# 滤波器的工作原理

## 低通滤波器

### 示例 1

``7 5 2 4 8 3 3 1 5``

``值 = ((7 + 5 + 2) + (4 + 8 + 3) + (3 + 1 + 5)) / 9 = 38 / 9 = 4.222``

### 示例 2

• 输入像元值：
``2.000 3.000 4.000 5.000 6.000 2.000 3.000 4.000 NoData 6.000 2.000 3.000 4.000 5.000 6.000 2.000 30.000 4.000 5.000 NoData 1.000 2.000 2.000 3.000 NoData``
• 选中在计算中忽略 NoData 参数的输出像元值（滤波窗口中的 NoData 像元将在计算中被忽略）：
``2.500 3.000 3.800 5.000 5.667 2.500 3.000 3.875 5.000 5.600 7.000 6.000 7.250 4.857 5.500 6.667 5.556 6.444 4.143 4.750 8.750 6.833 7.667 3.500 4.000``
• 取消选中在计算中忽略 NoData 参数的输出像元值（如果滤波窗口中的任何像元为 NoData，则输出将为 NoData）：
``NoData NoData NoData NoData NoData NoData 3.000 NoData NoData NoData NoData 6.000 NoData NoData NoData NoData 5.556 6.444 NoData NoData NoData NoData NoData NoData NoData``

## 高通滤波器

``-0.7 -1.0 -0.7 -1.0 6.8 -1.0 -0.7 -1.0 -0.7``

### 示例 1

``7 5 2 4 8 3 3 1 5``

``值 = ((7*-0.7) + (5*-1.0) + (2*-0.7) + (4*-1.0) + (8*6.8) + (3*-1.0) + (3*-0.7) + (1*-1.0) + (5*-0.7)) = ((-4.9 + -5.0 + -1.4) + (-4.0 + 54.4 + -3.0) + (-2.1 + -1.0 + -3.5) = -11.3 + 47.4 + -6.6 = 29.5``

## 参考

Gonzalez, R. C., and P. Wintz. 1977. Digital Image Processing. Massachusetts: Addison–Wesley.

Hord, R. M. 1982. Digital Image Processing of Remotely Sensed Data. New York: Academic.

Moik, J. G. 1980. Digital Processing of Remotely Sensed Images. New York: Academic.

Richards, J. A. 1986. Remote Sensing Digital Image Analysis: An Introduction. Berlin: Springer-Verlag.

Rosenfeld, A. 1978. Image Processing and Recognition, Technical Report 664. University of Maryland Computer Vision Laboratory.