CN107886538A - A kind of stellar camera asterism detection method and system - Google Patents
A kind of stellar camera asterism detection method and system Download PDFInfo
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Abstract
A kind of stellar camera asterism detection method and system, the continuous acquisition multiple image within the time of integration, multiple image are added up, as detector dark current benchmark image；Continue to gather multiple image, obtain image to be compensated, the pixel value of each pixel in image to be compensated and the pixel value of each pixel in detector dark current benchmark image are made the difference, obtain target image；The pixel domain of target image is chosen, according to comparison criterion, whether detection pixel domain is asterism, completes asterism detection.Detecting system includes image capture module, image processing module, asterism detection module.The present invention has the advantages that amount of calculation is few, recognition efficiency is high, robustness is high compared with conventional method.
Description
Technical field
The present invention relates to a kind of stellar camera asterism detection method and system, belongs to aerospace optical remote sensing technical field, application
In high-resolution earth observation remote sensing camera attitude measurement.
Background technology
The geometric positioning accuracy for improving remote sensing image is the basis of high-definition remote sensing application, realizes that high-precision geometry is determined
Position, primary work are the systematic errors of calibration and compensation high-definition remote sensing camera.Stellar camera is as gesture stability system on star
Attitude measurement accuracy highest measuring part in system, the posture relation square between calibration remote sensing camera and stellar camera is commonly used in practice
Battle array realizes the compensation of systematic error, and is intuitively reflected by being crosslinked angle between remote sensing camera and stellar camera primary optical axis.
With remote sensing camera resolution ratio more and more higher, this also proposes higher want to the attitude measurement accuracy of stellar camera
Ask.It would generally use and reduce stellar camera visual field, improve optical system sensitivity, the design method for expanding detector pixel scale is come
Obtain higher measurement accuracy.Expanding detector pixel scale can make pixel count be multiplied, and this directly affects stellar camera asterism
Detection efficiency.Using more asterism detection method be threshold method in engineering, by set the method for background threshold by background with
Target is separated, and wherein fixed threshold method is fixed due to threshold value, it is impossible to the ambient noise that fine adaptive temperature change, veiling glare are brought
Change, application are less；It is main that threshold value is carried out according to the view data obtained in real time and dynamic thresholding method has very strong flexibility
Calculating, due to need count entire image all pixels, operand is larger, influences system real time.
The content of the invention
The technology of the present invention solves problem：A kind of overcome the deficiencies in the prior art, there is provided stellar camera asterism detection method
And system, solve the problems such as fixed threshold method can not adapt to environmental change very well, dynamic thresholding method is computationally intensive, improve astrology
Machine asterism detection efficiency.
The technical scheme is that：
1st, a kind of stellar camera asterism detection method, it is characterised in that comprise the following steps：
1) the continuous acquisition multiple image within the time of integration, the pixel of the multiple image same position collected is carried out
Accumulation process, as detector dark current benchmark image；
2) after interval time t, the continuous acquisition multiple image within the time of integration, by the same position of the multiple image collected
The pixel put carries out accumulation process, obtains image to be compensated, and the pixel value of each pixel and detector in image to be compensated is dark
The pixel value of each pixel makes the difference in current reference image, obtains target image；
3) pixel domain to be detected is chosen on target image, detects whether pixel domain to be detected is asterism；
4) different pixel domains to be detected, repeat step 3 are chosen), until having analyzed all pictures to be detected of target image
Prime field, complete asterism detection.
The pixel domain to be detected is 4*4 pixel domains, and 4*4 pixel domains are divided into first quartile pixel domain to fourth quadrant
Pixel domain, and center pixel domain.
The 4*4 pixel domains are divided into first quartile pixel domain to fourth quadrant pixel domain, and the side in center pixel domain
Method is：4*4 pixel domains are divided into four quadrants, the pixel domain for having a 2*2 in each quadrant, define the 2* in first quartile
2 pixel domains are first quartile pixel domain, define the second quadrant in 2*2 pixel domains be the second quadrant pixel domain, definition the 3rd as
2*2 pixel domains in limit are third quadrant pixel domain, and the 2*2 pixel domains defined in fourth quadrant are fourth quadrant pixel domain, 4*4
Pixel domain centered on 4 pixel definitions at pixel domain center.
