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copter/cam_optical_flow_dense.py

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+# Blog: [OpenCV Optical Flow介紹](https://meetonfriday.com/posts/e2795e5a/)
+import sys
+import cv2
+import numpy as np
+
+if len(sys.argv) >1:
+    vid = int(sys.argv[1])
+else:
+    vid = 0
+cap = cv2.VideoCapture(vid)
+
+ret, first_frame = cap.read()
+first_frame = cv2.flip(first_frame, 1) # horizontal flip for mirror effect
+prev_gray = cv2.cvtColor(first_frame, cv2.COLOR_BGR2GRAY)
+mask = np.zeros_like(first_frame)
+mask[..., 1] = 255
+
+while(cap.isOpened()):
+    ret, frame = cap.read()
+    #cv2.imshow("input", frame)
+    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
+    flow = cv2.calcOpticalFlowFarneback(prev_gray, gray, None, 0.5, 3, 15, 3, 5, 1.2, 0)
+    magnitude, angle = cv2.cartToPolar(flow[..., 0], flow[..., 1])
+    mask[..., 0] = angle * 180 / np.pi / 2
+    mask[..., 2] = cv2.normalize(magnitude, None, 0, 255, cv2.NORM_MINMAX)
+    bgr = cv2.cvtColor(mask, cv2.COLOR_HSV2BGR)
+    cv2.imshow("optical-flow dense", bgr)
+    prev_gray = gray
+    if cv2.waitKey(1) & 0xFF == ord('q'):
+        break
+
+cap.release()
+cv2.destroyAllWindows()