opencv-077-视频读取与处理

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知识点

OpenCV中对视频内容的处理本质上对读取视频的关键帧进行解析图像，然后对图像进行各种处理，OpenCV的VideoCapture是一个视频读取与解码的API接口，支持各种视频格式、网络视频流、摄像头读取。正常的视频处理与分析，主要是针对读取到每一帧图像，衡量一个算法处理是否能够满足实时要求的时候通常通过FPS（每秒多少帧的处理能力）。一般情况下每秒大于5帧基本上可以认为是在进行视频处理。

代码（c++,python）

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#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

void process_frame(Mat &image, int opts);

/*
 * 视频读取与处理
 */
int main() {
    VideoCapture capture("../images/roadcars.avi");
    if (!capture.isOpened()){
        cout << "could not open video.." << endl;
        return -1;
    }
    namedWindow("input");

    int fps = capture.get(CAP_PROP_FPS);
    int width = capture.get(CAP_PROP_FRAME_WIDTH);
    int height = capture.get(CAP_PROP_FRAME_HEIGHT);
    int num_of_frames = capture.get(CAP_PROP_FRAME_COUNT);
    printf("frame width: %d, frame height: %d, FPS : %d \n", width, height, fps);

    Mat frame;
    int index = 0;
    while(capture.isOpened()){
        bool ret = capture.read(frame);
        if (!ret) break;
        imshow("input", frame);
        char c = waitKey(50);
        if (c >= 49){
            index = c - 49;
        }
        process_frame(frame, index);
        imshow("result", frame);
        if (c == 27){
            break;
        }
    }

    waitKey(0);
    return 0;
}

void process_frame(Mat &image, int opts) {
    Mat dst = image.clone();
    if (opts == 0){
        bitwise_not(image, dst);
    }
    if (opts == 1){
        GaussianBlur(image, dst, Size(0,0), 15);
    }
    if (opts == 2){
        Canny(image, dst, 100, 200);
    }
    dst.copyTo(image);
    dst.release();
}
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import cv2 as cv

capture = cv.VideoCapture("../images/roadcars.avi")
height = capture.get(cv.CAP_PROP_FRAME_HEIGHT)
width = capture.get(cv.CAP_PROP_FRAME_WIDTH)
count = capture.get(cv.CAP_PROP_FRAME_COUNT)
fps = capture.get(cv.CAP_PROP_FPS)
print(height, width, count, fps)


def process(image, opt=1):
    dst = None
    if opt == 0:
        dst = cv.bitwise_not(image)
    if opt == 1:
        dst = cv.GaussianBlur(image, (0, 0), 15)
    if opt == 2:
        dst = cv.Canny(image, 100, 200)
    return dst


index = 0
while(True):
    ret, frame = capture.read()
    if ret is True:
        cv.imshow("video-input", frame)
        c = cv.waitKey(50)
        if c >= 49:
            index = c -49
        result = process(frame, index)
        cv.imshow("result", result)
        print(c)
        if c == 27:  #ESC
            break
    else:
        break
cv.waitKey(0)
cv.destroyAllWindows()

结果

代码地址

github