opencv4(五) VideoCapture获取摄像头图像

71 阅读 0 评论 47 点赞

我是靠谱客的博主繁荣大炮，最近开发中收集的这篇文章主要介绍opencv4(五) VideoCapture获取摄像头图像，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

环境：ubuntu18.04 opencv4.4.0

摄像头：usb摄像头，挺老的摄像头，还是usb2.0的

csi摄像头也支持这种方法

插入摄像头后 ls /dev可以看到 /dev/video0

video后面的数字就是后面需要的设备id

代码段摘自opencv手册，基本使用这段代码就够用了

#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>
#include <stdio.h>
using namespace cv;
using namespace std;
int main(int, char**)
{
    Mat frame;
    //--- INITIALIZE VIDEOCAPTURE
    VideoCapture cap;
    // open the default camera using default API
    // cap.open(0);
    // OR advance usage: select any API backend
    int deviceID = 0;             // 0 = open default camera
    int apiID = cv::CAP_ANY;      // 0 = autodetect default API
    // open selected camera using selected API
    cap.open(deviceID, apiID);
    // check if we succeeded
    if (!cap.isOpened()) {
        cerr << "ERROR! Unable to open cameran";
        return -1;
    }
    //--- GRAB AND WRITE LOOP
    cout << "Start grabbing" << endl
        << "Press any key to terminate" << endl;
    for (;;)
    {
        // wait for a new frame from camera and store it into 'frame'
        cap.read(frame);
        // check if we succeeded
        if (frame.empty()) {
            cerr << "ERROR! blank frame grabbedn";
            break;
        }
        // show live and wait for a key with timeout long enough to show images
        imshow("Live", frame);
        if (waitKey(5) >= 0)
            break;
    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}

API选择

在linux下自然选择v4l2，也可以用CAP_ANY让opencv自己选择，在linux下gstreamer也是基于V4L实现的，所以gstreamer和v4l2都可以。

需要注意的是，在编译opencv时就要把WITH_V4L打勾，好在在默认情况下WITH_V4L是勾选的

enum

cv::VideoCaptureAPIs {
  cv::CAP_ANY = 0,
  cv::CAP_VFW = 200,
  cv::CAP_V4L = 200,
  cv::CAP_V4L2 = CAP_V4L,
  cv::CAP_FIREWIRE = 300,
  cv::CAP_FIREWARE = CAP_FIREWIRE,
  cv::CAP_IEEE1394 = CAP_FIREWIRE,
  cv::CAP_DC1394 = CAP_FIREWIRE,
  cv::CAP_CMU1394 = CAP_FIREWIRE,
  cv::CAP_QT = 500,
  cv::CAP_UNICAP = 600,
  cv::CAP_DSHOW = 700,
  cv::CAP_PVAPI = 800,
  cv::CAP_OPENNI = 900,
  cv::CAP_OPENNI_ASUS = 910,
  cv::CAP_ANDROID = 1000,
  cv::CAP_XIAPI = 1100,
  cv::CAP_AVFOUNDATION = 1200,
  cv::CAP_GIGANETIX = 1300,
  cv::CAP_MSMF = 1400,
  cv::CAP_WINRT = 1410,
  cv::CAP_INTELPERC = 1500,
  cv::CAP_REALSENSE = 1500,
  cv::CAP_OPENNI2 = 1600,
  cv::CAP_OPENNI2_ASUS = 1610,
  cv::CAP_GPHOTO2 = 1700,
  cv::CAP_GSTREAMER = 1800,
  cv::CAP_FFMPEG = 1900,
  cv::CAP_IMAGES = 2000,
  cv::CAP_ARAVIS = 2100,
  cv::CAP_OPENCV_MJPEG = 2200,
  cv::CAP_INTEL_MFX = 2300,
  cv::CAP_XINE = 2400
}

CAP_PROP属性

高分辨率下有时延：在缺省情况下用VideoCapture打开摄像头，小分辨率640x480可以实时显示，但1920x1080时就会有将近1秒多的时延，这是不可接受的的事情

解决：用set接口将buffersize改小，使得高分辨率下也可以实时显示

cap.set(cv::CAP_PROP_BUFFERSIZE,1)；

尝试过修改CAP_PROP_FPS，发现效果并没有改变，猜测这不是一个从软件层面限制帧率的接口，而是与硬件通信修改帧率，而我的摄像头是固定帧率，所以这个属性并不生效，手册中许多属性后面都有一句only for those cameras that support

大部分摄像头的属性我都没有通过设定这些属性而成功，我的摄像头是支持VISCA协议的，我是通过这个协议来设定摄像头属性的，尚不清楚哪些摄像头能够支持这些CAP_PROP

常用的已标红

frame_width，frame_height：图像长宽

fourcc：四个字母用于表示图像格式，当不能自主识别时就需要自行设定

buffersize：缓冲区 value 0-10

enum

cv::VideoCaptureProperties {
  cv::CAP_PROP_POS_MSEC =0,
  cv::CAP_PROP_POS_FRAMES =1,
  cv::CAP_PROP_POS_AVI_RATIO =2,
  cv::CAP_PROP_FRAME_WIDTH =3,
  cv::CAP_PROP_FRAME_HEIGHT =4,
  cv::CAP_PROP_FPS =5,
  cv::CAP_PROP_FOURCC =6,
  cv::CAP_PROP_FRAME_COUNT =7,
  cv::CAP_PROP_FORMAT =8,
  cv::CAP_PROP_MODE =9,
  cv::CAP_PROP_BRIGHTNESS =10,
  cv::CAP_PROP_CONTRAST =11,
  cv::CAP_PROP_SATURATION =12,
  cv::CAP_PROP_HUE =13,
  cv::CAP_PROP_GAIN =14,
  cv::CAP_PROP_EXPOSURE =15,
  cv::CAP_PROP_CONVERT_RGB =16,
  cv::CAP_PROP_WHITE_BALANCE_BLUE_U =17,
  cv::CAP_PROP_RECTIFICATION =18,
  cv::CAP_PROP_MONOCHROME =19,
  cv::CAP_PROP_SHARPNESS =20,
  cv::CAP_PROP_AUTO_EXPOSURE =21,
  cv::CAP_PROP_GAMMA =22,
  cv::CAP_PROP_TEMPERATURE =23,
  cv::CAP_PROP_TRIGGER =24,
  cv::CAP_PROP_TRIGGER_DELAY =25,
  cv::CAP_PROP_WHITE_BALANCE_RED_V =26,
  cv::CAP_PROP_ZOOM =27,
  cv::CAP_PROP_FOCUS =28,
  cv::CAP_PROP_GUID =29,
  cv::CAP_PROP_ISO_SPEED =30,
  cv::CAP_PROP_BACKLIGHT =32,
  cv::CAP_PROP_PAN =33,
  cv::CAP_PROP_TILT =34,
  cv::CAP_PROP_ROLL =35,
  cv::CAP_PROP_IRIS =36,
  cv::CAP_PROP_SETTINGS =37,
  cv::CAP_PROP_BUFFERSIZE =38,
  cv::CAP_PROP_AUTOFOCUS =39,
  cv::CAP_PROP_SAR_NUM =40,
  cv::CAP_PROP_SAR_DEN =41,
  cv::CAP_PROP_BACKEND =42,
  cv::CAP_PROP_CHANNEL =43,
  cv::CAP_PROP_AUTO_WB =44,
  cv::CAP_PROP_WB_TEMPERATURE =45,
  cv::CAP_PROP_CODEC_PIXEL_FORMAT =46,
  cv::CAP_PROP_BITRATE =47
}