Method for restoring blurred image of spaceborne camera

Abstract

The invention discloses a method for restoring a blurred image of a spaceborne camera. The method comprises the following steps: acquiring an original blurred image to be restored; setting an initial attitude and an end attitude of the satellite, and a push-broom angular velocity and integration time of the satellite, and controlling the satellite to image a fixed star target to obtain a fixed star target image; searching fixed star point targets at different positions from the fixed star target image, and cutting to obtain a star point image; performing normalization processing on the star point image to obtain a point spread function; and using the point spread function to perform a Wiener filtering-based deconvolution operation on the original blurred image to obtain a deblurred restored image. According to the method, the satellite is controlled to image the fixed star target, the accurate point spread function can be obtained, the extracted point spread function can eliminate adverse effects such as atmosphere, and the recovery effect is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of image restoration, and in particular relates to a method for restoring a blurred image of a satellite-borne camera. Background Art

[0002] As the number of in-orbit optical remote sensing satellites increases and their service time increases, the aging of the optomechanical structure of the onboard camera will cause aberrations in the optical system, which manifests as blurred images. If the problem cannot be improved through in-orbit focusing or there are non-axial aberrations such as coma and astigmatism, the image clarity can only be improved through ground restoration methods to reduce the impact on the interpretation of ground targets.

[0003] Currently, restoring blurred images by simulating degradation models using point spread functions is a mainstream image restoration method. However, for spaceborne cameras, it is difficult to accurately obtain the point spread function. Summary of the invention

[0004] The technology of the present invention solves the problem: Overcoming the shortcomings of the prior art, providing a method for restoring blurred images of a satellite-borne camera, by controlling the satellite to image stellar targets, an accurate point spread function can be obtained, and the extracted point spread function can eliminate adverse effects such as the atmosphere, thereby improving the restoration effect.

[0005] In order to solve the above technical problems, the present invention discloses a method for restoring a blurred image of a spaceborne camera, comprising:

[0006] Obtaining the original blurred image to be restored;

[0007] Set the satellite's initial attitude, final attitude, push-scan angular velocity and integration time, control the satellite to image the star target, and obtain the star target image;

[0008] Find star point targets at different positions from the star target image and crop them to obtain the star point image;

[0009] Normalize the star point image to obtain the point spread function;

[0010] The point spread function is used to perform a deconvolution operation based on the Vina filter on the original blurred image to obtain the deblurred restored image.

[0011] In the above-mentioned method for restoring a blurred image of a satellite-borne camera, the original blurred image to be restored is a blurred image captured by the satellite-borne camera.

[0012] In the above-mentioned restoration method of the blurred image of the onboard camera, the initial attitude and the final attitude of the satellite are determined by the following method:

[0013] Select the star target to be observed from the Hipparcos catalog;

[0014] Determine the six orbital numbers of the satellite;

[0015] The determined six orbital numbers of the satellite are input into the STK software to simulate the satellite attitude at the start and end times of the observation of the selected star target, thereby determining the initial attitude and end attitude of the satellite.

[0016] In the above-mentioned method for restoring blurred images from a satellite-borne camera, the satellite attitude includes: the satellite's yaw angle, pitch angle and roll angle.

[0017] In the above-mentioned restoration method of the blurred image of the onboard camera, the push-scan angular velocity of the satellite is determined by the following method:

[0018]

[0019] Where ω represents the satellite’s push-scan angular velocity, T int It represents the integration time, and IFOV_pixel represents the instantaneous field of view corresponding to one pixel of the satellite camera.

[0020] In the above-mentioned restoration method of the blurred image of the space-borne camera, star point targets at different positions are found from the star target image, and star point images are obtained by cropping, including: finding star point targets with only 1 to 2 pixels and unsaturated pixel values ​​from the star target image; cropping a star point image with a size of K×K pixels with the found star point target as the center; wherein K represents the size of the cropped star point image.

[0021] In the above-mentioned method for restoring blurred images from a spaceborne camera, the value range of K is 3 to 256.

[0022] In the above-mentioned restoration method of the blurred image of the spaceborne camera, the normalization processing formula is as follows:

[0023]

[0024] Among them, DN i,j Represents the pixel value of the i-th row and j-th column of the star point image, DN sum Represents the sum of all pixel values ​​of the star point image, DN i,j Represents the normalized matrix, point spread function.

[0025] In the above-mentioned method for restoring a blurred image of a space-borne camera, a point spread function is used to perform a deconvolution operation based on Wiener filtering on the original blurred image to obtain a deblurred restored image, including: setting a ringing coefficient N according to the type of ground object in the original blurred image to be restored, constructing an inverse function based on Wiener filtering to perform a deconvolution operation on the original image to be restored, and then obtaining a deblurred restored image.