Whether detection pixel domain to be detected is that the method for asterism is：Meet 4 pixels in each 2*2 pixel domains
Pixel value sum is respectively less than inactive pixels threshold value H, and the pixel value sum of 4 pixels in center pixel domain is more than asterism sensitivity
Threshold value h；The pixel value of at least 2 pixels of 4 pixels in center pixel domain is more than asterism threshold of sensitivity m, and at least meets
A condition in following condition：
A) in all 2*2 pixel domains, the pixel value sum in center pixel domain is maximum；
B) the pixel value sum of first quartile pixel domain is more than asterism threshold of sensitivity h, the pixel of third quadrant pixel domain
Value sum is more than asterism threshold of sensitivity h, and the pixel value sum of the second quadrant pixel domain is less than or equal to asterism threshold of sensitivity h,
The pixel value sum of fourth quadrant pixel domain is less than or equal to asterism threshold of sensitivity h；
C) the pixel value sum of the second quadrant pixel domain is more than asterism threshold of sensitivity h, the pixel of fourth quadrant pixel domain
Value sum is more than asterism threshold of sensitivity h, and the pixel value sum of first quartile pixel domain is less than or equal to asterism threshold of sensitivity h,
The pixel value sum of third quadrant pixel domain is less than or equal to asterism threshold of sensitivity h.
The inactive pixels threshold value H is the 95% of pixel saturation value, and asterism threshold of sensitivity h is the full dark conditions of stellar camera
Lower 8~12 times of picture noises；Asterism threshold of sensitivity m is 4~6 times of picture noises under the full dark conditions of stellar camera.
The interval time t=1/f, wherein f are stellar camera working frame frequency.
It is described by each pixel in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The method that pixel value makes the difference is：The pixel value of each pixel subtracts the same position of detector dark current benchmark image in image to be compensated
The pixel value of pixel is put, pixel value difference is more than or equal to 0, then pixel value difference retains, and pixel value difference is less than 0 progress, and then pixel value difference is put
Zero.
A kind of stellar camera asterism detecting system includes image capture module, image processing module, asterism detection module；
Image capture module continuous acquisition multiple image within the time of integration, by the picture of the image same position collected
Element carries out accumulation process, as detector dark current benchmark image；After interval time t, the continuous acquisition multiframe within the time of integration
Image, the pixel of the multiple image same position collected is subjected to accumulation process, obtains image to be compensated；
Image processing module will be every in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The pixel value of individual pixel makes the difference, and obtains target image；
Asterism detection module chooses pixel domain to be detected on target image, according to comparison criterion, detects pixel to be detected
Whether domain is asterism；Then new pixel domain to be detected is obtained, continues to carry out asterism detection to new pixel domain to be detected, until
All pixel domains to be detected of target image have been detected, have completed asterism detection.
The pixel domain to be detected is 4*4 pixel domains, and 4*4 pixel domains is divided into four quadrants, is had in each quadrant
One 2*2 pixel domain, the 2*2 pixel domains defined in first quartile are first quartile pixel domain, define the 2*2 in the second quadrant
Pixel domain is the second quadrant pixel domain, and the 2*2 pixel domains defined in third quadrant are third quadrant pixel domain, defines fourth quadrant
Interior 2*2 pixel domains are fourth quadrant pixel domain, pixel domain centered on 4 pixel definitions at 4*4 pixel domains center.
Whether detection pixel domain to be detected is that the method for asterism is：Meet 4 pixels in each 2*2 pixel domains
Pixel value sum is respectively less than inactive pixels threshold value H, and the pixel value sum of 4 pixels in center pixel domain is more than asterism sensitivity
Threshold value h；The pixel value of at least 2 pixels of 4 pixels is more than asterism threshold of sensitivity m in center pixel domain, and at least meets
A condition in following condition：
D) in all 2*2 pixel domains, the pixel value sum in center pixel domain is maximum；
E) the pixel value sum of first quartile pixel domain is more than asterism threshold of sensitivity h, the pixel of third quadrant pixel domain
Value sum is more than asterism threshold of sensitivity h, and the pixel value sum of the second quadrant pixel domain is less than or equal to asterism threshold of sensitivity h,
The pixel value sum of fourth quadrant pixel domain is less than or equal to asterism threshold of sensitivity h；
F) the pixel value sum of the second quadrant pixel domain is more than asterism threshold of sensitivity h, the pixel of fourth quadrant pixel domain
Value sum is more than asterism threshold of sensitivity h, and the pixel value sum of first quartile pixel domain is less than or equal to asterism threshold of sensitivity h,
The pixel value sum of third quadrant pixel domain is less than or equal to asterism threshold of sensitivity h.
