opencv之打开摄像头、边缘检测

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文章目录

使用opencv打开摄像头预备知识

VideoCapture的官网api
opencv io示意图

OpenCV 视频I / O模块是一组用于读取和写入视频或图像序列的类和功能。

打开笔记本自带摄像头代码实战

按q退出

import cv2
if __name__ == '__main__':
    cap = cv2.VideoCapture(0)  # 设置摄像头 0是默认的摄像头 如果你有多个摄像头的话呢，可以设置1,2,3....
    while True:  # 进入无限循环
        ret, frame = cap.read()  # 将摄像头拍到的图像作为frame值
        cv2.imshow('frame', frame)  # 将frame的值显示出来 有两个参数 前一个是窗口名字，后面是值
        c = cv2.waitKey(1)  # 判断退出的条件 当按下'Q'键的时候呢，就退出
        if c == ord('q'):
            break
    cap.release()  # 常规操作
    cv2.destroyAllWindows()

esc退出

import cv2 as cv


def video_demo():
    # 0是代表摄像头编号，只有一个的话默认为0
    capture = cv.VideoCapture(0)
    while (True):
        ref, frame = capture.read()

        cv.imshow("1", frame)
        # 等待30ms显示图像，若过程中按“Esc”退出
        c = cv.waitKey(30) & 0xff
        if c == 27:
            capture.release()
            break

video_demo()
cv.waitKey()
cv.destroyAllWindows()

代码注释

1、cv2.VideoCapture()函数：
cap = cv2.VideoCapture(0)
VideoCapture()中参数是0，表示打开笔记本的内置摄像头。
cap = cv2.VideoCapture(“…/1.avi”)
VideoCapture(“…/1.avi”)，表示参数是视频文件路径则打开视频。

2、cap.isOpened()函数：
返回true表示成功，false表示不成功

3、ret,frame = cap.read()函数：
cap.read()按帧读取视频，ret,frame是获cap.read()方法的两个返回值。其中ret是布尔值，如果读取帧是正确的则返回True，如果文件读取到结尾，它的返回值就为False。frame就是每一帧的图像，是个三维矩阵。

4、cv2.waitKey()函数：
参数是1，表示延时1ms切换到下一帧图像，参数过大如cv2.waitKey(1000)，会因为延时过久而卡顿感觉到卡顿。
参数为0，如cv2.waitKey(0)只显示当前帧图像，相当于视频暂停。

5、cap.release()与destroyAllWindows()函数：
cap.release()释放视频，调用destroyAllWindows()关闭所有图像窗口。

6、c得到的是键盘输入的ASCII码，esc键对应的ASCII码是27，即当按esc键是if条件句成立。

使用第三方驱动程序或照相机注意事项

许多工业相机或某些视频I / O设备不为操作系统提供标准的驱动程序接口。因此，您不能在这些设备上使用VideoCapture或VideoWriter。

为了访问他们的设备，制造商提供了自己的C ++ API和库，您必须包括它们并与OpenCV应用程序链接。

这是一种常见的情况，该库从/向存储器缓冲区读取/写入图像。如果是这样，Mat则可以为内存缓冲区（用户分配的数据）创建标头，并使用OpenCV函数对其进行就地处理。有关更多详细信息，请参见cv :: Mat :: Mat（）。

opencv打开jeston tx2板载摄像头

因为查询到tx1和tx2打开板载摄像头的命令不一样。其中arg1函数是打开 tx1 的参数。arg2函数是打开 tx2 的参数。这里参考了一篇国外的原文附带的GitHub地址查询到的。找不到原文了。我将GitHub的源码附录在最后以表达对原作者的尊重（带有作者个人信息）


import cv2
def arg1(width, height):
    gst_str = ('nvcamerasrc ! '
                'video/x-raw(memory:NVMM), '
                'width=(int)2592, height=(int)1458, '
                'format=(string)I420, framerate=(fraction)30/1 ! '
                'nvvidconv ! '
                'video/x-raw, width=(int){}, height=(int){}, '
                'format=(string)BGRx ! '
                'videoconvert ! appsink').format(width, height)
    return gst_str

def arg2(width,height):
    gst_str = ('nvarguscamerasrc ! '
                'video/x-raw(memory:NVMM), '
                'width=(int)1920, height=(int)1080, '
                'format=(string)NV12, framerate=(fraction)30/1 ! '
                'nvvidconv flip-method=2 ! '
                'video/x-raw, width=(int){}, height=(int){}, '
                'format=(string)BGRx ! '
                'videoconvert ! appsink').format(width, height)
    return gst_str


def open_1():
    path = arg1(100, 100)
    print("11111path",path)
    cap =cv2.VideoCapture(path)
    if not cap.isOpened():
       print('Failed to open camera!111111111111111111111')
    return cap

