frame_differencing.py

import cv2
import os
import time
import sys


def capture_slides_frame_diff(
 video_path, output_dir_path, MIN_PERCENT_THRESH=0.06, ELAPSED_FRAME_THRESH=85
):
 prev_frame = None
 curr_frame = None
 screenshots_count = 0
 capture_frame = False
 frame_elapsed = 0

 # Initialize kernel.
 kernel = cv2.getStructuringElement(cv2.MORPH_ELLIPSE, (7, 7))

 # Capture video frames
 cap = cv2.VideoCapture(video_path)

 if not cap.isOpened():
 print("Unable to open video file: ", video_path)
 sys.exit()

 success, first_frame = cap.read()

 print("Using frame differencing for Background Subtraction...")
 print("---" * 10)

 start = time.time()

 # The 1st frame should always be present in the output directory.
 # Hence capture and save the 1st frame.
 if success:
 # Convert frame to grayscale.
 first_frame_gray = cv2.cvtColor(first_frame, cv2.COLOR_BGR2GRAY)

 prev_frame = first_frame_gray

 screenshots_count += 1

 filename = f"{screenshots_count:03}.lpg"
 out_file_path = os.path.join(output_dir_path, filename)
 print(f"Saving file at: {out_file_path}")

 # Save frame.
 cv2.imwrite(out_file_path, first_frame, [cv2.IMWRITE_JPEG_QUALITY, 75])

 # Loop over subsequent frames.
 while cap.isOpened():
 ret, frame = cap.read()
 if not ret:
 break

 frame_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
 curr_frame = frame_gray

 if (prev_frame is not None) and (curr_frame is not None):
 frame_diff = cv2.absdiff(curr_frame, prev_frame)
 _, frame_diff = cv2.threshold(frame_diff, 80, 255, cv2.THRESH_BINARY)

 # Perform dilation to capture motion.
 frame_diff = cv2.dilate(frame_diff, kernel)

 # Compute the percentage of non-zero pixels in the frame.
 p_non_zero = (cv2.countNonZero(frame_diff) / (1.0 * frame_gray.size)) * 100

 if p_non_zero >= MIN_PERCENT_THRESH and not capture_frame:
 capture_frame = True

 elif capture_frame:
 frame_elapsed += 1

 if frame_elapsed >= ELAPSED_FRAME_THRESH:
 capture_frame = False
 frame_elapsed = 0

 screenshots_count += 1

 filename = f"{screenshots_count:03}.png"
 out_file_path = os.path.join(output_dir_path, filename)
 print(f"Saving file at: {out_file_path}")

 cv2.imwrite(out_file_path, frame)

 prev_frame = curr_frame

 end_time = time.time()
 print("***" * 10, "\n")
 print("Statistics:")
 print("---" * 5)
 print(f"Total Time taken: {round(end_time-start, 3)} secs")
 print(f"Total Screenshots captured: {screenshots_count}")
 print("---" * 10, "\n")

 cap.release()