Wherein, inactive pixels threshold value H is the 95% of pixel saturation value, and asterism threshold of sensitivity h is the full shading strip of stellar camera
8~12 times of picture noises under part；Asterism threshold of sensitivity m is 4~6 times of picture noises under the full dark conditions of stellar camera.
The interval time t=1/f, wherein f are stellar camera working frame frequency.
It is described by each pixel in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The method that pixel value makes the difference is：The pixel value of each pixel subtracts the same position of detector dark current benchmark image in image to be compensated
The pixel value of pixel is put, pixel value difference is more than or equal to 0, then pixel value difference retains, and difference is less than 0 and carries out then pixel value difference zero setting.
Compared with the prior art, the invention has the advantages that：
1) this asterism detection method, the threshold of sensitivity are determined by Laboratory Calibration, non real-time calculating, do not consume processor
Operation time, be advantageous to improve asterism detection efficiency；
2) this asterism detection method asterism detection process amount of calculation is few, only exists plus and minus calculation and size compares, be easy to hard
Part is realized, therefore recognition efficiency is high；
3) this asterism detection method improves signal noise ratio (snr) of image using multi-frame accumulation, compensates detector dark current processing procedure,
Influence of noise is substantially reduced, lower magnitude can be detected, increases the magnitude number detected, is applicable engineering applied to high-precision
Stellar camera development process is spent, improves stellar camera attitude measurement accuracy.
Brief description of the drawings
Fig. 1 is the stellar camera asterism detection method flow chart being related in the present invention；
Fig. 2 is multiple image cumulative process schematic diagram；
Fig. 3 is 4*4 pixel region schematic diagrames.
Embodiment
A kind of stellar camera asterism detection method and system, as shown in figure 1, system module includes：IMAQ, image procossing
Detected with asterism.
Described image acquisition module：As shown in Fig. 2 the continuous acquisition multiple image within the time of integration, usual N takes 3 or 4
Frame, and accumulation process is carried out, signal noise ratio (snr) of image is improved, obtains piece image F1.
Described image processing：Using piece image F1 as compensation detector dark current benchmark image D.After interval time t,
The continuous acquisition multiple image within the time of integration, the pixel of the multiple image same position collected is subjected to accumulation process,
It is stellar camera working frame frequency to obtain the second width image F2, wherein interval time t=1/f, f.By the second width image and the first width figure
As making the difference carry out dark current compensation, reducing dark current influences, and obtains target image S, i.e. S=F2-D, target image S is carried out anti-
Saturated process, if pixel value difference is more than or equal to 0, pixel value difference retains, and difference is less than 0 and carries out then pixel value difference zero setting.
The asterism detection module：As shown in figure 3,4*4 pixel domains are divided into four quadrants, there is one in each quadrant
2*2 pixel domain, the 2*2 pixel domains defined in first quartile are first quartile pixel domain S2, define the 2*2 pictures in the second quadrant
Prime field is the second quadrant pixel domain S1, and the 2*2 pixel domains defined in third quadrant are third quadrant pixel domain S3, defines four-quadrant
2*2 pixel domains in limit are pixel domain S0 centered on 4 pixel definitions at fourth quadrant pixel domain S4,4*4 pixel domain center, root
According to comparison criterion, whether detection 4*4 pixel domains are asterism.
