A real-time dark current estimation method for visible light array detectors without dark pixels

Abstract

A method for real-time dark current estimation of a visible light array detector without dark pixels belongs to the field of remote sensing image processing technology and includes the following steps: the first step is to select the integration time gear and the temperature fluctuation range according to the on-orbit application requirements and the imaging time of the detector; the second step is to collect data at different integration times and at different times; the third step is to perform data preprocessing on the response output of the detector at different integration times to remove noise; the fourth step is to perform linear fitting on the image data at different integration times according to the formation mechanism of the camera dark current, and calculate the fitting coefficients P and Q; the fifth step is to use P and Q to estimate the dark current in real time. The present invention provides an effective dark current estimation method for a visible light array detector without dark pixels, which is particularly suitable for applications with limited hardware resources and high data real-time requirements.

Description

Technical Field

[0001] The invention relates to a real-time dark current estimation method for a visible light array detector without dark pixels, which is suitable for an on-board processing platform with limited hardware resources and high real-time processing requirements, and belongs to the field of real-time remote sensing image processing. Background Art

[0002] With the development of remote sensing technology, people's requirements for imaging quality are getting higher and higher. Therefore, remote sensors are equipped with some on-orbit real-time image processing capabilities. At present, the on-board image processing algorithms are mainly image preprocessing and some adaptive adjustment algorithms based on image processing. Among them, the preprocessing algorithms mainly include non-uniformity correction and grayscale stretching. The non-uniformity correction algorithm can effectively remove the non-uniform noise of the detector and improve the imaging signal-to-noise ratio. For the non-uniformity correction algorithm, the removal of dark current can not only improve the imaging quality, but also improve the accuracy of non-uniformity correction. The removal of dark current requires accurate knowledge of the size of dark current. For detectors with dark pixel output, the output of dark pixel can accurately and in real time characterize the size of dark current. Therefore, dark pixel is usually used as the reference value of dark current. For detectors without dark pixel output, how to accurately estimate the dark current in real time is crucial to the removal effect of dark current. Summary of the invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a real-time dark current estimation method for a visible light array detector without dark pixels, and to establish an approximate linear relationship model between dark current and integration time based on a dark current estimation model and the feature of high precision of on-orbit temperature control; further, to calibrate dark current estimation coefficients P and Q through ground data, store P and Q in a hardware operation unit, and to estimate the size of the dark current on-orbit based on parameters such as the integration time, series, gain, etc. actually used.

[0004] The technical solution of the present invention is: a method for real-time estimation of dark current of a visible light array detector without dark pixels, comprising:

[0005] According to the integration time range of the on-orbit application, select the integration time gear that needs to be collected;

[0006] In total darkness, data is collected M times in a cycle according to the determined integration time level;

[0007] De-noising the collected output data of detectors with different integration times and cycles;

[0008] The imaging data with different integration times and different cycle numbers were fitted to obtain the dark current estimation coefficients P and Q;

[0009] According to the integration time I currently applied on the trackT , stage Stg, gain Gain, and dark current estimation coefficients P and Q, and real-time estimate of the detector dark current value.

[0010] Furthermore, the integration time gear is the minimum integration time I in actual application. Tmin , Default integration time I Tdef , Maximum integration time I Tmax Select the characteristic integration time gear according to the actual situation.

[0011] Furthermore, the integration time gear to be collected is selected. If the integration time gear is not unique, the selected integration time range must cover the minimum integration time and the maximum integration time of the application.

[0012] Furthermore, the number of acquisitions M required is determined based on the single imaging duration Tim of the detector on orbit. During data acquisition, the detector working state is kept consistent with the actual application scenario.

[0013] Furthermore, the number of collected data cycles M ≥ 2*Tim / 3 / t Img , t Im is the storage interval between two images, and the collected data duration is the power-on duration, so that the dark signal fluctuation caused by temperature change during the actual operation of the detector is included in the collected image data.

[0014] Furthermore, the method for fitting the imaging data with different integration times and different cycle numbers is the least squares method.

[0015] Furthermore, when calculating the dark current estimation coefficient, if the detector is a linear array TDI detector, P is calculated separately according to different TDI levels. stg , Q stg .

[0016] Furthermore, the estimated value of the detector dark current is D Actual =(P*I T +Q)*Gain.

[0017] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of a method for real-time estimation of dark current of a visible light array detector without dark pixels are implemented.

[0018] A device for real-time estimation of dark current of a visible light array detector without dark pixels comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for real-time estimation of dark current of a visible light array detector without dark pixels are implemented.

