CN111854736B - Error-suppression star point centroid positioning method - Google Patents
Error-suppression star point centroid positioning method Download PDFInfo
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- CN111854736B CN111854736B CN202010534272.5A CN202010534272A CN111854736B CN 111854736 B CN111854736 B CN 111854736B CN 202010534272 A CN202010534272 A CN 202010534272A CN 111854736 B CN111854736 B CN 111854736B
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Abstract
The invention relates to a star point positioning method, in particular to an error-suppressed star point centroid positioning method, which effectively suppresses systematic errors and random errors of centroid method star point positioning. The method combines the advantages of two mass center positioning methods, namely a mass center method and a surface fitting method, and adopts cubic spline fitting to process the image gray of the star point window, so that the smoothness of the star point window is improved, and the influence of random noise is inhibited; the algorithm is adopted for defocusing, under the condition that the signal to noise ratio of the system is not reduced, the light spot diffusion area is enlarged by the interpolation algorithm, and the image space sampling frequency is increased to inhibit the influence of system errors. The method effectively inhibits positioning errors, combines the advantages of two mass center positioning methods, namely a mass center method and a curved surface fitting method, and has good noise resistance and high positioning accuracy.
Description
Technical Field
The invention relates to a star point positioning method, in particular to an error-suppressed star point centroid positioning method.
Background
The star point detection is an important link for measuring the indexes of the optical system. The positioning precision of the centroid of the star point image directly influences the debugging and detection of the optical system index. In the star sensor, the positioning of the star point image centroid is particularly important, and the precision of the star point image centroid determines the precision of the attitude measurement of the star sensor. The star point image centroid positioning has wide and important application value in the detection and use of an optical instrument.
The commonly used star point image centroid localization algorithms can be divided into two categories: one type is a three-dimensional surface fitting algorithm such as a Gaussian surface fitting method, a paraboloid fitting method and the like, the surface fitting algorithm has a restraining effect on noise, the accuracy is high, but the surface fitting calculation is complex. The other type is an algorithm for calculating the centroid by using the first moment, such as a traditional centroid method, a weighted centroid method and the like, the first moment of the star point image gray value is directly calculated to obtain the centroid, the calculation speed is high, the robustness is good, but the anti-interference capability of the centroid method is weak, and the star point positioning by using the centroid method can be influenced by systematic errors and random errors.
Disclosure of Invention
The invention provides an error-suppressed star point centroid positioning method aiming at the problems that a surface fitting algorithm is complex and a centroid method is easily interfered by system errors and random errors in the existing star point centroid positioning calculation, combines the advantages of the centroid method and the surface fitting algorithm, starts from the error suppression principle, does not depend on a specific star point imaging model to perform cubic spline fitting to suppress the random errors, utilizes cubic spline interpolation to realize algorithm defocusing suppression of the system errors, and suppresses the overall positioning errors to improve the positioning accuracy.
The technical scheme adopted by the invention is as follows:
an error-suppressed star point centroid positioning method is characterized by comprising the following steps:
step 1, selecting a star point window image X according to the imaging size of star points in an original image X0Size is M0×N0Wherein M is0、N0Respectively as a star point window image X0The transverse, longitudinal dimension of (a);
step 2, aiming at star point window image X0Performing cubic spline fitting on natural boundary in transverse and longitudinal directions to obtain I1And I2Two fitting correction images;
step 3, for I1And I2Adding the two fitting correction images and taking the mean value to obtain a star point window image X after primary error suppression1；
Step 4, determining a simulated defocusing interpolation step S, and utilizing a cubic spline interpolation principle to perform interpolation on a star point window image X1Interpolation is carried out to obtain a star point window image X after interpolation2；
Reading star point window image X2The gray value G (i, j) of the pixel is shown in the specification, wherein (i, j) is a star point window image X2The position of the pixel;
star point window image X2The transverse dimension M and the longitudinal dimension N of the pixel are respectively as follows:
M＝(M0-1)/S+1，
N＝(N0-1)/S+1；
step 5, calculating star point window image X2To obtain the centroid coordinate (x)c，yc)，
In the formula, xij、yijAs a star point window image X2The horizontal and vertical coordinates of the pixel;
step 6, making star point window image X2The coordinates of the center of mass of the image are converted into coordinates (X) under the original image Xz，yz)，
xz＝x0+(S(xc-1)+1)
yz＝y0+(S(yc-1)+1)
In the formula (x)0，y0) As a star point window image X0And positioning the coordinates of the points in the upper left corner of the original image X.