[0026] In the above-mentioned restoration method of the blurred image of the space-borne camera, the expression of the inverse function is as follows:

[0027]

[0028] Among them, f'(x,y) represents the restored image after deblurring, g(x,y) represents the original blurred image to be restored, and h(x,y) represents the point spread function. Represents a convolution operation.

[0029] The present invention has the following advantages:

[0030] The present invention discloses a method for restoring a blurred image of a satellite-borne camera, which can effectively restore the original blurred image of the satellite-borne camera and improve the influence of the blurred image caused by aberration due to camera failure or equipment aging on the interpretation of ground targets. Compared with the existing restoration method, the present invention can quickly and accurately obtain the point spread function through star calibration, and the extracted point spread function can eliminate the adverse effects of the atmosphere and improve the restoration effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flowchart of the steps of a method for restoring a blurred image of a spaceborne camera in an embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of a point spread function in an embodiment of the present invention;

[0033] Figure 3 It is a comparison diagram of a deblurred restored image and an original blurred image in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] Reference Figure 1 In this embodiment, the method for restoring the blurred image of the spaceborne camera includes:

[0036] Step 1: Obtain the original blurred image to be restored.

[0037] In this embodiment, the original blurred image to be restored is a blurred image captured by a satellite-borne camera.

[0038] Step 2, setting the satellite's initial attitude, final attitude, push-scan angular velocity and integration time, controlling the satellite to image the star target, and obtaining the star target image.

[0039] In this embodiment, the initial attitude and the final attitude of the satellite can be determined based on simulation means. For example, the initial attitude and the final attitude of the satellite can be obtained by simulation based on the STK software. Specifically: select the star target to be observed from the Hipparcos star catalog; determine the six orbital numbers of the satellite; input the determined six orbital numbers of the satellite into the STK software, and simulate the satellite attitude (including: the satellite's yaw angle, pitch angle and roll angle) at the start and end times of the satellite observing the selected star target to be observed, and then determine the initial attitude and the final attitude of the satellite.

[0040] Furthermore, when the satellite is imaging a star target, in order to obtain a star target that matches a pixel, the satellite needs to actively push-scan to move through one pixel within an integration time range, that is, the instantaneous field of view angle corresponding to one pixel of the onboard camera. The push-scan angular velocity of the satellite can be determined as follows:

[0041]

[0042] Where ω represents the satellite’s push-scan angular velocity, T int It represents the integration time, and IFOV_pixel represents the instantaneous field of view corresponding to one pixel of the satellite camera.

[0043] Step 3: Find star point targets at different positions in the star target image and crop them to obtain the star point image.

[0044] In this embodiment, the cropping process is as follows: find a star point target with only 1 to 2 pixels and unsaturated pixel values ​​from the star target image; and crop a star point image with a size of N×N pixels with the found star point target as the center. K represents the size of the cropped star point image, and the value range of K is 3 to 256. For example, K=32.

[0045] Step 4: normalize the star point image to obtain a point spread function.

[0046] In this embodiment, the normalization processing formula is as follows:

[0047]

[0048] Among them, DN i,j Represents the pixel value of the i-th row and j-th column of the star point image, DN sum Represents the sum of all pixel values ​​of the star point image, DN i,j Represents the normalized matrix, point spread function.

[0049] Step 5: Use the point spread function to perform a deconvolution operation based on Vina filtering on the original blurred image to obtain a deblurred restored image.

[0050] In this embodiment, the ringing coefficient N can be set according to the type of ground object in the original blurred image to be restored, and an inverse function is constructed based on the Wiener filter to perform a deconvolution operation on the original image to be restored, thereby obtaining a deblurred restored image. The expression of the inverse function is as follows:

[0051]

[0052] Among them, f'(x,y) represents the restored image after deblurring, g(x,y) represents the original blurred image to be restored, and h(x,y) represents the point spread function. Represents a convolution operation.

[0053] Preferably, the process of step 5 can be operated using the deconvwnr function of the matlab software, and the processing code is as follows:

[0054] Image_deblur=deconvwnr(image,psf,N)

[0055] Among them, Image_deblur is the restored image after deblurring; image is the original blurred image to be restored; psf is the point spread function; N is the ringing suppression coefficient.

[0056] Based on the above embodiment, a specific example is described below.

[0057] In this embodiment, the method for restoring a blurred image of a spaceborne camera includes:

[0058] (1) Obtain the original blurred image to be restored.

[0059] (2) Setting the satellite’s initial attitude, final attitude, push-scan angular velocity, and integration time, and controlling the satellite to image the stellar target to obtain the stellar target image.

