CN108111759A - Towards the emulation design method of area array CCD opto-electronic conversion - Google Patents
Towards the emulation design method of area array CCD opto-electronic conversion Download PDFInfo
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Abstract
本发明提出一种面向面阵CCD光电转换的仿真设计方法,包括:根据多光谱输入图像的源光谱响应曲线,根据设置的仿真波段范围仿真计算得到仿真波段的CCD光谱响应度;建立CCD光电转换模型,并以入射探测器面上的波段辐照度场为输入完成光电转换,输出CCD探测器响应的电压图像文件;建立模拟电路模型,进行预放大、滤波和后置放大的模拟电路传输过程;建立模数量化模型,并对输出的电压值数据进行数字量化处理,完成由模拟信号到数字信号的量化过程,及输出数字图像文件。本发明可以更好的仿真模拟不同载荷的光电转换过程,适用于各种全色成像载荷,可为载荷设计方提供载荷设计参数参考。
The present invention proposes a simulation design method for area array CCD photoelectric conversion, including: according to the source spectral response curve of the multi-spectral input image, and according to the set simulation band range simulation calculation to obtain the CCD spectral responsivity of the simulation band; establish CCD photoelectric conversion model, and complete the photoelectric conversion with the band irradiance field incident on the detector surface as input, and output the voltage image file of the CCD detector response; establish an analog circuit model, and carry out the analog circuit transmission process of pre-amplification, filtering and post-amplification ; Establish a modulus and quantization model, and perform digital quantization processing on the output voltage value data, complete the quantization process from analog signals to digital signals, and output digital image files. The invention can better simulate the photoelectric conversion process of different loads, is applicable to various full-color imaging loads, and can provide load design parameter references for load designers.
Description
技术领域technical field
本发明属于卫星遥感相机仿真技术领域,涉及一种面向面阵CCD 光电转换的仿真设计方法。The invention belongs to the technical field of satellite remote sensing camera simulation, and relates to a simulation design method for area array CCD photoelectric conversion.
背景技术Background technique
卫星成像仿真是在卫星设计、预研阶段,针对复杂成像条件下对地 观测成像质量保障技术研究的重要环节。通过模拟卫星成像过程中各个 环节对像质的影响因素,仿真获取卫星的模拟影像,可以支持用户对于 卫星应用能力的分析,进而指导指标需求的提出;可以辅助进行卫星成 像质量的分析。在实际应用前,通过实验模拟验证可以及时诊断并排除 隐患和故障、能有效地提高研制质量;另外,通过使用仿真技术进行研 究,还可以大大减少实验次数和数量,从而起到了缩短研制周期、节约 研制经费、提高性价比的目的。对于新型的高分辨率、高光谱、多波段 对地观测卫星在未来成像过程中将遇到的问题,以及影响图像质量的因 素,目前尚无实际实例可以参考。因此在卫星遥感相机研制工作开展前期,进行卫星成像载荷光电转换仿真,有助于直观的、定量地分析卫星 运行中的实际状态和图像质量。Satellite imaging simulation is an important link in the satellite design and pre-research stages, aiming at the research on the quality assurance technology of earth observation imaging under complex imaging conditions. By simulating the influence factors of each link in the satellite imaging process on the image quality, the simulated satellite image can be obtained through simulation, which can support the user's analysis of satellite application capabilities, and then guide the proposal of index requirements; it can also assist in the analysis of satellite imaging quality. Before practical application, through experimental simulation verification, hidden dangers and faults can be diagnosed and eliminated in time, and the quality of development can be effectively improved; in addition, by using simulation technology for research, the number and number of experiments can be greatly reduced, thereby shortening the development cycle, The purpose of saving research and development funds and improving cost performance. For the problems that new high-resolution, hyperspectral, and multi-band earth observation satellites will encounter in the future imaging process, as well as the factors that affect image quality, there are no practical examples to refer to. Therefore, in the early stage of satellite remote sensing camera development, the photoelectric conversion simulation of satellite imaging load is helpful to intuitively and quantitatively analyze the actual status and image quality of satellite operation.
发明内容Contents of the invention
发明所要解决的课题是,针对遥感卫星成像载荷设计阶段无法准确 直观获取相机成像质量的问题。The problem to be solved by the invention is to solve the problem that the imaging quality of the camera cannot be accurately and intuitively obtained in the design stage of the remote sensing satellite imaging load.
用于解决课题的技术手段是,提出一种面向面阵CCD光电转换的仿 真设计方法,仿真光电转换过程中各阶段影响因素,为载荷设计提供参 考。The technical means to solve the problem is to propose a simulation design method for area array CCD photoelectric conversion, simulate the influencing factors of each stage in the photoelectric conversion process, and provide reference for load design.
本发明提出一种面向面阵CCD光电转换的仿真设计方法,包括 如下步骤:The present invention proposes a kind of simulation design method facing area array CCD photoelectric conversion, comprises the following steps:
步骤1、根据多光谱输入图像的源光谱响应曲线,根据设置的仿真 波段范围仿真计算得到仿真波段的CCD光谱响应度;Step 1, according to the source spectral response curve of multi-spectral input image, obtain the CCD spectral responsivity of simulation band according to the simulation band range simulation of setting;
步骤2、建立CCD光电转换模型,并以入射探测器面上的波段辐 照度场为输入完成光电转换,输出CCD探测器响应的电压图像文件;Step 2, set up the CCD photoelectric conversion model, and complete the photoelectric conversion with the band irradiance field on the incident detector surface as input, and output the voltage image file that the CCD detector responds to;
步骤3、建立模拟电路模型,并对CCD光电转换模型输出的电压 图像文件进行预放大、滤波和后置放大的模拟电路传输过程,输出电压 值数据;Step 3, set up the analog circuit model, and carry out the analog circuit transmission process of pre-amplification, filtering and post-amplification to the voltage image file output by the CCD photoelectric conversion model, output voltage value data;
步骤4、建立模数量化模型,并对模拟电路模型输出的电压值数据 进行数字量化处理,同时考虑量化过程中产生的量化噪声,完成由模拟 信号到数字信号的量化过程,及输出数字图像文件。Step 4. Establish an analog quantization model, and perform digital quantization processing on the voltage value data output by the analog circuit model, while considering the quantization noise generated during the quantization process, complete the quantization process from analog signals to digital signals, and output digital image files .
