A space target adaptive image size information evaluation method

Abstract

The present invention relates to the technical field of image evaluation, and in particular to a method for evaluating the size information of an adaptive image of a space target. The method comprises: establishing a target coordinate system; wherein the origin of the target coordinate system is the center of the target, and the target coordinate system includes a spatial rectangular coordinate system and a polar coordinate system with the same origin; calculating the solar illumination angle and observation angle in an image based on the target coordinate system; wherein the solar observation angle includes the solar illumination azimuth angle and the solar illumination pitch angle, and the observation angle includes the observation azimuth angle and the observation pitch angle; calculating the angular coverage of the image based on the solar illumination angle and the observation angle; calculating the pixel area of ​​the minimum bounding rectangle of the target in the image; calculating the number of pixels covered by the point spread function of the image; and evaluating the size information of the image based on the angular coverage, the pixel area, and the number of pixels.

Description

Technical Field

[0001] The present invention relates to the technical field of image evaluation, and in particular to a method for evaluating the size information of space target adaptive images. Background Art

[0002] There are numerous satellites, debris, and other targets in Earth orbit. Studying the flight status, shape, and posture of these targets requires extensive image data. Extracting the target's size is crucial for extracting its shape and posture information from images. Optical images of targets obtained through telescope measurements are a crucial method for obtaining this information. Long-term astronomical observations have accumulated a vast amount of target image data, and processing this data is a crucial task. Prior to adaptive image processing of space targets, image quality must be evaluated. This quality evaluation is crucial for evaluating the processing results.

[0003] Image quality assessment is a common requirement in the field of image processing. Key metrics used for evaluation include signal-to-noise ratio, contrast, and edge sharpness. While supported by some image parameters, image quality assessment remains a highly subjective process, requiring evaluation based on the image's intended use. The primary goal of adaptive image processing for spatial targets is to extract the target's size and grayscale distribution. These characteristics are dependent on the target's illumination angle and observation angle. Therefore, simply evaluating image quality cannot provide reliable information about the target's size.

[0004] Therefore, in view of the above shortcomings, an evaluation method for image size information is urgently needed. Summary of the Invention

[0005] The embodiment of the present invention provides a method for evaluating the size information of a space target adaptive image, which can provide an evaluation method for image size information.

[0006] An embodiment of the present invention provides a method for evaluating the size information of a space target adaptive image, comprising:

[0007] Establishing a target coordinate system; wherein the origin of the target coordinate system is the center of the target, and the target coordinate system includes a spatial rectangular coordinate system and a polar coordinate system with the same origin;

[0008] The solar radiation angle and observation angle in the image are calculated based on the target coordinate system; wherein the solar observation angle includes the solar radiation azimuth angle α λ射 and the solar pitch angle β 入射 , the observation angle includes the observation azimuth angle α 观测 and the observed pitch angle β 观测 ;

[0009] Calculating the angular coverage of the image according to the sun illumination angle and the observation angle;

[0010] Calculate the pixel area of ​​the minimum bounding rectangle of the target in the image;

[0011] Calculate the number of pixels covered by the point spread function of the image;

[0012] Image size information is evaluated based on the angular coverage, the pixel area, and the number of pixels.

[0013] In one possible design, the z-axis of the spatial rectangular coordinate system is the line connecting the target position and the center of the earth, the direction of outer space is the positive direction of the z-axis, the tangent of the target orbit is the x-axis direction of the spatial rectangular coordinate system, the velocity direction of the target is the positive direction, and based on the x-axis and the z-axis, the direction of the y-axis is determined by the right-hand screw rule. The pitch angle ρ of the polar coordinate system is the angle between the ray direction and the xy plane, and the azimuth angle α of the polar coordinate is the angle between the projection of the ray direction on the xy plane and the positive direction of the x-axis.

