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一维傅里叶变换
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什么是傅里叶变换
笔记
Fourier Transform (FT)
G(f)=\int_{-\infty}^{\infty} g(t) e^{-i 2 \pi f t} d t=F{g(t)}
Inverse Fourier Transform
g(t)=\int_{-\infty}^{\infty} G(f) e^{i 2 \pi f t} d f=F^{-1}{G(f)}
其中,i=\sqrt{-1},表示复数虚部
单位
Temporal Coordinates, e.g. t in seconds, f in cycles/second
\begin{array}{rrr}G(f)&=\int_{-\infty}^{\infty} g(t) e^{-i 2 \pi f t} d t&\text { Fourier Transform } \\ \\
g(t)&=\int_{-\infty}^{\infty} G(f) e^{i 2 \pi f t} d f&\text { Inverse Fourier Transform }\end{array}
Spatial Coordinates, e.g. x in \mathrm{cm}, k_{x} is spatial frequency in cycles/ \mathrm{cm}
\begin{array}{lc}G\left(k_{x}\right)=\int_{-\infty}^{\infty} g(x) e^{-i 2 \pi k_{x} x} d x&\text { Fourier Transform } \\
g(x)=\int_{-\infty}^{\infty} G\left(k_{x}\right) e^{i 2 \pi k_{x} x} d k_{x}&\text { Inverse Fourier Transform }\end{array}
Euler’s Formula
\begin{aligned}
&e^{i \theta}=\cos \theta+i \sin \theta \\
&z=x+i y=|z| e^{i \theta}
\end{aligned}
根据欧拉公式将傅里叶变换展开:
\begin{aligned}
G\left(k_{x}\right) &= \int_{-\infty}^{\infty} g(x) e^{-i 2 \pi k_{x} x} d x \\
& = \int_{-\infty}^{\infty} g(x) \left(cos(- 2 \pi k_{x} x) + i sin(- 2 \pi k_{x} x) \right) d x \\
& = \int_{-\infty}^{\infty} g(x) cos(2 \pi k_{x} x) d x - i\int_{-\infty}^{\infty} g(x) sin(2 \pi k_{x} x) d x
\end{aligned}
Spatial Coordinates, e.g. x in \mathrm{cm}, k_{x} is spatial frequency in cycles/ \mathrm{cm}
一维傅里叶变换的Python实现
来源:python实现一维傅里叶变换和逆变换_bilibili
代码如下:
附原视频:
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