def open_2():
    path = arg2(100, 100)
    print("2222path",path)
    cap = cv2.VideoCapture(path)
    if not cap.isOpened():
       print('Failed to open camera!2222222222222222')
    return cap

def openVideo(cap):
    while True:  # 进入无限循环
        ret, frame = cap.read()  # 将摄像头拍到的图像作为frame值
        cv2.imshow('frame', frame)  # 将frame的值显示出来 有两个参数 前一个是窗口名字，后面是值
        c = cv2.waitKey(1)  # 判断退出的条件 当按下'Q'键的时候呢，就退出
        if c == ord('q'):
            break
    cap.release()  # 常规操作
    cv2.destroyAllWindows()

if __name__ == '__main__':
    cap_1 = open_1()
    cap_2 = open_2()
    openVideo(cap_1)
    # openVideo(cap_2)

附录、GitHub打开摄像头的源码

# --------------------------------------------------------
# Camera sample code for Tegra X2/X1
#
# This program could capture and display video from
# IP CAM, USB webcam, or the Tegra onboard camera.
# Refer to the following blog post for how to set up
# and run the code:
# https://jkjung-avt.github.io/tx2-camera-with-python/
#
# Written by JK Jung <jkjung13@gmail.com>
# --------------------------------------------------------


import sys
import argparse
import subprocess

import cv2


WINDOW_NAME = 'CameraDemo'


def parse_args():
    # Parse input arguments
    desc = 'Capture and display live camera video on Jetson TX2/TX1'
    parser = argparse.ArgumentParser(description=desc)
    parser.add_argument('--rtsp', dest='use_rtsp',
                        help='use IP CAM (remember to also set --uri)',
                        action='store_true')
    parser.add_argument('--uri', dest='rtsp_uri',
                        help='RTSP URI, e.g. rtsp://192.168.1.64:554',
                        default=None, type=str)
    parser.add_argument('--latency', dest='rtsp_latency',
                        help='latency in ms for RTSP [200]',
                        default=200, type=int)
    parser.add_argument('--usb', dest='use_usb',
                        help='use USB webcam (remember to also set --vid)',
                        action='store_true')
    parser.add_argument('--vid', dest='video_dev',
                        help='device # of USB webcam (/dev/video?) [1]',
                        default=1, type=int)
    parser.add_argument('--width', dest='image_width',
                        help='image width [1920]',
                        default=1920, type=int)
    parser.add_argument('--height', dest='image_height',
                        help='image height [1080]',
                        default=1080, type=int)
    args = parser.parse_args()
    return args


def open_cam_rtsp(uri, width, height, latency):
    gst_str = ('rtspsrc location={} latency={} ! '
               'rtph264depay ! h264parse ! omxh264dec ! '
               'nvvidconv ! '
               'video/x-raw, width=(int){}, height=(int){}, '
               'format=(string)BGRx ! '
               'videoconvert ! appsink').format(uri, latency, width, height)
    return cv2.VideoCapture(gst_str, cv2.CAP_GSTREAMER)


def open_cam_usb(dev, width, height):
    # We want to set width and height here, otherwise we could just do:
    # return cv2.VideoCapture(dev)
    gst_str = ('v4l2src device=/dev/video{} ! '
               'video/x-raw, width=(int){}, height=(int){} ! '
               'videoconvert ! appsink').format(dev, width, height)
    return cv2.VideoCapture(gst_str, cv2.CAP_GSTREAMER)


def open_cam_onboard(width, height):
    gst_elements = str(subprocess.check_output('gst-inspect-1.0'))
    if 'nvcamerasrc' in gst_elements:
        # On versions of L4T prior to 28.1, add 'flip-method=2' into gst_str
        gst_str = ('nvcamerasrc ! '
                   'video/x-raw(memory:NVMM), '
                   'width=(int)2592, height=(int)1458, '
                   'format=(string)I420, framerate=(fraction)30/1 ! '
                   'nvvidconv ! '
                   'video/x-raw, width=(int){}, height=(int){}, '
                   'format=(string)BGRx ! '
                   'videoconvert ! appsink').format(width, height)
    elif 'nvarguscamerasrc' in gst_elements:
        gst_str = ('nvarguscamerasrc ! '
                   'video/x-raw(memory:NVMM), '
                   'width=(int)1920, height=(int)1080, '
                   'format=(string)NV12, framerate=(fraction)30/1 ! '
                   'nvvidconv flip-method=2 ! '
                   'video/x-raw, width=(int){}, height=(int){}, '
                   'format=(string)BGRx ! '
                   'videoconvert ! appsink').format(width, height)
    else:
        raise RuntimeError('onboard camera source not found!')
    return cv2.VideoCapture(gst_str, cv2.CAP_GSTREAMER)