Further, in step 1, M0、N0Taking the horizontal and longitudinal sizes of the star point imaging to be 1.5-2.5 times;
further, in step 1, M0、N0The star point imaging is taken to be twice the transverse and longitudinal dimension.
Further, in step 4, in order to take account of the interpolation calculation amount and the accuracy, the step S is 0.1 pel.
The invention has the beneficial effects that:
1) according to the method, the three-time spline fitting is adopted to process the gray level of the star point window image, so that the smoothness of the star point window image is improved, and the influence of random noise is inhibited; the algorithm is adopted for defocusing, under the condition that the signal to noise ratio of the system is not reduced, the light spot diffusion area is enlarged by the interpolation algorithm, and the image space sampling frequency is increased to inhibit the influence of system errors.
2) The error-suppressed star point centroid positioning method provided by the invention effectively suppresses positioning errors, combines the advantages of two types of centroid positioning methods, namely a centroid method and a curved surface fitting method, has better noise resistance and high positioning precision, and can be widely applied without depending on a specific star point model.
Drawings
FIG. 1 is a schematic diagram of a coordinate system and a star point image calculation window selection under an original image X according to the present invention;
FIG. 2 is a star point window image X selected by the present invention0A grey scale map.
Detailed Description
In order to more clearly explain the technical solution of the present invention, the following detailed description of the present invention is made with reference to the accompanying drawings and specific examples.
The invention provides an error-suppressed star point centroid positioning method, which adopts the following specific technical scheme:
1) in the original image X, determining a centroid calculation window according to the size of star point imaging, namely a star point window image X0Defining the size of star point window image as M0×N0Wherein M is0，N0The same value or different values can be taken, the value size is related to the imaging size of the star point, generally 1.5-2.5 times of the diameter of the star point, the star point image data is easy to lose due to the fact that the window of the star point is too small, positioning distortion is caused, and excessive noise is possibly introduced due to the fact that the window is too large, so that positioning accuracy is reduced.
In the embodiment of the invention, M is selected0，N0Twice the imaging size of the star point, as shown in fig. 1, in the original image X, the (0, 0) point is the origin coordinate, the star point image diameter is about 5 pixels, and then the star point window image M is selected0×N0Is 10X 10, where (x)0，y0) Coordinates of the upper left corner of the star point window image in the original image X are obtained; FIG. 2 is a graph showing (x)0,y0) Star image of small window as origin (i.e. star window image X)0) A grey scale map.
2) Window image of opposite star point X0Performing cubic spline fitting on natural boundary in transverse and longitudinal directions to obtain I1And I2And fitting the two corrected images.
3) To I1And I2Adding the two fitting correction images and taking the mean value to obtain a star point window image X after primary error suppression1：
Star point window image X1The size of (2) is unchanged, and is still 10 × 10 in the present embodiment.
4) Determining a simulated defocusing interpolation step S, wherein the step S is 0.1 pixel, namely performing 10-time interpolation on the image, and utilizing a cubic spline interpolation principle to perform star point window image X1Interpolation is carried out to obtain a star point window image X after interpolation2Can directly read the matrix elements to obtain a star point window image X2The gray value G (i, j) of the pixel is shown in the specification, wherein (i, j) is a star point window image X2The position of the picture element.
In other embodiments, different defocus interpolation steps S can be set as required, but the selection of the defocus interpolation step is not too large or too small. If the step distance of the selected out-of-focus interpolation is too large, the requirement of interpolation precision cannot be met; if the step distance of the defocused interpolation is too small, the interpolation calculation amount is large. The embodiment of the invention sets the defocusing step distance as 0.1 pixel, and can better consider the interpolation calculated amount and the precision.
Interpolated star point window image X2The transverse longitudinal dimensions M, N of the picture elements are respectively:
M＝(M0-1)/S+1
N＝(N0-1)/S+1
in this embodiment, the star point window image X1Is 10X 10, the window image X of the star point is obtained1Obtaining a star point window image X after 10 times of interpolation2The size of (a) is 91 × 91.
