'**SUMMARY**
Perform a Fast Fourier Transform on the line scan and return
the FFT output and the frequency of each value.
**RETURNS**
The FFT as a numpy array of irrational numbers and a one dimensional
list of frequency values.
**EXAMPLE**
>>>> import matplotlib.pyplot as plt
>>>> img = Image(\'lenna\')
>>>> sl = img.getLineScan(y=128)
>>>> fft,freq = sl.fft()
>>>> plt.plot(freq,fft.real,freq,fft.imag)
>>>> plt.show()'

def fft(self):

    signal = np.array(self, dtype='float32')
    fft = np.fft.fft(signal)
    freq = np.fft.fftfreq(len(signal))
    return (fft, freq)
