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import cv2 as cv | |
import numpy as np | |
# Parameters for Shi-Tomasi corner detection | |
# feature_params = dict(maxCorners = 300, qualityLevel = 0.2, minDistance = 2, blockSize = 7) | |
# Parameters for Lucas-Kanade optical flow | |
# lk_params = dict(winSize = (15,15), maxLevel = 2, criteria = (cv.TERM_CRITERIA_EPS | cv.TERM_CRITERIA_COUNT, 10, 0.03)) | |
# The video feed is read in as a VideoCapture object | |
# cap = cv.VideoCapture("shibuya.mp4") | |
# Variable for color to draw optical flow track | |
# color = (0, 255, 0) | |
# ret = a boolean return value from getting the frame, first_frame = the first frame in the entire video sequence | |
# ret, first_frame = cap.read() | |
# Converts frame to grayscale because we only need the luminance channel for detecting edges - less computationally expensive | |
# prev_gray = cv.cvtColor(first_frame, cv.COLOR_BGR2GRAY) | |
# Finds the strongest corners in the first frame by Shi-Tomasi method - we will track the optical flow for these corners | |
# https://docs.opencv.org/3.0-beta/modules/imgproc/doc/feature_detection.html#goodfeaturestotrack | |
# prev = cv.goodFeaturesToTrack(prev_gray, mask = None, **feature_params) | |
# Creates an image filled with zero intensities with the same dimensions as the frame - for later drawing purposes | |
mask = np.zeros_like(first_frame) | |
# while(cap.isOpened()): | |
# ret = a boolean return value from getting the frame, frame = the current frame being projected in the video | |
# ret, frame = cap.read() | |
# Converts each frame to grayscale - we previously only converted the first frame to grayscale | |
# gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY) | |
# Calculates sparse optical flow by Lucas-Kanade method | |
# https://docs.opencv.org/3.0-beta/modules/video/doc/motion_analysis_and_object_tracking.html#calcopticalflowpyrlk | |
# next, status, error = cv.calcOpticalFlowPyrLK(prev_gray, gray, prev, None, **lk_params) | |
# Selects good feature points for previous position | |
# good_old = prev[status == 1] | |
# Selects good feature points for next position | |
# good_new = next[status == 1] | |
# Draws the optical flow tracks | |
for i, (new, old) in enumerate(zip(good_new, good_old)): | |
# Returns a contiguous flattened array as (x, y) coordinates for new point | |
a, b = new.ravel() | |
# Returns a contiguous flattened array as (x, y) coordinates for old point | |
c, d = old.ravel() | |
# Draws line between new and old position with green color and 2 thickness | |
mask = cv.line(mask, (a, b), (c, d), color, 2) | |
# Draws filled circle (thickness of -1) at new position with green color and radius of 3 | |
frame = cv.circle(frame, (a, b), 3, color, -1) | |
# Overlays the optical flow tracks on the original frame | |
output = cv.add(frame, mask) | |
# Updates previous frame | |
# prev_gray = gray.copy() | |
# Updates previous good feature points | |
# prev = good_new.reshape(-1, 1, 2) | |
# Opens a new window and displays the output frame | |
cv.imshow("sparse optical flow", output) | |
# Frames are read by intervals of 10 milliseconds. The programs breaks out of the while loop when the user presses the 'q' key | |
# if cv.waitKey(10) & 0xFF == ord('q'): | |
# break | |
# The following frees up resources and closes all windows | |
# cap.release() | |
# cv.destroyAllWindows() |
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