[0014] In one possible design, calculating the angular coverage of an image according to the solar illumination angle and the observation angle includes:

[0015] Establishing a target observation angle coverage set; wherein the observation angle coverage set includes point coordinates uniformly distributed on the surface of a unit sphere;

[0016] An incident coverage set is calculated based on the observation angle coverage set and the sun's illumination angle; wherein the incident coverage set is a spatial matrix of points illuminated by the sun;

[0017] Calculating an observation coverage set based on the observation angle coverage set and the observation angle; wherein the observation coverage set is the observed spatial matrix points;

[0018] The angular coverage is calculated according to the intersection of the incident coverage set and the observed coverage set.

[0019] In one possible design, calculating the pixel area of ​​the minimum bounding rectangle of the target in the image includes:

[0020] Binarize the image;

[0021] Separation of target and background is achieved through connected domain extraction;

[0022] Find the target connected domain and extract the minimum outer rectangle side length;

[0023] The pixel area of ​​the minimum outer rectangle is obtained using the area formula.

[0024] In a possible design, the number of pixels covered by the point spread function of the calculated image includes:

[0025] Extract the standard deviation E and mean Ne of the background area;

[0026] Set multiple points from the four sides of the image, connect the points and the target center, and obtain connecting lines;

[0027] Extracting the grayscale values ​​of the points on the connecting line to obtain multiple vector sets;

[0028] Calculate the average value N of all points in the vector set whose vectors are greater than Ne+3E;

[0029] All values ​​less than N+3E in the vector are set to 0, and traversal is started from the beginning, starting from the first non-zero value in the vector and ending when the grayscale value is greater than 0.7*N, to obtain the image edge value in the vector;

[0030] The average value of the edge values ​​of all the vectors is the number of pixels covered by the point spread function of the image.

[0031] In one possible design, evaluating the image size information according to the angular coverage, the pixel area, and the number of pixels includes:

[0032] H=2*r*s / m 2

[0033] Wherein, H is the image size information, r is the angle coverage, s is the pixel area, and m is the number of pixels.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] In the present invention, the image size information is calculated by angle coverage, pixel area and pixel number. By setting different grading thresholds for the image size information, the size extractability of the image can be evaluated into different levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a flow chart of a method for evaluating the size information of a space target adaptive image provided by an embodiment of the present invention;

[0038] Figure 2 This is a flow chart for calculating image angle coverage provided by an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of a sampling method for calculating the number of image pixels provided by an embodiment of the present invention.

[0040] In the picture:

[0041] 301-background area;

[0042] 302-target area;

[0043] 303-connecting wire. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] In the description of the embodiments of the present invention, unless otherwise expressly specified or limited, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "plurality" refers to two or more; the terms "connected" and "fixed" should be understood in a broad sense. For example, "connected" can mean a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] In the description of this specification, it should be understood that the directional terms such as "upper" and "lower" described in the embodiments of the present invention are described from the perspectives shown in the accompanying drawings and should not be understood as limiting the embodiments of the present invention. In addition, in the context, it should be understood that when it is mentioned that an element is connected "upper" or "lower" of another element, it can not only be directly connected "upper" or "lower" of the other element, but also indirectly connected "upper" or "lower" of the other element through an intermediate element.

[0047] like Figures 1 to 3 As shown, an embodiment of the present invention provides a method for evaluating the size information of a space target adaptive image, comprising:

[0048] Establish a target coordinate system; wherein the origin of the target coordinate system is the center of the target, and the target coordinate system includes a spatial rectangular coordinate system and a polar coordinate system with the same origin;

[0049] The solar radiation angle and observation angle in the image are calculated based on the target coordinate system; the solar observation angle includes the solar radiation azimuth angle α 入射 and the solar pitch angle β 入射 , the observation angle includes the observation azimuth angle α 观测 and the observed pitch angle β 观测 ;

[0050] Calculate the angular coverage of the image based on the sun's illumination angle and the observation angle;

[0051] Calculate the pixel area of ​​the minimum bounding rectangle of the target in the image;

[0052] Calculate the number of pixels covered by the point spread function of the image;

[0053] Image size information is evaluated based on angular coverage, pixel area, and pixel number.

[0054] In the present invention, the image size information is calculated by angle coverage, pixel area and pixel number. By setting different grading thresholds for the image size information, the size extractability of the image can be evaluated into different levels.

