EVM/eulerian.py

import numpy as np
import scipy.fftpack as fftpack


# Temporal bandpass filter with Fast-Fourier Transform
def fft_filter(video, freq_min, freq_max, fps):
    fft = fftpack.fft(video, axis=0)
    frequencies = fftpack.fftfreq(video.shape[0], d=1.0 / fps)
    bound_low = (np.abs(frequencies - freq_min)).argmin()
    bound_high = (np.abs(frequencies - freq_max)).argmin()
    fft[:bound_low] = 0
    fft[bound_high:-bound_high] = 0
    fft[-bound_low:] = 0
    iff = fftpack.ifft(fft, axis=0)
    result = np.abs(iff)
    result *= 100  # Amplification factor

    return result, fft, frequencies