进一步地,作为本发明的一种优选技术方案,所述步骤1仿真计算 得到仿真波段的CCD光谱响应度,包括:Further, as a kind of preferred technical scheme of the present invention, described step 1 simulation calculation obtains the CCD spectral responsivity of simulation band, comprises:
根据相机光学系统的CCD光谱响应曲线中的光谱透过率和设置的 仿真波段范围,进行仿真波段的光学系统透过率提取;According to the spectral transmittance in the CCD spectral response curve of the camera optical system and the set simulated band range, the optical system transmittance of the simulated band is extracted;
根据CCD的光谱响应度曲线和设置的仿真波段范围,完成仿真波 段的CCD响应度提取。According to the spectral responsivity curve of the CCD and the set simulation band range, the CCD responsivity extraction of the simulation band is completed.
进一步地,作为本发明的一种优选技术方案,所述步骤2以入射探 测器面上的波段辐照度场为输入完成光电转换,具体为:Further, as a preferred technical solution of the present invention, said step 2 takes the band irradiance field on the incident detector surface as input to complete the photoelectric conversion, specifically:
输入待采样的照度图像,采样得到CCD实际接收到的照度图像;Input the illuminance image to be sampled, and sample the illuminance image actually received by the CCD;
根据CCD元器件的占空比,计算出单一探元实际接收到的照度图 像;Calculate the illuminance image actually received by a single detector according to the duty cycle of the CCD components;
根据单一探元的响应度以及积分时间,对单一探元进行积分处理;According to the responsivity and integration time of a single detector, integrate the single detector;
根据探元的不一致性响应系数,计算及输出单一探元的电压;Calculate and output the voltage of a single probe according to the inconsistency response coefficient of the probe;
根据CCD动态范围对单一探元输出电压的影响因素,保存和输出 CCD单一探元光电转换后的电压图像文件。According to the influence factors of the CCD dynamic range on the output voltage of a single detector, save and output the voltage image file of the photoelectric conversion of the CCD single detector.
进一步地,作为本发明的一种优选技术方案,所述CCD动态范围 对单一探元输出电压的影响因素包括暗电流、饱和输出电压和CCD的 噪声。Further, as a preferred technical solution of the present invention, the influence factors of the dynamic range of the CCD on the output voltage of a single probe include dark current, saturation output voltage and noise of the CCD.
进一步地,作为本发明的一种优选技术方案,所述步骤3对电压图 像文件进行预放大、滤波和后置放大的模拟电路传输过程,具体为:Further, as a preferred technical solution of the present invention, said step 3 carries out the analog circuit transmission process of pre-amplification, filtering and post-amplification to the voltage image file, specifically:
对CCD光电转换模型输出的电压图像文件进行阻抗匹配和放大, 及根据设置的低通滤波器频率进行低通滤波后输出模拟电压;Perform impedance matching and amplification on the voltage image file output by the CCD photoelectric conversion model, and output the analog voltage after low-pass filtering according to the set low-pass filter frequency;
根据设置的后置放大的增益放大倍数和偏置放大量,对低通滤波所 输出的模拟电压进行调整及输出电压信号;Adjust the analog voltage output by the low-pass filter and output the voltage signal according to the set post-amplification gain magnification and bias magnification;
根据相机噪声仿真模块产生的电路噪声,对后置放大输出的电压信 号叠加模拟电路噪声,及输出电压值数据。According to the circuit noise generated by the camera noise simulation module, the analog circuit noise is superimposed on the voltage signal output by the post-amplification, and the output voltage value data.
进一步地,作为本发明的一种优选技术方案,所述方法中低通滤波 包括空间滤波和频率滤波。Further, as a preferred technical solution of the present invention, the low-pass filtering in the method includes spatial filtering and frequency filtering.
进一步地,作为本发明的一种优选技术方案,所述频率滤波采用巴 特沃斯低通滤波器。Further, as a preferred technical solution of the present invention, the frequency filtering adopts a Butterworth low-pass filter.
进一步地,作为本发明的一种优选技术方案,所述步骤4对模拟电 路模型输出的电压值数据进行数字量化处理,具体为:Further, as a preferred technical solution of the present invention, said step 4 performs digital quantization processing on the voltage value data output by the analog circuit model, specifically:
将相机噪声仿真模块生成的量化噪声叠加到模拟电路模型输出 的电压值数据上;Superimpose the quantization noise generated by the camera noise simulation module on the voltage value data output by the analog circuit model;
根据建立的量化模型,将所述叠加后的输出电压值数据进行模数 量化,及输出数字图像文件。According to the established quantization model, the output voltage value data after the superposition is subjected to modulus quantization, and a digital image file is output.
发明效果是,本发明的仿真设计方法具备如下优点:The effect of the invention is that the simulation design method of the present invention has the following advantages:
(1)、在遥感相机光电转换系统的现有理论基础上,针对项目任务的 实际需求,建立基于CCD探测器详细器件参数的遥感相机光电转换系统 模型,针对CCD光谱响应曲线的特点,建立光谱响应模型,并实现了软 件化,拓展了光电成像软件的功能,实现了多光谱图像的仿真与处理;细 化光电成像过程,将光电转换过程分为四个子系统,实现了针对每个子系 统的对成像影响的仿真研究。(1) On the basis of the existing theory of photoelectric conversion system of remote sensing camera, according to the actual needs of the project task, a model of photoelectric conversion system of remote sensing camera based on detailed device parameters of CCD detector is established, and a spectrum is established according to the characteristics of CCD spectral response curve Response model, and realized the software, expanded the function of photoelectric imaging software, realized the simulation and processing of multi-spectral images; refined the photoelectric imaging process, divided the photoelectric conversion process into four subsystems, and realized the control of each subsystem Simulation studies of the effects on imaging.
(2)、通过在实验室自行搭建实验平台与仿真图像对比,开展了针对 遥感相机光电转换系统的仿真模型验证工作,实验结果表明:仿真软件仿 真退化出的图像与实验拍摄图像的MTF下降率的相似度为90%,证明仿 真软件模型是正确且可靠的。(2) By comparing the experimental platform built in the laboratory with the simulated images, the simulation model verification work for the photoelectric conversion system of the remote sensing camera was carried out. The experimental results show that: the MTF decline rate of the image degraded by the simulation software simulation and the experimentally captured image The similarity is 90%, which proves that the simulation software model is correct and reliable.
附图说明Description of drawings
图1为本发明仿真设计方法的流程示意图。Fig. 1 is a schematic flow chart of the simulation design method of the present invention.
图2为本发明的光谱响应曲线图。Fig. 2 is a graph of the spectral response curve of the present invention.
图3为本发明CCD光电转换建模仿真处理流程图。Fig. 3 is a flow chart of CCD photoelectric conversion modeling and simulation processing in the present invention.
图4为本发明的模拟电路建模仿真处理流程图。Fig. 4 is a flow chart of the analog circuit modeling simulation process of the present invention.
图5为本发明模数量化建模仿真处理流程图。Fig. 5 is a flow chart of the modular and quantitative modeling and simulation processing of the present invention.
