openCV doc

オプティカルフロー(Practical：グリッチ)

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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もとに座標変換しています。グリッチ(glitch)は海外のゲーム業界ではバグと同義で扱われていて、一時的に画面表示エラーになることも意味します。

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 warp_flow(cv::Mat img, cv::Mat flow){
    int height = flow.rows;
    int width = flow.cols;

cv::Mat opti_flow(height, width, CV_32FC2), dst;

for(int w = 0; w < width; w++){
        for(int h = 0; h < height; h++){
            const cv::Point2f& src_xy = flow.at<cv::Point2f>(h, w);
            cv::Point2f& opti_xy = opti_flow.at<cv::Point2f>(h, w);
            opti_xy.x = w + src_xy.x;
            opti_xy.y = h + src_xy.y;
        }
    }

cv::remap(img, dst, opti_flow, cv::Mat(), cv::INTER_LINEAR);
    return dst;
}

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;
    }

/* 初期設定 */
    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 << warp_flow(frame, flow);
        old_gray = frame_gray.clone();
    }

capture.release();
    writer.release();

return 0;
}

cook code Python

import numpy as np
import cv2
import argparse

def warp_flow(img, flow):
    h, w = flow.shape[:2]
    flow[:,:,0] += np.arange(w)
    flow[:,:,1] += np.arange(h)[:,np.newaxis]
    res = cv2.remap(img, flow, None, cv2.INTER_LINEAR)
    return res

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)

frame = prev.copy()

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)
        prevgray = gray

frame = warp_flow(frame, flow)
        writer.write(frame)

frame = img.copy()

cap.release()
    writer.release()

if __name__ == '__main__':
    main()

Reference

https://github.com/opencv/opencv/blob/4.4.0/samples/python/opt_flow.py
https://heapsmag.com/urban-english-glitch-computer-trouble-broken-issue-bug
GIFMAGAZINE - タイガーステップ
Book : 詳細 OpenCV3 17章トラッキング pp565-570