5) Calculating star point window image X2To obtain the centroid coordinate (x)c，yc)，
Wherein M, N are respectively window images X of interpolated star points2The transverse and longitudinal dimensions of the picture element, M, N in this embodiment being both 91; g (i, j) is a star point window image X2Is the gray value of the pixel (i, j), i.e. the star point window image X1The gray value after interpolation can be directly obtained; x is the number ofij、yijAs a star point window image X2The horizontal and vertical coordinates of the picture element.
6) Corresponding to 0.1 pixel of defocusing step distance, namely performing coordinate conversion by 10-time interpolation, and converting a star point window image X2The coordinates of the center of mass of the image are converted into coordinates (X) under the original image Xz，yz)，
xz＝x0+((xc-1)/10+1)
yz＝y0+((yc-1)/10+1)
In the formula (x)0，y0) Locating point coordinates of the star point window image at the upper left corner in the original image X;
(xc，yc) As a star point window image X2The centroid coordinates of the lower.
In other words, a star point window image X2The lower centroid coordinates are converted into coordinates in a coordinate system with (0, 0) as the origin in the original image X in fig. 1.
The method starts from the error inhibition principle, cubic spline fitting is carried out to inhibit random errors without depending on a specific star point imaging model, the algorithm defocusing inhibition system errors are realized by utilizing cubic spline interpolation, and the positioning precision is improved by inhibiting the whole positioning errors.
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (4)
1. An error-suppressed star point centroid positioning method is characterized by comprising the following steps:
step 1, selecting a star point window image X according to the imaging size of star points in an original image X0Size is M0×N0Wherein M is0、N0Respectively as a star point window image X0The transverse, longitudinal dimension of (a);
step 2, aiming at star point window image X0Performing cubic spline fitting on natural boundary in transverse and longitudinal directions to obtain I1And I2Two fitting correction images;
step 3, for I1And I2Adding the gray values of the pixels of the two fitting correction images to obtain an average value, and obtaining a star point window image X after primary error suppression1；
Step 4, determining a simulated defocusing interpolation step S, and utilizing a cubic spline interpolation principle to perform interpolation on a star point window image X1Interpolation is carried out to obtain a star point window image X after interpolation2；
Reading star point window image X2The gray value G (i, j) of the pixel is shown in the specification, wherein (i, j) is a star point window image X2The position of the pixel;
star point window image X2The transverse dimension M and the longitudinal dimension N of the pixel are respectively as follows:
M＝(M0-1)/S+1，
N＝(N0-1)/S+1；
step 5, calculating star point window image X2To obtain the centroid coordinate (x)c，yc)，
In the formula, xij、yijAs a star point window image X2The horizontal and vertical coordinates of the pixel;
step 6, making star point window image X2The coordinates of the center of mass of the image are converted into coordinates (X) under the original image Xz，yz)，
xz＝x0+(S(xc-1)+1)
yz＝y0+(S(yc-1)+1)
In the formula (x)0，y0) As a star point window image X0And positioning the coordinates of the points in the upper left corner of the original image X.
2. The method of claim 1, wherein the method comprises: in step 1, M0、N0And taking the star point to image, wherein the transverse and longitudinal sizes are 1.5-2.5 times.
3. The method of claim 2, wherein the method comprises: in step 1, M0、N0The star point imaging is taken to be twice the transverse and longitudinal dimension.
4. An error-suppressed star centroid localization method according to claim 2 or 3, wherein said method comprises: in step 4, the step S is 0.1 pel.
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| US5512743A (en) * | 1994-01-25 | 1996-04-30 | The United States Of America As Represented By The Secretary Of The Navy | Space-based asteroid detection and monitoring system |
| US6804693B2 (en) * | 2001-08-14 | 2004-10-12 | Cidra Corporation | Method for reducing skew in a real-time centroid calculation |
| US7447591B2 (en) * | 2004-10-18 | 2008-11-04 | Trex Enterprises Corp. | Daytime stellar imager for attitude determination |
| CN101907463B (en) * | 2010-07-05 | 2012-05-30 | 中国人民解放军国防科学技术大学 | Star image point position extracting method for star sensor |
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