图6为本发明重采样过程示意图。Fig. 6 is a schematic diagram of the resampling process of the present invention.
图7为本发明采样区域划分示意图。Fig. 7 is a schematic diagram of sampling area division in the present invention.
图8为本发明基于傅里叶变换域的低通滤波器的工作原理图。Fig. 8 is a working principle diagram of the low-pass filter based on the Fourier transform domain of the present invention.
具体实施方式Detailed ways
以下,基于附图针对本发明进行详细地说明。Hereinafter, the present invention will be described in detail based on the drawings.
如图1所示,本发明提出了一种面向面阵CCD光电转换的仿真设 计方法,包括如下步骤:As shown in Figure 1, the present invention proposes a kind of emulation design method facing area array CCD photoelectric conversion, comprises the steps:
步骤1、根据多光谱输入图像的源光谱响应曲线,根据设置的仿真 波段范围仿真计算得到仿真波段的CCD光谱响应度。Step 1. According to the source spectral response curve of the multi-spectral input image, the CCD spectral responsivity of the simulated band is simulated and calculated according to the set simulated band range.
所述步骤1中,根据多光谱输入图像源光谱响应曲线,如图2所示, 根据相机光学系统的CCD的光谱响应曲线,并根据仿真波段范围,分析 出仿真波段的CCD光谱响应度,主要步骤如下:In described step 1, according to multi-spectral input image source spectral response curve, as shown in Figure 2, according to the spectral response curve of the CCD of camera optics system, and according to simulation band range, analyze the CCD spectral responsivity of simulation band, mainly Proceed as follows:
101)根据相机光学系统的光谱透过率曲线和仿真波段范围,完成仿 真波段的光学系统透过率提取,保存成单独文件。101) According to the spectral transmittance curve of the camera optical system and the simulation band range, complete the extraction of the optical system transmittance of the simulation band, and save it as a separate file.
102)根据CCD的光谱响应度曲线和仿真波段范围,完成仿真波 段的CCD响应度提取,保存成单独文件。102) According to the spectral responsivity curve of CCD and simulation band scope, finish the CCD responsivity extraction of simulation band, save into separate file.
步骤2、建立CCD光电转换模型,并以入射探测器面上的波段辐 照度场为输入完成光电转换,输出CCD探测器响应的电压图像文件。Step 2, establish the CCD photoelectric conversion model, and complete the photoelectric conversion with the band irradiance field incident on the detector surface as input, and output the voltage image file of the CCD detector response.
所述步骤2中,原理如图3所示,CCD光电转换根据CCD的积分时 间、探元尺寸等参数,建立CCD光电转换模型,以入射探测器面上的波 段辐照度场为输入,完成光电转换,输出CCD探测器响应的电压图像文 件,主要步骤如下:In the step 2, the principle is as shown in Figure 3. The CCD photoelectric conversion model is established according to the parameters such as the integration time of the CCD and the size of the probe, and the band irradiance field on the incident detector surface is used as input to complete the process. Photoelectric conversion, output the voltage image file of CCD detector response, the main steps are as follows:
201)输入待采样的照度图像,考虑分辨率的影响,经过采样过程,201) Input the illuminance image to be sampled, consider the impact of resolution, after the sampling process,
得到CCD实际接收到的照度图像;Obtain the illuminance image actually received by the CCD;
202)根据CCD元器件的占空比,计算出单一探元实际接收到的照 度图像;202) Calculate the illuminance image actually received by a single probe according to the duty cycle of the CCD components;
203)根据单一探元的响应度以及积分时间,对单一探元进行积分处 理;203) According to the responsivity and the integration time of a single probe, integral processing is carried out to a single probe;
204)根据探元的不一致性响应系数的影响,计算然后输出单一探元 的电压Vi。204) Calculate and then output the voltage Vi of a single probe according to the influence of the inconsistency response coefficient of the probe.
205)最后根据CCD动态范围对单一探元输出电压的影响,动态 范围的影响主要包括暗电流、饱和输出电压和CCD的噪声,最后保存 输出CCD单一探元光电转换输出的电压图像文件。205) Finally, according to the influence of the CCD dynamic range on the output voltage of a single detector, the influence of the dynamic range mainly includes dark current, saturated output voltage and noise of the CCD, and finally save the output voltage image file of the photoelectric conversion output of the CCD single detector.
步骤3、建立模拟电路模型,并对CCD光电转换模型输出的电压 图像文件进行预放大、滤波和后置放大的模拟电路传输过程,输出电压 值数据。Step 3, establish an analog circuit model, and carry out the analog circuit transmission process of pre-amplification, filtering and post-amplification to the voltage image file output by the CCD photoelectric conversion model, and output voltage value data.
其原理如图4所示,所述模拟电路建模仿真用于模拟CCD输出的电 压图像数据进行预放大、滤波和后置放大等模拟电路传输过程,在仿真电 路的各个环节时,根据设计电路的特性参数,仿真电压数据经过这些电路 器件后的响应数据,主要步骤如下:Its principle is as shown in Figure 4, the analog circuit modeling simulation is used to simulate the voltage image data output by the CCD to carry out analog circuit transmission processes such as pre-amplification, filtering and post-amplification, when simulating each link of the circuit, according to the design circuit The characteristic parameters of the simulated voltage data pass through the response data of these circuit devices. The main steps are as follows:
301)根据预放电路的放大倍数,对CCD传感器输出的模拟电压信 号进行阻抗匹配和放大。301) Perform impedance matching and amplification on the analog voltage signal output by the CCD sensor according to the amplification factor of the pre-amplification circuit.
302)根据滤波电路的低通滤波器3dB频率(Hz),对预放电路输出的 模拟电压信号进行低通滤波后,输出输出模拟电压。302) According to the 3dB frequency (Hz) of the low-pass filter of the filter circuit, the analog voltage signal output by the pre-amplification circuit is low-pass filtered, and the output analog voltage is output.
303)根据后置放大器的增益放大倍数和偏置放大量,对滤波输出的 模拟电压进行调整,及输出电压信号。303) Adjust the analog voltage output by the filter according to the gain amplification factor and the bias amplification amount of the post amplifier, and output the voltage signal.
304)根据相机噪声仿真模块产生的电路噪声,对后置放大电路输 出的电压信号叠加模拟电路噪声,及输出电压值数据。304) According to the circuit noise generated by the camera noise simulation module, the analog circuit noise is superimposed on the voltage signal output by the post amplifier circuit, and the voltage value data is output.
优选地,所述方法中低通滤波包括空间滤波和频率滤波。所述频率 滤波采用巴特沃斯低通滤波器。Preferably, the low-pass filtering in the method includes spatial filtering and frequency filtering. The frequency filtering adopts Butterworth low-pass filter.