[0055] In some embodiments of the present invention, the z-axis of the spatial rectangular coordinate system is the line connecting the target position and the center of the earth, the direction of outer space is the positive direction of the z-axis, the tangent of the target orbit is the x-axis direction of the spatial rectangular coordinate system, the velocity direction of the target is the positive direction, and based on the x-axis and the z-axis, the direction of the y-axis is determined by the right-hand screw rule. The pitch angle ρ of the polar coordinate system is the angle between the ray direction and the xy plane, and the azimuth angle α of the polar coordinate is the angle between the projection of the ray direction on the xy plane and the positive direction of the x-axis.

[0056] In some embodiments of the present invention, calculating the angular coverage of an image based on the sun's illumination angle and the observation angle includes:

[0057] Establishing a target observation angle coverage set; wherein the observation angle coverage set includes point coordinates uniformly distributed on the surface of the unit sphere;

[0058] The incident coverage set is calculated based on the observation angle coverage set and the sun's radiation angle; the incident coverage set is the spatial matrix point illuminated by the sun;

[0059] The observation coverage set is calculated based on the observation angle coverage set and the observation angle; wherein the observation coverage set is the observed spatial matrix point;

[0060] The angular coverage is calculated from the intersection of the incident coverage set and the observed coverage set.

[0061] First, establish the target observation angle coverage set M. The set contains different elements m n =(x n ,y n , z n , v n ), n is the serial number subscript, (x n ,y n , z n ) is the point coordinate, corresponding to the point coordinate of a unit sphere surface in the target coordinate system. The points in the set M are evenly distributed on the unit sphere surface. n Used to record whether the corresponding angle is illuminated or observed. Set M (x n ,y n , z n A preferred method is to traverse and obtain values ​​according to the azimuth angle α and pitch angle ρ of the target polar coordinates to obtain a series of αρ value combinations, and then calculate the value of the target polar coordinates according to the formula x. n =cos(ρ)cos(α),y n =cos(ρ)sin(α),z n =sin(ρ) establishes a mapping relationship between the point coordinates and the azimuth angle α and pitch angle ρ.

[0062] Secondly, calculate the angular coverage of the image. According to the incident angle (α 入射 , β 入射 ) corresponds to (x 入射 ,y 入射 , z 入射 ) direction vector, find the rotation matrix R that rotates it to the (0, 0, 1) direction 入射 , using the rotation matrix R 入射 Transform the first three parameters of the elements in the observation angle coverage set M (x n ,y n , z n ), the conversion formula is

[0063]

[0064] If z nr If it is less than 0, the sequence number n is included in the incident cover set K n入 ;

[0065] Similarly, according to the image observation angle (α 观测 , β 观测 ) corresponds to (x 观测 ,y 观测 , z 观测) direction vector, find the rotation matrix R that rotates it to the (0, 0, 1) direction 观测 , using the rotation matrix R 观测 Processing transforms the first three parameters of the elements in the observation angle coverage set M (x n ,y n , z n ), the conversion formula is

[0066]

[0067] If z nr If it is less than 0, the sequence number n is included in the observation covering set K n观 ;

[0068] Find the image incident cover set K n入 and observation covering set K n观 The intersection of K n交 , K n交 The ratio of the number of elements in to the elements in set M is the angular coverage value r of the image.

[0069] In some embodiments of the present invention, calculating the pixel area of ​​the minimum bounding rectangle of an object in an image includes:

[0070] Binarize the image;

[0071] Separation of target and background is achieved through connected domain extraction;

[0072] Find the target connected domain and extract the minimum outer rectangle side length;

[0073] The pixel area of ​​the minimum outer rectangle is obtained using the area formula.