Detection 4*4 pixel domains are that asterism must meet that the 4 pixels and value in each 2*2 pixel domains is respectively less than inactive pixels
Threshold value H, and 4 pixels in center pixel domain and value be more than asterism threshold of sensitivity h；4 pixels are at least in center pixel domain
The pixel value for having 2 pixels is more than asterism threshold of sensitivity m, and at least meets a condition in following condition：
F) in all 2*2 pixel domains, the pixel and value in center pixel domain are maximum；
G) pixel of first quartile pixel domain and value are more than asterism threshold of sensitivity h, the pixel of third quadrant pixel domain with
Value is more than asterism threshold of sensitivity h, and the pixel and value of the second quadrant pixel domain are less than or equal to asterism threshold of sensitivity h, four-quadrant
The pixel and value for limiting pixel domain are less than or equal to asterism threshold of sensitivity h；
H) pixel of the second quadrant pixel domain and value are more than asterism threshold of sensitivity h, the pixel of fourth quadrant pixel domain with
Value is more than asterism threshold of sensitivity h, the pixel and value of first quartile pixel domain less than or equal to asterism threshold of sensitivity h, the 3rd as
The pixel and value for limiting pixel domain are less than or equal to asterism threshold of sensitivity h.
Usual inactive pixels threshold value H values are pixel saturation value, asterism threshold of sensitivity h=12 δ, the asterism threshold of sensitivity
M=6 δ, δ are that dark conditions hypograph noise criteria is poor.
A row or a line of staggering with the 4*4 pixel domains obtained obtain new 4*4 pixel domains, repeat asterism detection process,
Until having analyzed all 4*4 pixel domains of target image S, asterism detection is completed.
In real work, after detector work certain time, changing with external working environment, dark current reference frame is degenerated,
Detector dark current benchmark image D must be resurveyed, carries out dark current benchmark image renewal.
A kind of stellar camera asterism detection method comprises the following steps：
1) the continuous acquisition multiple image within the time of integration, the pixel of the multiple image same position collected is carried out
Accumulation process, as detector dark current benchmark image；
2) after interval time t, the continuous acquisition multiple image within the time of integration, by the same position of the multiple image collected
The pixel put carries out accumulation process, obtains image to be compensated, and the pixel value of each pixel and detector in image to be compensated is dark
The pixel value of each pixel makes the difference in current reference image, obtains target image；
3) it is summit that an angle is arbitrarily taken in 4 angles of target image, chooses a 4*4 pixel domain；
4) the 4*4 pixel domains of selection are divided into first quartile pixel domain to fourth quadrant pixel domain, and center pixel
Domain, according to comparison criterion, whether detection 4*4 pixel domains are asterism；
5) stagger a row with the 4*4 pixel domains that have obtained or a line obtain new 4*4 pixel domains, repeat step 4), until
All 4*4 pixel domains of target image have been analyzed, have completed asterism detection.
It is described by each pixel in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The method that pixel value makes the difference is：The pixel value of each pixel subtracts the same position of detector dark current benchmark image in image to be compensated
The pixel value of pixel is put, pixel value difference is more than or equal to 0, then pixel value difference retains, and difference is less than 0 and carries out then pixel value difference zero setting.
It is described that the 4*4 pixel domains of selection are divided into first quartile pixel domain to fourth quadrant pixel domain and center pixel
The method in domain is：4*4 pixel domains are divided into four quadrants, the pixel domain for having a 2*2 in each quadrant, define first quartile
Interior 2*2 pixel domains are first quartile pixel domain, and the 2*2 pixel domains defined in the second quadrant are the second quadrant pixel domain, definition
2*2 pixel domains in third quadrant are third quadrant pixel domain, and the 2*2 pixel domains defined in fourth quadrant are fourth quadrant pixel
Domain, pixel domain centered on 4 pixel definitions at 4*4 pixel domains center.
Whether the detection 4*4 pixel domains are that the method for asterism is：Meet the sum of 4 pixels in each 2*2 pixel domains
Value be respectively less than inactive pixels threshold value H, and 4 pixels in center pixel domain and value be more than asterism threshold of sensitivity h；Center pixel
The pixel value of at least 2 pixels of 4 pixels in domain is more than asterism threshold of sensitivity m, and at least meets in following condition
One condition：
A) in all 2*2 pixel domains, the pixel and value in center pixel domain are maximum；
B) pixel of first quartile pixel domain and value are more than asterism threshold of sensitivity h, the pixel of third quadrant pixel domain with
Value is more than asterism threshold of sensitivity h, and the pixel and value of the second quadrant pixel domain are less than or equal to asterism threshold of sensitivity h, four-quadrant
The pixel and value for limiting pixel domain are less than or equal to asterism threshold of sensitivity h；
C) pixel of the second quadrant pixel domain and value are more than asterism threshold of sensitivity h, the pixel of fourth quadrant pixel domain with
Value is more than asterism threshold of sensitivity h, the pixel and value of first quartile pixel domain less than or equal to asterism threshold of sensitivity h, the 3rd as
The pixel and value for limiting pixel domain are less than or equal to asterism threshold of sensitivity h.
