Some Stuff

optical_flow.py

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+import numpy as np
+import cv2
+
+def detect_feature_points(frame, max_corners=1000):
+    """
+    Detect good features to track in the frame.
+    """
+    # Convert frame to grayscale if it's not already
+    if len(frame.shape) == 3:
+        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
+    else:
+        gray = frame
+        
+    # Detect corners using Shi-Tomasi method
+    corners = cv2.goodFeaturesToTrack(
+        gray,
+        maxCorners=max_corners,
+        qualityLevel=0.001,
+        minDistance=10,
+        blockSize=7
+    )
+    
+    return corners
+
+def calculate_optical_flow(prev_frame, curr_frame, prev_points):
+    """
+    Calculate optical flow for given points between two frames.
+    """
+    # Convert frames to grayscale
+    if len(prev_frame.shape) == 3:
+        prev_gray = cv2.cvtColor(prev_frame, cv2.COLOR_BGR2GRAY)
+        curr_gray = cv2.cvtColor(curr_frame, cv2.COLOR_BGR2GRAY)
+    else:
+        prev_gray = prev_frame
+        curr_gray = curr_frame
+    
+    # Calculate optical flow using Lucas-Kanade method
+    curr_points, status, error = cv2.calcOpticalFlowPyrLK(
+        prev_gray,
+        curr_gray,
+        prev_points,
+        None,
+        winSize=(15, 15),
+        maxLevel=2,
+        criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03)
+    )
+    
+    # Filter out points where flow wasn't found
+    good_new = curr_points[status == 1]
+    good_old = prev_points[status == 1]
+    
+    return good_new, good_old
+
+def estimate_camera_motion(prev_points, curr_points, threshold=5.0):
+    """
+    Estimate camera motion and identify outlier points.
+    Returns mask of points that don't follow the dominant motion pattern.
+    """
+    # Calculate motion vectors
+    motion_vectors = curr_points - prev_points
+    
+    # Calculate median motion as an estimate of camera motion
+    median_motion = np.median(motion_vectors, axis=0)
+    
+    # Calculate the difference from median motion for each point
+    motion_differences = np.linalg.norm(motion_vectors - median_motion, axis=1)
+    
+    # Calculate the median absolute deviation (MAD)
+    mad = np.median(np.abs(motion_differences - np.median(motion_differences)))
+    
+    # Points with motion significantly different from the camera motion
+    # are considered outliers (using modified z-score)
+    outliers_mask = motion_differences > (threshold * mad)
+    
+    return outliers_mask
+
+def analyze_motion(video_path):
+    """
+    Analyze motion in video and detect objects moving differently from camera motion.
+    """
+    cap = cv2.VideoCapture(video_path)
+    
+    # Read first frame
+    ret, prev_frame = cap.read()
+    if not ret:
+        raise ValueError("Could not read video")
+
+    prev_points = None
+    
+    while True:
+        ret, curr_frame = cap.read()
+        if not ret:
+            break
+
+        
+        # Detect initial points
+        if prev_points is None:        
+            prev_points = detect_feature_points(prev_frame)
+        elif  curr_points.shape[0] < 600:
+            prev_points = detect_feature_points(prev_frame)
+        
+
+        print(prev_points.shape)
+                
+        # Calculate optical flow
+        curr_points, prev_points_matched = calculate_optical_flow(
+            prev_frame, curr_frame, prev_points
+        )
+        
+        if len(curr_points) > 0 and len(prev_points_matched) > 0:
+            # Find points not moving with camera
+            outliers_mask = estimate_camera_motion(prev_points_matched, curr_points)
+            
+            # Visualize results
+            frame_vis = curr_frame.copy()
+            
+            # Draw all tracked points
+            for i, (new, old) in enumerate(zip(curr_points, prev_points_matched)):
+                a, b = new.ravel()
+                c, d = old.ravel()
+                
+                # Draw line between old and new position
+                color = (0, 0, 255) if outliers_mask[i] else (0, 255, 0)
+                cv2.line(frame_vis, (int(c), int(d)), (int(a), int(b)), color, 2)
+                cv2.circle(frame_vis, (int(a), int(b)), 3, color, -1)
+            
+            cv2.imshow('Frame', frame_vis)
+            
+            # Exit if 'q' is pressed
+            if cv2.waitKey(30) & 0xFF == ord('q'):
+                break
+        
+        # Update for next iteration
+        prev_frame = curr_frame.copy()
+        prev_points = curr_points.reshape(-1, 1, 2)
+    
+    cap.release()
+    cv2.destroyAllWindows()
+
+if __name__ == "__main__":
+    # Example usage
+    video_path = 0
+    analyze_motion(video_path)