[0074] In some embodiments of the present invention, calculating the number of pixels covered by the point spread function of the image includes:

[0075] Extract the standard deviation E and mean Ne of the background area;

[0076] Set multiple points from the four sides of the image, connect the points and the target center, and obtain connecting lines;

[0077] Extract the grayscale values ​​of the points on the connecting line to obtain multiple vector sets;

[0078] Calculate the average value N of all points in the vector set whose vectors are greater than Ne+3E;

[0079] All values ​​in the vector that are less than N+3E are set to 0, and the traversal starts from the beginning. The counting starts from the first non-zero value in the vector and ends when the grayscale value is greater than 0.7*N. The image edge value in the vector is obtained.

[0080] The average of the edge values ​​of all vectors is the number of pixels covered by the point spread function of the image.

[0081] In some embodiments of the present invention, evaluating image size information based on angular coverage, pixel area, and pixel count includes:

[0082] H=2*r*s / m 2

[0083] Among them, H is the image size information, r is the angle coverage, s is the pixel area, and m is the number of pixels.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A space target adaptive image size information evaluation method, characterized in that: include: Establishing a target coordinate system; wherein the origin of the target coordinate system is the center of the target, and the target coordinate system includes a spatial rectangular coordinate system and a polar coordinate system with the same origin; The solar radiation angle and observation angle in the image are calculated based on the target coordinate system; wherein the solar observation angle includes the solar radiation azimuth angle α 入射 and the solar pitch angle β 入射 , the observation angle includes the observation azimuth angle α 观测 and the observed pitch angle β 观测 ; Calculating the angular coverage of the image according to the sun illumination angle and the observation angle; Calculate the pixel area of ​​the minimum bounding rectangle of the target in the image; Calculate the number of pixels covered by the point spread function of the image; evaluating image size information according to the angular coverage, the pixel area, and the number of pixels; The evaluating the image size information degree according to the angle coverage, the pixel area and the number of pixels includes: H=2*r*s / m 2 Wherein, H is the image size information, r is the angle coverage, s is the pixel area, and m is the number of pixels.

2. The method according to claim 1, characterized in that The z-axis of the spatial rectangular coordinate system is the line connecting the target position and the center of the earth, the direction of outer space is the positive direction of the z-axis, the tangent of the target orbit is the x-axis direction of the spatial rectangular coordinate system, the velocity direction of the target is the positive direction, and based on the x-axis and the z-axis, the direction of the y-axis is determined by the right-hand screw rule. The pitch angle ρ of the polar coordinate system is the angle between the ray direction and the xy plane, and the azimuth angle α of the polar coordinate is the angle between the projection of the ray direction on the xy plane and the positive direction of the x-axis.

3. The method according to claim 1, characterized in that The calculating the angular coverage of the image according to the solar illumination angle and the observation angle includes: Establishing a target observation angle coverage set; wherein the observation angle coverage set includes point coordinates uniformly distributed on the surface of a unit sphere; An incident coverage set is calculated based on the observation angle coverage set and the sun's illumination angle; wherein the incident coverage set is a spatial matrix of points illuminated by the sun; Calculating an observation coverage set based on the observation angle coverage set and the observation angle; wherein the observation coverage set is the observed spatial matrix points; The angular coverage is calculated according to the intersection of the incident coverage set and the observed coverage set.

4. The method according to claim 1, wherein The calculating the pixel area of ​​the minimum bounding rectangle of the target in the image includes: Binarize the image; Separation of target and background is achieved through connected domain extraction; Find the target connected domain and extract the minimum outer rectangle side length; The pixel area of ​​the minimum outer rectangle is obtained using the area formula.

5. The method according to claim 1, characterized in that The number of pixels covered by the point spread function of the calculated image includes: Extract the standard deviation E and mean Ne of the background area; Set multiple points from the four sides of the image, connect the points and the target center, and obtain connecting lines; Extracting the grayscale values ​​of the points on the connecting line to obtain multiple vector sets; Calculate the average value N of all points in the vector set whose vectors are greater than Ne+3E; All values ​​in the vector that are less than N+3E are set to 0, and the traversal starts from the beginning, starting from the first non-zero value in the vector and ending when the grayscale value is greater than 0.7*N, to obtain the image edge value in the vector; The average value of the edge values ​​of all the vectors is the number of pixels covered by the point spread function of the image.

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