[0019] The advantages of the present invention compared with the prior art are:

[0020] (1) The present invention solves the problem of real-time dark current estimation on-orbit for a visible light array detector without dark pixel output, and effectively improves the accuracy of on-orbit consistency correction for the detector without dark pixel output;

[0021] (2) The algorithm proposed in the present invention has low complexity and is easy to implement in engineering, and the estimated dark current can be dynamically changed according to different parameters such as integration time, number of stages, gain, etc.;

[0022] (3) The method proposed in the present invention occupies less hardware resources and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the algorithm flow chart of the present invention. DETAILED DESCRIPTION

[0024] In order to better understand the above technical scheme, the technical scheme of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical scheme of the present application, rather than limitations on the technical scheme of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0025] The following is a further detailed description of a method for real-time estimation of dark current of a visible light array detector without dark pixels provided in an embodiment of the present application in conjunction with the accompanying drawings of the specification. The specific implementation method may include (eg Figure 1 The steps are as follows:

[0026] (1) According to the integration time range of the on-orbit application, select the integration time gear that needs to be collected. If the integration time gear is not unique, the selected integration time range must be able to cover the minimum and maximum integration times of the application; according to the single imaging time Tim of the detector on-orbit, determine the number of times M that need to be collected. When collecting data, keep the detector working state consistent with the actual application scenario.

[0027] (2) In total darkness, data is collected M times in a cycle according to the integration time level determined in step (1), where different cycles are represented by 1, 2, 3, ..., M.

[0028] (3) De-noising the collected detector output data with different integration times and cycles to reduce the influence of circuit noise and detector noise;

[0029] (4) Perform least squares fitting on the imaging data with different integration times and different cycle numbers to obtain the dark current estimation coefficients P and Q. If the detector is a linear array TDI detector, P needs to be calculated separately according to different TDI levels. stg , Q stg ;

[0030] (5) Based on the integration time I currently applied on orbit T , stage Stg, gain Gain, and the dark current estimation coefficients P and Q obtained in step (4), using the dark current estimation model, according to formula D Actual =(P*I T +Q)*Gain, real-time estimation of the detector dark current value;

[0031] Furthermore, the integral time in step (1) is generally set at the minimum integral time I in practical application. Tmin , Default integration time I Tdef , Maximum integration time I Tmax Flexible selection among the characteristic integration time gears. The number of collected data cycles M≥2*Tim / 3 / t Img , t Im is the storage interval between two images. The data acquisition duration is generally the power-on duration, so that the dark signal fluctuation caused by temperature change during actual operation of the detector can be included in the acquired image data as much as possible;

[0032] In a possible implementation, in step (3), denoising is performed on images with different integration times and different cycles, and the denoising method adopts a summing and averaging method.

[0033] In one possible implementation, in step (4), according to the dark current imaging model D R represents the average dark current, P s represents the pixel area, D FM Dark current quality factor, T represents the device temperature of the detector, E g represents the band gap energy of silicon, k represents the Boltzmann constant, I T represents the integration time, G represents the equivalent gain of the imaging circuit. For a fixed detector, the dark current is related to the device temperature and the integration time. Usually, the focal plane temperature control accuracy of the on-orbit camera is relatively high, generally ±1°C, and can reach ±0.3°C at most. Within the temperature fluctuation range of no more than ±1°C, it can be approximately considered that D R With integration time I T Satisfy the linear relationship D R =P*I T+Q. In order to obtain a sufficient number of samples, test data of the power-on time are collected. The data collected under the dark condition with different integration times and different number of cycles are calculated according to step (3) to obtain the mean value D of the dark image collected in the i-th cycle under the corresponding integration time gear. R _I Tmin(i) , D R _I Tdef(i) , D R _I Tmax(i) , i = 1, 2, ..., M. The estimated coefficients P and Q of the dark current are obtained by fitting using the least squares method. If the detector is a linear array TDI type detector, the estimated coefficients P are fitted for different TDI levels stg , Q stg , where stg represents the TDI level.

[0034] In one possible implementation, in step (5), taking into account the effect of gain on circuit output, the dark current estimation model obtained in step (4) is improved to obtain an improved dark current estimation model, D Actual =(P*I T +Q)*Gain, where Gain is the gain conversion factor.

[0035] In the solution provided in the embodiment of the present application, Figure 1 Shown is the algorithm flow chart of the present invention, from Figure 1 It can be seen that the present invention provides an on-orbit real-time dark current estimation method for a visible light array detector without dark pixel output, and the specific steps are as follows:

[0036] (1) According to the actual application of the integration time range, select the different integration time gears that need to be collected. If the integration time gear is not unique, the selected integration time range should be able to cover the minimum integration time and maximum integration time of the application. The integration time gear is generally within the minimum integration time of the actual application. Tmin , Default integration time I Tdef , Maximum integration time I Tmax Flexible selection among the characteristic integral time gears, the selected integral time gear shall be ≥ 3 gears.

[0037] According to the single imaging time Tim of the detector on orbit, determine the number of cycles M required for acquisition, M≥2*Tim / 3 / t Img .t Im is the storage interval of two images, 3 represents 3 different integration times, and the data acquisition duration is generally the power-on duration, so that the dark signal fluctuation caused by temperature changes in the actual working state of the detector can be included in the acquired image data as much as possible. It should be noted that before data acquisition, the working state of the detector should be kept consistent with the actual application scenario, which is a very critical condition for data acquisition.

[0038] (2) After the working state meets the requirements, the output of the detector in the dark condition is collected according to the integration time gear and the number of collection cycles M determined in step (1). The collected data is D R _I Tmin(i) (x,y),D R _I Tdef(i) (x,y),D R _I Tmax(i) (x,y), where D R _I Tmin(i) (x,y) represents the Tmin Under the integration time, the dark image collected in the i-th cycle, the value range of i is 1, 2, 3…M.

