a new 4*4 pixel field by staggering one column or one row from the obtained 4*4 pixel field, repeat the star point detection process until all 4*4 pixel fields of the target image S are analyzed, and the star point detection is completed.
实际工作中，探测器工作一定时间后，随外界工作环境变化，暗电流基准帧退化，须重新采集探测器暗电流基准图像D，进行暗电流基准图像更新。In actual work, after the detector works for a certain period of time, the dark current reference frame degrades with the change of the external working environment, and the dark current reference image D of the detector must be collected again to update the dark current reference image.
一种星相机星点检测方法包括如下步骤：A star camera star point detection method comprises the steps:
1)在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，作为探测器暗电流基准图像；1) Continuously collect multiple frames of images within the integration time, and accumulate and process the pixels at the same position of the collected multiple frames of images as the reference image of the dark current of the detector;
2)间隔时间t后，在积分时间内连续采集多帧图像，将采集得到的多帧图像同一位置的像素进行累加处理，获得待补偿图像，将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差，获得目标图像；2) After the interval time t, multiple frames of images are collected continuously within the integration time, and the pixels in the same position of the collected multiple frames of images are accumulated and processed to obtain the image to be compensated, and the pixel value of each pixel in the image to be compensated is compared with the detected The pixel value of each pixel in the dark current reference image of the device is compared to obtain the target image;
3)在目标图像4个角中任意取一个角为顶点，选取一个4*4像素域；3) Take any one of the 4 corners of the target image as the vertex, and select a 4*4 pixel field;
4)将选取的4*4像素域划分为第一象限像素域至第四象限像素域，以及中心像素域，根据比较准则，检测4*4像素域是否为星点；4) Divide the selected 4*4 pixel field into the first quadrant pixel field to the fourth quadrant pixel field, and the central pixel field, and detect whether the 4*4 pixel field is a star point according to the comparison criterion;
5)与已取得的4*4像素域错开一列或一行获取新的4*4像素域，重复步骤4)，直至分析完目标图像所有的4*4像素域，完成星点检测。5) Obtain a new 4*4 pixel field by staggering one column or one row from the obtained 4*4 pixel field, repeat step 4), until all 4*4 pixel fields of the target image are analyzed, and the star point detection is completed.
所述将待补偿图像中每个像素的像素值与探测器暗电流基准图像中每个像素的像素值做差的方法为：待补偿图像中每个像素的像素值减去探测器暗电流基准图像同一位置像素的像素值，像素差值大于等于0，则像素差值保留，差值小于0进行则像素差值置零。The method for making a difference between the pixel value of each pixel in the image to be compensated and the pixel value of each pixel in the detector dark current reference image is: the pixel value of each pixel in the image to be compensated minus the detector dark current reference The pixel value of the pixel at the same position in the image, if the pixel difference value is greater than or equal to 0, the pixel difference value is retained, and the pixel difference value is set to zero if the difference value is less than 0.
所述将选取的4*4像素域划分为第一象限像素域至第四象限像素域以及中心像素域的方法为：将4*4像素域划分为四个象限，每个象限中有一个2*2的像素域，定义第一象限内的2*2像素域为第一象限像素域，定义第二象限内的2*2像素域为第二象限像素域，定义第三象限内的2*2像素域为第三象限像素域，定义第四象限内的2*2像素域为第四象限像素域，4*4像素域中心的4个像素定义为中心像素域。The method of dividing the selected 4*4 pixel field into the first quadrant pixel field to the fourth quadrant pixel field and the central pixel field is: divide the 4*4 pixel field into four quadrants, and each quadrant has a 2 *2 pixel field, define the 2*2 pixel field in the first quadrant as the first quadrant pixel field, define the 2*2 pixel field in the second quadrant as the second quadrant pixel field, define the 2*2 pixel field in the third quadrant The 2 pixel domain is the third quadrant pixel domain, the 2*2 pixel domain in the fourth quadrant is defined as the fourth quadrant pixel domain, and the 4 pixels in the center of the 4*4 pixel domain are defined as the central pixel domain.
所述检测4*4像素域是否为星点的方法为：满足每个2*2像素域内的4个像素的和值均小于无效像素阈值H，且中心像素域的4个像素的和值大于星点灵敏度阈值h；中心像素域中的4个像素至少有2个像素的像素值大于星点灵敏度阈值m，且至少满足下列条件中的一个条件：The method for detecting whether the 4*4 pixel field is a star point is: the sum of the 4 pixels in each 2*2 pixel field is less than the invalid pixel threshold H, and the sum of the 4 pixels in the central pixel field is greater than Star point sensitivity threshold h; the pixel value of at least 2 pixels in the 4 pixels in the central pixel domain is greater than the star point sensitivity threshold m, and at least one of the following conditions is met:
A)在所有2*2像素域中，中心像素域的像素和值最大；A) In all 2*2 pixel domains, the pixel sum value of the central pixel domain is the largest;
B)第一象限像素域的像素和值大于星点灵敏度阈值h，第三象限像素域的像素和值大于星点灵敏度阈值h，第二象限像素域的像素和值小于等于星点灵敏度阈值h，第四象限像素域的像素和值小于等于星点灵敏度阈值h；B) The pixel sum value of the first quadrant pixel field is greater than the star point sensitivity threshold h, the pixel sum value of the third quadrant pixel field is greater than the star point sensitivity threshold value h, and the pixel sum value of the second quadrant pixel field is less than or equal to the star point sensitivity threshold value h , the pixel sum value of the fourth quadrant pixel domain is less than or equal to the star point sensitivity threshold h;
C)第二象限像素域的像素和值大于星点灵敏度阈值h，第四象限像素域的像素和值大于星点灵敏度阈值h，第一象限像素域的像素和值小于等于星点灵敏度阈值h，第三象限像素域的像素和值小于等于星点灵敏度阈值h。C) The pixel sum value of the second quadrant pixel field is greater than the star point sensitivity threshold h, the pixel sum value of the fourth quadrant pixel field is greater than the star point sensitivity threshold value h, and the pixel sum value of the first quadrant pixel field is less than or equal to the star point sensitivity threshold value h , the sum of pixels in the third quadrant pixel domain is less than or equal to the star point sensitivity threshold h.
所述间隔时间t＝1/f，其中f为星相机工作帧频。The interval time t=1/f, where f is the working frame rate of the star camera.
所述无效像素阈值H为像素饱和值的95％，星点灵敏度阈值h为星相机全遮光条件下8～12倍图像噪声；星点灵敏度阈值m为星相机全遮光条件下4～6倍图像噪声。The invalid pixel threshold H is 95% of the pixel saturation value, the star point sensitivity threshold h is 8 to 12 times the image noise under the full shading condition of the star camera; the star point sensitivity threshold m is 4 to 6 times the image noise under the full shading condition of the star camera noise.
本发明说明书中未作详细描述的内容属本领域专业技术人员的公知技术。The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.
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