The interval time t=1/f, wherein f are stellar camera working frame frequency.
The inactive pixels threshold value H is the 95% of pixel saturation value, and asterism threshold of sensitivity h is the full dark conditions of stellar camera
Lower 8~12 times of picture noises；Asterism threshold of sensitivity m is 4~6 times of picture noises under the full dark conditions of stellar camera.
The known technology for the content category professional and technical personnel in the field not being described in detail in description of the invention.
Claims (10)
1. a kind of stellar camera asterism detection method, it is characterised in that comprise the following steps：
1) the continuous acquisition multiple image within the time of integration, the pixel of the multiple image same position collected is added up
Processing, as detector dark current benchmark image；
2) after interval time t, the continuous acquisition multiple image within the time of integration, by the multiple image same position collected
Pixel carries out accumulation process, image to be compensated is obtained, by the pixel value and detector dark current of each pixel in image to be compensated
The pixel value of each pixel makes the difference in benchmark image, obtains target image；
3) pixel domain to be detected is chosen on target image, detects whether pixel domain to be detected is asterism；
4) different pixel domains to be detected, repeat step 3 are chosen), until all pixel domains to be detected of target image have been analyzed,
Complete asterism detection.
A kind of 2. stellar camera asterism detection method according to claim 1, it is characterised in that：The pixel domain to be detected is
4*4 pixel domains, and 4*4 pixel domains are divided into first quartile pixel domain to fourth quadrant pixel domain, and center pixel domain.
A kind of 3. stellar camera asterism detection method according to claim 2, it is characterised in that：The 4*4 pixel domains division
It is for first quartile pixel domain to fourth quadrant pixel domain, and the method in center pixel domain：4*4 pixel domains are divided into four
Quadrant, there is 2*2 pixel domain in each quadrant, the 2*2 pixel domains defined in first quartile be first quartile pixel domain, calmly
2*2 pixel domains in adopted second quadrant are the second quadrant pixel domain, and the 2*2 pixel domains defined in third quadrant are third quadrant picture
Prime field, the 2*2 pixel domains defined in fourth quadrant are fourth quadrant pixel domain, during 4 pixel definitions at 4*4 pixel domains center are
Imago prime field.
A kind of 4. stellar camera asterism detection method according to claim 3, it is characterised in that：The detection pixel to be detected
Whether domain is that the method for asterism is：Meet that the pixel value sum of 4 pixels in each 2*2 pixel domains is respectively less than inactive pixels threshold
Value H, and the pixel value sum of 4 pixels in center pixel domain is more than asterism threshold of sensitivity h；4 pixels in center pixel domain
The pixel value of at least 2 pixels is more than asterism threshold of sensitivity m, and at least meets a condition in following condition：
A) in all 2*2 pixel domains, the pixel and value in center pixel domain are maximum；
B) the pixel value sum of first quartile pixel domain is more than asterism threshold of sensitivity h, the pixel value of third quadrant pixel domain it
With more than asterism threshold of sensitivity h, the pixel value sum of the second quadrant pixel domain is less than or equal to asterism threshold of sensitivity h, and the 4th
The pixel value sum of quadrant pixel domain is less than or equal to asterism threshold of sensitivity h；
C) the pixel value sum of the second quadrant pixel domain is more than asterism threshold of sensitivity h, the pixel value of fourth quadrant pixel domain it
With more than asterism threshold of sensitivity h, the pixel value sum of first quartile pixel domain is less than or equal to asterism threshold of sensitivity h, and the 3rd
The pixel value sum of quadrant pixel domain is less than or equal to asterism threshold of sensitivity h.
A kind of 5. stellar camera asterism detection method according to claim 4, it is characterised in that：The inactive pixels threshold value H
For the 95% of pixel saturation value, asterism threshold of sensitivity h is 8~12 times of picture noises under the full dark conditions of stellar camera；Asterism spirit
Sensitivity threshold value m is 4~6 times of picture noises under the full dark conditions of stellar camera.