[0039] (3) In the dark, the detector output data collected with different integration times and cycles are denoised to reduce the interference of circuit noise and detector noise. The denoising method is the average denoising method. R _I Tmin(i) (x, y) to obtain the global mean, the calculation method is:

[0040]

[0041] Among them, D R _I Tmin(i) Indicates that Tmin Under the integration time, the dark average data collected in the i-th cycle, LN represents the number of columns of the collected image, that is, the number of pixels, and RN represents the number of rows of the collected image. Generally, RN ≥ 1024.

[0042] (4) According to the dark current formation principle of the detector, the dark current estimation model is:

[0043]

[0044] Where D R represents the average dark current, P s represents the pixel area, D FM Dark current quality factor, T represents the device temperature of the detector, E g represents the band gap energy of silicon, k represents the Boltzmann constant, I T Represents the integration time, G represents the equivalent gain of the imaging circuit. For a fixed detector, the dark current is mainly related to the device temperature and integration time.

[0045] Usually, the temperature control accuracy of the detector focal plane on orbit is relatively high, generally ±1°C, and the accuracy requirement can reach ±0.3°C. Within the temperature fluctuation range of no more than ±1°C, it is approximately considered that D RWith integration time I T At the same time, in order to obtain a sufficient number of samples, the test data of the power-on time is collected. When fitting, the data of different cycles need to be added to the fitting data set. The least squares method is used to fit the data D under different integration times in the dark condition. R _I Tmin(i) , D R _I Tdef(i) , D R _I Tmax(i) , the preliminary estimation model of dark current is as follows:

[0046] D R '=(P*I T +Q)

[0047] D R ' is the preliminary estimated dark current, I T is the integration time, P is the linear fitting coefficient of dark current and integration time, and Q is the constant term coefficient of linear fitting.

[0048] If the detector is a linear array TDI type detector, it is necessary to use data from different levels to calculate P stg , Q stg At the same time, the effect of gain on dark current conforms to a multiplicative relationship. Therefore, in a circuit with gain adjustment, the dark current estimate is corrected as follows:

[0049] DR=(Pstg*IT+Qstg)*g

[0050] Where g is the gain conversion factor, P stg , Q stg The gain g during fitting is "1", and other gains are converted based on this gain. stg , Q stg , g, and these three types of parameters are stored in the hardware respectively.

[0051] (5) In actual application, the currently used integral time I T , stage Stg, gain g and other parameters are input into the dark current estimation model, and the detector dark current size D can be estimated in real time. Actual =(P stg *I T +Q stg )*g.

[0052] The present invention establishes an estimation model of dark current, integration time, gain and series, and realizes real-time estimation of dark current of a visible light array detector without dark pixels.

[0053] The present application provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and when the computer instructions are executed on a computer, the computer executes Figure 1 The method described.

[0054] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) that contain computer-usable program code.

[0055] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0056] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0057] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

[0059] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for real-time estimation of dark current of a visible light array detector without dark pixels, characterized in that: include: According to the integration time range of the on-orbit application, select the integration time gear that needs to be collected; In total darkness, data is collected M times in a cycle according to the determined integration time level; De-noising the output data of the collected linear array TDI detectors with different integration times and cycles; The imaging data with different integration times and different cycle numbers are fitted, and the dark current estimation coefficient P is calculated separately according to different TDI levels Stg. stg , Q stg ; According to the integration time I currently applied on the track T , stage Stg, gain Gain, and dark current estimation coefficient P stg , Q stg , real-time estimation of the dark current value of the linear array TDI detector; The estimated dark current of the linear array TDI detector is D Actual =(P stg *I T +Q stg )*Gain.

2. The method for real-time dark current estimation of a visible light array detector without dark pixels according to claim 1, characterized in that: The minimum integral time I of the integral time gear in actual application Tmin , Default integration time I Tdef , Maximum integration time I Tmax Select the characteristic integration time gear according to the actual situation.

3. The method for real-time estimation of dark current of a visible light array detector without dark pixels according to claim 2, characterized in that: The integration time gear to be collected is selected. If the integration time gear is not unique, the selected integration time range must cover the minimum integration time and the maximum integration time of the application.

4. The method for real-time dark current estimation of a visible light array detector without dark pixels according to claim 1, characterized in that: According to the single imaging time Tim of the detector on orbit, the number of times M required for collection is determined. When collecting data, the working state of the detector is kept consistent with the actual application scenario.

5. The method for real-time estimation of dark current of a visible light array detector without dark pixels according to claim 4, characterized in that: The number of collected data cycles M≥2*Tim / 3 / t Img , t Im is the storage interval between two images, and the collected data duration is the power-on duration, so that the dark signal fluctuation caused by temperature change during the actual operation of the detector is included in the collected image data.

6. The method for real-time dark current estimation of a visible light array detector without dark pixels according to claim 1, characterized in that: The method for fitting the imaging data with different integration times and different cycle numbers is the least squares method.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

8. A device for real-time estimation of dark current of a visible light array detector without dark pixels, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

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