步骤4、建立模数量化模型,并对模拟电路模型输出的电压值数据 进行数字量化处理,同时考虑量化过程中产生的量化噪声,完成由模拟 信号到数字信号的量化过程,及输出数字图像文件。Step 4. Establish an analog quantization model, and perform digital quantization processing on the voltage value data output by the analog circuit model, while considering the quantization noise generated during the quantization process, complete the quantization process from analog signals to digital signals, and output digital image files .
所述步骤4中,其原理如图5所示,模数量化建模仿真对模拟电路输 出的电压值数据进行数字量化处理,同时考虑量化过程中产生的量化噪声, 完成由模拟信号到数字信号的量化过程。,主要步骤如下:In the step 4, the principle is shown in Figure 5. The analog and quantitative modeling simulation performs digital quantization processing on the voltage value data output by the analog circuit, and at the same time considers the quantization noise generated during the quantization process, and completes the conversion from analog signals to digital signals. the quantification process. , the main steps are as follows:
401)将相机噪声仿真模块生成的量化噪声叠加到模拟电路输出的电 压值数据上;401) superimposing the quantization noise generated by the camera noise simulation module on the voltage value data output by the analog circuit;
402)根据模数转换器的量化最大电压、最小电压和量化位数,建立 量化模型;402) Establish a quantization model according to the quantization maximum voltage, minimum voltage and quantization bit number of the analog-to-digital converter;
403)根据量化模型,将步骤401)中叠加后输出的电压值数据结 果进行模数量化,完成量化过程,输出数字图像文件。403) According to the quantization model, carry out modulus quantization on the voltage value data result output after superposition in step 401), complete the quantization process, and output a digital image file.
通过以上卫星成像载荷光电转换仿真算法,可以更好的仿真模拟不 同载荷的光电转换过程,适用于各种全色成像载荷,可为载荷设计方提 供载荷设计参数参考。Through the above photoelectric conversion simulation algorithm of satellite imaging payload, the photoelectric conversion process of different payloads can be better simulated, applicable to various panchromatic imaging payloads, and can provide payload design parameter reference for payload designers.
下面结合附图2至8对本发明的具体实施方式进行进一步的详细描述, 其中CCD光电转换建模仿真处理流程如图3所示。模拟电路建模仿真处 理流程如图4所示。模数量化建模仿真处理流程如图5所示。The specific implementation of the present invention will be further described in detail below with reference to FIGS. 2 to 8 , wherein the CCD photoelectric conversion modeling and simulation processing flow is shown in FIG. 3 . The process flow of analog circuit modeling and simulation is shown in Fig. 4. Figure 5 shows the processing flow of modular and quantitative modeling and simulation.
对于光谱响应仿真建模:CCD的响应度可以用光电流IL用积分期间t 内一个面积为Ag的像元所积累的信号电荷数Ns表示,其可以写成如下形 式:For spectral response simulation modeling: the responsivity of CCD can be represented by the photocurrent I L and the number of signal charges N s accumulated by a pixel with an area A g during the integration period t, which can be written as follows:
式中,Φ为景物的辐射度。SI的单位用mA/W表示。In the formula, Φ is the radiance of the scene. The unit of SI is expressed in mA/W.
对于CCD,常采用FDA方式,因此实际应用中响应度也可以定义为 像元的单位流密度σ所产生的输出电压VS的大小,即:For CCD, the FDA method is often used, so in practical applications, the responsivity can also be defined as the size of the output voltage V S generated by the unit current density σ of the pixel, namely:
光辐射能流密度在光度学中常用照度(lx)表示,可利用关系式 1W/m2=20lx换算。The energy flux density of light radiation is usually expressed by illuminance (lx) in photometry, and can be converted by using the relational formula 1W/m 2 =20lx.
对于多光谱输入图像源,可根据其光谱波段划分情况分波段计算其对 应的响应度,假定光谱响应曲线如图2所示。图中所示数据及所示图像曲 线都是假设值,并无实际物理意义。For the multi-spectral input image source, the corresponding responsivity can be calculated in different bands according to the division of the spectral bands, assuming that the spectral response curve is shown in Figure 2. The data shown in the figure and the image curve shown are hypothetical values and have no actual physical meaning.
对于输入光谱而言,当输入波长为λi时,其对应的光谱响应度为Rλi, 则对于成像波段范围在λi~λj,i<j,其CCD光谱响应度为:For the input spectrum, when the input wavelength is λ i , the corresponding spectral responsivity is R λi , then for the imaging band range λ i ~ λ j , i<j, the CCD spectral responsivity is:
CCD的光电转换过j程主要是把入射在光敏元上的光信号转换为电 信号的过程,CCD光敏面上的光通量是在一定时间内(曝光时间)的入射 总量;同时CCD在成像过程中也具有空间采样效应,主要原因是由CCD 面阵的结构造成的,它并不是连续,而是由一个个小面元组成的,这些小 面元对连续的入射光线进行空间采样,在整个CCD光电转换过程中主要 有三个阶段。The photoelectric conversion process of CCD is mainly the process of converting the optical signal incident on the photosensitive element into an electrical signal. There is also a spatial sampling effect, the main reason is caused by the structure of the CCD area array, it is not continuous, but composed of small facets, these small facets perform spatial sampling on the continuous incident light, in the whole There are three main stages in the photoelectric conversion process of CCD.
第一阶段是把入射的光信号转换为电信号(电子/空穴),并通过电极 产生的电场加以搜集;The first stage is to convert the incident optical signal into an electrical signal (electron/hole), and collect it through the electric field generated by the electrode;
第二阶段是电荷转移过程,把成像区得到的电信号根据一定的时序 控制转移输出;The second stage is the charge transfer process, which transfers and outputs the electrical signal obtained in the imaging area according to a certain timing control;
第三阶段是信号读出放大过程,考虑到光电转换过程中的影响因素, 把光生电荷(电子/空穴)转换为电压信号,并放大读出。The third stage is the signal readout amplification process. Considering the influence factors in the photoelectric conversion process, the photogenerated charges (electrons/holes) are converted into voltage signals and amplified for readout.
(1)CCD重采样。由于CCD探元尺寸不可能无穷小,所以只能依 次对区域景物进行积分成像,这就是空间采样过程。考虑到待采样的照度 图像和采样后的照度图像都是离散的数字图像,在采样时将可以将采样的 照度图像的像素看成矩形块而非像素点。先计算CCD各采样点(取像素 中心)在原照度图上的坐标位置,然后计算出每个采样后像素的边界位置, 重新划分图像像素,如图6所示。(1) CCD resampling. Since the size of the CCD detector cannot be infinitesimally small, it is only possible to perform integral imaging on the regional scene in turn, which is the process of spatial sampling. Considering that both the illuminance image to be sampled and the illuminance image after sampling are discrete digital images, the pixels of the sampled illuminance image can be regarded as rectangular blocks rather than pixel points during sampling. First calculate the coordinate position of each sampling point of the CCD (take the pixel center) on the original illumination map, then calculate the boundary position of each sampled pixel, and re-divide the image pixels, as shown in Figure 6.
