CN111105446B - Star extraction and compensation method - Google Patents
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Abstract
A star point extraction and compensation method comprises the steps of establishing a star point image spot template based on a star point imaging model, extracting star points in a window where the star points are located by using the star point image spot template through an image registration method with the maximum correlation, adjusting the gray value of the star point image spot template based on the actual gray value of the image spots, and compensating the star points by using the star point image spot template after the gray value is adjusted. The invention can reduce the influence of background noise under the condition of low signal-to-noise ratio and improve the extraction rate of the star point and the positioning precision of the star point. The invention is suitable for the whole life cycle of the star sensor, in particular to the end of the life cycle of the star sensor.
Description
Technical Field
The invention relates to a star point extraction and compensation method.
Background
At present, key type tasks represented by atmospheric environment detection and Fengyun four satellites put higher requirements on the detection precision of a star sensor, and the star sensor is required to ensure the precision in the whole life cycle in order to ensure that the satellites normally execute in-orbit tasks. A life of 8 years or more is generally required for LEO orbit, and a life of 10 years or more is generally required for GEO orbit. Compared with the initial stage of orbit entering, after long-term orbit running, due to factors such as device aging and space radiation, noise is increased, the image signal-to-noise ratio is obviously reduced, and the star point extraction rate and the star point mass center positioning accuracy are influenced. If no related algorithm exists, the effective rate and the precision of the attitude measurement are difficult to ensure only by hardware means such as a high-grade detector, refrigeration and the like, and the stable output of the attitude information and the guarantee of the precision meeting the requirements are difficult to ensure at the end of the service life of the star sensor.
Generally speaking, the longer the on-orbit working time of the star sensor is, the higher the noise energy mean value is, and the larger the variance is, the target is in a superposition relationship with the background and the noise, as shown in formula (1), and the three are independent and divisible.
G(x,y)＝S(x,y)+B(x,y)+η(x,y) (1)
In the formula, G (x, y) is a gray-scale value of a certain pixel, S (x, y) is a gray-scale value of a star point on the pixel, B (x, y) is a gray-scale value of a background on the pixel, and η (x, y) is noise.
Under the condition of low signal-to-noise ratio, because S (x, y) is too small and eta (x, y) is too large, the threshold segmentation method cannot select an appropriate threshold T to segment the star spot, and even if individual pixels with high energy can be segmented, the individual pixels with too few pixels are judged as high-energy noise points by the connected domain method.
Therefore, under the condition of low signal-to-noise ratio, it is not feasible to use the gray value as the criterion to judge whether a pixel is a star spot.
Disclosure of Invention
The invention provides a star point extraction and compensation method which can reduce the influence of background noise under the condition of low signal-to-noise ratio and improve the star point extraction rate and the star point positioning accuracy.
In order to achieve the above object, the present invention provides a method for extracting and compensating star points, comprising the following steps: establishing a star point image spot template based on a star point imaging model, extracting star points in a window where the star points are located by using the star point image spot template through an image registration method with the maximum correlation, adjusting the gray value of the star point image spot template based on the actual gray value of the image spots, and compensating the star points by using the star point image spot template after the gray value is adjusted.
And (4) taking the energy peak value coordinate of the star point imaging model as a center, and intercepting the image in a set range as a star point image spot template w.
And moving the star point image spot template w in the window where the star point is located, calculating the relevant response of the area covered by the star point image spot template w point by point, and finding out the maximum response area s as the area where the star point is located.
The adjusted star spot template is w ', w' = alpha w, wherein alpha is a gray scale, and alpha = G 1 /G 2 ，G 1 Is the sum of the gray levels of three pixels with the maximum gray value in the star spot template w 2 Is the sum of the gradations of three pixels having the largest gradation value among the first order differential values s' of the maximum response region.
When the gray scale beta of each pixel of the first differential value s ' of the maximum response area and the adjusted star spot template w ' is larger than a set threshold, the adjusted star spot template w ' is adopted to compensate the first differential value s ' of the maximum response area, and the compensated star spot s ' is obtained after the compensation is finished;
calculating the coordinates (x) of the centroid of the star point image spots according to the compensated star point image spots s' by using a gray-scale weighting method c ,y c )；
The invention adopts the image registration method with the maximum correlation to extract the star points, and compensates the star points by utilizing the adjusted star point image spot template, thereby reducing the influence of background noise under the condition of low signal to noise ratio and improving the star point extraction rate and the star point positioning precision. The invention is suitable for the full life of the star sensor, in particular to the end of the life of the star sensor.
Drawings
Fig. 1 is a flowchart of a star point extraction and compensation method provided in an embodiment of the present invention.
Detailed Description
The preferred embodiment of the present invention is described in detail below with reference to fig. 1.
The star imaging model is a model for describing the energy distribution of star image spots, and can accurately fit the energy distribution of star points, so that a new criterion is provided for star point extraction, namely, the star points are extracted by utilizing gray distribution characteristics and adopting an image registration method. According to the formula G (x, y) = S (x, y) + B (x, y) + η (x, y), where the background gray level B (x, y) is generally a constant value, and the noise η (x, y) is randomly distributed, so the star point gray level S (x, y) can affect the gray level value G (x, y) of the pixel where it is located, so that it exhibits a distribution characteristic similar to S (x, y).
The invention provides a star point extraction and compensation method based on a fixed star imaging model, which aims to realize stable star point extraction of a star sensor under the condition of low signal-to-noise ratio at the end of service life.