6. according to a kind of any described stellar camera asterism detection methods of claim 1-5, it is characterised in that：
The interval time t=1/f, wherein f are stellar camera working frame frequency.
The pixel by each pixel in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The method that value makes the difference is：The pixel value of each pixel subtracts detector dark current benchmark image same position picture in image to be compensated
The pixel value of element, pixel value difference are more than or equal to 0, then pixel value difference retains, and pixel value difference is less than 0 and carries out then pixel value difference zero setting.
A kind of 7. stellar camera asterism detecting system, it is characterised in that：Including image capture module, image processing module, asterism inspection
Survey module；
Image capture module continuous acquisition multiple image within the time of integration, the pixel of the image same position collected is entered
Row accumulation process, as detector dark current benchmark image；After interval time t, the continuous acquisition multiple image within the time of integration,
The pixel of the multiple image same position collected is subjected to accumulation process, obtains image to be compensated；
Image processing module is by each picture in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The pixel value of element makes the difference, and obtains target image；
Asterism detection module chooses pixel domain to be detected on target image, and according to comparison criterion, detecting pixel domain to be detected is
No is asterism；Then new pixel domain to be detected is obtained, continues to carry out asterism detection to new pixel domain to be detected, until detection
All pixel domains to be detected of complete target image, complete asterism detection.
A kind of 8. stellar camera asterism detecting system according to claim 7, it is characterised in that：The pixel domain to be detected is
4*4 pixel domains, and 4*4 pixel domains are divided into four quadrants, the pixel domain for having a 2*2 in each quadrant, define first as
2*2 pixel domains in limit are first quartile pixel domain, and the 2*2 pixel domains defined in the second quadrant are the second quadrant pixel domain, fixed
2*2 pixel domains in adopted third quadrant are third quadrant pixel domain, and the 2*2 pixel domains defined in fourth quadrant are fourth quadrant picture
Prime field, pixel domain centered on 4 pixel definitions at 4*4 pixel domains center.
A kind of 9. stellar camera asterism detecting system according to claim 8, it is characterised in that：The detection pixel to be detected
Whether domain is that the method for asterism is：Meet that the pixel value sum of 4 pixels in each 2*2 pixel domains is respectively less than inactive pixels threshold
Value H, and the pixel value sum of 4 pixels in center pixel domain is more than asterism threshold of sensitivity h；4 pixels in center pixel domain
The pixel value of at least 2 pixels is more than asterism threshold of sensitivity m, and at least meets a condition in following condition：
D) in all 2*2 pixel domains, the pixel value sum in center pixel domain is maximum；
E) the pixel value sum of first quartile pixel domain is more than asterism threshold of sensitivity h, the pixel value of third quadrant pixel domain it
With more than asterism threshold of sensitivity h, the pixel value sum of the second quadrant pixel domain is less than or equal to asterism threshold of sensitivity h, and the 4th
The pixel value sum of quadrant pixel domain is less than or equal to asterism threshold of sensitivity h；
F) the pixel value sum of the second quadrant pixel domain is more than asterism threshold of sensitivity h, the pixel value of fourth quadrant pixel domain it
With more than asterism threshold of sensitivity h, the pixel value sum of first quartile pixel domain is less than or equal to asterism threshold of sensitivity h, and the 3rd
The pixel value sum of quadrant pixel domain is less than or equal to asterism threshold of sensitivity h.
Wherein, inactive pixels threshold value H is the 95% of pixel saturation value, and asterism threshold of sensitivity h is 8 under the full dark conditions of stellar camera
~12 times of picture noises；Asterism threshold of sensitivity m is 4~6 times of picture noises under the full dark conditions of stellar camera.
10. according to a kind of any described stellar camera asterism detecting systems of claim 7-9, it is characterised in that：
The interval time t=1/f, wherein f are stellar camera working frame frequency.
The pixel by each pixel in the pixel value of each pixel in image to be compensated and detector dark current benchmark image
The method that value makes the difference is：The pixel value of each pixel subtracts detector dark current benchmark image same position picture in image to be compensated
The pixel value of element, pixel value difference are more than or equal to 0, then pixel value difference retains, and difference is less than 0 and carries out then pixel value difference zero setting.
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