此后,将划分在同一个像素里的照度进行累加。需要注意的是,由 于CCD像素尺寸不一定是原像素的整数倍,很容易出现原像素被新像素 边界分割的情况。此时,按照进入新像素的面积百分比计算计入采样像 素的照度大小。这里将每个采样后的新像素分为9个区域,采样区域划 分示意图如图7所示。Thereafter, the illuminance divided into the same pixel is accumulated. It should be noted that since the CCD pixel size is not necessarily an integer multiple of the original pixel, it is easy to cause the original pixel to be divided by the new pixel boundary. At this time, calculate the illuminance size included in the sampling pixel according to the area percentage entering the new pixel. Here, each sampled new pixel is divided into 9 regions, and the schematic diagram of sampling region division is shown in Figure 7.
中间区域所包含的照度图像素均为整个像素,其照度直接计入采样 后的像素中。而边角区域按照围入新像素的原像素面积百分比计算照度, 计算中原像素矩阵长宽都定义为1,这样,B1、B2、B3、B4的坐标均为 整数。The pixels of the illuminance map contained in the middle area are all whole pixels, and their illuminance is directly counted into the sampled pixels. In the corner area, the illuminance is calculated according to the area percentage of the original pixel enclosed in the new pixel, and the length and width of the original pixel matrix in the calculation are all defined as 1, so that the coordinates of B1, B2, B3, and B4 are all integers.
如左上角区域: Such as the upper left corner area:
再如上中区域: Another example is the upper middle area:
A1A2A3A4所围采样后像素的总照度:The total illuminance of the sampled pixels surrounded by A1A2A3A4:
E=E左上+E中上+E右上+E左+E中+E右+E左下+E中下+E右下 E=E upper left +E upper middle +E upper right +E left +E middle +E right +E lower left +E middle lower +E lower right
(2)探元实际接收光照度计算。在CCD成像过程中,不同的器件有 着不同的占空比(mark/space ratio,MSR),则每一个CCD探元实际接收到 的辐照度为:(2) Calculation of the actual received illuminance of the detector. During the CCD imaging process, different devices have different duty ratios (mark/space ratio, MSR), and the actual irradiance received by each CCD detector is:
Ereal=E×MSRE real = E × MSR
注:Ereal为流程图中实际接收的光照度,MSR为参数列表中的DutyRatio (CCD占空比)。Note: E real is the actual received illuminance in the flowchart, and MSR is the DutyRatio (CCD duty cycle) in the parameter list.
(3)探元积分时间。探元的积分是空间上分立的各光敏元对光生电 荷的存储过程,而在光敏元中存储电荷的多少取决于入射在该光敏元上的 光强以及积分时间。用数学表达式表示为(3) Probe integration time. The integration of the probe is the storage process of the photogenerated charge of each photosensitive element separated in space, and the amount of charge stored in the photosensitive element depends on the light intensity incident on the photosensitive element and the integration time. Expressed mathematically as
其中,g(x,y)为CCD在像元(x,y)位置处接收到的光信号的大小,h(x’,y’,t) 表示像元(x,y)上任意点(x’,y’)光信号在t时刻的能量密度,T表示曝 光时间,a,b则表示像元的长和宽。Among them, g(x, y) is the magnitude of the optical signal received by the CCD at the position of the pixel (x, y), and h(x', y', t) represents any point on the pixel (x, y) ( x', y') The energy density of the optical signal at time t, where T represents the exposure time, and a and b represent the length and width of the pixel.
从仿真实现的角度,对单波段图像而言,可以用下式表示。From the perspective of simulation implementation, for a single-band image, it can be expressed by the following formula.
其中Rλ为对应谱段的响应,Erealλ为实际相面接收到的辐照度信息,τ 为面阵CCD的积分时间。Where R λ is the response of the corresponding spectral segment, E realλ is the irradiance information received by the actual phase surface, and τ is the integration time of the area array CCD.
(4)探元非均匀性。在CCD制造过程中,导致像元响应非均匀性的 主要原因有:器件基板扩散浓度的不一致、探元大小的不一致以及表面透 明电极在工艺上外延长度无法精确控制等。表现为在均匀光照下,各个探 元产生电荷多少不同,最终导致各个探元的图像亮度不同。(4) Probe non-uniformity. In the CCD manufacturing process, the main reasons for the non-uniformity of the pixel response are: the inconsistency of the diffusion concentration of the device substrate, the inconsistency of the probe size, and the inability to accurately control the external extension of the surface transparent electrode in the process, etc. The performance is that under uniform illumination, the amount of charge produced by each detector is different, which eventually leads to different image brightness of each detector.
响应的非均匀性尚无统一定义,但一种较为严谨的定义方法是将光响 应的均方根偏差值与响应的平均比值来作为CCD光响应的非均匀性。通 常认为光敏元是非均匀的,而CCD是近似均匀的,也意味着每一次的转 移效率是一样的。那么有:There is no unified definition of the non-uniformity of the response, but a more rigorous definition method is to use the ratio of the root mean square deviation of the photoresponse to the average value of the response as the photoresponse non-uniformity of the CCD. It is generally considered that the photosensitive element is non-uniform, while the CCD is approximately uniform, which also means that the transfer efficiency is the same every time. Then there are:
这里:here:
为平均原始响应等效电压;m为线阵CCD的总位数;Von为第n个 光敏元原始响应的等效电压。 is the equivalent voltage of the average original response; m is the total number of digits of the linear CCD; V on is the equivalent voltage of the original response of the nth photosensitive element.
由于转移损失的存在,CCD的输出信号Vn与它所对应的光敏元原始响 应Von并不相等。但根据前边的假设,可以间接算出Von为:Due to the existence of the transfer loss, the output signal V n of the CCD is not equal to the original response V on of the corresponding photosensitive element. However, according to the previous assumptions, V on can be indirectly calculated as:
式中,N为转移次数;ncp为CCD的相数。In the formula, N is the number of transfers; n cp is the phase number of CCD.
