openCV doc

オプティカルフロー(Practical：オーラグラフィー)

Gallery

src

dst

what process?

密なオプティカルフロー(dense optical flow)を使ってエフェクトを生成しました。 フレーム間の移動量ベクトルを算出し、HSV色空間に変換したものです。 角度は色相(H)、移動距離は明度(V)と関連付けています。

cook code C++

#include <iostream> #include <opencv2/core.hpp> #include <opencv2/core/utility.hpp> #include <opencv2/highgui.hpp> #include <opencv2/imgproc.hpp> #include <opencv2/videoio.hpp> #include <opencv2/video.hpp> cv::Mat draw_hsv(cv::Mat flow){ cv::Mat flow_parts[2]; cv::split(flow, flow_parts); cv::Mat magnitude, angle, magn_norm; cv::cartToPolar(flow_parts[0], flow_parts[1], magnitude, angle, true); cv::normalize(magnitude, magn_norm, 0.0f, 1.0f, cv::NORM_MINMAX); angle *= ((1.f / 360.f) * (180.f / 255.f)); cv::Mat _hsv[3], hsv, hsv8, bgr, gray; _hsv[0] = angle; //色相 _hsv[1] = cv::Mat::ones(angle.size(), CV_32F); //彩度 _hsv[2] = magn_norm; //明度 cv::merge(_hsv, 3, hsv); hsv.convertTo(hsv8, CV_8U, 255.0); cv::cvtColor(hsv8, bgr, cv::COLOR_HSV2BGR); return bgr; } int main(int argc, const char* argv[]) { // ./out -src=[image path] cv::String keys = "{src||}"; cv::CommandLineParser parser(argc, argv, keys); cv::String src_path = parser.get<cv::String>("src"); cv::VideoCapture capture(src_path); if (!capture.isOpened()){ //error in opening the video input std::cerr << "Unable to open file!" << std::endl; return 0; } int cap_width = int(capture.get(cv::CAP_PROP_FRAME_WIDTH)); int cap_height = int(capture.get(cv::CAP_PROP_FRAME_HEIGHT)); int fps = int(capture.get(cv::CAP_PROP_FPS)); int fourcc = cv::VideoWriter::fourcc('m','p','4','v'); cv::Size video_size = cv::Size(cap_width,cap_height); cv::VideoWriter writer("output.mp4", fourcc, fps, video_size); cv::Mat old_frame, old_gray; capture >> old_frame; cv::cvtColor(old_frame, old_gray, cv::COLOR_BGR2GRAY); while(true){ cv::Mat frame, frame_gray; capture >> frame; if (frame.empty()) break; cv::cvtColor(frame, frame_gray, cv::COLOR_BGR2GRAY); cv::Mat flow(old_gray.size(), CV_32FC2); cv::calcOpticalFlowFarneback(old_gray, frame_gray, flow, 0.5, 3, 15, 3, 5, 1.2, 0); writer << draw_hsv(flow); old_gray = frame_gray.clone(); } capture.release(); writer.release(); return 0; }

cook code Python

import numpy as np import cv2 import argparse def draw_hsv(flow): h, w = flow.shape[:2] fx, fy = flow[:,:,0], flow[:,:,1] ang = np.arctan2(fy, fx) + np.pi v = np.sqrt(fx*fx+fy*fy) hsv = np.zeros((h, w, 3), np.uint8) hsv[...,0] = ang*(180/np.pi/2) #色相 hsv[...,1] = 255 #彩度 hsv[...,2] = np.minimum(v*4, 255) #明度 bgr = cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR) return bgr def main(): parser = argparse.ArgumentParser() parser.add_argument('--src') args = parser.parse_args() cap = cv2.VideoCapture(args.src) cap_width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH)) cap_height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT)) fps = cap.get(cv2.CAP_PROP_FPS) fmt = cv2.VideoWriter_fourcc('m', 'p', '4', 'v') writer = cv2.VideoWriter('output.mp4', fmt, fps, (cap_width,cap_height)) _ret, prev = cap.read() prevgray = cv2.cvtColor(prev, cv2.COLOR_BGR2GRAY) while cap.isOpened(): _ret, img = cap.read() if img is None: break gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) flow = cv2.calcOpticalFlowFarneback(prevgray, gray, None, 0.5, 3, 15, 3, 5, 1.2, 0) frame = draw_hsv(flow) writer.write(frame) prevgray = gray cap.release() writer.release() if __name__ == '__main__': main()

Reference

• https://github.com/opencv/opencv/blob/4.4.0/samples/cpp/tutorial_code/video/optical_flow/optical_flow_dense.cpp
• https://github.com/opencv/opencv/blob/4.4.0/samples/python/opt_flow.py
• http://labs.eecs.tottori-u.ac.jp/sd/Member/oyamada/OpenCV/html/py_tutorials/py_video/py_lucas_kanade/py_lucas_kanade.html#opencv
• GIFMAGAZINE - タイガーステップ
• Book : Book : 詳細 OpenCV3 17章 トラッキング pp565-570