def open_window(width, height):
    cv2.namedWindow(WINDOW_NAME, cv2.WINDOW_NORMAL)
    cv2.resizeWindow(WINDOW_NAME, width, height)
    cv2.moveWindow(WINDOW_NAME, 0, 0)
    cv2.setWindowTitle(WINDOW_NAME, 'Camera Demo for Jetson TX2/TX1')


def read_cam(cap):
    show_help = True
    full_scrn = False
    help_text = '"Esc" to Quit, "H" for Help, "F" to Toggle Fullscreen'
    font = cv2.FONT_HERSHEY_PLAIN
    while True:
        if cv2.getWindowProperty(WINDOW_NAME, 0) < 0:
            # Check to see if the user has closed the window
            # If yes, terminate the program
            break
        _, img = cap.read() # grab the next image frame from camera
        if show_help:
            cv2.putText(img, help_text, (11, 20), font,
                        1.0, (32, 32, 32), 4, cv2.LINE_AA)
            cv2.putText(img, help_text, (10, 20), font,
                        1.0, (240, 240, 240), 1, cv2.LINE_AA)
        cv2.imshow(WINDOW_NAME, img)
        key = cv2.waitKey(10)
        if key == 27: # ESC key: quit program
            break
        elif key == ord('H') or key == ord('h'): # toggle help message
            show_help = not show_help
        elif key == ord('F') or key == ord('f'): # toggle fullscreen
            full_scrn = not full_scrn
            if full_scrn:
                cv2.setWindowProperty(WINDOW_NAME, cv2.WND_PROP_FULLSCREEN,
                                      cv2.WINDOW_FULLSCREEN)
            else:
                cv2.setWindowProperty(WINDOW_NAME, cv2.WND_PROP_FULLSCREEN,
                                      cv2.WINDOW_NORMAL)


def main():
    args = parse_args()
    print('Called with args:')
    print(args)
    print('OpenCV version: {}'.format(cv2.__version__))

    if args.use_rtsp:
        cap = open_cam_rtsp(args.rtsp_uri,
                            args.image_width,
                            args.image_height,
                            args.rtsp_latency)
    elif args.use_usb:
        cap = open_cam_usb(args.video_dev,
                           args.image_width,
                           args.image_height)
    else: # by default, use the Jetson onboard camera
        cap = open_cam_onboard(args.image_width,
                               args.image_height)

    if not cap.isOpened():
        sys.exit('Failed to open camera!')

    open_window(args.image_width, args.image_height)
    read_cam(cap)

    cap.release()
    cv2.destroyAllWindows()


if __name__ == '__main__':
    main()

附录、c++打开摄像头

#include <opencv.hpp>
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main() {
	// 显示opencv的版本
	cout << "the version of opencv is : " << CV_VERSION << endl;
	Mat image;
	image = imread("lena.jpg");
	if (image.empty()) {
		printf("src is empty");
		return -1;
	}
	//VideoCapture capture("1.mp4");
	VideoCapture capture;
	capture.open("1.mp4");
	while (true)
	{
		Mat frame;
		capture >> frame;
		if (frame.empty())
		{
			break;
		}
		else {
			imshow("frame by frame", frame);
			waitKey(10);
		}

	}
	return 0;
}

附录、c++打开图片

#include <opencv.hpp>
#include <opencv2/opencv.hpp>
#include <iostream>
#include<opencv4/opencv2/core.hpp>
using namespace cv;
using namespace std;
int main(){
    Mat src = imread("lena.jpg");
	// 非空判断
	if (src.empty()) {
		printf("src is empty");
		return -1;
	}
	// opencv的UI窗口，由opencv自己创建和释放
	// WINDOW_AUTOSIZE 自适应文件大小，不支持窗口大小调整
	// WINDOW_NORMAL 可以在qt上使用，用来调增大小
	namedWindow("show image windos", WINDOW_AUTOSIZE);
	imshow("show image windos", src);

	// 色彩空间转换
	namedWindow("change_image");
	Mat out_image;
	cvtColor(src,out_image, COLOR_BGR2GRAY);
	imshow("change_image", out_image);
	waitKey(0);

}

附录c++、边缘检测

#include <opencv2/opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;
int main() {
	Mat image;
	image = imread("lena.jpg");
	if (image.empty()) {
		printf("src is empty");
		return -1;
	}
    // 调用摄像头
	VideoCapture capture(0);
	while (true)
	{
		Mat frame;
		capture>>frame;
		// 图像转为灰度
		cvtColor(frame, frame, COLOR_BGR2GRAY);
		// 3*3内核降噪
		blur(frame, frame, Size(7, 7));
		// canny边缘检测
		Canny(frame,
		 frame, 0, 30, 3);
		imshow("frame by frame", frame);
		waitKey(10);
	}
	return 0;
}

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