在仿真实现上一般采用线性函数来表征这种非均匀性:In the simulation implementation, a linear function is generally used to characterize this non-uniformity:
y[i]=k[i]×x[i]+b[i]y[i]=k[i]×x[i]+b[i]
其中,x[i]为第i个探元的电压值,y[i]为对应探元的输出,k[i]为第i 个探元的不一致性响应系数;b[i]为第i个探元的不一致性偏置系数。在 CCD的器件手册中一般会给出光响应不一致性(PRNU)和固定图形噪声 (FPN),其中b[i]即为光谱响应的不一致性,k[i]即为PRNU-FPN也就是 分布强度,这两个参数的分布服从正态分布,标准差主要由FPN和PRNU 确定。Among them, x[i] is the voltage value of the i-th probe, y[i] is the output of the corresponding probe, k[i] is the inconsistency response coefficient of the i-th probe; b[i] is the The inconsistency bias coefficient of each probe. In the CCD device manual, photoresponse inconsistency (PRNU) and fixed pattern noise (FPN) are generally given, where b[i] is the inconsistency of spectral response, k[i] is PRNU-FPN, which is the distribution intensity , the distribution of these two parameters obeys the normal distribution, and the standard deviation is mainly determined by FPN and PRNU.
(5)器件噪声。在CCD光电转换过程中主要存在光子噪声、散粒噪 声、肥零噪声、转移噪声、暗电流噪声和输出噪声;在模拟电路仿真过程 中主要存在模拟噪声;在模数量化过程中主要存在量化噪声。在CCD光 电转换中存在的几种主要噪声:(5) Device noise. Photon noise, shot noise, fat zero noise, transfer noise, dark current noise and output noise mainly exist in the photoelectric conversion process of CCD; analog noise mainly exists in the analog circuit simulation process; quantization noise mainly exists in the analog quantization process . Several main noises exist in CCD photoelectric conversion:
1)光子噪声:光子的发射过程是随机的,因此,CCD在收集光信 号电荷同样也认为是一个随机过程,这样的随机过程就构成了一种噪声源, 这个噪声源是由光子的性质决定的。这种噪声在低照度摄像时会较严重。1) Photon noise: The emission process of photons is random. Therefore, the CCD is also considered as a random process when collecting light signal charges. Such a random process constitutes a noise source, which is determined by the nature of photons. of. This kind of noise will be more serious when shooting in low light.
2)散粒噪声:散粒噪声的存在是由于光或者电流处在运动中的离散 且量化的波包构成。当单位时间产生的光生电荷数目相较于平均值有略微 差异后,即导致了散粒噪声产生。根据白噪声的特性,散粒噪声与频率没 有关系,它在所有频率范围内的功率分布都是均匀。在照度较低、反差不 明显的环境下,在其他噪声信息经过电路处理被抑制掉后,散粒噪声成为 了CCD成像过程中的主要噪声信息,它决定了CCD器件的极限噪声水平。2) Shot noise: The existence of shot noise is due to the discrete and quantized wave packets of light or current in motion. Shot noise occurs when the number of photogenerated charges per unit time is slightly different from the average value. According to the characteristics of white noise, shot noise has nothing to do with frequency, and its power distribution in all frequency ranges is uniform. In an environment with low illumination and inconspicuous contrast, after other noise information is suppressed through circuit processing, shot noise becomes the main noise information in the CCD imaging process, which determines the limit noise level of the CCD device.
3)肥零噪声:即使用肥零电荷补充势阱位置,使信号电荷能够通过 无规则区域进行转移,可以降电荷分为电子肥零和光学肥零。因此产生的 噪声也分为电子肥零噪声和光学肥零噪声,光学肥零噪声主要由CCD的 偏置光的大小决定,电子肥零噪声则由电子注入肥零机构决定。3) Fat zero noise: That is to use fat zero charge to supplement the potential well position, so that the signal charge can be transferred through the irregular area, and the charge can be divided into electronic fat zero and optical fat zero. Therefore, the generated noise is also divided into electronic noise and optical noise. The optical noise is mainly determined by the bias light of the CCD, and the electronic noise is determined by the electron injection mechanism.
4)转移噪声:在CCD转移过程中,前一电荷包尚未完全转移,一 部分电荷残存在势阱中,从而对后一电荷包形成噪声干扰。引起转移噪声 的根本原因主要有三个:界面态俘获、转移损失和体态俘获。4) Transfer noise: During the CCD transfer process, the previous charge packet has not been completely transferred, and a part of the charge remains in the potential well, thus forming noise interference to the latter charge packet. There are three main causes of transfer noise: interface state trapping, transfer loss, and bulk state trapping.
5)暗电流噪声:暗电流产生的主要原因是在半导体内部由于热运动 产生的载流子添加到势阱中,然后在驱动脉冲的作用下被转移,并输出电 流。暗电流即使在无光照的情况下也存在。暗电流分为扩散暗电流和表面 暗电流等。5) Dark current noise: The main cause of dark current is that the carriers generated by thermal motion inside the semiconductor are added to the potential well, and then transferred under the action of the driving pulse to output current. Dark current exists even in the absence of light. Dark current can be divided into diffusion dark current and surface dark current.
扩散暗电流是由CCD的导电沟道和势阱下的自由区域产生的,并且其 扩散长度越短,势阱数目越多,暗电流越大。Diffusion dark current is generated by the free region under the conduction channel and potential well of CCD, and the shorter the diffusion length, the more potential wells, the greater the dark current.
表面暗电流是由电子在热激发下从界面态跃跳到导带,产生自由电子 后又被势阱当作暗电荷接收最后形成的电流。The surface dark current is the current formed by electrons jumping from the interface state to the conduction band under thermal excitation, generating free electrons and then being received by the potential well as dark charges.
所有的CCD探测器都会受到暗电流的影响,它会决定器件的灵敏度和 动态范围。由于温度的大小决定了热运动过程中产生的暗电流噪声的大小, 并且温度每增加5℃~6℃,暗电流将增大到原来的两倍。All CCD detectors are affected by dark current, which determines the sensitivity and dynamic range of the device. Because the size of the temperature determines the size of the dark current noise generated during the thermal movement, and every time the temperature increases by 5°C to 6°C, the dark current will double to the original.
暗电流还与电荷包在势阱中存储的时间有关,存储时间越长,产生的 暗电流噪声也就越大。在弱信号条件下,当CCD采用长时间积分的方式 成像时,暗电流噪声将是主要的影响成像质量的主要因素。The dark current is also related to the storage time of the charge packet in the potential well, the longer the storage time, the greater the dark current noise will be. Under weak signal conditions, when the CCD uses long-time integration for imaging, dark current noise will be the main factor affecting the imaging quality.
另外,在CCD中,局部晶格存在杂志或者存在缺陷都有可能造成暗电 流峰。随着掺杂浓度增加,离表面距离越近,电场强度相应越大。在离表 面最近处,电场强度达到最大,暗电流峰值就越容易出现。暗电流峰值会 导致图像背景出现较大的涨落。In addition, in the CCD, the presence of impurities or defects in the local lattice may cause dark current peaks. As the doping concentration increases, the closer the distance to the surface, the greater the electric field intensity. At the closest point to the surface, the electric field strength reaches the maximum, and the dark current peak is more likely to appear. Dark current peaks can cause large fluctuations in the image background.
