Showcase-EVM/ideal_filter.py

import scipy.fftpack as fftpack
import numpy as np
import cv2
from scipy.signal import find_peaks

import pyramid
import video

def start(vidFile, alpha, low, high, chromAttenuation, fps, width, height):
    '''
    Performs color magnification on the video by applying an ideal bandpass filter,
    i.e. applies a discrete fourier transform on the gaussian downsapled video and
    cuts off the frequencies outside the bandpass filter, magnifies the result and
    saves the output video. Additionally, it detects heartbeat and returns BPM.
    
    :param vidFile: Video file
    :param alpha: Magnification factor
    :param low: Low frequency cut-off
    :param high: High frequency cut-off
    :param chromAttenuation: Chrominance attenuation factor
    :param mode: Processing mode (unused in this example, but kept for compatibility)
    :param fps: Frames per second of the video
    :param width: Width of the video frame
    :param height: Height of the video frame
    :return: final processed video, heart rate in BPM
    '''
    
    # Convert from RGB to YIQ for better processing of chrominance information
    t = video.rgb2yiq(vidFile)

    levels = 4

    # Build Gaussian pyramid and use the highest level
    gauss_video_list = pyramid.gaussian_video(t, levels)

    print('Apply Ideal filter')
    # Apply discrete Fourier transformation (real)
    fft = fftpack.rfft(gauss_video_list, axis=0)
    frequencies = fftpack.rfftfreq(fft.shape[0], d=1.0 / fps)  # Sample frequencies
    mask = np.logical_and(frequencies > low, frequencies < high)  # Logical array if values between low and high frequencies

    fft[~mask] = 0  # Cutoff values outside the bandpass

    filtered = fftpack.irfft(fft, axis=0)  # Inverse Fourier transformation

    filtered *= alpha  # Magnification

    # Chromatic attenuation
    filtered[:, :, :, 1] *= chromAttenuation
    filtered[:, :, :, 2] *= chromAttenuation

    print(chromAttenuation)

    # Resize last Gaussian level to the frame size
    filtered_video_list = np.zeros(t.shape)
    for i in range(t.shape[0]):
        f = filtered[i]
        filtered_video_list[i] = cv2.resize(f, (t.shape[2], t.shape[1]))

    final = filtered_video_list

    # Add to original
    final += t

    # Convert back from YIQ to RGB
    final = video.yiq2rgb(final)

    # Cutoff invalid values
    final[final < 0] = 0
    final[final > 255] = 255
    
    # Detect heartbeat and return BPM
    bpm = detect_heartbeat(filtered_video_list, fps)

    return final, bpm


def detect_heartbeat(video_frames, fps):
    '''
    Detects heartbeat by analyzing pixel intensity variations in the filtered video over time.
    
    :param video_frames: Processed video frames (filtered and magnified)
    :param fps: Frames per second of the video
    :return: Detected heart rate in BPM (beats per minute)
    '''
    # Focus on the green channel for heart rate detection (more sensitive to blood flow changes)
    green_channel = video_frames[:, :, :, 1]  # Extract green channel

    # Calculate the average intensity of the green channel for each frame
    avg_intensity = np.mean(green_channel, axis=(1, 2))  # Shape: (num_frames,)

    # Normalize intensity values
    avg_intensity -= np.mean(avg_intensity)
    avg_intensity /= np.std(avg_intensity)

    # Detect peaks in the intensity signal (peaks correspond to heartbeats)
    peaks, _ = find_peaks(avg_intensity, distance=fps // 2)  # Ensure at least half a second between peaks

    # Calculate the time differences between peaks to compute the heart rate
    peak_intervals = np.diff(peaks) / fps  # Convert frame intervals to seconds

    if len(peak_intervals) > 0:
        avg_heartbeat_interval = np.mean(peak_intervals)
        bpm = 60 / avg_heartbeat_interval  # Convert to beats per minute
    else:
        bpm = 0  # No peaks detected

    return bpm