As shown in fig. 1, in an embodiment of the present invention, the method for extracting and compensating star points includes:
s1, establishing a star point image spot template w based on a star point imaging model;
establishing a star point imaging model w 0 (s, t) imaging the model energy distribution peak coordinates(s) with the star points 0 ,t 0 ) Taking the image with the size of 3 multiplied by 3 as a center, and taking the image as a star spot template w;
the energy peak value coordinate of the star point imaging model is taken as a center, and a certain range of images are intercepted to be used as a template, so that the template and the actual star imaging image spot energy distribution have high fitting precision and high accuracy for image registration;
s2, moving a star spot template w in a window where a star point is located, and calculating the relevant response c (x, y) of an area covered by the star spot template w point by point;
moving the star spot image spot template w point by point in a window f (x, y) where the star points predicted by the star sensor with the size of M multiplied by N are positioned so as to ensure that the star point image spot templateUpper left corner of w(s) 0 -1,t 0 -1) coinciding with the point (x, y), calculating the correlation response c (x, y) of the star spot template w with the image area covered by the star spot template w in the window f in which the star is located;
s3, finding a maximum response area S;
traversing all points in a window where the star points are located, and then finding out a maximum response area s as an area where the star points are located;
the star point is extracted by adopting the image registration method with the maximum correlation, the method is suitable for the full life cycle of the star sensor, and particularly, the star point extraction rate is high and the positioning accuracy is stable under the condition of low signal-to-noise ratio;
s4, calculating a first differential value S' of the maximum response area S;
s5, solving a gray scale alpha;
selecting three pixels with the maximum gray value from the star spot template w, and recording the gray sum as G 1 Similarly, three pixels with the largest gray scale value are selected from the region s', and the sum of the gray scales is recorded as G 2 Calculating a gray scale ratio of α = G 1 /G 2 ；
S6, adjusting the gray value of the star point image spot template;
adjusting the gray value of the star spot template according to the proportion alpha, and recording the adjusted star spot template as w ', w' = alpha w;
the gray value of the star spot image template is adjusted based on the actual gray value of the image spot, so that the star spot image template is more accurate and better meets the requirement of subsequent compensation;
s7, calculating the gray scale ratio beta of each pixel of S 'and w';
s8, compensating the star point image spots by using the adjusted star point image spot template w';
setting a threshold value T (the threshold value T can be determined according to engineering experience), and if beta is larger than T, adopting the adjusted star point image spot template w ' to compensate s ', and obtaining the extracted star point image spot s ' after compensation is finished;
the adjusted star point image spot template is used for compensating the star points, so that the influence of background noise can be reduced, and the star point positioning precision is improved; after obtaining the area of the star point (namely the star point image spot), the template is used for compensating the star point image spot, so that the influence of high-energy noise can be eliminated or reduced, the star point image spot is supplemented to a certain extent, and the positioning precision of the star point mass center under the condition of low signal-to-noise ratio is higher;
s9, calculating coordinates of the mass centers of the star points in the window;
the method adopts gray-scale weighting method to obtain the coordinates (x) of the center of mass of the image spot of the star point c ,y c )。
The invention generates a template based on a star point imaging model of the star sensor, and performs star point extraction and compensation by using a star point image spot template, thereby realizing the star point extraction under the condition of low signal-to-noise ratio at the end of the service life of the star sensor and improving the star point extraction rate and the star point positioning precision. The method is different from the existing method for segmenting and extracting the planet points and the background by utilizing the gray threshold, and can be used as an effective supplement of the existing method for extracting the planet points.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (6)
1. A star point extraction and compensation method is characterized by comprising the following steps: establishing a star point image spot template based on a star point imaging model, extracting star points in a window where the star points are located by using the star point image spot template through an image registration method with the maximum correlation, adjusting the gray value of the star point image spot template based on the actual gray value of the image spots, and compensating the star points by using the star point image spot template after the gray value is adjusted.
2. The method for extracting and compensating the star points according to claim 1, wherein the image in the set range is intercepted as a star point image spot template w by taking the energy peak value coordinates of the star point imaging model as the center.
3. The method of claim 2, wherein the star point image spot template w is moved in the window where the star point is located, the correlation response of the area covered by the star point image spot template w is calculated point by point, and the maximum response area s is found as the area where the star point is located.
4. The method of claim 3, wherein the adjusted star spot template is w ', w' = α w, where α is gray scale, α = G 1 /G 2 ，G 1 Is the sum of the gray levels of three pixels with the maximum gray value in the star spot template w 2 Is the sum of the gradations of three pixels having the largest gradation value among the first order differential values s' of the maximum response region.
5. The method of claim 4, wherein when the gray scale β of each pixel of the first differential value s ' of the maximum response region and the adjusted star spot template w ' is greater than the predetermined threshold, the adjusted star spot template w ' is used to compensate the first differential value s ' of the maximum response region, and the compensated star spot s ' is obtained after the compensation;
6. the method for extracting and compensating for star points of claim 5 wherein the gray-scale weighting method is used to determine the coordinates of the centroid (x) of the star point image spots from the compensated star point image spots s c ,y c )；
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| CN112729276A (en) * | 2020-11-27 | 2021-04-30 | 上海航天控制技术研究所 | Star point extraction system and method of star sensor |
| CN112634295B (en) * | 2020-12-29 | 2022-05-20 | 中国人民解放军国防科技大学 | Star sensor star point segmentation method based on double gradient thresholds |
| CN113514054A (en) * | 2021-06-16 | 2021-10-19 | 北京遥感设备研究所 | Star sensor star point image spot detection method and system |
| CN114189631B (en) * | 2022-02-16 | 2022-07-01 | 荣耀终端有限公司 | Shooting method and electronic equipment |
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