6)输出噪声:CCD信号是通过浮置电容将CCD的信号电荷转换成 为相应的电压然后输出的,并多采用浮置扩散型电容的方式进行输出。6) Output noise: The CCD signal is output by converting the signal charge of the CCD into a corresponding voltage through the floating capacitor, and the floating diffusion capacitor is mostly used for output.
在上述噪声中,由于暗电流噪声、转移噪声在光电转换一节中已考虑, 所以在接下来的建模方案中,就不再考虑暗电流以及转移噪声的影响,主 要考虑散粒噪声,输出噪声的影响。Among the above noises, since dark current noise and transfer noise have been considered in the photoelectric conversion section, in the next modeling scheme, the influence of dark current and transfer noise is no longer considered, and shot noise is mainly considered. The output the effect of noise.
针对以上噪声,在仿真过程中要对不同的噪声进行分类,根据不同的 噪声类型建立不同的噪声模型。CCD采样和光电转换过程中引入的噪声是 不可避免的,CCD引入的噪声是系统噪声的主要来源,更是影响系统成像 质量的主要因素。在仿真实现上,由于CCD的噪声在微观层面上很难进 行量化,没有合适的噪声模型来逐个分析这些噪声,所以仿真过程中需要 采用量化模型代替微观层面上的噪声,将它们等效为一个叠加在电路末端 的白噪声。For the above noises, different noises should be classified in the simulation process, and different noise models should be established according to different noise types. The noise introduced in the process of CCD sampling and photoelectric conversion is inevitable. The noise introduced by CCD is the main source of system noise, and it is the main factor affecting the system imaging quality. In the simulation implementation, because the noise of CCD is difficult to quantify at the micro level, there is no suitable noise model to analyze these noises one by one, so the quantization model needs to be used in the simulation process to replace the noise at the micro level, and they are equivalent to a White noise superimposed on the end of a circuit.
由于CCD光电转换过程中产生的噪声多数属于高斯白噪声,因此本文 的研究及后续仿真中将假设光电转换过程中所有噪声均服从均值为μ、方 差为σ的高斯分布:Since most of the noise generated in the photoelectric conversion process of CCD belongs to Gaussian white noise, the research in this paper and the follow-up simulation will assume that all the noise in the photoelectric conversion process obeys the Gaussian distribution with mean value μ and variance σ:
根据高斯噪声模型,将模型产生的高斯噪声叠加到最后的真实信号中:According to the Gaussian noise model, the Gaussian noise generated by the model is superimposed on the final real signal:
Vreal=V+Vnoise V real = V + V noise
在电路中产生的主要噪声有暗电流噪声、输出噪声以及复位噪声等。 同样由于没有合适的噪声模型来逐个分析这些噪声,因此假设电路模块产 生的噪声都服从正态分布模型,其概率密度函数为:The main noises generated in the circuit are dark current noise, output noise and reset noise. Also because there is no suitable noise model to analyze these noises one by one, it is assumed that the noise generated by the circuit module is subject to a normal distribution model, and its probability density function is:
其中μ和σ都是噪声的统计值,μ是等效输出噪声电压的平均值,即为Among them, μ and σ are statistical values of noise, and μ is the average value of the equivalent output noise voltage, which is
σ则为噪声电压随时间涨落的均方根值,即为σ is the root mean square value of the noise voltage fluctuation with time, that is,
一般,成像载荷光电转换的模拟电路部分主要包括四个模块:前置放大 器模块、低通滤波器模块、运算放大器模块以及相关双采样电路模块。其 中相关双采样电路的主要作用是用来消除复位噪声,提取出有用的信号, 并传输给模数量化电路。在仿真模块中,由于影响噪声的因素过多,将噪 声简化为正态分布模型,并没有添加复位噪声信息,所以在建模时可以不 考虑相关双采样电路。因此在仿真实现上,可以将模拟电路分为三个部分即为前置放大电路、低通滤波电路以及后置放大电路。模拟电路仿真就是 仿真上述各个环节对信号的响应。Generally, the analog circuit part of the photoelectric conversion of the imaging load mainly includes four modules: a preamplifier module, a low-pass filter module, an operational amplifier module, and a related double-sampling circuit module. Among them, the main function of the correlated double sampling circuit is to eliminate reset noise, extract useful signals, and transmit them to the analog quantization circuit. In the simulation module, due to too many factors affecting the noise, the noise is simplified to a normal distribution model, and no reset noise information is added, so the correlation double sampling circuit can be ignored when modeling. Therefore, in terms of simulation implementation, the analog circuit can be divided into three parts, that is, the preamplifier circuit, the low-pass filter circuit, and the postamplifier circuit. Analog circuit simulation is to simulate the response of the above-mentioned links to the signal.
根据电路的特性参数,仿真信号经过这些电路模块后的响应数据。According to the characteristic parameters of the circuit, the response data of the simulation signal after passing through these circuit modules.
(1)前置放大电路和后置放大电路。前置放大器模块的主要作用是 接收光信号并把光信号转换成电信号,然后对电信号进行放大,再将放大 后的电信号传输到后面的信号处理系统中。前置放大电路在整个光电转换 过程中是非常重要的,主要是因为前置放大电路接收的光信号经过放大电 路放大后,信号都是非常微弱的,很容易淹没在噪声中,因此它的性能好 坏直接决定了整个电路系统的性能的好坏。在仿真实现上,可以将整个放 大电路表示成下式所示。(1) Pre-amplification circuit and post-amplification circuit. The main function of the preamplifier module is to receive the optical signal and convert the optical signal into an electrical signal, then amplify the electrical signal, and then transmit the amplified electrical signal to the subsequent signal processing system. The preamplifier circuit is very important in the whole process of photoelectric conversion, mainly because the optical signal received by the preamplifier circuit is amplified by the amplifier circuit, the signal is very weak, and it is easy to be submerged in noise, so its performance The quality directly determines the performance of the entire circuit system. In terms of simulation implementation, the entire amplifying circuit can be expressed as the following formula.
V1=V0×B1 V 1 =V 0 ×B 1
式中V0为初始的输入电压图像,V1为经过预防大电路后的电压,上式中 B1代表预放大倍数。In the formula, V 0 is the initial input voltage image, V 1 is the voltage after the large circuit is prevented, and B 1 in the above formula represents the pre-amplification factor.
后置放大电路在仿真实现上可以表示成下式。The post-amplification circuit can be expressed as the following formula in the simulation implementation.
