面阵电荷耦合器件错位成像的建模与仿真

Modeling and simulation of subpixel imaging for area charge coupled device

为了定量研究面阵电荷耦合器件(CCD)错位成像技术图像质量的提高以及CCD像元填充因子对图像质量的影响,建立了仿真不同像元填充因子的面阵CCD错位成像的数学模型。以Matlab为平台,不考虑噪声的干扰,对ISO12233标准分辨率测试卡子图像进行了仿真,结果表明,CCD像元填充因子为100%时,与普通成像模式相比,对角错位、四点错位成像模式图像的灰度平均梯度分别提高了2.9970、3.4136,拉普拉斯能量分别提高了0.5676、0.7478,且CCD像元填充因子为其他值时,相较于普通成像模式,对角错位、四点错位成像模式图像的GMG和EOL均得到提高;采用四点错位成像模式时,与填充因子为100%的面阵CCD相比,填充因子为69%、44%、25%的面阵CCD四点错位模式图像的灰度平均梯度分别提高了1.433 0、3.337 3、5.153 2,拉普拉斯能量分别提高了0.638 0、1.704 4、3.196 8,且采用其他成像模式时,填充因子为100%、69%、44%、25%的图像的GMG和EOL均不断提高。研究表明,面阵CCD错位成像技术能够提高图像质量,且四点错位成像模式图像质量优于对角错位成像模式;在满足信噪比指标要求的前提下,对于面阵CCD同一成像模式,像元填充因子越小,图像质量越高。

In order to quantitatively investigate image quality improvement of area CCD subpixel imaging and influence of fill factor on image quality, a mathematical model was established to simulate subpixel imaging of array CCD with different fill factors. Without consideration of noise influence, simulation experiment for a sub-image of ISO12233 standard resolution card was performed on Matlab. Experiment results illustrate that, when fill factor is 100%, compared with common imaging mode of array CCD, gray mean gradient （GMG） of diagonal subpixel and four-point subpixel imaging mode was increased by 2.997 0, 3.413 6 respectively, and energy of Laplacian （EOL） is enhanced by 0.567 6, 0.747 8 respectively.With the same fill factor other than 100%, GMGs and EOLs of common imaging mode, diagonal subpixel imaging mode, and four-point subpixel mode are increasing in that order too. For four-point subpixel imaging mode, GMG of 69%, 44%, 25% fill factor is improved by 1.433 0, 3.337 3, 5.153 2 respectively compared with that of 100% fill factor, and EOL increased by 0.638 0, 1.704 4, 3.196 8 respectively. With the same imaging mode other than four-point subpixel, GMGs and EOLs of images obtained with CCDs whose fill factor is 100%, 69%, 44%, 25% increase too. Research shows that subpixel technique of array CCD can improve image quality, and four-point subpixel imaging mode provides more improvement on image quality than diagonal subpixel imaging mode. In the condition of signal-to-noise ratio is met, the image quality performance becomes better when fill factor decrease for the same CCD imaging mode.