59 lines
2.1 KiB
Python
Executable File
59 lines
2.1 KiB
Python
Executable File
#!/usr/bin/env python3
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"""
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Webcam motion presence detector using frame differencing.
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Exit codes: 0 = motion detected, 1 = no motion, 2 = camera error (busy/unavailable)
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Usage: presence_detect.py [camera_id]
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"""
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import sys
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import time
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import cv2
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import numpy as np
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FRAMES_TO_CHECK = 8
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DIFFS_NEEDED = 2 # require motion in at least N consecutive-frame diffs
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PIXEL_DELTA_THRESHOLD = 18 # per-pixel grayscale delta to count as "changed"
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MOTION_AREA_RATIO = 0.008 # fraction of pixels that must change to call it motion
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BLUR_KSIZE = (21, 21) # Gaussian blur kernel to suppress sensor noise
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# Spacing between the frames we diff. Without it the frames are grabbed
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# back-to-back within a few milliseconds, so (a) slow, small movements barely
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# differ between adjacent frames and (b) reading off the ffmpeg v4l2loopback
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# mirror can hand back the SAME buffered frame twice → a zero delta even while
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# you're moving. Spacing the grabs out gives slow motion a real temporal
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# baseline and guarantees each compared frame is a fresh one.
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INTER_FRAME_DELAY = 0.06 # seconds between grabs (~0.5s total observation window)
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def detect(camera_id: int) -> int:
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cap = cv2.VideoCapture(camera_id)
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if not cap.isOpened():
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return 2
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motion_diffs = 0
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prev_gray = None
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try:
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for i in range(FRAMES_TO_CHECK):
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if i > 0:
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time.sleep(INTER_FRAME_DELAY)
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ok, frame = cap.read()
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if not ok:
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continue
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gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
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gray = cv2.GaussianBlur(gray, BLUR_KSIZE, 0)
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if prev_gray is not None:
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delta = cv2.absdiff(prev_gray, gray)
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changed = np.count_nonzero(delta > PIXEL_DELTA_THRESHOLD)
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if changed / delta.size >= MOTION_AREA_RATIO:
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motion_diffs += 1
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prev_gray = gray
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finally:
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cap.release()
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return 0 if motion_diffs >= DIFFS_NEEDED else 1
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if __name__ == "__main__":
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camera_id = int(sys.argv[1]) if len(sys.argv) > 1 else 0
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sys.exit(detect(camera_id))
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