V3=V2×B2+AV 3 =V 2 ×B 2 +A
V2为经过低通滤波后的电压,V2与增益放大倍数B2相乘再加上偏置放大 量A即为最后模拟电路仿真输出结果V3。V 2 is the voltage after low-pass filtering. Multiplying V 2 with the gain amplification factor B 2 and adding the bias amplification value A is the final analog circuit simulation output result V 3 .
(2)低通滤波器,一般比较常见的滤波方法有空间滤波和频率滤波 两种方式。空间滤波是指在域中直接对图像各像素作空间变化然后进行处 理,频率滤波则是指将图像信息经过傅里叶变化后转到频率域中对频谱成 分进行处理。对于两种处理方式而言,空间域滤波是一种邻域运算,而频 率域滤波则更为直观。频率域滤波的关键问题在于选择滤波器传递函数, 建立数学模型,最后通过将频域内处理完成的图像信息经过傅里叶逆变换,最终得到处理后的输出图像。(2) Low-pass filter. Generally, there are two common filtering methods: spatial filtering and frequency filtering. Spatial filtering refers to directly changing the space of each pixel of the image in the domain and then processing it, while frequency filtering refers to transforming the image information into the frequency domain after Fourier transformation to process the spectral components. For the two processing methods, spatial domain filtering is a neighborhood operation, while frequency domain filtering is more intuitive. The key issue of frequency domain filtering is to select the filter transfer function, establish a mathematical model, and finally obtain the processed output image by inverse Fourier transforming the image information processed in the frequency domain.
空间域滤波和频率域滤波的理论基础都是卷积定理。The theoretical basis of spatial domain filtering and frequency domain filtering is the convolution theorem.
公式两端的表达式是一组傅里叶变换对,也即意味着两个空间函数的卷积 可以通过傅里叶变化的乘积的逆变换得到。也就是说,在空间域中,待滤 波图像f(x,y)与滤波掩模h(x,y)的卷积运算,可以在频率域中通过F(u,v)乘 以H(u,v)计算得到。The expressions at both ends of the formula are a set of Fourier transform pairs, which means that the convolution of two spatial functions can be obtained by the inverse transform of the product of Fourier transforms. That is to say, in the spatial domain, the convolution operation of the image to be filtered f(x,y) and the filter mask h(x,y) can be multiplied by F(u,v) in the frequency domain by H(u ,v) is calculated.
在频率域中进行滤波可以看成是使用一个滤波器传递函数来修改 F(u,v),然后计算H(u,v)F(u,v)的傅里叶逆变换,就可以相应得到空间域滤 波的图像。其原理如图8所示。Filtering in the frequency domain can be seen as using a filter transfer function to modify F(u,v), and then calculating the inverse Fourier transform of H(u,v)F(u,v), which can be obtained accordingly Spatial domain filtered image. Its principle is shown in Figure 8.
巴特沃斯(Butterworth)滤波器的平坦幅度响应最大,广泛应用于 通信领域。相比于贝塞尔(bessl)、契比雪夫(chebyshev)滤波器,巴特 沃斯滤波具有在线性相位、衰减斜率以及加载特性方面均衡性的优点,使 得巴特沃斯低通滤波器更适用于图像处理。The Butterworth filter has the largest flat amplitude response and is widely used in the communication field. Compared with Bessel (bessl) and Chebyshev (chebyshev) filters, Butterworth filter has the advantages of balance in linear phase, attenuation slope and loading characteristics, making Butterworth low-pass filter more suitable for Image Processing.
对于n阶巴特沃斯低通滤波器而言,这种滤波器非锐截至,其传递函 数为:For an nth-order Butterworth low-pass filter, which has a non-sharp cutoff, its transfer function is:
式中,D0是截至频率,其中当D(u,v)=D0时, n为滤波器阶数,为正整数,主要用来控制频率的衰减速度。In the formula, D 0 is the cut-off frequency, where When D(u,v)=D 0 , n is the order of the filter, which is a positive integer and is mainly used to control the attenuation speed of the frequency.
一般来说,低通滤波器的截至频率一般选使H(u,v)下降到其处 的频率值,此时的传递函数可以写为:Generally speaking, the cut-off frequency of the low-pass filter is generally selected so that H(u,v) drops to its The frequency value at , the transfer function at this time can be written as:
当n=1时,巴特沃斯低通滤波器无“振铃”现象,同时可以提高图像的对比 度;当n=2时,会出现微弱的“振铃”现象;而当n越大时,“振铃”现象则 越明显,此时也越接近理想的低通滤波器。When n=1, the Butterworth low-pass filter has no "ringing" phenomenon, and can improve the contrast of the image; when n=2, there will be a weak "ringing" phenomenon; and when n is larger, The more obvious the "ringing" phenomenon is, the closer it is to an ideal low-pass filter.
最后,成像载荷模数量化模数量化仿真对模拟电路输出的电压值数据 进行数字量化处理,同时考虑量化过程中产生的量化噪声,完成由模拟信 号到数字信号的量化过程。Finally, the imaging load modulus and quantization simulation performs digital quantization processing on the voltage value data output by the analog circuit, and at the same time considers the quantization noise generated during the quantization process, and completes the quantization process from the analog signal to the digital signal.
模数量化仿真对模拟电路输出的电压值数据进行数字量化处理,根据模数 转换器的量化最大电压、最小电压和量化位数,建立量化模型;The analog and quantitative simulation performs digital quantization processing on the voltage value data output by the analog circuit, and establishes a quantization model according to the quantized maximum voltage, minimum voltage and quantized digits of the analog-to-digital converter;
其中,N为量化位数;Vmax和Vmin分别为输出的最大和最小信号电压。Among them, N is the number of digits quantized; V max and V min are the output maximum and minimum signal voltages, respectively.
综上,本发明通过在实验室自行搭建实验平台与仿真图像对比,开 展了针对遥感相机光电转换系统的仿真模型验证工作,实验结果表明: 仿真软件仿真退化出的图像与实验拍摄图像的MTF下降率的相似度为 90%,证明仿真软件模型是正确且可靠的。In summary, the present invention has carried out the simulation model verification work for the photoelectric conversion system of the remote sensing camera by building an experimental platform in the laboratory and comparing it with the simulated image. The experimental results show that the MTF of the image degraded by the simulation software simulation and the image taken by the experiment decreases The similarity rate is 90%, which proves that the simulation software model is correct and reliable.
需要说明的是,以上说明仅是本发明的优选实施方式,应当理解, 对于本领域技术人员来说,在不脱离本发明技术构思的前提下还可以做 出若干改变和改进,这些都包括在本发明的保护范围内。It should be noted that the above description is only a preferred embodiment of the present invention, and it should be understood that for those skilled in the art, several changes and improvements can be made without departing from the technical concept of the present invention, which are included in within the protection scope of the present invention.
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Application publication date: 20180601 |
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