[0060] In this example, the Southern Pleiades is selected as the star target to be observed; the six orbital parameters of the satellite are determined as follows: orbital time: 2024 / 5 / 13 0:59:58.000, semi-major axis: 6879.960km, orbital eccentricity: 0.001, orbital inclination: 34.95°, ascending node right ascension: 191.02°, perigee depression angle: 32.83°, mean anomaly: 1.71°. Then, using STK software, the initial and final attitudes of the satellite are simulated as shown in Table 1 below:

[0061]

[0062] Table 1. Schematic diagram of the initial and final attitudes of the satellite

[0063] In this example, the focal length of the onboard camera is 7000 mm, and the pixel size is 7 μm. It can be calculated that the instantaneous field of view IFOV_pixel corresponding to one pixel of the onboard camera is 5.73*10 -5 Degrees, set the integration time T int is 191 microseconds, then it can be calculated that the satellite's push-scan angular velocity ω is 0.3 degrees / second.

[0064] (3) Find star point targets at different positions from the star target image and crop them to obtain the star point image

[0065] In this example, star point targets with only 1 to 2 pixels and unsaturated pixel values ​​are found from the star target image; a star point image with a size of 32×32 pixels is cropped with the found star point target as the center.

[0066] (4) Normalize the star point image to obtain the point spread function

[0067] The normalization formula is as follows:

[0068]

[0069] The 32×32 matrix obtained after processing is the point spread function, such as Figure 2 shown.

[0070] (5) Use the point spread function to perform a deconvolution operation based on the Wiener filter on the original blurred image to obtain the deblurred restored image.

[0071] According to the type of ground objects in the original blurred image to be restored, the ringing coefficient N is set, and the inverse function is constructed based on the Wiener filter to perform a deconvolution operation on the original image to be restored, thereby obtaining the deblurred restored image. In this example, N is set to 0.001, and the deconvwnr function of the matlab software is used for processing. The comparison results between the deblurred restored image and the original blurred image are shown in the figure below. Figure 3 shown.

[0072] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0073] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for restoring a blurred image of a spaceborne camera, characterized in that: include: Obtaining the original blurred image to be restored; Set the satellite's initial attitude, final attitude, push-scan angular velocity and integration time, control the satellite to image the star target, and obtain the star target image; Find star point targets at different positions from the star target image and crop them to obtain the star point image; Normalize the star point image to obtain the point spread function; The point spread function is used to perform a deconvolution operation based on the Vina filter on the original blurred image to obtain the deblurred restored image.

2. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: The original blurred image to be restored is a blurred image taken by a satellite-borne camera.

3. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: The initial and final attitudes of the satellite are determined as follows: Select the star target to be observed from the Hipparcos catalog; Determine the six orbital numbers of the satellite; The determined six orbital numbers of the satellite are input into the STK software to simulate the satellite attitude at the start and end times of the observation of the selected star target, thereby determining the initial attitude and end attitude of the satellite.

4. The method for restoring blurred images of a spaceborne camera according to claim 3, characterized in that: Satellite attitude, including: satellite's yaw angle, pitch angle and roll angle.

5. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: The push-scan angular velocity of the satellite is determined as follows: Where ω represents the satellite’s push-scan angular velocity, T int It represents the integration time, and IFOV_pixel represents the instantaneous field of view corresponding to one pixel of the satellite camera.

6. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: Finding star point targets at different positions from a star target image and cropping to obtain a star point image includes: finding a star point target with only 1 to 2 pixels and unsaturated pixel values ​​from the star target image; cropping a star point image with a size of K×K pixels with the found star point target as the center; wherein K represents the size of the cropped star point image.

7. The method for restoring blurred images of a spaceborne camera according to claim 6, characterized in that: The value range of K is 3 to 256.

8. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: The normalization formula is as follows: Among them, DN i,j Represents the pixel value of the i-th row and j-th column of the star point image, DN sum Represents the sum of all pixel values ​​of the star point image, DN i,j Represents the normalized matrix, point spread function.

9. The method for restoring blurred images of a spaceborne camera according to claim 1, characterized in that: The point spread function is used to perform a deconvolution operation based on Wiener filtering on the original blurred image to obtain a deblurred restored image, including: setting a ringing coefficient N according to the type of ground object in the original blurred image to be restored, constructing an inverse function based on Wiener filtering to perform a deconvolution operation on the original image to be restored, and then obtaining a deblurred restored image.

10. The method for restoring blurred images of a spaceborne camera according to claim 9, characterized in that: The expression of the inverse function is as follows: Among them, f'(x,y) represents the restored image after deblurring, g(x,y) represents the original blurred image to be restored, and h(x,y) represents the point spread function. Represents a convolution operation.

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